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Introduction 560
SmartWare Software Configuration Guide 46 • Context SIP gateway overview
Introduction
This chapter provides an overview of the context SIP gateway. The main purpose of a context SIP gateway is
forwarding and reception of SIP packets according to a RFC 3261 User Agent. In SmartWare, the context SIP
gateway represents the interface between the Call-Router (Context CS) and the IP Router (Context IP). It is
responsible for dispatching incoming initial SIP requests to the right call control SIP interface and for the
determination of the right IP interface for outgoing SIP messages. This is also called SIP Transport Routing.
Figure 78 shows where the context SIP gateway is located in SmartWare and how it interacts with other com-
ponents.
Figure 78. Routing Architecture
There is a relationship between the call control SIP interface and the context SIP gateway. Every call control
SIP interface must be bound to a context SIP gateway. One of the responsibilities of this interface is to build
Request-URI and to determine a possible outbound proxy. If a proxy is available, it represents the next SIP hop
and all outgoing messages will be sent to this host. If no proxy has been configured, the messages will be sent to
the Request-URI's host. Depending on these two SIP parameters, the context SIP gateway chooses the right
outgoing IP interface. The IP address of the outgoing IP interface will be placed in all SIP and SDP headers
that need a direct routable contact address (VIA, Contact).
In the other direction, the context SIP gateway dispatches incoming SIP requests according to the Request-
URI and the From-URI. The call control SIP interface has configuration parameters called “remote” and
“local” to build the Request-URI, the To-URI and the From-URI for outgoing requests. These parameters will
also used for identifying the best matching call control SIP interface for incoming requests according to the fol-
lowing rule:
Call Routing
Tables
Location Services
IP Routing
Tables
Context
CS
Context
SIP
Gateway
Context
IP
Call Routing
Context CS Interfaces
Transport Routing
Context SIP - Gateway Interfaces
Network Routing
Context IP Interfaces