Used Cisco 3600 Series -
Serial Connectivity Network Modules

Part # NM-4T

Product Description: 4 serial ports; uses Cisco DB-60 connectors (same cabling as Cisco 2500, Cisco 7000, NM-4A/S, and NM-8A/S); supports sync mode only (nc mode is not supported); provides synchronous data rate of 8 Mbps on port 0, 4 Mbps each on port 0 and port 2, or 2 Mbps on all four ports simultaneously; and does not support bisync or half-duplex.