Multiuse subcarriers in multipoint-to-point communication using orthogonal frequency division multiplexing

Abstract

systems and methods for bidirectional communication are provided. In one embodiment, a multipoint-to-point, orthogonal frequency division multiplexed (ofdm) communication system comprises: a plurality of remote units, a host unit; wherein the host sends an adjustment signal to a remote instructing the remote to adjust the timing of transmissions from the remote to improve orthogonality of the ofdm waveform received at the host, wherein the host sends an adjustment signal to a remote instructing the remote to adjust the frequency of transmissions from the remote to improve orthogonality of the ofdm waveform received at the host, wherein payload data is transmitted between a remote and the host over a first orthogonal tone within the ofdm communication system during a first time interval, and wherein control data is transmitted between a remote and the host over the first orthogonal tone within the ofdm communication system during a second time interval.

Description

CROSS REFERENCE TO RELATED CASES

This application is a continuation of application Ser. No. 11/420,851 filed on May 30, 2006, entitled “DYNAMIC BANDWIDTH ALLOCATION” (currently pending), which is a divisional of application Ser. No. 09/903,273 filed Jul. 11, 2001, entitled “DYNAMIC BANDWIDTH ALLOCATION” (now U.S. Pat. No. 7,069,577), which is a continuation of application Ser. No. 09/397,443, filed Sep. 15, 1999, entitled “DYNAMIC BANDWIDTH ALLOCATION” (now U.S. Pat. No. 6,279,158), which is a divisional of U.S. application Ser. No. 08/673,002 filed Jun. 28, 1996 (now U.S. Pat. No. 6,334,219) which is a continuation-in-part of U.S. application Ser. No. 08/650,408 filed May 20, 1996 (abandoned)
B′=A−jBW^1k−CW^2k+jDW^3k
C′=A−BW^1k+CW^2k−DW^3k
D′=A+jBW^1k−CW^2k−jDW^3k

The function performed in a reverse transform is simply the complex conjugate of the above set of equations.
A′=A+BW^1k+CW^2k+DW^3k
B′=A+jBW^1k+CW^2k−jDW^3k
C′=A−BW^1k+CW^2k−DW^3k
D′=A−jBW^1k−CW²+jDW^3k

Note that the twiddle-factor W which is used for each A on the right side of the above equations is one (that is, the complex number 1+j0).

The multiplication of two complex numbers, each having a real part and an imaginary part, for example, results in the following equation:
X0×W0=(X0R+jX0I)×(W0R+jW0I)
=(X0R×W0R−X0I×W0I)+
j(X0I×W0R+X0R×W0I)+
X0R×W0R+jX0I×W0R
(for example, the first multiplier cycle in multipliers 2620-2621)
−X0I×W0I+jX0R×W0I
(for example, the first multiplier cycle in multipliers 2620-2621).
Thus, four multiplier operations are needed for each complex multiply operation.

In order to speed the transform function, the factors for the parallel multipliers are fetched in parallel under the control of control and clocking sequencer 2640. Routing logic 2634 routes the products of the multipliers 2620-2627 to the thirty-two adder-subtractor-accumulators 2633. In one embodiment, eight multiplier cycles, C0 through C7, are used to generate four radix-4 butterfly operations, resulting in sixteen complex output values. For discussion purposes, row-column array 2632 is shown having four rows (A, B, C, and D) and four columns (W, X, Y, and Z) of complex value pairs. The real value and the imaginary value of each of these sixteen complex value pairs has its own associated adder-subtractor-accumulator 2633, for a total of thirty-two adder-subtractor-accumulators 2633, as shown in FIG. 74 and FIG. 91. In one embodiment, scaling-factor shift logic 2644 (under the control of bit-growth selector 2643) is provided in the path between adder-subtractor-accumulators 2633 and conversion RAM bank 2252. The scaling-factor shift logic 2644 provides a right-shift function of 0 bits, 1 bit, 2 bits or three bits (divide by 1, two, four or eight respectively) on each output data value as it is being returned to conversion RAM 2252. Bit-growth pins 2117 through 2118, which control the divide function for each of the passes are coupled to bit-growth selector 2643 under control of sequencer 2640.

FIGS. 75-82 are a table 2800 showing the order of calculations for a “normal butterfly sub-operation.” The data points in conversion RAM 2252 are arranged within conversion RAM 2252 such that the four input points for one radix-4 operation are each located in different sub-banks if the points are successively addressed (for example, addresses 0, 1, 2, and 3 are each in different sub-banks, for example, sub-banks 2290, 2291, 2292, and 2293 respectively), but points whose addresses differ by a factor of 4 are located in the same bank (for example, addresses 0, 4, 8, and 12 are all within bank 2290, as are addresses 0, 16, 32, and 48, addresses 0, 64, 128, and 192, and addresses 0, 256, 512, and 768). The butterfly passes for this second set of points (those whose addresses-mod-4 are equal) are handled by the equations shown in the table of FIGS. 75-82. FIG. 75 shows the operations at each of the thirty-two adder-subtractor-accumulators 2633 at a multiplier clock cycle command denoted C0. For example, at C0, the adder-subtractor-accumulator 2633 for the real portion of the AW point in row-column array 2632 (called the AWR accumulator) gets loaded with the output (called WR) of multiplier 2620, and the adder-subtractor-accumulator 2633 for the imaginary portion of the DZ point in row-column array 2632 (called the DZI accumulator) gets loaded with the output (called ZI) of multiplier 2627. By performing load operations at clock C0, the previous values of the accumulators do not need to be zeroed. As shown in FIG. 91, multipliers 2620, 2621, 2622, 2623, 2624, 2625, 2626 and 2627 produce products called WR, WI, XR, XI, YR, YI, ZR and ZI, respectively, however the -R and -I designations of these products are not strictly correlated to real and imaginary numbers. FIG. 91 also shows the row and column locations for the thirty-two adder-subtractor-accumulators 2633, with AWR shown in the upper-left corner and DZI in the lower right corner.

FIG. 76 shows the operations at each of the thirty-two adder-subtractor-accumulators 2633 at a multiplier clock cycle command denoted C1. For example, at C1, the adder-subtractor-accumulator 2633 for the real portion of the AW point in row-column array 2632 (called the AWR accumulator) gets loaded with the difference of subtracting from its previous value (called AWR, this value happens to be the WR value loaded in cycle C0) the output (called WI) of multiplier 2621, and the adder-subtractor-accumulator 2633 for the imaginary portion of the DZI point in row-column array 2632 (called the DZI accumulator) gets loaded with the sum of its previous value (called DZI, this value happens to be the ZI value loaded in cycle C0) and output (called ZR) of multiplier 2626. Similarly, FIGS. 77 through 82 show the operations which take place at multiplier clocks C2 through C7, respectively.

Since each complex-multiply operation takes a total of four multiplier operations, and two multipliers (for example, the pair 2620 and 2621) are used, two multiplier cycles are needed for each complex-multiply operation. In a 1024-point transform (that is, either an FFT or an IFFT), four of the five passes involve sets of four points wherein all four points are in a single sub-bank (for example, 2290), and therefore must be fetched on four successive even-clocks. Each of these four passes takes eight clocks, called C0 through C7. These four passes are each called “normal butterfly.” Table 2800 shows the order of calculation for all of the sub-operations for one embodiment of a normal butterfly (calculating four radix-4 butterfly operations in eight multiplier clock cycles), where each of the four points for one radix-4 butterfly are in the same sub-bank (for example, either sub-bank 2290 or 2291 or 2292 or 2293).

FIGS. 83-90 are a table 2810 showing the order of calculations for a “transposed butterfly sub-operation.” The transposed butterfly sub-operation is used for one pass of each transform performed. The data points in conversion RAM 2252 are arranged within conversion RAM 2252 such that the four input points for one radix-4 operation are each located in different sub-banks if the points are successively addressed (for example, addresses 0, 1, 2, and 3 are each in different sub-banks; sub-banks 2290, 2291, 2292, and 2293 respectively). The transposed butterfly passes for this one set of points (those whose addresses-mod-4 are equal) are handled by the equations shown in the table of FIGS. 83-90. FIG. 83 shows the operations at each of the thirty-two adder-subtractor-accumulators 2633 at a multiplier clock cycle command denoted C0 (note that only eight adder-subtractor-accumulators 2633 are affected, the other twenty-four do nothing). For example, at C0, the adder-subtractor-accumulator 2633 for the real portion of the AW point in row-column array 2632 (called the AWR accumulator) gets loaded with the result of a four-way addition of the outputs (called WR+XR+YR+ZR, these are the real-times-real portions) of multipliers 2620, 2622, 2624 and 2626, and the adder-subtractor-accumulator 2633 for the imaginary portion of the AZ point in row-column array 2632 (called the AZI accumulator) gets loaded with the sum/difference of outputs (called WI−XR−YI+ZR) of multipliers 2621, 2622, 2625, and 2626, respectively. By performing load operations at clock C0 with no accumulation of the prior value (for example, in AWR), the previous values of the accumulators do not need to be zeroed. Note that, since all four points for a single butterfly operation can be fetched simultaneously from conversion RAM 2252, and the results of the respective multiply operations must all be combined as they are formed, five-way mixed add/subtract operations are provided for by each adder-subtractor-accumulator 2633.

FIG. 84 shows the operations at each of the thirty-two adder-subtractor-accumulators 2633 at a multiplier clock cycle command denoted C1. For example, at C1, the adder-subtractor-accumulator 2633 for the real portion of the AW point in row-column array 2632 (called the AWR accumulator) gets loaded with the result of a five-way subtraction/addition of the outputs (called AWR−(WI+XI+YI+ZI), these are the imaginary-times-imaginary portions) of multipliers 2621, 2623, 2625 and 2627 and the prior contents of AWR. The adder-subtractor-accumulator 2633 for the imaginary portion of the AZ point in row-column array 2632 (called the AZI accumulator) gets loaded with the sum/difference of outputs (called AZI+(WR+XI−YR−ZI)) of multipliers 2620, 2623, 2624, and 2627, respectively.

Similarly, FIGS. 85 through 90 show the four-way and five-way operations which take place at multiplier clocks C2 through C7, respectively. Table 2810 shows the order of calculation for one embodiment of a transposed butterfly (calculating four radix-4 butterfly operations in eight multiplier clock cycles), where each of the four points for one radix-4 butterfly are each in different sub-banks (for example, one point in sub-bank 2290, one point in 2291, one point in 2292, and one point in 2293).

Twiddle-Factor Lookup Table 2610

In one embodiment, the twiddle-factor lookup table 2610 (also called a sine-cosine ROM lookup table) comprises 512 fifteen-bit words, wherein four words can be fetched in parallel. Each complex twiddle factor value pair is fetched sequentially, wherein the first 15-bit word represents the real part of the twiddle factor value pair and the second 15-bit word represents the imaginary part, and four values are fetched simultaneously (that is, four real values, having 60 bits total, are fetched on an even clock (for example, clocks C0, C2, C4 or C6) and four imaginary values are fetched on the following odd clock (for example, clocks C1, C3, C5 or C7). In another embodiment, the twiddle factor lookup table 2610 comprises of 256 thirty-bit words. The upper 15 bits represent the real part of the twiddle factor whereas the lower 15 bits represent the imaginary part. Although 1024 complex-value pairs are required in order to produce a 1024-point FFT or IFFT, the values are not unique, and the number of twiddle factors was reduced by a factor of four by making use of the simple trigonometric identities in mapping 360 degrees of twiddle factors to a 90-degree lookup table. In one embodiment, the twiddle-factor lookup table was designed to minimize DC offset caused by integer-based twiddle factors.

FIG. 92 shows a more-detailed block diagram of an adder-subtractor-accumulator 2633. In one embodiment, multipliers 2620 through 2627 are each a 16-bit-by-16-bit multiplier. In one embodiment, only the upper-order 16 bits of the resultant product are passed by MUX 2834. (In one embodiment, MUX 2834 is part of router logic 2634.) Adder-subtractor 2833 performs a five-way addition/subtraction as defined in FIGS. 83-90 and the two-way addition/subtraction as defined in FIGS. 75-82, under the control of sequencer 2640. In one embodiment, accumulator 2835 maintains enough bits above the binary point to accommodate overflow bits and to provide an indication of overflow which does not get lost as further addition/subtractions are performed on the accumulating data (in other embodiments, one, two, or three such bits are maintained).

Input and Output Timing

Tables 7 and 8 below are the detailed timings for one embodiment of the input and output RAMs.

TABLE 7
Read Cycle for Output RAM bank 2253
	Symbol	Parameters	Condition	Nom
	Tcc	Clock Cycle Time Pulse	Minimum	20 ns
		Width
	Tchpw	Minimum Positive CK	Minimum	6 ns
		Pulse Width
	Tclpw	Minimum Negative CK	Minimum	6 ns
		Pulse Width
	Tavch	Address valid to CK high	Minimum	4 ns
	Tchax	CK high to address change	Minimum	1.0 ns
	Tchdox	CK high to Data Output	Minimum	2 ns
		change
	Tcd	CK high to data valid	Maximum	15 ns
	Toe	Output Enable time	Minimum	0 ns
	Toz	Output Disable time	Minimum	7 ns
	NOTE:
	The RAM clocks for the input and output banks are limited to 10.24 MHz

TABLE 8
Write Cycle for Input RAM bank 2251
	Symbol	Parameters	Condition	Nom
	Tcc	Clock Cycle time	Minimum	20 ns
	Tchpw	Minimum positive CK	Minimum	6 ns
		pulse width
	Tclpw	Minimum negative CK	Minimum	6 ns
		pulse width
	Tavch	Address valid to CK low	Minimum	4 ns
	Tchax	CK low to address change	Minimum	1 ns
	Twch	˜WE low to CK low	Minimum	4 ns
	Tchw	CK low to ˜WE high	Minimum	1 ns
	Tdivch	Data Input valid to CK low	Minimum	4 ns
	Tchdix	CK low to Data input	Minimum	1 ns
		change
	Tchdov	CK low to Data Output	Maximum	15 ns
		valid
	Tchdox	CK low to Data Output	Minimum	2 ns
		change
	NOTE:
	The RAM clocks for the input and output banks are limited to 10.24 MHz

Package for ASIC 2101

Package Dimensions and pin out for one embodiment: The ASIC 2101 generates 5V TTL output levels and accepts 5V CMOS or 5V TTL input levels. TTL Input Levels are defined as follows:

VIL max=0.8 Volts

VIH min=2.0 Volts

CMOS Input Levels are defined as follows:

VIL max=0.2*VDD(0.9V<VIL<1.1V over 4.5V to 5.5V VDD range)

VIH min=0.7*VDD(3.15V<VIH<3.85V over 4.5V to 5.5V VDD range)

TTL Output Levels:

VOL max=0.4 Volts

VOH min=2.4 Volts

Functional Tests

Testing is broken down into a functional segment to verify device functionality and a scan segment to test for faults in the physical silicon. In one embodiment, the vectors are included in a test bench compatible with LSI Logic's tools. The functions to be tested in the device are listed below.

• a. FFT/IFFT Operation—Vectors are provided which are characteristic of the expected use in the system. The frequency domain vectors are passed through an inverse transform (with appropriate bit scaling) and the results stored. The vectors are then passed through a forward transform (with appropriate scaling), and this final result analyzed. These tests are performed for the 1024-, 512-, and 256-point transforms. There are 10 frames of data for each test. The test bench includes 1024 vectors for the 1024-point transform, 5120 for the 512-point transform, and 2560 for the 256-point transform. There are twice this number of vectors passed through the device to complete the test. The total number of test vectors for this test segment are about 36,000.
• b. FFT/IFFT Verification—A single sinusoid is passed through the 128-, 64-, and 32-point transforms. Both forward and reverse directions are tested.
• c. Bit Growth Tests. Each bit-growth pin (2117-2118) is exercised for the 1024- and 512-point transform in the forward and reverse direction.
• d. Power Down Tests—The device is placed in the middle of a transform, then powered down. The outputs are evaluated for correct state. The device is then asked to perform a forward and reverse transform to validate that the device can function after the reset.
• e. Overflow Tests—An overflow condition is induced, and the device evaluated for correct response (e.g. the overflow pin is actuated and the event does not cause an adder to wrap around). The test includes an overflow in the positive and negative direction.
• f. Reset—The device is placed into the middle of a transform operation, then reset. The outputs are evaluated for correct state. The device is then asked to perform a forward and reverse transform to validate that the device can function after the reset.

FIG. 93 is a high-level block diagram of one embodiment of modem receiver 2402 as shown in FIG. 71. The analog received signal-in is first processed by bandpass-and-down-convert block 2750. In one embodiment, the analog received signal-in is either 425 to 600 MHz or 550 to 770 MHz, and is converted by bandpass-and-down-convert block 2750 to a signal which is 100 kHz on both sides of a 18.432 MHz center frequency. In one embodiment, the tuning step size is 99 MHz. In one embodiment, analog-to-digital decimator system (ADDS) 2850 (in one embodiment, this is a Sigma-Delta decimator system that uses a Sigma-Delta analog-to-digital converter 2840) converts this band-limited signal into decimated I and Q quadrature signals, each 15 bits wide, which have a symbol rate of 288 K symbols per second (denoted 288 KBS), which are then processed by FFT block 2849. In one embodiment, FFT block 2849 is equivalent to FFT system 2100 of FIG. 70. The outputs of FFT block 2849 are then processed by post-processing block 2990 into digital data out.

FIG. 94 is a more detailed block diagram of modem receiver 2402. Analog received signal in is fed to band-pass filter (BPF) 2740 which limits the input signal to either 425 to 600 MHz or 550 to 770 MHz. The signal is then amplified by variable-gain amplifier 2741, and mixed by mixer 2742 with a demodulator signal of either 627-802 MHz or 752-973 MHz generated by signal generator 2747 as controlled by phase-locked-loop block 2746. The mixer 2742 produces a difference-frequency signal centered at 202.752 MHz which is filtered by BPF 2743. The resultant signal is again amplified, this time by variable-gain amplifier 2744, and then mixed by mixer 2745 with a demodulator signal of either 221.184 MHz generated by signal generator 2749 as controlled by phase-locked-loop block 2748. The resultant signal is an analog signal centered at 18.432 MHz and having a 200 kHz bandwidth. The resultant 18.432 MHz analog signal is then passed to an analog-to-digital decimator which, in this embodiment, is denoted as the components encircled by the dotted line referenced as Sigma-Delta decimator system (SDDS) 2850′. The exact mix of components which are included in SDDS 2850 can vary from embodiment to embodiment (that is, where the dotted line for SDDS 2850′ is drawn may vary).

In FIG. 94, the 18.432 MHz analog signal is passed through BPF 2839 which is centered at 18.432 MHz. The 221.183 MHz signal is divided by divider network 2838 to produce a 73.728 MHz signal which drives Sigma-Delta converter 2840, and two 18.432 MHz signals (one of which is 90 degrees shifted from the other) which drive digital I/Q detector 2841. Sigma-Delta converter 2840 is any conventional Sigma-Delta converter, such as described in An overview of Sigma-Delta Converters, by Pervez M. Aziz et al., Vol. 13, No. 1, IEEE Signal Processing Magazine, January 1996, which is hereby incorporated by reference. Sigma Delta converter 2840 achieves high resolution by oversampling the input signal at a frequency much above the Nyquist frequency, and by providing a negative feedback path which uses an analog representation, y_a[n] of the quantized output signal y[n]. FIG. 95 shows one such Sigma Delta converter 2840, having difference block 2860 that forms u[n] which is input x[n] minus feedback y_a[n]. Signal u[n] then is processed by discrete-time integrator 2863 and quantizer 2864, which is simply a comparator. By providing a sampling frequency which is high enough, the Sigma-Delta converter 2840 allows the use of a 1-bit quantizer to achieve high overall resolution.

Referring back to FIG. 94, the 73.728 MHz quantized output of Sigma-Delta converter 2840 is coupled to digital I/Q block 2841. In one embodiment, digital I/O block 2841 is simply two 2-input AND-gates; one input of both AND gates is connected to the 73.728 MHz quantized output of Sigma-Delta converter 2840, the other input of the first and the second AND-gate is coupled to the 0□ and the 90□ 18.432 MHz outputs of divider 2838. The outputs of digital I/Q detector 2841 are thus two serial streams, that represent I and Q quadrature signals respectively. The serial I and Q signals are then fed to coarse decimator and MUX 2842, which converts the two serial streams into a single N-bit-wide time-multiplexed I/Q parallel stream. In one embodiment, this time-multiplexed I/Q parallel stream is 10 bits wide. This time-multiplexed I/Q parallel stream is clocked at 2.304 MHz, and provides 10 bits of I followed by 10 bits of Q, thus having 1.152 million samples of I interleaved in time with 1.152 million samples of Q. This time-multiplexed I/Q parallel stream is then fed to I/Q demux 2843 which de-multiplexes the time-multiplexed I/Q parallel stream into separate I and Q streams clocked at 1.152 MHz each, and each 10 bits wide. These separate I and Q streams are then processed by three digital-processing blocks: DC-offset adjust block 2844 that digitally adjusts for DC (direct current) balance, DS_gain adjust block 2845 that digitally adjusts the decimated signal gain, and DS_mix block 2846 that digitally adjusts the phase.

The Sigma Delta decimator system (SDDS) 2850 is a N-bit A-to-D converter which generates a one-bit serial data stream having resolution and accuracy of N bits (in one embodiment, 15-bit resolution is obtained; in another embodiment, the A/D has a 10-bit resolution with 9-bit linearity). SDDS 2850 is running on the clock generator 2749 divided to 73.728 MHz which oversamples the SDDS input signal in order that it only passes data at the 18.432 MHz±100 kHz, approximately. The following circuits 2841-2847 then take that 200 kHz of frequency that Sigma-Delta converter 2840 passes and shift it down a base band, providing a range from 0-200 kHz. SDDS 2850 turns this relatively slow signal into 10-bit parallel words. The Sigma-Delta converter 2840 outputs a 1-bit serial stream, which is ANDed with two 18.432 MHz square waves to produce serial digital I and Q that are two 18.432 MHz gated square waves.

In one embodiment, the entire SDDS 2850 is integrated on a single VLSI chip using 0.8 micron BiCMOS 4S+ technology fabricated by IBM Corporation, with the analog circuits operating from a 5 volt supply voltage and the digital circuits operating from a 3.3 volt supply voltage. This single-chip implementation facilitates bit growth from stage-to-stage in order to prevent or reduce truncation or round-off errors. Thus 10-bit I and Q signals at the output of I/Q demux block 2843 are allowed, in one embodiment, to grow to 25-bits at the output of DS_mix block 2846 through the digital processing of DC-offset adjust block 2844, DS_gain adjust block 2845, and DS_mix block 2846. For example, the N bits each of the I and Q data streams at the output of I/Q demux block 2843 grow a little to N⁺ bits after the digital processing of DC-offset adjust block 2844, N⁺⁺ bits after DS_gain adjust block 2845, and N⁺⁺⁺ bits after DS_mix block 2846. Decimators 2847 and 2847′ select one out of every four values from the I and Q data streams, respectively, thus producing a 288 kHz rate of 25 bits each for the I and Q streams. These then pass through scaling blocks 2848 and 2848′ which scale each data stream to 15 bits, which are denoted I′ and Q′ and are coupled to 15-bit FFT 2849.

One consideration with the large number of signals on such a single-chip implementation is to minimize the number of different clock signals. In the embodiments described for FIG. 94, for example, this is accomplished by running a large number of blocks from a single clock, even though some of those blocks might be able to run off a different and slower clock.

Overview of Data-Delivery Architecture

Referring now to FIGS. 96 and 97, there is shown the overall architecture of a data delivery system 500 according to another embodiment of the invention. The data delivery system 500 provides high speed data access to the home 510 or office 512 (alternately referred to above in FIG. 1 as remote units 46) over the HFC distribution network 11 using the infrastructure of the modem-based telephony transport system 10 described hereinabove. FIG. 97 illustrates the integration of the data delivery elements in the HDT 12. The system allows users to have access to local content 520 and the Internet 530 through services available at the cable providers' premises or head end 32.

Among other things, system 500 provides: (1) user data access to the Internet 530 and local content on a head-end server 520 through the above-described access platform; (2) support for TCP/IP and transparent bridging at the data link layer using a Dynamically Adaptive Transport Switching (DATS) methodology (described below); (3) guaranteed, reliable symmetrical data service at transfer rates from 64 Kbps to 512 Kbps, in increments of 64 Kbps, for geographically dispersed individuals;

(4) guaranteed, reliable, symmetric shared access to a 8.192 Mbps data pipe for geographically limited group of users connected in a routed configuration; (5) mixing of data and telephony within a single HDT 12; (6) network management for telephony, video, and data through integrated CMISE and SNMP; (7) routed service through a head-end server; and (8) use of HISU and MISU RF modem technology for transport.

Referring now to FIGS. 98-100, the Cable Data Modem (CDM) 535 for the system 500 preferably can take three forms: a stand-alone box called the Personal Cable Data Modem (PCDM) 540, a HISU add-in card called the Data Modem Service Module (DMSM) 550, or a MISU add-in card called the Data Modem Channel Unit (DMCU) 560. The stand-alone PCDM 540 has several connector options; including standard F style coax cable, 10baseT Ethernet 542, and RS232 544. The DMSM add-in card preferably resides in an expansion slot on HISU 68 enclosure and will terminate a customer's computer with a 10BaseT Ethernet connection. The DMCU 560 add-in card will reside in a line-card slot of the MISU and will provide a 10BaseT Ethernet routed connection to four users. Customers without an integrated Ethernet port can add one to their system at minimal cost.

The system 500 provides connection to head end 32 services via the DATS methodology. The DATS methodology intelligently allocates bandwidth in the system to maximize both transport bandwidth and number of users while providing guaranteed bandwidth. Under TR303/V5 switching environments a central resource within the HDT 12 (described below) provides the intelligence to allocate bandwidth and efficiently manage transport load. This capability is implemented at the customer end by initiating a connection to the head end 32 when data is available to send. When the session is initiated, the head end 32 equipment determines the amount of bandwidth to be allocated to the subscriber as configured during pre-provisioning. The connection is maintained as needed and dropped when transmission is complete. During the time that the connection is maintained, bandwidth is guaranteed, providing the efficiency of packet switching and the guaranteed bandwidth of connection switching. All processing is performed through standard TR303/V5 call processing and therefore integrates completely with telephony provided over system 500. The architecture of the system 500 provides guaranteed bandwidth and latency to all supported users. As indicated in FIG. 101, up to 24 concurrent users can be supported at 512 Kbps within a single 6 MHz transport channel.

Using the DATS methodology, bandwidth is dynamically allocated to support a maximum of 240 users per 6 MHz channel (for example, see FIG. 13) at 64 Kbps. Each user on the system is guaranteed the allocated bandwidth for the duration of the session. As such, the bandwidth and latency seen by the user remains constant, independent of the traffic load, application type, or number of users. Assuming even distribution across all applications, the average frame size carried downstream is 378 bytes, while the average upstream frame size is 69 bytes.

The downstream latency from the HDT 12 is dominated by filling a 512 K data pipe, all other latencies in the system are insignificant. Therefore on average the latency to transfer a TCP/IP frame from the HDT to the customer is 5.9 ms. With Forward Error Correction (FEC) disabled, the average latency in the upstream direction, from the customer end to the HDT is also dominated by filling a 512 K data pipe. Therefore, on average the latency to transfer a TCP/IP frame from the HDT to the customer is 1 ms. Adding FEC will add up to 7 ms to the upstream latency.

Data Transport and Framing

The system 500 provides transparent bridging and data transport. A schematic representation of the data transport and framing is shown in FIG. 102. Upstream data traffic begins at the customer end equipment 511 where frames are put out on the Ethernet link 542. The CDM 535 buffers the frames and encapsulates them with HDLC framing 570. The HDLC frame 570 is then sent out over the coax by a modem 101 as one or more of the possible 240 payloads on the coax. The frame, along with other data and telephony streams is converted at the ODN 18 and sent to the head end 32 over optical fiber. At the head end, the CXMU 56 demodulates and sends the stream to the CTSU 54, where it is routed to the appropriate LANU 580 as part of a MARIO data stream. The LANU 580 buffers the complete frame, stripping the HDLC framing prior to putting the frame on the local Ethernet. All routing for the Internet is performed by the head-end server 590. The routing services could also be incorporated in LANU 580.

In the case of downstream traffic, the head-end server 590 puts Ethernet packets on the LAN. One to potentially seven LANUs 580 examine the Ethernet address and selectively pick up packets destined for the customer-end machines. Once the Ethernet packet has been accepted, the packet is framed in HDLC and sent, via a MARIO stream, to the CTSU 54 according to the routing established when the call was initially provisioned (explained further below). The CTSU 54 forwards the stream to the CXMU 56 where it is sent over the HFC distribution network 11 to the customer premises equipment 511. At the CDM 535, all packets received are passed on to the local Ethernet connection 542. In the case of a broadcast message, the LANU 580 at the head end will replicate the packet across all attached connections. This allows the bridge to support protocols such as ARP.

The system 500 will utilize the telephony error correction mechanism described above with respect to system 10 of FIG. 1. Under the telephony error correction scheme, forward error correction codes are generated for upstream traffic but not for downstream traffic. Forward error correction on upstream is generated at the ISU 100 (HISU 68 or MISU 66) and consumes the 10th bit of each DS0, thereby protecting each DS0 separately. The error correction can be disabled, but this is not recommended for data transport.

The error detection/correction processing occurs on the CXMU 56 of FIG. 3 and corrected data is delivered to LANUs 580, DS1Us 48, in MARIO streams. Therefore, the system 500 data architecture does not explicitly have to deal with error correction. The CRC of the HDLC frames provide for a level of error detection above the error detection/correction of the CXMU 56. Errors detected in the LANU 580 will be reported through the SNMP agent of the LANU 580.

Component Design

The data delivery hardware for the head end 32 equipment consists of the LANU 580 which interfaces with the HDT 12. The LANU 580 includes a board responsible for all data transport to and from the head-end server LAN 591. In that function, the LANU 580 operates as a point-to-multipoint connection that is responsible for concentrating up to 128 DS0s onto a single Ethernet connection. The LANU 580 has the following features:

• • (1) It sits in a DS1U 48 slot and is form/fit compatible with the HDT 12 backplane.
  • (2) It provides 10BaseT Ethernet connection to head-end LAN.
  • (3) It supports multiple LANUs 580 on a single LAN through a 10BaseT connection or fast Ethernet through hub.
  • (4) It concentrates up to 128 DS0s into a single Ethernet Connection.
  • (5) It supports time slot assignment and super-channel aggregation across four MARIO data streams independent of the CTSU 54.
  • (6) It supports Dual HDT 12 LAN ports.
  • (7) It maintains on-board FLASH for storage of operational code image.
  • (8) It supports N×64 service for super-channels up to 512 Kbps.
  • (9) It guarantees time ordering of multi-channel calls independent of transport system.
  • (10) It provides transparent bridging and broadcast of Ethernet frames between head-end LAN 591 and CDM 535.
  • (11) It self-discovers Medium Access Control (MAC) addresses of CDM 535 and filters Ethernet frames with on-board CAM.

A high-level block diagram of the LANU 580 is shown in FIG. 103. The LANU 580 preferably employs a single processor, unified memory design. In this embodiment, the main processor on the LANU 580 is the Motorola MC68 MH360 QUICC32 (581), running at 33 MHz, which can deliver approximately 5 MIPS. The QUICC32 is actually a dual processor embedded controller that also contains a dedicated independent RISC processor communications called the CPM. The CPM along with Direct Memory Access (DMA) can access memory and move communication traffic without placing any performance burden on the main processor. In addition to acting as the host processor, the QUICC32 can also act as a slave. The LANU 580 implementation is preferably based on 4 QUICC32s with one acting as master and the remaining three operating in slave mode. The combination of the four QUICC32s provide the majority of the system peripherals.

There are several types of memory 582 on the LANU 580. The first and largest is 8 MB of page-mode DRAM for the storage of LANU operational code. In addition to operational code, the DRAM also holds the routing tables, data buffers, and buffer descriptors needed to process data traffic. Second, the LANU contains 2 MB of FLASH memory to store an image of its operational code. On power-up, the image is loaded into DRAM. Finally, the LANU also contains 128 Kbytes of EPROM to hold boot code. The boot code will load the contents of the FLASH into DRAM on power-up. If greater performance is desired, fast SRAM can be added to hold the data buffers and buffer descriptors for the data traffic.

There are two sets of system peripherals on the LANU: those that are contained within the QUICC32s and those that are not. Regardless of location, peripheral control on the LANU 580 is managed by the System Integration Module (software) (SIM) of the master QUICC32. The SIM is responsible for managing generation of Chip Select (CS) and other control lines.

The most important of the system peripherals are the QMC HDLC controllers 586 located in the QUICC32s. The QMC of the QUICC32 can implement up to 32 HDLC controllers running at 64 Kbps and are used to process the data traffic in the MARIO streams from the CTSU 54. The QMCs 586 can also support super channels by aggregating multiple 64 Kbit channels into higher data rate channels. The QMC 586 is implemented in the CPM of each QUICC32 and with the addition of SDMA can autonomously move communications data to and from main memory 582. Operation of the QMC 586 is controlled by the master processor 581 through the use of buffer descriptors that reside in external memory 582.

In addition to the QMC 586, three additional HDLC controllers 587 are used to provide two 2 Mbps HDT backplane LAN ports and a 10 Mbit Ethernet port. As with the QMC 586, the master processor 581 controls the HDLCs through the use of buffer descriptors, but unlike the QMC, these data structures reside in dual ported RAM (DPR) that are internal to the QUICC32s.

There are two additional system peripherals that reside outside of the master and salve QUICC32s. The first is the Rate Adaptation/Ninth Bit Signaling/Time Slot Assigner logic block (RA/NBS/TSA) 588. The RA/NBS/TSA 588, as its name suggests has three functions. The rate adaptation function is responsible for converting the 2.56 Mbps, 9 bit data format of the input MARIOs to the 2.048 Mbps, 8 bit data format of the QMC 586 in both receive and transmit directions. In both directions the RA is also responsible for managing any information that may be placed in the 9th bit.

The NBS is responsible for transmitting and receiving the data that is carried with each DS0 in the ninth bit. The ninth bit is used for two distinct functions. In the upstream direction the ninth bit carries information regarding the ordering of data within a multi-channel call. The signaling consists of a repeating number that indicates which time position the DS0 occupies in the multi-channel call. The format of the upstream ninth bit signaling is shown in Table 9.

TABLE 9
Upstream Ninth Bit Signaling
Bit	Contents	Description
1	“1”	Sync Pattern
2	“1”	Sync Pattern
3	“1”	Sync Pattern
4	“1”	Sync Pattern
5	“0”	Sync Pattern
6	“0”	Sync Pattern
7	D[8]	Order Number, Bit 8 [MSB]
8	D[8]*	Inv. Order Number, Bit 8 [MSB]
9	D[7]	Order Number, Bit 7
10	D[7]*	Inv. Order Number, Bit 7
11	D[6]	Order Number, Bit 6
12	D[6]*	Inv. Order Number, Bit 6
13	D[5]	Order Number, Bit 5
14	D[5]*	Inv. Order Number, Bit 5
15	D[4]	Order Number, Bit 4
16	D[4]*	Inv. Order Number, Bit 4
17	D[3]	Order Number, Bit 3
18	D[3]*	Inv. Order Number, Bit 3
19	D[2]	Order Number, Bit 2
20	D[2]*	Inv. Order Number, Bit 2
21	D[1]	Order Number, Bit 1
22	D[1]*	Inv. Order Number, Bit 1
23	“0”	Sync Pattern
24	“0”	Sync Pattern

The numbers can range from 1 to 128 with a 0 indicating that the DS0 has not been assigned a position. During a call, the processor 581 will monitor the ninth bit signals from all the channels and once the order has been established, the processor will configure the TSA function to order the channels. Once the order has been established, the processor will periodically monitor the ninth bit signaling to detect any changes in ordering (that is, frequency hoping due to excessive errors). In the downstream direction, the NBS is used to enable data transmission. Once the LANU 580 receives the ordering information for the channels, the processor will enable transmission by sending a data pattern over the downstream ninth bit of the first DS0 of a multi-channel call. The format for the “Data Dial Tone” signaling is shown in Table 10.

TABLE 10
“Data Dial Tone” Downstream Ninth Bit Signaling
Bit	Contents	Description
1	“1”	Sync Pattern
2	“1”	Sync Pattern
3	“1”	Sync Pattern
4	“1”	Sync Pattern
5	“0”	Sync Pattern
6	“0”	Sync Pattern
7	CMD[15]	Command Bit 15, MSB
8	CMD[14]	Command Bit 14
9	CMD[13]	Command Bit 13
10	CMD[12]	Command Bit 12
11	CMD[11]	Command Bit 11
12	CMD[10]	Command Bit 10
13	CMD[9]	Command Bit 9
14	CMD[8]	Command Bit 8
15	CMD[7]	Command Bit 7
16	CMD[6]	Command Bit 6
17	CMD[5]	Command Bit 5
18	CMD[4]	Command Bit 4
19	CMD[3]	Command Bit 3
20	CMD[2]	Command Bit 2
21	CMD[1]	Command Bit 1
22	CMD[0]	Command Bit 0, LSB
23	“0”	Sync Pattern
24	“0”	Sync Pattern

Two commands are defined. The first is “Idle Sync” (bit pattern for CMD[15:0] is 0000 0000 0000 0000) is sent during idle times to synchronize the receivers. All idle syncs sent from the LANU 580 will be synchronized themselves to simplify the reception of order information in the upstream ninth bit signaling. The second command is “Data Dial Tone” (bit pattern for CMD[15:0] is 1000 0000 0000 0000) and is sent once the order of the super-channel has been established. This command will instruct the CDMs to enable transmission.

The TSA is responsible for ordering and aggregating channels that are sent to the QMCs 586. Although TSA has the ability to aggregate up to 128 channels into a single data stream, most applications will aggregate multiple superchannels, up to 8 DS0s per super-channel, among four DS1-like channels feeding the four onboard HDLC controllers. For 1 to 32 DS0 data streams, the DS0s are aggregated and sent to the QMC 586 as a 2.048 Mbps serial stream. Within a single DS1-like stream, multiple super-channels can be supported by connecting to a single QUICC32 QMC 586. The TSA can also aggregate 128 DS0s into a single 8.192 Mbps data stream and connect it to a QUICC32 HDLC controller. In both cases the TSA is configured to insure that the time ordering of the data is maintained.

The final peripheral that does not reside in a QUICC32 is the Contents Addressable Memory (CAM) 589. The CAM performs memory accesses based upon data rather than address and is used to quickly determine whether an Ethernet frame should be accepted. The Ethernet controller 587a interfaces to the CAM 589 through glue logic and the reject input. When a frame is received that is not in the CAM, the CAM logic asserts the reject control line and the received portion of the frame is discarded. The buffer depth of the Ethernet controller is set so that no memory accesses are generated on rejected frames. The CAM is available off the shelf from MUSIC semiconductor.

The LANU 580 sits in a DS1U 48 slot at the HDT 12 and is form and fit compatible with the DS1U 48 to be backplane compatible. The LANU 580 has four major system connections: MARIO 592, Ethernet 593, HDT LAN 591, and clocking (input not shown in FIG. 103). The four MARIO connections connect the LANU to the CTSU over the backplane. The four MARIO connections provide up to 128 bi-directional, 64 Kbit channels. The Ethernet connection connects the LANU to a local 10 Mbit, 10BaseT LAN. The 10BaseT connection will take the place of a single T1 connection of a DS1U. The connection is terminated by wire-wrapping the 10BaseT to the backplane and routing to a patch panel. For call provisioning and other system functions, the LANU 580 connects to two common 2 Mbps HDLC LANs on the backplane. Finally, system clocking is provided by an external source such as a Building Integrated Timing Supply (BITS).

Functional Description of Upstream Communications

For upstream traffic, the HDLC framed data available on the MARIO interface passes through the rate adaptation and TSA block 588. In this block, the 2.56 Mbps MARIO interface is rate adapted down to 2.048 Mbps. As part of rate adaption, the ninth bit of each DS0+ of the MARIO stream is stripped and sent to the NBS logic. The ninth bit carried an order number that is used to time order the DS0s in multi-channel calls. Once the order numbers are established, the processor 581 configures the TSA to re-order the multi-channel calls and target the super-channel to a QMC 586. For super-channels composed of 32 or less DS0s, the call is placed in a single 2.048 Mbps data stream, along with other calls and sent to a QMC 586. For 128 DS0 calls, the DS0s are placed in a single 8.192 Mbps stream that is target to a QUICC32 HDLC controller 586 configured for 8.192 Mbps HDLC. Whether targeted to a 2.048 Mbps QMC or 8.192 Mbps HDLC, the frames are accumulated and transmitted on the local Ethernet LAN.

Functional Description of Downstream Communications

For downstream traffic, data on the LAN is filtered according to the destination MAC address. If the MAC address is in the Content Addressable Memory (CAM) 589, the LANU 580 will accept the Ethernet frame. Once the frame is accepted, the LANU 580 accesses a routing table in memory 582 to select the appropriate MARIO slot for transport. The frame is then scheduled for transmission and the HDLC controller 586 takes over. In the downstream direction for 32 DS0or less calls, the HDLC controller 586 is responsible for creating the MARIO stream and encoding the data into HDLC format. For 128 DS0 calls, the 8.192 Mbps HDLC data stream is split among the four MARIO interfaces (A-D). The time ordering and aggregation in the downstream direction is controlled by the TSA. After the data passes through the TSA, the ninth bit signaling information is added to indicate that data transmission is enabled. At the same time that the ninth bit signal is added, the data stream is rate adapted up to the 2.56 Mbps rate of the MARIOs.

For data movement the on-board memory 582 provides the switching and buffering necessary to move traffic from the Ethernet to the MARIO and vice-versa. The data switching provides a virtual circuit based upon routing information constructed during call provisioning that maps the MAC address to MARIO time slot. The LANU 580 constructs this routing table from information provided during call provisioning and by examining the source MAC address of Ethernet frames received from the customer end. The MAC addresses supported by the LANU are then placed in the CAM 589 where they can be used to filter Ethernet traffic.

In addition to the MARIO and Ethernet interfaces, the LANU 580 also supports two HDT backplane LAN 591 interfaces at 2.048 Mbps. The HDT LAN is maintained by the SCNU 58 at the head end 32 and is used to pass configuration information to the LANU 580. The combination of LANU 580, call processing, and pre-provisioning will provide the MARIO route (time slot in the MARIO data stream) to all customer devices.

Customer Premises Equipment (CPE)

The CPE of the system 500 comes in different implementations. Although the basic data framing and transport remain the same across all the implementations the underlying modem technology and form factor differs. There are currently three general types of CPE defined: HSU based, MISU based, and Stand-alone (a variant of the HISU based implementation). Each of these implementations are discussed separately below.

Data Modem Service Module

A simplified block diagram of the DMSM is shown in FIG. 104. DMSM 550 supports up to 8 DS0's for data traffic. Data is interfaced to the HISU 68 through a Service Growth Module (SGM) interface that implements the bridge router functions of the data connection. The bridge/router is based upon a 68302 embedded processor 605 with 2 MB of DRAM 604 and 256 Kbytes of FLASH memory 606. One embodiment of the customer interface is a 10BaseT, 10 Mbit Ethernet connection 602. The interface between the bridge/router and the HISU modem is a Super-LUIGI (SLUIGI) interface operating at 2.048 Mbps. Data in the upstream direction is accepted by the Ethernet connection and relayed to the HISU 101 modem over the SLUIGI interface as HDLC encoded data. In the downstream direction, data from the SLUIGI interface is passed to the HDLC controller 607 and then sent out the Ethernet connect through Ethernet controller 609. System memory consists of 2 Mbytes of DRAM 604 which contains the operational code that implements the bridge/router functions as well as an SNMP agent. The 256 KBytes of FLASH 606 is used for storage of the operational image and can be updated with TFTP transfers.

In the upstream direction, the HISU interface logic 608 is responsible for generating the ninth bit signaling information for each DS0 and interfacing with the SLUIGI stream of the HISU. The 2.048 Mbps serial data from the HDLC controller is stuffed in the appropriate time slots of the SLUIGI interface. In the case of 64 Kbit traffic, all HDLC data is placed in a single SLUIGI time slot. In the case of multi-channels calls, all HDLC is placed in adjacent SLUIGI time slot receiving the first byte of HDLC data. In addition, the interface logic will generate an order number for each DS0 with “1” assigned to the first DS0 and “8” assigned to the last DS0, “0” is reserved to indicate that the position of the DS0 has not been set. In the event of frequency hopping, the interface logic will continue to number the DS0 time-slots in the order that they are received. For example, under normal circumstances DS0 ninth bit signaling would tag the time slots as “12345678-” for an eight channel call. If DS0 4 is lost due to ingress, then the new order would be “123-45678.” This signaling information is used at the head-end to reorder the DS0s independent of the frequency hopping and transport services.

In the downstream direction the HISU interface logic 608 is responsible for taking data from the SLUIGI interface from the RF modem 101 and giving it to the HDLC controller. In addition, the HISU interface logic monitors the ninth bit signaling information of the first DS0 to detect the “Data Dial Tone” sequence. The “Data Dial Tone” sequence is sent by the head-end to enable data transmission. During the call provisioning process the HISU interface logic sends the ninth bit ordering information as soon as the SLUIGI time slots indicate that they can accept data. It is not until the HISU interface logic gets a positive acknowledgment through the “Data Dial Tone” that data is sent to the head-end in the upstream direction.

Data Modem Channel Unit (DMCU)

A simplified block diagram of a DMCU 610 is shown in FIG. 105. The DMCU supports up to 128 DS0s for data traffic. The data interface to the MISU is a specialized channel that sits on the MISU backplane. The basic design of the DMCU 560 is very similar to the design of DMSM 550. The most notable difference is the interface to the RF portion is two 8.192 MHz serial channels. This allows the MISU interface to support a symmetrical 8.192 Mbps Ethernet connection. Because of the higher throughput the MISU is based on the MC68360 614 that can support both the 8.192 Mbps HDLC connection as well as the 10 Mbit Ethernet. In front of the 10 Mbit Ethernet interface 612 is a router 616 that allows four users access to the 8.192 Mbit data connection. The router 616 design ensures security for all connected users. The design contains 2 Mbytes of DRAM 618 and 256 bytes of FLASH 619. Like the HISU design, the FLASH can be remotely updated with TFTR

The DMCU 610 has an equivalent interface function that moves data from the HDLC controller 611 to the RF modem and works in a very similar way to the DMSM 600 with the exception that the MISU modem interface is formatted as two SLUIGI streams that are clocked at 8.192 Mbps. Between the two SLUIGI streams, 128 DS0s can be carried between the HDLC controller 611 and the modem. The MISU interface logic 613 is responsible for buffering and then sending data over the dual S-LUIGI interface to and from the RF modem. In the upstream direction the MISU interface logic 613 generates order numbers for each of the 128 DS0s over the ninth bit of the DS0+ (the order numbers generated on the MISU work in the same way as they do on the HISU). In the downstream direction, the MISU interface logic 613 is responsible for moving data from the S-LUIGI streams to the HDLC controller 611. The MISU interface logic also monitors the ninth bit data stream from the first DS0 to detect the “Data Dial Tone” that enables data transmission. Ethernet controller 617 moves the data to the router 616.

Stand-Alone Data Modems

The stand-alone data CDMs are based upon the HISU design. In the stand-alone designs, the RF modem 101 of the HISU is tightly integrated with the bride/router design. Like the DMSM 600, the stand-alone supports from 64 K to 512 K. The interfaces are identical with several options: standard “F” style connector to the cable, 10 Mbit Ethernet and RS232 connection to the customers equipment.

System Software and Call Processing

In the TR-008/V2 system, calls are provisioned and nailed up at time of installation. Under this scenario an operator at the head-end 32 is responsible for determining the MARIO configuration and transfer rates (64 K to 512 K). The DATS methodology of present invention utilizes TR-303/V5 call processing to provide dynamic allocation of bandwidth. To maintain the telephony oriented architecture of the access platform of the present invention, the LANU 580 takes on responsibility of a limited subset of the Central Office (CO) functions. This approach has the distinct advantage that the data sessions are fully integrated with telephony.

At the time of deployment, a LANU 580 will be identified as a “Master” LANU (mLANU). The mLANU will have the responsibility to maintain the CO-like functionality for all data calls to the HDT 12. In order to perform these functions, the mLANU will represent itself to the HDT as an IDT. When the mLANU is pre-provisioned, the mLANU will be given an IDT identifier and assigned a Time Slot Management Channel (TMC) channel from the CTSU 54. Regardless of the number of LANUs 588 in the HDT 12 a single mLANU will allocate and keep track of available DS0s for all the LANUs in the HDT. As customers are configured, a Call Reference Value (CRV) for the selected CDM will be assigned to identify the customer. The CRV along with the number of data channels will be added to a call provisioning database on the mLANU.

The call processing sequence for call origination is shown in FIGS. 106-109. Call processing begins when the CDM generates an “Off-Hook” message over the IOC associated with the HISU, MISU, or Stand alone CDM (described above). After the “Off-Hook” message is received at the CXMU 56 then sends a “Request Service” message over the backplane. LAN 591 to the CTSU 54 identifying the CRV of the originator. After receiving the “Request Service” message, the CTSU 54 sends a set-up message to the mLANU 580 over the TMC (DS0 in a MARIO stream). The mLANU uses the CRV to access the on-board database in memory 582 and determine the number of DS0s to allocate the call. Once the number of channels has been determined, the mLANU identifies the DS0 and DS1 for the call. The mLANU then sends a “Make Cross Connect” message to the CTSU 54 over the TMC identifying the DS0 and DS1 and their association with the CRV. In response the CTSU 54 sends a “Req. Bandwidth” message to the CXMU 56 over the backplane LAN 591 to allocate the bandwidth in the transport.

Preferably, the DAT methodology and system provides that each subscriber is represented in the database as having subscribed to a certain level of bandwidth per data connection. For example, a subscriber may sign up for 512K of bandwidth. Upon call setup or connection, the DAT methodology thus assigns each user the number of channels required to achieve the subscriber's bandwidth. However, in certain cases, the transport system 500 may not have the necessary bandwidth to allocate to a subscriber their normal subscripted bandwidth. Under these circumstances, the subscriber is allocated a lesser amount of bandwidth, for example 64K of bandwidth. By dynamically adjusting the amount of bandwidth assigned at call setup for each call, the mLANU can maintain a minimum level of bandwidth for each subscriber. However, existing constraints prevent small decremental bandwidth re-allocations. Constraints existing within the system 500 as described above will enforce the halving of bandwidth of some subscribers to accommodate additional subscribers, rather than by means of a more evenly distributed loading. As shown in FIG. 107, as the number of subscribers increase (on the horizontal axis) any given user's allocated bandwidth will halve at a certain user density. The spread around the average indicates that some users will necessarily lose half their existing bandwidth earlier under loading than will others.

The constraining factor in preventing a more equitable burden is the window nature of the present HISU 68 RF tuning. As noted above, the HISU tunes to one of 24 IOC channels spread throughout the 6 MHz cable channel and has access to five payload channels above and five payload channels below the selected IOC frequency. It cannot borrow payload channels outside this window of ten channels, so therefore there is no way for the “25th” user to borrow just one channel each from seven other users. It can only sit on top of one of the existing IOC payload windows and takeover half of the window bandwidth. At that point, 23 users would be granted 512 kbs bandwidth and two users would each get 256 kbs bandwidth. The “26th” user would result in 22 users with 512 kbs and four users with 256 kbs, and so on. This general pattern is repeated at a load of 72 users and 120 users. (There is a discontinuity in the pattern from 48 to 72 users due to the previously unused two of ten DS0's per window being pressed into two DS0 128 kbps service.) The graph of FIG. 109 illustrates the distribution of bandwidth to users as the number of users increases. It is also contemplated that a subscriber could have different default or standard data rates depending on the time of day or day of week, or based on system loading, such that a user can receive even more bandwidth than their standard rate under certain system loading conditions, such as if the system is loaded below a predetermined threshold at the time the subscriber seeks a connection. Also, using the ninth bit signaling, the mLANU can “steal” bandwidth from other (e.g. high capacity) users. This is done by removing the Data Dial Tone from a subscriber using the ninth bit signaling. This quiesces the user's line, allowing, the number of channels for that user can be reassigned to increase the bandwidth allocated to the user. This technique can also be used to decrease the number of channels assigned to a user.

In order to establish the transport, the CXMU 56 trains the modems (as described above with respect to system 10) and associates the available tones with DS0s. Once the training is complete, the CXMU 56 sends a “Pass” message to the CTSU 54, which in turn informs the mLANU over the TMC that the call is complete with the “Call Complete” message. In response, the mLANU configures the HDLC controllers 586 and the TSA 588 on the mLANU or another LANU through communications over the backplane LAN. At this point the pipe is established but data is not yet enabled.

In order to actually begin data transmission two additional steps have to occur across the ninth bit signaling of the DS0s. At the point where the modems are trained the HISU 68 or MISU 66 interface logic (608,613) will be enabled to transmit data. Once the transmit is enabled, the interface logic will begin transmitting the DS0 ordering number in the ninth bit of each DS0. At the LANU 580, the processor 581 will monitor the ninth bit signaling to determine when all DS0s have established their order. Once all DS0s have established order, the LANU 580 will send the “Data Dial Tone” pattern on the ninth bit of the first DS0 in the multi-channel call. When the ISU 100 receives the “Data Dial Tone” data communications are enabled and data transmission begins.

A session is terminated at the customer end when no data is available for transmission by generating an “On Hook” message. The call processing sequence for an “On Hook” message is shown in FIG. 110. When the CDM terminates the connection, an “On Hook” message is sent over the IOC to the CXMU 56. The CXMU 56 in response sends an “On Hook” message, identifying the CRV, to the CTSU 54. The CTSU 54 then sends a “Tear Down” message to the mLANU 584 over the TMC. At the mLANU 580, the connection is deleted from the connection database and then released. If the connection is not on the mLANU, the mLANU will send a “Release Channel” message to the target LANU 580 and also will send a “Release Cross Connect” message to the CTSU 54. The CTSU 54 will release the cross connects used for the connection and then send a “Release Bandwidth” message to the CXMU 56. At the CXMU 56 the mapping between tones and DS0s is lost and the connection is lost. When the connection is lost, the CDM will lose the “Data Dial Tone” in the ninth bit signaling of the first DS0 of the call.

The LANU 580 can also be configured to bring up connections to customer-end equipment. This allows for notification of incoming e-Mail and personal Web pages without tying up idle bandwidth. To do this, the master LANU in each system will maintain a mapping between the MAC address for each data element in the system and cross that with the CRV. Then an Ethernet packet is put on the head-end LAN 591, and a LANU 580 will read its MAC address and determine whether the connection is up to the device. If the connection is up, the packet will be forwarded over the HFC transport. If the connection is not in place, the receiving LANU 580 will generate a connection request to the mLANU. The mLANU will then signal the transport system over the TMC to bring up a connection to that device using the IOC. The receiving LANU 580 will then send the data once the connection has been established.

LANU Software

The LANU software 620 is responsible for the all major function of the data concentration of the head-end equipment. A simplified schematic diagram of the LANU software is shown in FIG. 111. The software 620 consists of three major components: bridging 621, HDLC LAN manager 622, and data IDT 623. All three tasks will operate as applications on top of the embedded controller operating system “pSOS” kernel in the processor 581. The pSOS kernel will provide the base for the multi-tasking operation of the software 620.

The most important task to the actual transport of data will be the bridging task. The bridging task has several functions. First, the task will be responsible for providing the virtual switch between the MARIO and Ethernet interfaces. The task will be implemented as an “interrupt on receive” task that will execute at interrupt level. At either interface, an interrupt is issued when an entire frame has been received and stored in buffer memory (FIG. 103, 582). During the interrupt service routine, the packet will be handed off by modifying the associated buffer descriptor after looking up the routing in the bridging table (stored in memory 582). For upstream traffic (HDLC to Ethernet), the source of the first packet will be read to discover its MAC address. This address will be added to the bridging table and written to the Ethernet CAM 589 for filtering.

A second function of the bridging task is the creation and maintenance of the bridging table. The bridging table will match the MAC address of the CDM 535 with the MARIO DS0s so that data can be moved between the Ethernet and HDLC. During call processing, the DS0s that are allocated to the call will be identified by the mLANU 580 through backplane LAN (591) Messaging and installed in the bridging table. As described above, when the first frames begin to flow from the CDM, the source MAC address will be identified and the table entry for the CDM will be complete. At this point data will flow in both directions. Once the MAC address has been discovered, the bridging table entry will remain intact until the connection is terminated by the CDM.

A third function of the bridging task is maintenance of an SNMP agent. SNMP traffic will be handled and processed from the Ethernet port. The agent will support a standard MB-II information database for transparent bridging. In addition, objects will be added to the MIB that are specific to the data architecture to facilitate CMISE-SNMP integration and different billing options.

Finally, the bridging function may support link-layer encryption/decryption on the bridged data. Encryption/Decryption may be software only or hardware assisted depending upon the desired performance of the system. In either case, this function will execute as an application on top of pSOS.

Another component of the LANU software 620 is the HDT LAN manager 622. The HDT 12 LAN 591 is used to communicate system messages between the elements of the HDT 12. During pre-provisioning, the SCNU 58 will communicate system parameters such as CRV, IDT ID, and number of channels accessible by the CDM to the mLANU 580. These parameters will be used in the construction of the call provisioning table resident on the mLANU. During call provisioning, the mLANU will examine the provisioning table for available DS0s and use the HDT LAN 591 to set up MARIO configurations on other LANUs 580.

Another important function of the HDT LAN manager software 622 is support for field software upgrades. During download, the LANU 580 will take the image from the HDT LAN and store it in on-board FLASH memory. Aside from the SCNU 58, the LANU will be the only board in the HDT 12 that will load its image from its own FLASH on power up. As such, support for image download from the SCNU 58 Ethernet port will need to be added to the SCNU software. A final function of the LAN manager software 622 is to provide the network management access to the SNMP environment of the LANU.

The final major task of the LANU software 620 is the data IDT 623. As described above, the system 10 of the present invention is designed to provide access from POTS to a CO switch. As such, the burden of resource allocation and assignment of DS0 terminates at the switch. Since the data architecture of the system 10 terminates at the head-end there is no such centralized resource in the architecture to provide the services of the switch. In order to provide the services required to terminate the data “calls” a single LANU 580 functions as the data IDT.

The function of the data IDT is to provide a single point of reference for the data resources of the HDT 12. During pre-provisioning of the LANU hardware a LANU 580 will be designated the “Master” LANU (mLANU) and assigned an IDT identifier. The mLANU 580 will then take on the function of the switch for data calls by maintaining a table that maps CRVs to service level (# of channels). In addition, the mLANU will maintain a map of all available DS0s an all LANUs (including the mLANU itself) installed at the HDT. A copy of the call provisioning table will be kept in on-board FLASH so it can survive a power loss.

In order to maintain compatibility with standard telephony traffic, the means of communication between the CTSU 54 and mLANU will be a TMC connection over one of the DS0s within a MARIO. During call provisioning, the CTSU 54 sends a setup message over the TMC and the mLANU will respond with a “Make Cross Connect” message that identifies the DS0, DS1, and CRV for the connection. As discussed previously, the mLANU will also configure the LANU 580 for the connection through communications over the HDT 12 LAN 591. Therefore the data IDT software 623 will emulate the switch though its communications with the CTSU 54 over the TMC using Q.931 compatible messaging.

On all LANUs in the HDT 12, whether master or not, the data IDT software 623 will be responsible for configuring the TSA and communicating with the bridging task. In configuring the TSA, the data IDT will monitor the sequence numbers in the ninth bit signaling and appropriately configure the interconnect so that the order within a multichannel call is maintained. In addition, the data IDT software 623 will communicate the state of the connection to the bridging task to open up the data pipe.

Another important function of the data IDT software 623 is to provide the information needed to provide billing and other accounting functions. As an IDT like function the data IDT will also support standard CMISE objects.

CDM Software

Software provided in a CDM 535 (executing on the local processor 605 or 614 and represented by such elements) will provide the same types of functions. The major function of the CDM software is to provide the bridge/router (brouter) functionality at the customer-end. In supporting the brouter function the CDM software supports IP routing, PPP, and SLIP. As part of IP support the CDM supports TFTP for downloading new code images. The CDM also supports a standard SNMP agent with a full MIB-II information base. Preferably, the software executes on either the 68302 (605) or 68360 (614) processor.

The control of the modem portion is with the standard MISU or HISU software running on a Motorola 68HC11. This code supports all the alarm conditions and communications set out above for IOC communications. The interface between the RF modem and the brouter is preferably a hardware only implementation.

Network Management

Network management of the data architecture of system 500 is preferably provided by both CMISE and SNMP. The CMISE portion of network management will be responsible for the transport mechanism for data, while SNMP will be used for data network oriented management. In this environment, SNMP is an overlay to the CMISE environment.

As with all telephony services, the data architecture will depend upon CMISE for network management of call provisioning and other transport related functions. In addition, CMISE will be responsible for accounting on data connections. This approach provides for a very flexible billing system where services can be billed per connection time, bytes passed, or packets passed. Statistics will be collected in the mLANU and reported to the network manager.

SNMP management is used to provide data services management for the data architecture. In this way the data architecture will resemble a standard data network. Within SNMP management, the LANU 580 and CDM will maintain SNMP agents compliant with the MIB-II standard. In order to support an SNMP agent both the LANU and the CDM will need to support the UDP and IP protocols in addition to the SNMP protocol. In order to provide a single point of management for data and telephony, both CMISE and SNMP are preferably integrated into the same element manager. This level of integration will simplify billing by providing several options such as bill by connection time, bytes passed and packet passed.

Asymmetrical Data Delivery

For many casual residential users, data traffic can be characterized as mostly “bursty” (intermittent), downstream traffic with relatively, small upstream needs. The most cost effective means of delivering services such as Web browsing, file downloads, and CD-ROM preview is asymmetrical transport. The asymmetrical data transport embodiment of the invention includes a customer premise unit or Personal Cable Data Modem that contains a 30 Mbps, QAM downstream demodulator (PCDM-30) 620a, as shown in FIG. 112. PCDM-30 also includes an OFDM upstream modulator supporting a minimum of 64 Kbps guaranteed, non-shared bandwidth. The connection to the customer-end equipment is 10BaseT Ethernet that supports standard TCP/IP.

At the head end 32, an ASMU 622a supports multiple users on a single 30 Mbps channel which occupies 6 MHz of spectrum outside of the channels of the telephony transport system 10. In addition to the downstream modulator, the ASMU 622a concentrates the return channels by interfacing with the HDT 12. Upstream traffic is carried over as a single DS0 and integrated with the downstream transport on the ASMU 622a. The connection from the ASMU to the headend services is 10BaseT, but higher capacity industry standard connections are also possible.

The ASMU 622a sits at the head end 32, but not in the HDT 12. The function of the ASMU 622a is to integrate the upstream path for up to 400 DS0s (Configurable from 64 Kbps to 512 Kbps) and a 30 Mbps shared downstream. Each LANU 580 will generate an 8.2 Mbps HDLC stream that contains the 64 Kbps Ethernet packets from all the users that are attached to LANU through the transport system. On the ASMU 622a, up to four of these, are aggregated, and sent out to the head services over 10BaseT Ethernet. In the downstream direction, the data on the 100BaseT is filtered on the ASMU, and those packets destined for the customer end products are accepted and then modulated onto the 30 Mbps shared medium.

In order to register a modem, the customer-end modem sends out an IP packet to identify itself. This causes the LANU 580 to assign an HDLC address that is mapped to the MAC address of device. This information is passed to the ASMU 622a so that the HDLC address can be used by the modulator over the HDT 12 backplane LAN 591. The HDLC address and frequency for the tuner is also sent to the customer-end over the downstream telephony path and registered at the customer end. This address is then used by the customer-end equipment to filter the 30 Mbps downstream channel.

One advantage of the asymmetrical system is that a relatively large number of casual users (300+) can be supported by a single multi-megabit downstream transport, with an optimal amount of upstream capacity. The implementation of the downstream matches the downstream of other cable data modems in use and additionally provides superior, high capacity upstream. Since casual users place lesser demands on the network (peak utilization is lower than that of business), users can be concentrated on the return channel, thus lowering head-end 32 costs.

The upstream channel in asymmetrical applications is still important due to the nature of the acknowledge protocol of TCP/IP, where blocks of data sent in the downstream must wait on an acknowledge message from the receiver before subsequent data blocks are sent. If the upstream channel is too small, the downstream channel will stall, reducing the utilization of the downstream bandwidth. By guaranteeing a minimum of 64 Kbps to each user, the asymmetrical system can deliver greater than 1 Mbps sustained to each user, matching the capacity of most residential computer equipment. Another advantage is the superior security of OFDM in the upstream. Unlike other shared upstream modem products currently available, the asymmetrical system herein described prevents information, such as bank accounts and credit card numbers exchanged during on-line Internet shopping, from being “seen” by other modems on the network.

Summary of Data Delivery System Advantages

Thus, the symmetrical embodiment of system 500 provides many options for the delivery of data services over HFC distribution network 11 to the residence or business. The DMSM 550 provides from 64 Kbps to 512 Kbps access to head-end resources over a 10BaseT connection or RS232 (64 Kbps service). The service is symmetrical (same data rate upstream and downstream), non-shared and dedicated to each user, providing a guaranteed level of service. As an add-in card to the HISU, the DMSM 550 provides complete transport integration with telephony, supplying high-speed data and two POTS lines to the residence. The PCDM 540 provides the same data transport capabilities as the DMSM 550 in a standalone configuration, packaged in a traditional modem housing. This implementation is ideal for premises or installations where telephony is not deployed.

The DMCU 560 is an MISU channel unit that provides higher data rates than either the DMSM or PCDM-512K. The DMCU 560 router manages four subscribers who share up to 8.192 Mbps of symmetrical bandwidth. The router implementation guarantees that all four subscribers on the DMCU 560 have private connections. The DMCU 560 works well for multiple dwelling installations for Internet access and small business connections where symmetrical, non-shared data access is required.

At the head end, the LANU 580 provides the concentration of up to 100 DS0s in flexible combinations of various data rates, from 641 Kbps to 512 Kbps for residential, and up to 8.192 Mbps for business applications on a single, industry standard 10BaseT connection. An HDT 12 can be configured with up to seven LANUs, concentrating up to 700 DS0s. In addition to the industry standard transparent bridging function, the LANU also provides the intelligence for the dynamic, adaptive allocation of bandwidth capacity to optimize transport during times of heavy loading. This capability enables an HFC service provider using system 10 to mix residential and business data services in a single 6 MHz channel without compromising the quality of service for business connections during peak Internet access times. Dynamic-allocation allows the customer units to efficiently utilize the data transport by dropping connections at times of no traffic and re-establishing them when data is ready to send. Each time a connection is established the LANU 580 will allocate bandwidth of up to a maximum of 512 Kbps, depending upon the network load, with a minimum of 64 Kbps. Finally, the LANU collects detailed traffic statistics that can be used for a variety of billing methods, for instance bill by connect time.

System 500 is particularly effective in meeting the special needs and higher expectations of business applications. Businesses tend to require a higher level of upstream signaling in order to support applications such as telecommuting and videoconferencing. Most cable data modem network architectures can provide only limited upstream capacity, but ADC is able to, offer a very high capacity upstream due to the efficiency of OFDM and frequency agility. Guaranteed bandwidth is of equal importance to upstream capabilities. Businesses must have full access to their pipeline at all times, regardless of other traffic on the network. With system 500, once a premium user's bandwidth has been established, it cannot be diminished, regardless of the number of users who subsequently access the network.

The security of the data being transported is also a major concern to businesses. Security at the transport layer (encryption and secure key exchange) and at the network layer (filtering) is provided by current transport technologies. System 500 also provides additional security at the physical layer, made possible by utilizing frequency scrambling within the OFDM transport.

The symmetrical product line is well suited for “power” Internet users who use their PC's not only for casual Web browsing but for remote LAN access, telecommuting, real-time audio, and possibly video teleconferencing. While these users are demanding, they are frequently early adopters of technology who will push the limits of Internet access and Internet applications, making the symmetrical, non-shared, guaranteed quality of service of the symmetrical products a requirement.

For both residence and business users, the symmetrical embodiment of system 500 provides for superior integration with telephony. By utilizing OFDM transport in both the upstream and downstream, the symmetrical system can carry data in the same 6 MHz channel as telephony traffic. This capability is ideal for smaller installations and early deployment where efficient use of spectrum is important. In addition, OFDM provides a very secure data delivery stern by implementing a point-to-multipoint bridge for data where two customer premises units never share the same digital data stream. The delivery of data over system 500 requires the efficient allocation of available bandwidth and network management of system resources.

System 500 provides a completely scalable data architecture by dynamically allocating bandwidth for data traffic through its utilization of a subset of standard TR303/V5 call processing software. This system capability gives HFC service providers the flexibility to tailor the configuration of head-end resources to satisfy the diverse needs of their subscriber base. Subscriber services can be provisioned at the head end as symmetrical fixed, symmetrical variable, or asymmetrical services. As the subscriber mix changes or subscribers upgrade service, head-end resources can be re-provisioned to meet the new requirements. For example, users can be easily reconfigured to upgrade from 64 Kbps service to 512 Kbps or even from asymmetrical to symmetrical. For capacity planning, data bandwidth is allocated as a number of DS0s to potential users with a single HDT supporting up to 720 DS0s. The number of users supported is then a function of service level (number of DS0S) and concentration ratio (number of users per DS0).

To ensure that service providers have an effective tool to manage their cable data networks, system 500 offers an integrated data/telephony network management solution. Data management is based on industry standard SNMP agents and MIBs (management information bases), which are then combined into an integrated data/telephony network management environment. Integration of data delivery and telephony into a single network management system has several advantages:

• • (1) Symmetrical data, asymmetrical data, and telephony elements can be managed by the same element manager.
  • (2) Less support staff is required.
  • (3) Better integration with billing.
  • (4) Better fault isolation.
  • (5) Lower Mean Time To Repair (MTTR).

Thus, system 500 provides a single, integrated system that can meet the diverse needs of potential subscribers, from casual Internet browsers to high-capacity business users. The integrated solution gives HFC service providers a single point of network management that results in reduced support costs, reduced staffing costs, and shortened time to turn-up new services. Finally, the OFDM technology of system 500 provides data, video and telephony services in a bandwidth-efficient system that reduces the demands on a very valuable commodity for HFC service providers spectrum.

ATM Embodiment

The system 500 of the present invention can also be configured to carry data from an Asynchronous Transport Mode (ATM) network. As shown in FIGS. 114 and 115, system 10 or 500 of the present invention is modified to include an ATM multiplexer/modulator 650 which can receive ATM data from an ATM network 652 and modulate it onto the HFC network. In one preferred embodiment, digital video data is delivered over ATM network 652, multiplexed and modulated using multiplexer/modulator 650 onto the HFC network in RF digital OFDM format on assigned data and/or telephony channels between the head end and a subscriber, as for example described above with respect to system 10 or 500. A digital set top box 654 receives the digital video, formatted for example in 4.0 Mbps MPEG or equivalent, and converts it to video for display on a television 656. A return path to the HDT 12 over a telephony or data channel allows for interactive digital video. A video server 658 and ATM switch 660, feeding the ATM multiplexer/modulator 650, is shown in FIG. 115.

Embodiment of Control Aspects of Telecommunications System Channel Manager

In one embodiment, communication system 10 of FIG. 1 includes channel manager 900 of FIG. 59 to control various aspects of the dynamic allocation of channels to ISUs 100. For example, channel manager 900 assigns each ISU 100 to a subband, allocates channels in the subband to an ISU to complete a communication link, and monitors the channel to detect and avoid use of corrupted channels. Channel manager 900 implements further functions as described below to coordinate the use of the channels in a 6 MHz transmission channel to ISUs 100.

Channel manager 900 may comprise software executed by a processor resident in each CXMU 56 of each HDT 12. Channel manager 900 receives events from board support software 902, IOC and modem communicators 904, ISU ranger 906, and administrator 908. Channel manager 900 also sends messages to IOC and modem communicators 904 for allocation or reallocation of channels. Channel manager 900 uses two types of channels to communicate control data to the ISUs. First, channel manager 900 broadcasts control data over the IOC channels to the ISUs. The control data on the IOC channels contains an identification signal that indicates the ISU to receive the control data. Further, channel manager 900 uses an ISU demand link channel, referred to as an IDL channel, for non-time-critical transport of data between head end 32 and an ISU when the data is of a size that would benefit from a transmission channel with more bandwidth than the IOC. Typically, the data rate for the IOC channel is 16 Kbps and the data rate for the IDL channel is 64 Kbps due to the amount of data contained in each package or frame. Typically, control signals contain four data bytes or less per frame or package. The IDL channel is used to transmit data packages that are larger than this. For example, the IDL channel is used to download software to an ISU, provision a channel unit, transmit future channel unit functions, or transmit protocols. In one embodiment, HDT 12 only implements one IDL at a time. The IDL channel is described in more detail below.

Subband Assignment and Channel Allocation

Channel manager 900 is responsible for assigning an ISU to a subband and for allocating payload channels for communications links to the ISU. Appropriate selection of subband and payload channel improve the performance of communication system 10. Channel manager 900 further monitors the channels and reassigns subbands and reallocates channels as necessary to maintain acceptable communications links between head end 32 and ISUs 100.

Channel manager 900 selects a subband for an ISU in several circumstances: during acquisition, when an HISU is assigned to a subband that has insufficient payload channels to meet a request, and during an HISU IOC timeout event. An IOC timeout event occurs when acknowledgments are not received by channel manager 900 from an ISU within a specified time period. With a timeout, it is assumed that the downstream communications to the ISU are still in tact even though the upstream communications have become corrupted due to noise or collisions. Thus, a message on the IOC to retune to a new subband is assumed to reach the ISU despite the lack of an acknowledgment.

In each case in which an ISU is assigned to a subband, channel manager 900 uses various criteria to select the subband for an ISU. FIG. 62 is a flow chart that illustrates one embodiment of a method for assigning an ISU to a subband. According to this method, channel manager 900 first selects a subband 6202. Channel manager 900 then determines whether addition of the ISU to the subband would provide an acceptable load on the IOC channel 6204. For example, channel manager considers the number of ISUs assigned to a subband. Further, channel manager considers the type of ISU and the likely load that the ISU will place on the IOC channel. By considering these factors, channel manager 900 can selectively distribute the load on the IOC channels so as to facilitate timely communication of control data to and from the ISU. This also allows channel manager 900 to evenly distribute the ISUs over the available subbands such that a like number of ISUs occupy each subband. Channel manager 900 also weighs the number of available channels 6206 within the subband and their transmission quality 6208 as recorded in the tables of channel manager 900. Channels with longer low-error rate histories will be used first. Channels previously marked bad and reallocated for monitoring will be used last. Based on these criteria, channel manager selects a subband for each ISU 6210.

FIGS. 63, 64 and 65 are frequency spectrum diagrams that illustrate initial assignment of HISUs and MISUs to various subbands in a 6 MHz transmission channel. These Figures show that channel manager 900 attempts to evenly distribute the ISUs across the transmission channel. As depicted in FIG. 63, channel manager 900 begins assigning subbands at the middle of the 6 MHz transmission channel. Channel manager 900 then moves out toward the ends of the transmission channel. For example, the first HISU is assigned to subband number 12 and the twenty-fourth HISU is assigned to subband 0. It is noted that more than one ISU can be assigned to a subband. As depicted in FIG. 64, channel manager 900 initially assigns the first MISU to subbands 0 through 12 and the next MISU to subbands 11 through 23. As depicted in FIG. 65, when HISUs and MISUs are assigned to the same subbands, channel manager assigns the subbands so as to evenly distribute the ISUs over the available subbands. It is noted that the factors listed for use in selecting a subband are shown by way of example and not by way of limitation. Other factors can be added and the weight given to each factor can be adjusted without departing from the spirit and scope of the present invention.

FIG. 60 is a flow chart that illustrates one embodiment for a method for allocating payload channels in a subband by channel manager 900. Channel manager 900 attempts to maintain an acceptable distribution of bandwidth within a subband to reduce the need for reallocation of payload channels within the subband. Further, the goal is to allocate channels appropriately across the 6 MHz transmission channel to avoid having to reallocate channels that are currently in use. A channel can be allocated to an ISU only from the available channels in the subband to which the ISU is assigned.

Channel manager 900 receives a request for allocation of a payload channel from either the SCNU 58 or CTSU 54. At block 912, channel manager 900 decides whether sufficient payload channels are available in the current subband to fulfill the request. If sufficient channels are available, the method proceeds to block 914 and determines whether one of the available channels is the IDL channel. If the IDL channel is not one of the available channels, channel manager 900 allocates a channel for each channel requested by CTSU 54 or SCNU 58 at blocks 916 and 918. Channel manager 900 selects the channels based on several criteria that increase the likelihood of achieving a connection with acceptable quality levels. For example, channel manager 900 can use the method shown in FIG. 61. According to this method, channel manager 900 begins the selection process 6100 by identifying available payload channels 6102 that are located toward the center of the 6 MHz transmission channel. Typically, channels that are nearer to the edge of the 6 MHz channel exhibit higher bit error rates than the channels that are closer to the center. Further, channel manager 900 can also consider limitations of the ISU and the requested service in selecting a payload channel. For example, the ISU may be preset for use only with odd or even payload channels. This information may be included in a ROM on the ISU and provided to the channel manager when channel allocation is requested or during acquisition. Further, channel manager 900 uses data on the quality of transmissions over the identified channels stored in tables in channel manager 900 to determine which available payload channels have an acceptable error history 6104, for example, bit error rate. Other appropriate criteria can be used in channel selection that also tend to increase the chances of producing a connection with acceptable quality 6104. Based on these criteria, channel manager selects a payload channel to allocate to the ISU 6106.

If, at block 914, channel manager 900 determines that one of the available channels is the IDL channel, channel manager 900 deallocates the payload channel allocated to be the IDL channel at blocks 920 and 922 due to the lower priority of communications over the IDL channel.

If, at block 912, channel manager 900 determines that sufficient payload channels are not available in the current subband, channel manager 900 determines whether the request is for an HISU 68 or an MISU 66 at block 924. If the request is for an MISU 66, channel manager 900 sends a message to the requestor that the request has failed at block 926.

If, at block 924, channel manager determines that the request is for an HISU, then channel manager 900 selects a different subband at block 928 by weighing the criteria as described above with respect to selecting a subband. Channel manager 900 further marks the channels unavailable in the new subband at block 930 and deallocates channels allocated to the ISU in the prior subband at block 932. At block 934, channel manager 900 assigns the new subband and proceeds to allocate channels as necessary at blocks 916 and 918.

An example of reassigning an ISU to a new subband to accommodate a request for a payload channel is shown in FIGS. 66 and 67. In this example, ISUs A, B, C, and D are initially assigned to subband 4 and ISUs E, F, and G are assigned to subband 17 as depicted in FIG. 66. In subband 4, all payload channels except payload channel 0 are allocated. In this case, channel manager 900 receives a request for two payload channels for ISU C. Since only one payload channel is available, channel manager 900 reassigns ISU C to subband 17 which has sufficient payload channels available to handle the current load of ISU C plus the additional two payload channels as shown in FIG. 67.

Channel Reallocation

Channel monitoring and allocation or reallocation based thereon may be used to avoid ingress. External variables can adversely affect the quality of a given channel. These variables are numerous, and can range from electromagnetic interference to a physical break in an optical fiber. A physical break in an optical fiber severs the communication link and cannot be avoided by switching channels, however, a channel which is electrically interfered with can be avoided until the interference is gone. After the interference is gone the channel could be used again.

Channel Monitoring

Channel monitor 900 monitors the payload channels for errors to help in determining which channels are acceptable for transmission for specific services. One input to channel manager 900 is parity errors which are available from hardware per the DS0+ channels; the DS0+ channels being 10-bit channels with one of the bits having a parity or data integrity bit inserted in the channel as previously discussed. The parity error information on a particular channel is used as raw data which is sampled and integrated over time to arrive at a quality status for that channel. In one embodiment, parity errors that are detected on downstream payload channels are communicated to head end 32 over an associated upstream channel. When the error is detected in the downstream transmission, the parity bit for the upstream transmission is corrupted by intentionally setting the parity bit to the wrong value to indicate the incorrect parity in the downstream transmission path. Thus, the ISU informs the head end of errors in the downstream path.

To monitor the payload channels, channel manager 900 needs an active upstream signal on each payload channel. However, at any given time, some payload channels may not be allocated and some allocated channels may not be active. Thus, these payload channels do not provide the necessary upstream signals to the head end to monitor the quality of the payload channels. To compensate for these idle and unallocated payload channels, channel manager 900 places these channels in loop back mode to monitor the quality. In this case, channel manager 900 sets up the payload channel, transmits data to the ISU on the payload channel and the ISU transmits back specified data on an associated upstream payload channel. Channel manager 900 monitors these channels at the head end to determine error rates for the channels. Thus, the unallocated or idle payload channel can be monitored for errors the same as with active channels. The goal of channel manager 900 is to have payload established on all of the payload channels at a given time. However, it may be acceptable to monitor the performance of each channel at least once an hour if not active.

Channel manager 900 randomly selects and uses ISUs to monitor payload channels in loopback mode described above. This provides several benefits to the system. First, this allows channel manager to handle the diverse layout of a cable plant. Channel manager 900 sets up and uses paths over different legs from the various ODNs of the system. Further, random cycling of the ISUs used in the loop back mode allows the system to properly distribute power in the coaxial network. Specifically, this random selection of ISUs for loopback mode applies to concentration type services.

As described below, some ISUs are powered down when not active. When the ISU is powered down, the upstream modem at the head end detects this condition and sends a specified signal to the CXMC so that channel manager does not use the ISU for loop back purposes. Thus, powered down ISUs do not produce unnecessary errors.

FIG. 68 is a flow chart that illustrates a method for monitoring payload channels by channel manager 900. Channel manager 900 reads parity error registers 901 of the CXMU 56 are read every 10 ms. Generally, the error counts are used to update the channel quality database and determine which (if any) channels require reallocation. The database of channel manager 900 contains an ongoing record of each channel 903. An accumulator sums the errors 905 with previously recorded errors to update the database. The database organizes the history of the channels in categories such as: current ISU assigned to the channel, start of monitoring, end of monitoring, total error, errors in last day, in last week, number of seconds since last error, severe errors in last day, in last week, and current service type, such as ISDN, assigned to the channel. When the channel is a regular (non-loop back) payload channel 907, channel manager 900 determines whether the performance statistics in the database are within service specific threshold 909. When the statistics unacceptably exceed the threshold 910, channel manager 900 reallocates the channel 911 using a “make before break” procedure to reduce the disruption from reallocating the channel. Thus, channel manager 900 allocates the new payload channel for the connection before deallocating the current payload channel.

Two issues presented by periodic parity monitoring as described above must be addressed in order to estimate the bit error rate corresponding to the observed count of parity errors in a monitoring period to determine if a channel is corrupted. The first is the nature of parity itself. Accepted practice for data formats using block error detection assumes that an errored block represents one bit of error, even though the error actually represents a large number of data bits. Due to the nature of the data transport system, errors injected into modulated data are expected to randomize the data. This means that the average errored frame will consist of four (4) errored data bits (excluding the ninth bit). Since parity detects only odd bit errors, half of all errored frames are not detected by parity. Therefore, each parity (frame) error induced by transport interference represents an average of 8 (data) bits of error. Second, each monitoring parity error represents 80 frames of data (10 ms/125 μs). Since the parity error is latched, all errors will be detected, but multiple errors will be detected as one error.

The bit error rate (BER) used as a basis for determining when to reallocate a channel has been chosen as 10⁻³. Therefore, the acceptable number of parity errors in a one second interval that do not exceed 10⁻³ must be determined. To establish the acceptable parity errors, the probable number of frame errors represented by each observed (monitored) parity error must be predicted. Given the number of monitored parity errors, the probable number of frame errors per monitored parity error, and the number of bit errors represented by a frame (parity) error, a probable bit error rate can be derived.

A statistical technique is used and the following assumptions are made:

• • 1. Errors have a Poisson distribution, and
  • 2. If the number of monitored parity errors is small (<10) with respect to the total number of “samples” (100), the monitored parity error rate (MPER) reflects the mean frame error rate (FER).

Since a monitored parity error (MPE) represents 80 frames, assumption 2 implies that the number of frame errors (FEs) “behind” each parity error is equal to 80 MPER. That is, for 100 parity samples at 10 ms per sample, the mean number of frame errors per parity error is equal to 0.8 times the count of MPEs in one second. For example, if 3 MPEs are observed in a one second period, the mean number of FEs for each MPE is 2.4. Multiplying the desired bit error rate times the sample size and dividing by the bit errors per frame error yields the equivalent number of frame errors in the sample. The number of FEs is also equal to the product of the number of MPEs and the number of FEs per MPE. Given the desired BER, a solution set is illustrated below in Equation 3. $\begin{array}{cc}\left(\mathrm{MPE}\frac{\mathrm{FE}}{\mathrm{MPE}}\right)-0.8\mathrm{MPE}& \left(\mathrm{Equation}3\right)\end{array}$

The Poisson distribution, as illustrated below in Equation 4, is used to compute the probability of a given number of FEs represented by a MPE (χ), and assumption 2, above, is used to arrive at the mean number of FEs per MPE (μ). $\begin{array}{cc}P\left(\chi \right)=\frac{e^{-\mu }{\mu }^{\chi }}{{\chi }^{!}}& \left(\mathrm{Equation}4\right)\end{array}$

Since the desired bit error rate is a maximum, the Poisson equation is applied successively with values for χ of 0 up to the maximum number. The sum of these probability is the probability that no more than χ frame errors occurred for each monitored parity error. The results for a bit error rate of 10⁻³ and bit errors per frame error of 1 and 8 are shown in Table 11.

TABLE 11
Bit Error Rate Probability
			Average Frame
Bit Errors	Monitored	Maximum Frame	Errors/	Probability
per Frame	Parity	Errors/Monitored	Monitored	of
Error	Errors	Parity Error (χ)	Parity Error (μ)	BER <-10−3
8	2	4	1.6	98%
	3	3	2.4	78%
	4	2	3.2	38%
1	8	8	6.4	80%
	9	7	7.2	56%
	10	7	8.0	45%

Using this technique, a value of 4 monitored parity errors detected during a one second integration was determined as the threshold to reallocate service of an ISU to a new channel. This result is arrived at by assuming a worst case of 8 bit errors per frame error, but a probability of only 38% that the bit error rate is better than 10⁻³. The product of the bit errors per frame, monitored parity errors and maximum frame errors per monitored parity error must be 64, for a bit error rate of 10⁻³ (64 errors in 64 k bits). Therefore, when the sampling of the parity errors in the error timer event is four or greater, the channel allocator is notified of a corrupted channel.

DS0 Reordering

Some telecommunications services use multiple DS0s (payload channels) to form a communication link in communication system 10. For example, ISDN uses three DS0s to form three payload channels identified namely as B1, B2, and D. To operate properly, the DS0s typically are assigned in a specific sequence. Once the payload channels for the service are assigned, the channel unit associated with the service expects to receive the payload channels in a specific order. When one of the payload channels becomes corrupted, channel manager 900 allocates a different DS0 channel for the corrupted channel and the sequence of the DS0s is altered.

This problem could be avoided by reallocating all three DS0s. However, this is a time consuming process and could cause transient disruption of the service. As an alternative, channel manager 900 can assign an address to the DS0s when the multiple DS0 service is initiated. This address can be used by the channel unit to reconstruct the order of the DS0s on the fly if one or more of the DS0s is reallocated out of sequence with the other DS0s. For example, in the channel enable signal from CXMU 56 on the IOC channel, a BIC state signal can be used to identify the correct order for each DS0. Thus, channel manager 900 can allocate the DS0s in any order and the channel unit can remap the DS0s to the correct order at the ISU. It is noted that the DS0s must still be allocated in different time slots.

ISU Data Link (IDL) Channel

The IDL is a standard payload channel that is dynamically assigned to transmit control data between HDT 12 and ISU 100 when the amount of data exceeds the parameters of the lower bandwidth IOC channel. The IDL channel can provide full duplex communication or simplex broadcast from HDT 12 to one or more ISUs 100. Channel manager 900 dynamically allocates the IDL channel as needed for non-time critical transport of data as described above.

The IDL messages in both directions are variable in length. The IDL data is transmitted over HFC distribution network 11 at a rate of 64 Kbps which is one byte per 8 kHz frame. The IDL channel uses one of the 240 payload channels and the protocol for transmitting IDL messages is handled by the processor on CXMU 56. The processor uses cyclical redundancy codes (CRC) and positive acknowledgments to manage error checking of IDL messages.

The IDL channel can be used to transmit various kinds of data. For example, the IDL channel can be used to provide data to an ISU to configure a payload channel for use with a specific protocol. For example, the IDL channel can be used to down load data to configure a payload channel for use with the LAPB protocol or any other appropriate protocol, including proprietary protocols. Similarly, the IDL channel can be used to download software to an ISU. Transmission over the IDL channel has a lower priority than regular payload transmissions. Thus, channel manager 900 deallocates an IDL channel before completion of the data transmission when channel manager 900 receives a request that requires use of the payload channel that is currently allocated to the IDL.

FIG. 69 is a flow chart that illustrates an embodiment of a method for allocating a payload channel to the ISU data link. At block 330a, channel manager 900 receives a request for an IDL channel. At block 332a, channel manager 900 determines whether a payload channel is available. If a payload channel is available, channel manager 900 allocates the payload channel to the IDL channel 335 and the data is transmitted to the identified ISU. If, however, a channel is not available, channel manager determines whether one of the allocated channels is idle by checking the hook state of a line of a channel unit 342. If the line is on hook 339, then channel manager 900 reallocates the channel to the IDL channel 343 until the IDL transmission is complete. If however, channel manager receives a request for a communication link to the line of the channel unit, channel manager interrupts the IDL channel and reallocates the payload channel to the channel unit.

Power Down

Channel manager 900 can power down an ISU during periods of non-use to reduce energy costs of communication system 10. To power down the ISU, channel manager 900 must determine that all conditions for powering down the ISU are met. For example, channel manager 900 can determine if the lines of the channel units of the ISU provide service that can be powered down. Such services may include, for example, analog services such as POTS and COIN. Further, the lines must be idle. For example, channel manager 900 can determine if a line is idle based on the line's hook status or other appropriate criteria. Channel manager 900 checks the status of the lines each time a line goes from off-hook to on-hook. Channel manager 900 further checks the status of the lines every second to monitor the hook status. It is noted, however, that channel manager 900 will not power down an ISU that is the monitoring ISU for a subband.

When channel manager 900 determines that an ISU can be powered down, the ISUs′ transmitter is disabled. Head end 32 detects the loss of power to the ISU and sends an idle pattern upstream to the switch. An IOC control message to or from the IOC will power-up the ISU. The IOC traffic to or from the ISU indicates to the background task in charge of powering down ISUs to check the ISU against the criteria for powering down again.

It is understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Further Embodiment of Telephony Transport System

With reference to FIG. 116, a general description of a hybrid fiber/coax communications network 1006 in accordance with the present invention shall be described. Telephony and video information from existing telephone and video services generally shown by trunk line 1008 is received by and processed by head end 1010. Head end 1010 includes a plurality of host distribution terminals (HDT) 1012 for telephony data interface and video host distribution terminal (VHDT) 1014 for video data interface. Host distribution terminals 1012 and VHDT 1014 include transmitters and receivers for communicating the video and telephony information between the video and telephony signal distribution network 1006 in accordance with the present invention and the existing telephony and video services as represented generally by trunk line 1008.

The video information is optically transmitted downstream via optical fiber line 1017 to splitter 1018 which splits the optical video signals for transmission on a plurality of optical fibers 1022 to a plurality of optical distribution nodes 1026. The HDT 1012 transmits optical telephony signals via optical fiber link 1020 to the optical distribution nodes 1026. The optical distribution nodes 1026 convert the optical video signals and telephony signals for transmission as electrical outputs via a coaxial distribution system 1007 to a plurality of remote units 1042. The electrical downstream video and telephony signals are distributed via a plurality of coaxial lines 1029 and coaxial taps 1034 of the coaxial distribution system 1007.

The remote units 1042 include means for transmitting upstream electrical data signals including telephony information from telephones 1076 and data terminals 1073 and in addition may include means for transmitting set top box information from set top boxes 1078. The upstream electrical data signals are provided by a plurality of remote units 1042 to an optical distribution node 1026 connected thereto. The optical distribution node 1026 converts the upstream electrical data signals to an upstream optical data signal for transmission via optical fiber link 1020 to the head end 1010.

The present invention shall now be described in further detail with reference to FIGS. 116-123. The first part of the description shall primarily deal with downstream transmission and the second part of the description shall primarily be with regard to upstream transmission. The video and telephony distribution network 1006 in accordance with the present invention, includes head end 1010 which receives video and telephony information from video and telephony service providers via trunk line 1008. Head end 1010 includes a plurality of host distribution terminals 1012 and a video host distribution terminal 1014. The HDT 1012 includes transmitters and receivers for communicating telephony information, such as T1, ISDN, or other data services information, to and from telephony service providers via trunk line 1008 and the VHDT 1014 includes transmitters and receivers for communicating video information, such as cable TV video information and interactive data of subscribers to and from video service providers via trunk line 1008.

The VHDT 1014 transmits downstream optical signals to a splitter 1018 via video feeder optical fiber line 1017. The passive optical splitter 1018 effectively makes four copies of the downstream high bandwidth optical video signals. The duplicated downstream optical video signals are distributed to the correspondingly connected optical distribution nodes 1026. One skilled in the art will readily recognize that although four copies of the downstream video signals are created, that any number of copies may be made by an appropriate splitter and that the present invention is not limited to any specific number.

The splitter 1018 is a passive means for splitting broad band optical signals without the need to employ expensive broad band optical to electrical conversion hardware. Optical signal splitters are commonly known to one skilled in the art and available from numerous fiber optic component manufacturers such as Gould, Inc. In the alternative, active splitters may also be utilized. In addition, a cascaded chain of passive or active splitters would further multiply the number of duplicated optical signals for application to an additional number of optical distribution nodes and therefore increase further the remote units serviceable by a single head end. Such alternatives are contemplated in accordance with the present invention as described by the accompanying claims.

The VHDT 1014 can be located in a central office, cable TV head end, or a remote site and broadcast up to about 112 NTSC channels. The VHDT 1014 includes a transmission system like that of the LITEAMP system available from American Lightwave Systems, Inc., currently a subsidiary of the assignee hereof. Video signals are transmitted optically by amplitude modulation of a 1300 nm laser source at the same frequency at which the signals are received (that is, the optical transmission is a terahertz optical carrier which is modulated with the RF video signals). The downstream video transmission bandwidth is about 54-725 MHz. One advantage in using the same frequency for optical transmission of the video signal as the frequency of the video signals when received is to provide high bandwidth transmission with reduced conversion expense. This same-frequency transmission approach means that the modulation downstream requires optical to electrical conversion or proportional conversion with a photodiode and perhaps amplification, but no frequency conversion. In addition, there is no sample data bandwidth reduction and little loss of resolution.

Alternative embodiments of the VHDT may employ other modulation and mixing schemes or techniques to shift the video signals in frequency, and other encoding methods to transmit the information in a coded format. Such techniques and schemes for transmitting analog video data, in addition to those transmitting digital video data, are known to one skilled in the art and are contemplated in accordance with the spirit and scope of the present invention as described in the accompanying claims.

Telephony information is transmitted downstream by HDT 1012 via optical fiber link 1020 to a corresponding optical distribution node 1026. A more detailed block diagram of one of the HDTs 1012 is shown in FIG. 117. Each HDT 1012 includes an RF modem bank 1050 which receives telephony information via trunk line 1008. The RF modem bank 1050 includes four RF modem modules 1052 and a protection modem module 1054. Each RF modem module receives telephony information, for example time division multiplexed channel signals from a public switched telephone service, via trunk line 1008 and the telephony information modulates an analog carrier for transmission of the downstream optical telephony data by downstream optical telephony transmitter 1080 of downstream telephony electrical to optical converter 1064 to a corresponding distribution node 1026. Each RF modem module includes a transceiver 1053 and provides a downstream electrical telephony signal in one of four frequency bandwidths, each bandwidth being about 6 MHz in width like that of a CATV channel. Each 6 MHz bandwidth channel transmits data at 22 Mbits/sec and can provide for transmission of 8T1 digital telephone signals; T1 being a conventional telephone signal where 24 voice channels are sampled at an 8 kHz rate, with 8 bits per sample (each 8 bit conversation sample is termed a DS0). Each of these signals from the four RF modem modules 1052 are transmitted via coax patch cables to a combiner 1082 of downstream telephony electrical to optical converter 1064 for transmission by optical transmitter 1080. Therefore, the spectrum for the downstream optical telephony data is four separated 6 MHz frequency bands containing 22 Mbits/sec of data within each 6 MHz bandwidth. The four 6 MHz frequency bands, separated by a guard band as is known to one skilled in the art, are transmitted in about the 725-800 MHz bandwidth.

Any number of modulation techniques may be used for transmission of the telephony information downstream. The transmission downstream is point to multipoint transmission using broadcast type transmission schemes. The modulation techniques utilized and performed by RF modem module 1052 may include quadrature phase shift keying (QPSK), quadrature amplitude modulation (QAM), or other modulation techniques for providing the desired data rate. Modulation techniques, such as QPSK and QAM, are known to those skilled in the art and the present invention contemplates the use of any such modulation techniques for downstream broadcast transmission.

The electrical to optical converter 1064 includes two transmitters 1080 for downstream telephony transmission to protect the telephony data transmitted. These transmitters are conventional and relatively inexpensive narrow band laser transmitters. One transmitter is in standby if the other is functioning properly. Upon detection of a fault in the operating transmitter, controller 1060 switches transmission to the standby transmitter. In contrast, the transmitter of the VHDT 1014 is relatively expensive as compared to the transmitters of HDT 1012 as it is a broad band analog DFB laser transmitter. Therefore, protection of the video information, non-essential services unlike telephony data, is left unprotected. By splitting the telephony data transmission from the video data transmission, protection for the telephony data alone can be achieved. If the video data information and the telephony data were transmitted over one optical fiber line by an expensive broad band analog laser, economies may dictate that protection for telephony services may not be possible. Therefore, separation of such transmission is of importance.

As an alternative embodiment for providing transmission of optical video and telephony signals to the optical distribution nodes 1027 from head end 1010 as shown in FIG. 120, the HDT 1012 and VHDT 1014 can utilize the same optical transmitter and the same optical fiber line 1016. The signal then is split by splitter 1018 and four split signals are provided to the optical distribution nodes 1027 for distribution to the remote units 1042 by the coaxial distribution system 1007 as further discussed below. However, as described above, the optical transmitter utilized would be relatively expensive due to its broad band capabilities, lessening the probabilities of being able to afford protection for essential telephony services.

As one skilled in the art will recognize, optical link 1020, as shown in FIG. 117, may include four fibers, two for transmission downstream from electrical to optical converter 1064 and two for transmission upstream to optical to electrical converter 1066. With the use of directional couplers, the number of such fibers may be cut in half. In addition, the number of protection transmitters and fibers utilized may vary as known to one skilled in the art and any listed number is not limiting to the present invention as described in the accompanying claims.

RF modem bank 1050 includes a protection RF modem module 1054 with a transceiver 1053 connected to combiner 1082 of electrical to optical converter 1064. Protection RF modem module 1054 is further coupled to controller 1060. When a fault is detected with regard to the transmission of one of the RF modem modules 1052, a signal is generated and applied to an input 1062 of controller 1060. Controller 1060 is alerted to the fault and provides appropriate signaling to switch the protection RF modem module 1054 for the faulted RF modem such that the protection RF modem module 1054 transmits within the 6 MHz bandwidth of the faulted RF modem module 1052 so that the four 6 MHz bandwidth signal transmission is continued on optical fiber link 1020. The use of one protection RF modem module 1054 for four RF modem modules 1052 is only one embodiment of the present invention and the number of protection RF modem modules relative to RF modem modules may vary as known to one skilled in the art and described in the accompanying claims. As shown in FIG. 123, RF modem bank 1050 may include one protection module 1054 for each RF modem module 1052. In this embodiment, the RF modem bank 1050 includes three RF modem modules 1052 and three protection modules 1054 for one-to-one protection.

An optical distribution node 1026 as shown in FIG. 118 receives both the downstream optical telephony signal and the split downstream optical video signal. The downstream optical video signal is applied by the optical fiber 1022 from splitter 1018 to a downstream video receiver 1120 of optical distribution node 1026. The optical distribution node 1026 further includes downstream telephony receiver 1121 for receiving the downstream optical telephony signal on optical link 1020. The optical video receiver 1120 utilized is like that available in the LITEAMP product line. The converted signal from video receiver 1120, proportionally converted utilizing photodiodes, is applied to bridger amplifier 1127 along with the converted telephony signal from downstream telephony receiver 1121. The bridging amplifier 1127 simultaneously applies four downstream electrical telephony and video signals to diplex filters 1134. The diplex filters 1134 allow for full duplex operation by separating the transmit and receive functions when signals of two different frequency bandwidths are utilized for upstream and downstream transmission. There is no frequency conversion performed at the optical distribution nodes with respect to the video or downstream telephony signals as the signals are passed through the optical distribution nodes to the remote units via the coaxial distribution system in the same frequency bandwidth as they are received.

After the optical distribution node 1026 has received downstream optical video signals via optical link 1022 and downstream optical telephony signals via optical link 1020 and such signals are converted to downstream electrical video and telephony signals, the four outputs of the optical distribution nodes 1026 are applied to four coaxial cables 1029 of coaxial cable distribution system 1007 for transmission of the downstream electrical video and telephony signals to the remote units 1042; such transmission occurs in about the 725-800 MHz bandwidth for telephony signals and about the 54-725 MHz bandwidth for the downstream electrical video signals. Each optical distribution node 1026 provides for the transmission over a plurality of coaxial cables 1029 and any number of outputs is contemplated in accordance with the present invention as described in the accompanying claims.

As shown in FIG. 116, each coaxial cable 1029 can provide a significant number of remote units with downstream electrical video and telephony signals through a plurality of coaxial taps 1034. Coaxial taps are commonly known to one skilled in the art and act as passive bidirectional pick-offs of electrical signals. Each coaxial cable 1029 may have a number of coaxial taps connected in series. In addition, the coaxial cable distribution system may use any number of amplifiers to extend the distance data can be sent over the coaxial portions of the network 1006.

The downstream electrical video and telephony signals are provided from the coaxial taps to the remote units 1042 in a number of different ways. In one embodiment, the signal from the coaxial tap 1034 is provided to a home integrated service unit 1070 as shown in FIG. 119. The home integrated service unit 1070 of FIG. 119 includes a power tap 1099 coupled to a conventional power supply and ring generator 1101. The downstream electrical video and telephony signals are provided to a tap 1097 for application of the signals to both diplex filter 1110 and ingress filter 1098. The downstream video signal is provided from ingress filter 1098 to video equipment 1072 via set top box 1078. The downstream telephony signal is applied from diplex filter 1110 to RF demodulator 1104 of RF modem module 1102 and the demodulated signal is applied to an applicable service interface for processing and connection to user equipment. For example, the RF demodulated signal is processed via Plain Old Telephone Service (POTS) service interface 1112 for output on twisted pairs 1118 to telephone 1076 by POTS connection 1114. The other service interfaces such as ISDN interface or a T1 interface perform their conventional functions as are known to those skilled in the art for transmittal of such information on outputs thereof to user equipment.

Ingress filter 1098 provides the remote unit 1042 with protection against interference of signals applied to the video equipment 1072 as opposed to those provided to other user equipment such as telephones or computer terminals. Filter 1098 passes the video signals; however, it blocks those frequencies not utilized by the video equipment. By blocking those frequencies not used by the video equipment, stray signals are eliminated that may interfere with the other services provided by the network to at least the same remote unit. The set top box 1078 is an optional element in the network 1006. It may include an additional modem for sending interactive data therefrom back to head end 1010 at frequencies unused by the video and telephony transmissions. Upstream transmission of such data is further discussed below.

Depending on the modulation processing techniques utilized at the head end 1010, the RF demodulator 1104 would include circuitry capable of demodulating the modulated signal. For example, if QPSK modulation is utilized then the demodulator would include processing circuitry capable of demodulating a QPSK modulated waveform as is known to one skilled in the art.

In another embodiment of providing downstream electrical video and telephony signals from the coaxial taps 1034 to remote units 1042, as shown in FIG. 116, a separate coaxial line from coaxial tap 1034 is utilized to provide transmission of the signals therefrom to set top box 1078, and thus for providing the downstream video signals to video equipment unit 1072. In such a case, a second coaxial line from coaxial tap 1034 would be utilized to provide the downstream telephony signals to a multiple integrated service unit (MISU) 1044 which would be much like the home integrated service unit 1070 as described with regard to FIG. 119 except lacking an ingress filter 1098 and tap 1097. Unlike home integrated service unit 1070, the MISU 1044 would be utilized to service several remote units 1042 with telephony services via various service interfaces. Whether the video and telephony signals are provided to the curb with use of the MISU 1044 or whether the video and telephony signals are provided directly to a home integrated service unit is strictly one of application and either can be utilized with regard to the same or different coaxial taps 1034 and within the same or different coaxial distribution systems 1007.

In addition, an optional network interface device (NID) 1075 is utilized in the connection of telephone services to the remote units 1042, whether they are homes or businesses, as is known to those skilled in the art and as shown in FIG. 116. The NID is generally shown by block 1070 representing the home integrated service unit but is not shown in the detail of FIG. 119. The NID performs service functions for the telephone service provider such as looping back signals to the service provider that reach the NID so as to indicate whether a failure has occurred somewhere in transmission to the NID or in connections from the NID to the user equipment when a failure is reported to the service provider.

The above description primarily involves the downstream transmission of video and telephony information from head end 1010 to remote units 1042. The upstream transmission of interactive data from set top boxes 1078 and other data, for example telephony from telephones 1076, shall now be described with reference to FIGS. 116-123. The description shall be limited to transmission from remote units via home integrated service units as transmission from an MISU is substantially similar and easily ascertainable from such description. Home integrated service unit 1074 provides set top box information from set top box 1078 and telephony information from the service interfaces 1112, including information from telephone 1076, to the optical distribution node 1026 connected thereto by the same coaxial path as for the downstream communication. The set top box signals are transmitted by a separate RF modem of the video service provider at a relatively low frequency in the bandwidth of about 5 to 40 MHz which is unused by telephony and video services. The telephony signals are also transmitted upstream in the 5-40 MHz bandwidth, usually from 10 MHz to 30 MHz. This 5-40 MHz bandwidth is reused in each coaxial path 1029 from each remote unit 1042 to the respectively connected optical distribution node 1026. As such, upstream electrical telephony data signals from the remote units are transmitted at the same reused frequency bandwidth of 5-40 MHz on each coaxial line 1029 for input to the optical distribution node 1026. Therefore, as shown in FIG. 118, four upstream electrical telephony signals, each in the 5-40 MHz bandwidth, are input to optical distribution node 1026, via the respectively connected coaxial cables 1029.

The upstream transmission from an integrated service unit for multipoint to point transmission utilizes time multiplexing techniques, although any of a number of multiple access techniques known to those skilled in the art are contemplated in accordance with the present invention. All the remote units are designated a time slot for transmission. In such a case each remote unit must transmit at a particular time to maintain multiple access with the timing being supplied using data on the downstream paths. The upstream data is transmitted on a bit-by-bit basis. With each remote unit assigned a time slot, the RF modem 1102 of the unit knows that it will not interfere with the others because it has determined the time delay for each one of them and each RF modem 1102 is signaled to transmit at a precise time. Due to the high volumes of multiplexed serial data from several outlining remote stations and limited bandwidth for transmission, short pulse durations are required for better resolution of the data transmitted to the head end 1010. Although the data modulates a carrier and is transmitted in the 5 to 40 MHz bandwidth by RF modulator 1108, because of the limited bandwidth in the upstream direction, a pulse shaping network at each remote unit is used to generate raised cosine pulses for the rectangular or square wave bit-by-bit stream of data transmitted along the coaxial cable in the coaxial network.

An optimal pulse shape for transmission in a band limited coaxial cable network is determined by the use of Fourier calculations with a given set of boundary conditions. Also, the Fourier calculations implement a spectral limitation constraint for the purposes of limiting the spectral content of the optimal pulse shape. Limiting the spectral content of the pulse shape serves two functions. The first function is to limit the spectral characteristics of the optimal pulse shape in order to prevent phase dispersion at the receiving end of the transmission system. The second benefit from the spectral limitation constraint is to allow the use of relatively simple finite impulse response filters with a minimal number of taps.

In one embodiment of the pulse shaping network as shown in FIG. 121, 50 nanosecond pulses from the RF modulator 1108 of RF modem 1102 are transmitted to a pulse sequencer 1301 for uniform digitization. The output from the pulse sequencer is then applied to a ten tapped finite impulse response filter (FIR filter) 1302 with associated electronics 1303 to provide the addition and subtraction

necessary for the filtering process. The output is sent to a line driver circuit for output to the coaxial cable through diplex filter 1110. The optimal pulse waveform is a raised cosine waveform. Using such pulse shaping techniques, overcomes the difficulty of sending extremely short pulse duration information along a band limited coaxial cable.

The upstream electrical telephony signals from a plurality of remote units, including signals from the RF modems 1102 and from modems in set top boxes 1078, are transmitted to the respectively connected optical distribution node 1026 as shown in FIG. 118 via the individual coaxial cables 1029. The upstream electrical signals are applied to a diplex filter 1134 respectively connected to a coaxial cable 1029. One of the diplex filters 1134 passes the upstream electrical telephony signal applied thereto through to combiner 1125 while the other diplex filters pass the upstream electrical telephony signals applied thereto to frequency shifters 1128, 1130, and 1132. Frequency shifter 1128 shifts the upstream electrical telephony signal into the 50-85 MHz bandwidth, frequency shifter 1130 shifts another upstream electrical telephony signal into the 100-135 MHz bandwidth and frequency shifter 1132 shifts the other upstream electrical telephony signal into the 150-185 MHz bandwidth. The shifted signals are combined by combiner 1125 and provided to upstream telephony and set top control transmitters 1123. The conventional optical transmitters 1123 transmit the upstream electrical telephony signal as an upstream optical telephony signal to head end 1010 via fiber optic link 1020. Once again, two transmitters are available for transmission, one in standby mode, like that in the downstream transmission path.

The upstream optical telephony signals are received by upstream telephony and set top box receiver 1084 of optical to electrical converter block 1066. The upstream optical telephony signals are converted, split, and all the split electrical signals in the 5-40 MHz, 50-85 MHz, 100-135 MHz, and 150-185 MHz are frequency shifted back to the 5-40 MHz bandwidth by frequency shifters 1086, 1088, and 1090 with the exception of the signal already in the 5-40 MHz bandwidth which is passed through with the other frequency shifted signals from the frequency shifters to RF switch 1094. A combined signal in the 5-40 MHz bandwidth from combiner 1092 is provided to the VHDT and the signal is processed for obtaining the interactive information transmitted from set top boxes 1078. The RF switch 1094 is controlled by controller 1060 and provides the upstream telephony signals to the transceivers 1053 of the corresponding RF modems 1052. The upstream telephony signals are then demodulated by RF modem modules 1052 and the telephony data is provided to the service providers via trunk line 1008. The RF modem modules 1052 include RF demodulator corresponding to the modulation techniques utilized to transmit the information upstream so such information can be recovered.

As discussed previously, the controller 1060 switches protection RF modem module 1054 for a transmitting RF modem module 1052 in the downstream communication when a fault is detected in that module. The controller also provides signaling for switching the RF switch 1094 such that the information which would have been provided to the faulted RF modem module 1052 is applied to the transceiver of the protection RF modem module 1054. Therefore, the protection modem module 1054 is then fully within the transmit and receive loop of the system.

As shown in FIG. 122, an alternative embodiment of the present invention includes an optical to electrical converter 1066 wherein the received optical upstream telephony signal is converted by receivers 1084 and the entire upstream electrical signal in the 5-200 MHz bandwidths is applied to the transceivers 1053 of the RF modem modules 1052. The RF modem modules 1052 are then operated under control of controller 1060 which assigns the RF modem module a carrier frequency to tune to for the recovery of telephony information; the assigned frequency being a function of the frequency shifting of the upstream signal. The electrical signal is still separated and frequency shifted by frequency shifters 1086, 1088 and 1090 except for the signal already in the 5-40 MHz bandwidth and then combined by combiner 1092 for application to VHDT 1014.

In this embodiment, the switching of the protection modem module 1054 into the system is accomplished through the controller 1060. When the controller 1060 detects and indicates a faulted modem module 1052, the controller 1060 assigns the frequency previously assigned to the faulted RF modem module to the protection module, thus establishing the protection RF modem module 1054 fully within the transmit and receive loop.

In another embodiment shown in FIG. 123 including one-to-one protection for the RF modem module, neither the RF switch used for protection switching for the configuration of FIG. 123 nor the additional control required for protection switching for the configuration of FIG. 122 is necessary. In this embodiment, the same electrical signal provided to the RF modem modules 1052 is applied to the corresponding protection module 1054, thus only a control signal indicating which module is to be used for transmission or reception is required for the one-to-one protection.

Claims

1. A system comprising:

a host unit;

a plurality of remote units using a multiple access scheme to communicate at the same time with the host unit on adjecent spectrally overlapping carriers of an orthogonal frequency division multiplexing (ofdm) waveform;

wherein the host unit sends an adjustment signal to at least one remote unit instructing the at least one remote unit to adjust the timing of transmissions from the at least one remote unit to improve orthogonality of ofdm transmissions received at the host unit,

wherein the host unit sends an adjustment signal to at least one remote unit instructing the at least one remote unit to adjust the frequency of transmissions from the remote unit to improve orthogonality of ofdm transmissions received at the host unit,

wherein the host unit allocates a first orthogonal tone to at least one remote unit to carry payload data during a first time interval, and

wherein the host unit allocates the first orthogonal tone to carry control data during a second time interval.

2. The system of claim 1 wherein the first time interval is after the second time interval.

3. A multipoint-to-point, orthogonal frequency division multiplexed (ofdm) communication system comprising:

a plurality of remote units,

a host unit that includes a demodulator;

wherein each of the remote units transmits an upstream ofdm signal to the host unit demodulator using a multiple access scheme on adjacent spectrally overlapping carriers of an ofdm waveform,

wherein the host unit receives the upstream ofdm signals from a plurality of the remote units, tones of the upstream signals being substantially orthogonal when received at the host unit;

wherein portions of upstream ofdm signals from at least two of the remote units arrive at the host unit at the same time,

wherein the host unit demodulator demodulates said portions,

wherein the host unit sends an adjustment signal to at least one remote unit instructing the at least one remote unit to adjust the timing of transmissions from the at least one remote unit to improve orthogonality of the ofdm waveform received at the host unit,

wherein the host unit sends an adjustment signal to at least one remote unit instructing the at least one remote unit to adjust the frequency of transmissions from the remote unit to improve orthogonality of the ofdm waveform received at the host unit,

wherein payload data is transmitted between at least one remote unit and the host unit over a first orthogonal tone within the ofdm communication system during a first time interval, and

wherein control data is transmitted between at least one remote unit and the host unit over the first orthogonal tone within the ofdm communication system during a second time interval.

4. The ofdm communication system of claim 3 wherein the payload data is sent upstream by a first remote unit to the host unit.

5. The ofdm communication system of claim 3 wherein the payload data is sent downstream by the host unit to a first remote unit.

6. The ofdm communication system of claim 3 wherein the first time interval is after the second time interval.

7. The ofdm communication system of claim 3 wherein the same remote unit transmits the payload and control data.

8. The ofdm communication system of claim 3 wherein the control data comprises at least one of a transmission characteristic adjustment signal, a bandwidth request, and a tone allocation signal.

9. The ofdm communication system of claim 3 wherein the payload data comprises at least one of voice, video, and digital data.

10. A multipoint-to-point, orthogonal frequency division multiplexed (ofdm) communication system comprising:

a plurality of remote units,

a host unit that includes a demodulator;

wherein each of the remote units transmits an upstream ofdm signal using a multiple access scheme to the host unit demodulator on adjecent spectrally overlapping carriers of an ofdm waveform,

wherein the host unit receives the upstream ofdm signals from a plurality of the remote units, tones of the upstream signals being substantially orthogonal when received at the host unit;

wherein portions of upstream ofdm signals from at least two of the remote units arrive at the host unit at the same time,

wherein the host unit demodulator demodulates said portions,

wherein the host unit sends an adjustment signal to at least one remote unit instructing the at least one remote unit to adjust the timing of transmissions from the at least one remote unit to improve orthogonality of the ofdm waveform received at the host unit,

wherein the host unit sends an adjustment signal to at least one remote unit instructing the at least one remote unit to adjust the frequency of transmissions from the remote unit to improve orthogonality of the ofdm waveform received at the host unit,

wherein payload data is transported between at least one remote unit and the host unit via at least one orthogonal tone within the ofdm communication system, and

wherein the at least one orthogonal tone is dynamically assigned by the host unit to temporarily carry control data between the host unit and at least one remote unit.

11. The ofdm communication system of claim 10 wherein the control data comprises at least one of a transmission characteristic adjustment signal, a bandwidth request, and a tone allocation signal.

12. The ofdm communication system of claim 10 wherein the payload data comprises at least one of voice, video, and digital data.