The ornamental design for a transmission, as shown and described.
FIG. 1 is a front perspective view of a transmission, showing my new design; and,
FIG. 2 is a left side view thereof.
My design shown in FIGS. 1 and 2 is radially symmetric such that the perspective views not shown are identical to the front perspective view shown in FIG. 1 and the side views not shown are identical to the left side view shown in FIG. 2. The bottom view forms no part of my claimed design.
The broken lines of even length shown in the drawings depict unclaimed environmental subject matter of the transmission.