M7i, M10i, and M40e routers with 12xT1/E1 Circuit Emulation PICs provide Layer 1 and Layer 2 circuit emulation service, support TDM interfaces using SAToP protocol encapsulation, and support for T1/E1 and SONET clocking features. The 12xT1/E1 CE can be configured to work as either 12 T1s or 12 E1s; however, mixing T1s and E1s is not allowed.