Switching to VoIP

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

VoIP Trunks

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Load-splitting

A similar problem can occur with simple load-splitting. Let’s say you have two or

more point-to-point links that all start and end at the same locations. Let’s also say

you use IP routers to split the traffic load equally (or unequally) across them. You

can use BGP (Border Gateway Protocol) and other routing protocols to accomplish

this, but be careful of the potential for variances in jitter and delay—especially if the

links run at different speeds or use different data link technologies (like a radio link

side by side with an FSO link).

Multipath jitter

Jitter that’s incurred by complex routing and/or load-balancing can be minimized.

Here are three things you want to avoid when setting up WAN links to support VoIP

trunks:

• Avoid using a multipath routing setup for parallel IP links that use differing

transport technologies (i.e., point-to-point T1 and a VPN). While it may be fine

to use one or the other as a backup link, daily use will sabotage the consistency

of phone calls.

• Avoid terminating any one end of a call path on more than a single router. This

will create jitter. If you want to use multiple routers for disaster preparedness

reasons, then take steps to make sure each RTP media stream (in both direc-

tions) is being handled by only one of them. ...