DSU/CSU Issues

Observe the following guidelines when using a DSU/CSU.

• Always make sure that only one source supplies the transmit and receive clocks on the line. Either the DCE (such as a modem or DSU/CSU) or the DTE (the WAN interface board) on one side of the link should supply the transmit and receive clocks.
• If your clocking is being provided by either the DSU/CSU or telco, make sure the Interface Speed option is set to External in NIASCFG (parameter path: Select Configure NIAS > Protocols and Routing > Network Interfaces > a specific interface). Do not set this option to reflect the speed of the line; this setting would be incorrect. Selecting an interface speed initializes the clocks built into the WAN board and confuses the DSU/CSU. The built-in clocks are commonly used for back-to-back testing.