Question on provisioning & mulitplexing SONET circuits

[pzrfxr]

OK, I am an IP guy and trying to get some knowledge on SONET and DWDM. I have a basic question that probably seems dumb, but is a fundamental issue for me that I have not figured out or read about yet. I understand that lower-speed links (Ethernet, ATM,etc) can be aggregated on a divice such as an MSPP and multiplexed into SONET frames to represent higher-speed links (OC-48, OC-192). When a SONET circuit is provisoned. What field in the SONET SPE determines which payloads belong to which ciruits so that when it reaches the termination point, and the payloads are demulitplexed, it knows the destinion interface for that provisioned circuit.

[Marvin Rhoads]

The various overhead type (line, section, path) take care of packaging the tributaries, as your inputs are sometime referred to, and making sure they drop at the destination multiplexer. When they are handed off at the destination interasfce card and port, they are disassembled/reassembled in their native framing format and handed off to your customer premises equipment for further transport.

See http://www.cisco.com/warp/public/127/concat_16147.html for an introduction to the overhead types. A more complete tutorial is at http://www.iec.org/online/tutorials/sonet/topic01.html