UDP is preferred for VoIP because by the time a dropped packet is
detected, the retransmission request is sent to the originator, and the
replacement packet arrives, it's too late (unless you are running a very
large jitter buffer which introduces problems of its own).
Conversely if your network has sufficient bandwidth to ensure the
retransmission happens fast enough, it has sufficient bandwidth to avoid
dropped packets in the first place.
One of the problems is that some WAN switches/routers discriminate
against UDP when they become congested because they reason dropping UDP
packets will cause less of a problem (because they are not
retransmitted) than dropping TCP packets (which will cause
retransmissions and not alleviate the congestion).
--
George Pajari, netVOICE communications 604 484 VOIP (484 8647 x102)
Open Source VoIP/Telephony Specialists 1 877 NET VOIP (638 8647 x102)
Hosted IP PBX Services for SOHO & Small Businesses - www.ip-centrex.ca
VoIP Service, Equipment, Systems, and Consulting - www.netvoice.ca
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