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The configurations for a Trunking application and Access application are very similar. Both are based on the "Trunk Group" concept. It may seem strange that a set of phones that register with unique IP addresses are considered a trunk group, but it is actually helpful in configuring and debugging the SBC Core.
As for how a set of phones can be considered a trunk group, this is accomplished by the following mechanism:
The key differences between an Access Configuration and a Trunking Configuration are shown below:
Table 1: Key Differences between Access and Trunking Configuration
Element | Access Details | Trunking Details |
---|---|---|
Trunk Group: Registration | On the Trunk group facing the phones (PHONES in our example), the "Registration Required" parameter must be set. You should also set the Expires timer which controls how often the phones will Register. And the Inside Expires timer, which is how often the SBC will Register with the Feature Server (PBX or Class 5 Softswitch) on behalf of the phone. The Inside timer is typically 1 hour, while the phones Registration timer is typically 60 seconds. | Registration is not required, so this parameter is not set. |
IP Peer: IP address | The IP Peer for messaging TO the phones is not explicitly configured (indicating to the SBC that it should look in its local stored Registration table to determine the IP | IP address of the far end. |
Ingress IP Prefix | The Ingress IP Prefix (Network Selector Table in GSX 9000 terminology) for messaging FROM the phones is 0.0.0.0. This indicates that no fixed IP address should be required in receiving messages from the phones (the Registration table is checked instead). The Ingress IP Prefix is located under the Trunk Group (which is under the Zone). | IP address of the far end. |
Trunk Group: NAT/NAPT Settings | If there is a NAT/NAPT device (Network Address Translation) between the phones and the SBC (common if phones are on the public internet), the NAPT for Signaling flag and the NAPT for Media flag should be turned on. These flags are part of the SIP Trunk group configuration. | Generally there is no NAT on |