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MPLS Network Reliance and Recovery
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The Need for Network Protection

MPLS has been primarily implemented in the core of the IP network. Often, MPLS competes head-to-head with ATM networks; therefore, it would be expected to behave like an ATM switch in case of network failure.

With a failure in a routed network, recovery could take from a few tenths of a second to several minutes. MPLS, however, must recover from a failure within milliseconds – the most common standard is 60 ms. To further complicate the recovery process, an MPLS recovery must ensure that traffic can continue to flow with the same quality as it did before the failure. So, the challenge for MPLS networks is to detect a problem and switch over to a path of equal quality within 60ms.

Failure Detection

There are two primary methods used to detect network failures:  heartbeat detection (or polling) and error messaging. The heartbeat method (used in fast switching) detects and recovers from errors more rapidly, but uses more network resources.  The error-message method requires far less network resources, but is a slower method.  Figure 2 shows the tradeoffs between the heartbeat and error-message methods.

Figure 2: Heartbeat vs. Error Message

The heartbeat method (Figure 3) uses a simple solution to detect failures. Each device advertises that it is alive to a network manager at a prescribed interval of time. If the heartbeat is missed, the path, link, or node is declared as failed, and a switchover is performed.  The heartbeat method requires considerable overhead functions - the more frequent the heartbeat, the higher the overhead. For instance, in order to achieve a 50ms switchover, the heartbeats would need to occur about every 10ms.

Figure 3: Heartbeat Method

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