MPLS Fundamentals

AToM Architecture

In networks that use AToM, all the routers in the service provider network run MPLS, and the PE routers have an AC toward the CE router. The PE router receives Layer 2 frames on the AC and encapsulates them with labels before sending them onto the PSN tunnel toward the remote PE. At the remote PE, the label(s) are removed and the frames are sent toward the remote CE.

In the case of AToM, the PSN tunnel is nothing other than a label switched path (LSP) between two PE routers. As such, the label that is associated with that LSP is called the tunnel label in the context of AToM. The LSRs can signal that LSP in different ways. First, the Label Distribution Protocol (LDP) can signal the LSP hop-by-hop between the two PEs. Second, ...