The following diagram shows three sites connected together via VPN. This network is not fully mesheddue to the lack of a VPN tunnel between Sites B and C.Figure 9-24 NEC SL2100 Network Example No. 2With Peer-to-Peer enabled, the IP phones on site A can communicate with IP phones on sites B andC. IP Phones on sites B and C cannot communicate directly with each other though. The IP phonefrom site B can set up a call to the IP phone at site C, but there is no speech path. Here are the stepsin 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 (VoIPDB).• 192.168.1.10 (VoIPDB) 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 SDPportion informs the IP phone where to send the media (voice) to. The SDP portion of this invitemessage 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 (VoIPDB). In the 200 OKmessage is the SDP field reporting the IP address of 192.168.3.26 (ext 130).• 192.168.1.10 (VoIPDB) 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 (VoIPDB).• 192.168.1.10 (VoIPDB) 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 noVPN connection between these sites the call is set up with no voice path.To correct this issue another VPN connection between sites B and C is required. If an additional VPNcannot be implemented, due to network limitations, the Peer-to-Peer feature can be disabled in theNEC SL2100. With Peer-to-Peer disabled, all packets (Signaling and Voice) route through the VoIPDBcard. This also affects IP phones at the REMOTE locations calling other IP phones at the samelocation. Without Peer-to-Peer enabled the voice path must route to the MAIN location and then backto the REMOTE instead of directly between the two stations on the REMOTE network. This forces theuse of additional bandwidth on the MAIN, and REMOTE locations. Peer-to-Peer is disabled incommand 15-05-50 per IP Phone.Figure 9-25 IP System Operation SetupSL2100 ISSUE 1.09-30 IP Multiline Station (SIP)
