SRLG Sharing Between Optical and IP Layers Within a Transport Network

Background

Although the IP layer and optical layer are connected, they cannot exchange routing information. The active and standby links at the IP layer can only be separated using statically planned SRLGs within the optical network, which delays service rollout and increases maintenance workload. To address these problems, the SRLG sharing function can be used. RSVP signaling at the optical layer sends SRLG attributes of transport links to the IP layer. The IP layer applies the SRLG attributes to IP links. This function helps select reliable paths for high reliability services at the IP layer based on SRLG constraints.

Principles

When a GMPLS UNI tunnel is established using RSVP, the extended RSVP protocol carries SRLG information on optical links to both ends of the GMPLS UNI tunnel. SRLG information is processed as TE SRLG information that is used to bind the GMPLS UNI tunnel to UNI links, which separates links for the primary and backup TE tunnels.

RSVP Path or Resv messages carry SRLG sub-objects to notify the IP layer of SRLG information about paths on an optical network. The ingress CN and egress CN at the IP layer flood the SRLG information to the other devices on at the IP layer. Then all devices on the network can establish the primary and backup TE tunnels on different links, preventing path overlapping.

Figure 1 SRLG sharing between optical and IP layers within a transport network