nel. In the event that you need to return a configured CSU/DSU WIC back to using all channels, you can do SO with the all keyword: Router (config)# int s0/1 Router (config-if)# service-module t1 timeslots all speed 64 Configure one side as the clock master, and the other side as the slave T1s are asynchronous, SO only one side has an active clock. The other side will determine the clocking from the data stream itself using a technology called phase-locked loop (PLL). To configure clocking on a CSU/DSU WIC, use the service-module t1 clock source interface command. The options are internal and line: Router(config)# int s0/1 Router (config-if)# service-module t1 clock source internal internal means that the CSU/DSU will provide clocking (master), and line indi- cates that the clocking will be determined from the data stream on the line (slave). The default behavior is to use the line for clocking. Some environments may require that clocking be set to line on both ends. Check with your provider if you are unsure of your clocking requirements. CSU/DSU Troubleshooting Having a CSU/DSU integrated into a router is an excellent improvement over using standalone CSU/DSUs. The ability to telnet to the CSU/DSU is marvelous during an outage. Standalone CSU/DSUs often have serial ports on them that can be hooked to console servers, but the average corporate environment rarely uses this feature. Additionally, many companies use many different brands and models of CSU/DSUs, each with their own menus, commands, features, and quirks. Chapter 20: T1 The Cisco T1 CSU/DSU WIC allows for CSU/DSU statistics to be viewed by telnet- ing to the router and issuing commands. The main command for troubleshooting a T1 CSU/DSU WIC is the show service-module interface command. This command outputs a wealth of information regarding the status of the CSU/DSU and the T1 circuit in general. Let's look at the output of this command with a T1 that is not connected on the far end: Router# sho service-module s0/1 Module type is T1/fractional Hardware r