Avaya 555-245-600 manual Dial backup, Multipath routing

Network recovery

Multipath routing

Modern routers and Layer 3 switches allow multiple routes for a particular destination to be installed in the routing table. Depending on the implementation, this can be as high as six routes. Some implementations require that all routes that are inserted in the routing table have the same metric, while others allow unequal metric routing. In cases where the metric for all installed routes are the same, the router will load balance traffic evenly across each path. When the metric for multiple routes vary, the traffic is load balanced in proportion to the metric (in other words, if one path is “twice as good” as another, two-thirds of the traffic travels down the good path, and one-third of the traffic selects the other one). Asymmetric routing is suboptimal for voice, so route-caching (described earlier) should be considered in this environment.

In addition to using all (up to 6) active paths and optimally using available bandwidth, multipath routing greatly improves convergence time. As soon as a router detects a path failure, it remove it from the routing table, and sends all traffic over the remaining links. If this is a physical link failure, the detection time is nearly instantaneous. Therefore, Avaya recommends the use of multipath routing, where available, across multiple links to a particular location.

Dial backup

One cost-effective technique for installing backup WAN links is to use dial backup. This can be done using either ISDN-BRI or analog lines. ISDN lines typically take 2 seconds to connect, while 56-k analog modems take approximately 1 minute. While this strategy is effective for data traffic, it is less effective for voice. First, the bandwidth may have been greatly reduced. If this is the case, the number of voice channels that can be supported might have been reduced proportionally. Also, if QoS is not properly applied to the backup interface, high packet loss and jitter can adversely affect voice quality. Finally, the time that is required to establish the new link can be up to 1 minute, which disrupts active calls. However, providing that these considerations are taken into account, proper QoS is applied, and a compressed codec is chosen, dial backup can be an effective solution for two to four users.

342 Avaya Application Solutions IP Telephony Deployment Guide