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M3SR Series 4100
The radios "ALPHA", "BRAVO" and "CHRIS" are connected with ALE-3G or SECOM-V. AL-
PHA is configured as a GWR and connected to the VoIP private branch exchange (VoIP-
PBX) "v-server" using ETHERNET. The PBX must support the IETF RFC 3261 SIP standard
and the RFC 3550 realtime transport protocol standard.
It is not a mandatory requirement to connect the GWR to a PBX – it is also possible to con-
nect just one phone peer to peer to the GWR. A PBX has the advantage to offer voice
prompts to inform caller or callee about a radio call and how to proceed with PTT on the
phone. This makes the system more user friendly. Additionally a PBX can be used as a gate-
way into a public network or could be used to transfer calls to other radio cells. Combinations
of two GWR over ETHERNET could be used to connect two radio nets over VoIP.
The communication between GWR and the other radios of the group is implemented using
a proprietary protocol, therefore the SIP settings in the CNRs must not be configured. Only
the GWR implements the SIP gateway to the PBX.
Inbound Calls
Inbound calls into the radio network allow the connection to one of the other radios of the
group or to the whole group using a broadcast target URI.
If the external caller wishes to be connected to a particular radio e.g. "BRAVO", the PBX
sends SIP invites e.g. to BRAVO@gwr_alpha (the hostname of GWR "ALPHA"). The voice
stream from the PBX in direction to "BRAVO" can be received only on this particular radio.
Receiving the voice stream at "CHRIS" is not possible. If the caller wishes to broadcast his
message to all members of a radio cell, the PBX sends the SIP invite to
RGA_BROADCAST@gwr_alpha. The GWR will be set to broadcast mode and the voice
stream from the caller can be received on all radios of the cell.
Because any one voice session is possible at a time, the GWR will reject any further calls.
Outbound Calls
The system behavior in case of outbound calls relies strongly on the configuration of the ra-
dios. In case of broadcast mode all radios of a cell are able to listen to the voice stream from
the particular radio to the PBX.
In difference to the first case nobody else can listen to the voice stream towards the GWR if
the operator of the radio has chosen a point-to-point station connection to the GWR radio.
There is no outgoing call towards the SIP network possible if the operator chooses a point-
to-point connection to a radio other than the GWR.
CNR Removal into another Radio Cell
There are scenarios where many GWR radios are installed along a line (e.g. border control).
The radios of the group are installed on vehicles moving between different locations and
changing from one radio cell to the next.
The operator needs to change to another preset page to connect to the GWR of the new ra-
dio cell. The preparation of those scenarios is possible using the RNMS Mission Planner soft-
ware.
Operating Manual 6175.4760.02 – 01
Voice over IP (VoIP)
5.103
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