Step 14. Different network segments
Case: The system site is located in one network segment and serves users and devices located in another segment. Calls between users' devices are made, subscribers can hear each other.
SG has the function of network delimitation. If SG is available on both network segments, user devices can address their SIP requests to it to address A2 on segment C2, and it in turn broadcasts the requests from address A1 on network segment C1, where B2BUA is located. And vice versa, B2BUA sends SIP requests and SIP responses to SG to address A1 on the network segment and SG translates them to segment C2 from address A2.
A particular SG instance can be configured so that all calls arriving at it will not apply media servers during service. Thus despite the complex organization of SIP exchanges over B2BUA, the end devices will exchange SDP directly with each other, and traffic will flow on the network segment where the devices are mutually available. With this approach, the system does not record the traffic and does not provide the ability to listen to the conversation later. But the load on the server infrastructure is also orders of magnitude lower with this approach.
This approach is not applicable in all cases, for example:
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if devices A and B are on different network segments and are not reachable by each other;
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if it is necessary to record and store calls;
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if it is necessary to connect subscribers to automatic services;
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if multi-user conferencing is to be possible;
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if it is necessary to be able to connect third parties to the conversation;
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if you want to play standby tones while holding.
Roles at the boundaries with the external environment have support for multiple network interfaces. According to the case conditions, subscribers are devices whose addresses are not directly reachable from the media servers of the MG roles. Accordingly, traffic must also be broadcast from one network to another at the edge that is formed by SG. To solve this problem, there is a BGMG role that can be activated on the same server as SG. Whenever the SG will broadcast from one network to another, it will invoke the BGMG.
BGMG can be configured with a configuration file and attached to any BGMG on the site. The context creation control request will find exactly the BGMG that resides on the same server as the SG initiator.
It is appropriate to recall corollary 6 step 11: In order for media traffic to be successfully transmitted between subscribers A and B in all cases, there must be full network availability between servers with the roles SG, B2BUA, and MG at those sites where subscribers A and B may be registered.
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