Using CPOS Interfaces to Converge E1/T1 Lines
As shown in Figure 16-7, some enterprise branches use mid-range and low-end routers to access the SONET/SDH network through E1/T1 lines. To obtain high bandwidth, other branches require several leased E1/T1 lines.
The SONET/SDH network converges E1/T1 lines of all branches to one CPOS interface or several CPOS interfaces. The CPOS interface connects the E1/T1 lines to RouterA, and RouterA identifies each mid-range and low-end router based on the timeslot. Logically, each mid-range and low-end router is connected to RouterA through the E1/T1 line or several E1/T1 lines.
In practice, there may be more than one level of transmission networks between CPOS interfaces and mid-range and low-end routers. The mid-range and low-end routers may require other transmission devices to connect to CPOS interfaces.
