The 4-ports Asynchronous/Synchronous Serial Network Module, NM-4A/S, provides 4 low-speed serial connections via DB-60 connectors that support five interface types (RS-232, RS-449, RS-530, V.35, X.21) in either DTE or DCE mode.
The low-speed serial connections can be configured for up to either 115.2 kbps asynchronous or 128 kbps synchronous serial traffic.

Compatibility:
Cisco 2600 series with IOS 11.3(2)XA
Cisco 2600XM Series with IOS 12.1(14) or 12.2(8)T1
Cisco 2650 with IOS 12.1(3)T
Cisco 2691 with IOS 12.2(8)T1
Cisco 3620, 3640 with IOS 11.1(7)AA
Cisco 3660 with IOS 12.0(5)T
Cisco 3725, 3745 with IOS 12.2(8)T