Just to clarify (or muddle) things further, the RJ48M cable is a 25pair cable with a D50 clamshell connector on one end (what people around here refer to as an "amphenol") and a harmonica of 8 RJ48C jacks on the other end. All pairs are individually shielded. Pairs 1+2 on the D50 go to TX/RX pairs on port 1 of the harmonica, pairs 3+4 go to port 2 of the harmonica, etc etc

EDIT: I was a bit wrong on the wiring. The above applies to the RJ48H connector (D50 to 12 RJ48C). In the RJ48M, the D50 end skips one pair per harmonica port. So the wiring for RJ48M would be:

pair 1+2 = port1
skip
pair 4+5 = port2
skip

etc etc