Appendix C. Cables
C–30
Table C–18. DCE X.21 Pin Assignments
MCS
Network
26-Pin
Description
Function
15-Pin
2
Transmit A
T
2
11
Transmit B
T
9
4
Control A
C
3
13
Control B
C
10
3
Receive A
R
4
12
Receive B
R
11
5
Indication A
I
5
14
Indication B
I
12
7
Common return
G
8
19
Signal element timing A
S
6
20
Signal element timing B
S
13
The remaining pins are not used.