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M3SR Series 4100
5.5.3 SIP – Useful Information for System Integration
The VoIP service uses the Session Initiation Protocol (SIP) for the establishment and termi-
nation of a call session. Therefore more information about the use of SIP and the call initia-
tion and termination procedures can be useful when setting up the system.
The session endpoints supporting SIP are called the SIP user agents. In case of the radio
network, the VoIP gateway radio operates as the SIP user agent. Since it is able to generate
session requests and also to respond session requests from another SIP user, the VoIP
gateway radio is able to operate both as User Agent Client (UAC) and as User Agent Server
(UAS).
SIP Proxy and SIP Registrar
The VoIP gateway radio supports a connection to a SIP Proxy and a SIP Registrar. These
SIP entities are useful for the routing of requests when an end-to-end connection is not fea-
sible. The proxy server is an intermediary entity that acts as both a server and a client for the
purpose of making requests on behalf of other clients. It ensures that a request is sent to an-
other entity closer to the destination. The SIP registrar is a server that accepts SIP register
requests and stores information about the sender into the location service for the domain it
handles. A SIP registrar for a domain is often co-located with the SIP proxy for that domain.
5.5.3.1
Session Signalling
There are two types of signalling in the proceeding of a session initiation and termination.
Between the VoIP gateway radio and the external VoIP user, SIP signalling is supported in
accordance with the SIP standard. For the signalling between the VoIP gateway radio and
all the radio units inside the radio network, a proprietary signalling is used.
For the examples below, it is considered to have the waveform SECOM-V being used inside
the radio network.
In case of ALE-3G, the proprietary signalling from the VoIP gateway radio to the end-
point radios is not supported in broadcast mode, since ALE-3G makes use of the stan-
dard xDL for IPoA services, which does not allow broadcast.
Operating Manual 6172.5808.02 – 01
SIP – Useful Information for System Integration
5.119
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