Voice Compression Modules
by DougR on Oct.13, 2008, under Avaya, Best Practices, IP Office
Voice Compression Modules (VCM) are an important key to allowing the IP Office to handle such a wide range of phone types. These modules act as a bridge between the Digital/Analog phone world and the IP world. Each VCM is able to handle translations between H.323 or SIP signaling and the control plane, as well as be a real time CODEC for translation to the RTP (Real Time Protocol) used for the Audio streams of a VoIP call. They are very similar to a trunk between two systems.
The VCM acts as a translator between these resources. Since the VCM is a translator that does not always need to be connected, it can be oversubscribed much like a trunk is implemented. Typical installations will use a 4:1 ratio of phones or trunks to VCM. This method counts on the endpoints not being very busy in using the VCM. More active scenarios may need a 2:1 or even 1:1 ratio. Since the IP500 allows up to 128 VCM resources, it is possible to have a fully loaded IP500, with all IP sets, and still maintain a 2:1 VCM ratio. For more information on exactly when a VCM is in use, check out this Avaya documentation - http://marketingtools.avaya.com/knowledgebase/ipoffice/mergedProjects/ipphoneinst/index.htm?intro_vcm_channels.htm
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