MPLS-Enabled Applications: Emerging Developments and New Technologies

11.10. CIRCUIT CROSS CONNECT (CCC)

This section describes Circuit Cross Connect (CCC)[CCC]. CCC was the first method to be devised and implemented for carrying Layer 2 traffic over a MPLS network and was the precursor to the LDP and BGP schemes discussed so far in this chapter. It is still used by service providers, and indeed is having a renaissance as a method to couple Layer 2 traffic into point-to-multipoint LSPs.

The main difference between CCC and the other schemes described in this chapter is that CCC always uses an RSVP-signaled LSP as the transport tunnel between PEs. Each CCC connection has a dedicated RSVP-signaled LSP associated with it, so unlike the LDP and BGP schemes discussed previously in this chapter, the transport tunnel cannot be shared between multiple connections. This is fine for small deployments, but if a large number of connections are required between particular pairs of PEs in a network, the number of RSVP-signaled LSPs will be correspondingly large. As a consequence of having a dedicated LSP for each connection, the inner label (VPN label) that is used in the BGP and LDP schemes to identify the connection that a packet belongs to is not required in the CCC case. The Layer 2 media types supported by CCC are the same as for the BGP and LDP schemes.

By default, in most RSVP implementations the egress router declares an implicit null label for the last hop of the LSP, so penultimate hop-popping (PHP) occurs. However, in the case of CCC the egress PE needs ...