ZyXEL Communications P-2000W V2 - Manual (Page 14)

P2000W V2 Troubleshooting Guide
All contents copyright (c) 2005 ZyXEL Communications Corporation.
The corrected working capture should include starting of the call (The SIP
invite) to call pickup (The SIP ACK). An example of successful call capture is
listed below for your reference.
Once both of the above capture is completed, send both captured file to
support to analysis the cause.
The VoIP challenge
SIP is a session initiation protocol which is an application-layer control (signaling)
protocol for creating, modifying, and terminating sessions with one or more
participants. These sessions include Internet telephone calls, multimedia distribution,
and multimedia conferences.
For SIP to successfully massively deploy there are several challenge of the real
environment it must able to work with. The most common faced problem is NAT
pass-through issue and SIP client and call server interoperability issues.
When SIP protocol is proposed it self does not consider network environment and
other technology that maybe in the deployed network. Since IPv4 IP is insufficient
and will soon run out. Thus NAT is very commonly used. Unfortunately from field
test many vendor’s NAT are not SIP friendly.