Cisco offers a 56/64 KBPS CSU/DSU WAN Interface Card.The 4-wire 56k CSU/DSU implements switched 56k and DDS (leased line) operation. The hardware feature set is identical to the 4-wire 56/64k CSU/DSU for the Cisco 2524 and Cisco 2525; the Cisco IOS configuration is also the same. It supports DDS (leased line) operation (AT&T Pub. 62310), supports DDS loop rates 2.4, 4.8, 9.6, 19.2, 38.4, 56, and 64 kbps, supports switched 56 operation at 56 kbps (AT&T Pub. 41458, Sprint TS-0046). Receiver sensitivity is 45db at all loop rates. The card provides such diagnostic functions as Self Test Function (at power on and user initiated) and Network line and DTE loopbacks User initiated DTE, line, and remote V.54 loopbacks.