MPLS-Enabled Applications: Emerging Developments and New Technologies

3.2. THE BUSINESS DRIVERS

Traditionally, providers used IP/MPLS backbones to carry traffic with loose service level agreements (SLAs) and TDM networks for traffic with tight SLAs. Converging all services on to the same core is attractive because it eliminates the need to build and maintain separate physical networks for each service offering and because the flexibility of IP enables new services such as videotelephony integration. However, traffic with tight SLAs such as voice, video or ATM CBR has stringent requirements for availability and traffic loss. Thus, fast recovery following a failure is an essential functionality for multiservice networks.

One way to provide fast recovery following a link failure is to provide protection at Layer 1. This is the solution provided by SONET APS (Automatic Protection Switching). The idea is simple. Maintain a standby link that is ready to take over the traffic from the protected one in case of failure and switch traffic to it as soon as the failure is detected. Because the decision to move to the standby link is a local one, the switchover can happen within 50 ms, making any disruption virtually unnoticeable at the application layer. The quick recovery comes at the cost of maintaining the idle bandwidth and the additional hardware required for the switchover.

The goal of MPLS fast reroute (FRR) is to provide similar guarantees for MPLS tunnels. The advantage of fast reroute over SONET APS is that (a) it is not limited by the link type, ...