NEC Univerge SV9100 Manual page 440

Issue 2.0
SV9100 Networking Manual
The following diagram shows three sites connected together via VPN. This
network is not fully meshed due to the lack of a VPN tunnel between Sites B and
C.
Figure 8-33 SV9100 Network Example No. 3
With Peer-to-Peer enabled, the IP phones on site A can communicate with IP
phones on sites B and C. IP Phones on sites B and C cannot communicate
directly with each other though. The IP phone from site B can set up a call to the
IP phone at site C, but there is no speech path. Here are the steps in the call
scenario leading to the failed call.
Extension 120 goes off hook and dials ext 130.

An initial invite message is sent from 192.168.2.15 (ext 120) to 192.168.1.10

(IPLE).
192.168.1.10 (IPLE) forwards that message to 192.168.3.26 (ext 130).

In the original setup message there is a field labeled SDP (Session Description

Protocol). The SDP portion informs the IP phone where to send the media
(voice) to. The SDP portion of this invite message contains the IP address of
192.168.2.15 (ext 120).
192.168.3.26 (ext 130) sends a 200 OK message to 192.168.1.10 (IPLE). In the

200 OK message is the SDP field reporting the IP address of 192.168.3.26 (ext
130).
192.168.1.10 (IPLE) forwards this message to 192.168.2.15 (ext 120).

192.168.2.15 (ext 120) sends an ACK message to 192.168.1.10 (IPLE).

192.168.1.10 (IPLE) forwards this message to 192.168.3.26 (130).

At that point the two IP phones attempt to send voice packets directly to each

other. As there is no VPN connection between these sites the call is set up with
no voice path.
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