Chapter 4: Trunks
117
proxy represents its own domain. As the name suggests, the proxy model assumes that
you are talking to a SIP proxy or session border controller, while the gateway model
assumes you are talking to a SIP user agent. However, the two models are quite similar.
As a general rule, use the gateway trunk first, and if you have an issue, try changing the
trunk type.
SIP Gateway Trunk
SBC
PSTN
Figure 4-5.
Example of Outbound Proxy Trunk
Inbounds Calls
How the System Identifies a Trunk
When a new call comes into the system, the system must determine whether the call
is an internal extension or an outside call that is configured to a trunk. To do this, it
first looks at the
From
field to see if it matches an extension. If it’s not an extension,
then from a registration trunk, it looks for a
line
parameter in the SIP INVITE (see
Appendix B for information on the SIP INVITE). The
line
parameter is set by the
system when the trunk is registered (Figure 4-6). Although it is not a predefined SIP
parameter, the
line
parameter is used by many SIP implementations to identify where
the call is routed to.
Figure 4-6.
Line Parameter in REGISTER Request of SIP Trace
Summary of Contents for ONE IP
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