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Scenario

The 

Background Information

• Refer to the background information in Basic Service Availability - DNS.
• At the access edge the nature of the connections is temporary.
• The

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  maintains separate IP/transmission stacks on either side of the call and bridge the SIP application. This allows it to fully inter work between transmission protocols. This is also applicable for bridging between IPv4/IPv6 domains.

Description

1. The IADs may use a variety of different transmission layers for the transport of SIP protocol messages. In the access space, UDP is used predominantly but in some cases TCP is used.
2. The

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   s can talk to either AS1 or AS2. Since AS1 can only accept UDP, the sessions directed to AS1 will be over UDP. Since AS2 requires TCP, the SBCs host an TCP connection to AS2 and send sessions using TCP
3. AS1 only supports UDP, so

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   s connecting to it must use UDP irrespective of the access side protocol used by the IAD.

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    performs the protocol conversion.
4. AS1 only supports TCP, so

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   s connecting to it must use TCP irrespective of the access side protocol used by the IAD.

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   performs the protocol conversion.