Com.X Administrator Guide
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3.8.2.6 Viewing group members
Membership of trunks to their respective groups may be observed either by
expanding individual devices listed under the Trunk Ports node, where group
membership is denoted in parenthesis after trunks, or by selecting the desired group
in the group list under the Trunk Groups node, where the devices and trunks included
in the group are listed.
3.8.3 SIP trunks
Multiple SIP trunks can be configured for call routing. SIP trunks can also act as SIP
providers, providing the capability to configure back-to-back SIP trunks for inter-office
connections.
3.8.3.1 SIP call setup
SIP uses a peer to peer mechanism for call setup. In order for a call to be
established, two peers need to be defined and be able to communicate with each
other. This necessitates a SIP trunk entry for each peer of a given system.
Communication between two peers implies that the peer initiating the call knows the
IP address of the recipient, and that the recipient can match the caller's credentials in
order to allow and configure the call.
The peer initiating the call can either have the recipient's IP address configured, or
may know the recipient's IP address as the result of the recipient registering with the
it (i.e. the calling peer is acting as a provider.) When acting as a provider, a peer
allows registration of a remote peer by matching the incoming registration request's
username with the provider's SIP trunk name. At this point the provider's SIP trunk
moves from having an UNKNOWN peer to being associated with the registered IP
address.
An incoming call is matched by the recipient by looking at the incoming call's IP
address and FROM field, which defaults to the caller ID of the caller, or the calling
peer's from-user field if configured. The recipient first looks at the caller's FROM field,
and if this matches the username field of a peer that has “Identify by user” enabled or
a configured extension, a successful match is made.
If no such match can be made, the recipient matches the first SIP trunk entry that is
associated with the IP address of the caller. This implies that, if multiple SIP trunks
are associated with peers with the same IP address, they have to have “Identify by
username” enabled and a username specified, and the remote peers have to have
their from-user fields set to the appropriate username.
If a successful match is made and the password and codecs that are configured for
that matched peer are compatible with those in the call setup request, the call is
established.
This mechanism is used for call setup in both directions.
3.8.3.2 Adding a SIP trunk
To add a SIP provider, activate the Add menu on the Trunks panel. Select SIP
Provider.
3.8.3.3 Sip trunk configuration
SIP trunk configuration is divided into basic, advanced and codec configuration,
accessible from their accompanying tabs on the SIP Provider form.
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