Full VoIP SIP Deployment
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We gather that Cisco implemented call functionality this way with the assumption that two Cisco CMEs would be connected using SIP, with an administrator in control of both boxes. In other words, though Cisco supports SIP trunking by definition, it does not yet provide complete support for SIP as a connection to the PSTN. The company says it plans to support this SIP trunking functionality in CME in early 2007.
Another SIP trunking initiative under way is the SIP Forum's SIPconnect. Endorsed by companies such as Avaya, Cbeyond and Cisco Systems, SIPconnect aims to tie enterprises to VSPs with an end-to-end IP connection.
The Right Connection
One of the major caveats of any SIP trunking solution is that voice packets must arrive in time and in order. Losing only a few packets quickly garbles a conversation. This usually occurs due to overuse of available bandwidth or too many hops between the IP PBX and the VSP.