Operation3-493160-A2-GB22-10 December 1996TimingThe 316x DSU/CSU provides the ability to select amaster clock (timing) source that is used to synchronizeall of the T1 and data port interfaces on the DSU/CSU.When a master clock source is selected, the DSU/CSUwill synchronize to the master clock and derive clockingfor all of the interfaces on the DSU/CSU. The clock foreach interface will be at the appropriate rate for thatinterface (e.g., 1.544 Mbps for the T1 interfaces, theconfigured port rate for the data ports) and independent ofthe master clock rate. This means that the master clockrate and the DSU/CSU interface rates may be different.The DSU/CSU will automatically fall back to the internalmaster clock when a failure of the selected master clock isdetected.NOTEFor Model 3161 DSU/CSUs, theexternal clock provides timing forup to eight slots in the carrier.Each Auxiliary Backplane musthave its own external clock input.The DSU/CSU clock source configuration optionenables you to select one of five sources for the masterclock, either the Network T1 interface, the DSX-1Drop/Insert T1 interface, Port 1, internal clock, or externalclock. If external clocking is selected, you must use theclock rate configuration option to specify the clock rate.Two examples for configuring timing are given below. Formore information on the configuration options, refer toAppendix C. Figure 3-32 shows some common clockingconfigurations.496-14341a-013160/3164 NETWORKCLOCK: NETWORK3160/3164CLOCK: NETWORK3160/3164CLOCK: NETWORKCLOCK: INTERNAL3160/31643160/3164CLOCK: EXTERNAL3160/3164CLOCK: NETWORKPBXCLOCK: DTE (DSX-1 CONNECTOR)3160/3164CLOCK: NETWORK3160/3164TERMINALEQUIPMENTCLOCK: PORT 13160/3164CLOCK: NETWORK3160/3164Figure 3-32. Common Clocking Configurations
