Tutorial

MPLS Network Reliance and Recovery
(continued)

Network Protection

In a network, there are several possible areas for failure. Two major failures are link failure and node failure (Figure 6). Minor failures could include switch hardware, switch software, switch database, and/or link degradation.

Figure 6: Network Failures

The telecommunication industry has historically addressed link failures with two types of fault-tolerant network designs: one-to-one redundancy and one-to-many redundancy.  Another commonly used network protection tactic utilizes fault-tolerant hardware. 

To protect an MPLS network, you could pre-provision a spare path with exact QoS and traffic-processing characteristics.  This path would be spatially diverse and would be continually exercised and tested for operations. However, it would not be placed online unless there were a failure on the primary protected path.  This method, known as one-to-one redundancy protection (Figure 7), yields the most protection and reliability, but its cost of implementation can be extreme.

Figure 7: One-to-One Redundancy

A second protection scheme is one-to-many redundancy protection (Figure 8).

In this method, when one path fails, the back-up path takes over. The network shown in the Figure 8 can handle a single path failure, but not two path failures.

Figure 8: One-to-Many Redundancy

A third protection method is having fault tolerant switches (Figure 9).  In this design, every switch features inbuilt redundant functions – from power supplies to network cards. The drawing shows redundant network cards with a back-up controller.  Take note that the one item in common, and not redundant, is the cross-connect tables. If the switching data becomes corrupt, the fault tolerant hardware cannot address this problem.

Figure 9: Fault Tolerant Equipment

Now that you know the three network protection designs (one-to-one, one-to-many, and fault-tolerant hardware) and two methods for detecting a network failure (heartbeat and error message), we need to talk about which layers and protocols are responsible for fault detection and recovery.

<< Previous page      Next page >>

Page 4 of 7