Sip-interface Reuse-connections Not Working (Doc ID 2529500.1)

Last updated on NOVEMBER 13, 2023

Applies to:

Symptoms

SBC not reusing existing connection.

Scenario:

Endpoint registers to registrar server via SBC

Notable in the REGISTER request is:
Via address with same IP:Port as transport IP:port
Contact with same IP as transport, but different port than Via and Transport port.
Use of alias parameter in alias

If a request (session starter) is received by the SBC, the request will be forwarded using the existing connection.

The problem being reported pertains to existing dialogs. 

When the SBC receives new requests such as NOTIFY and INVITE within an active dialog that need to be forwarded to the registered endpoint,the SBC will refer to the last received Contact address if present, according to RFC 3261

If Contact header is present in messages from endpoint and the Contact IP:port do not match the stored Via IP:port, a new tcp connection to the endpoint will be created, and the existing tcp connection will not be used.

Example call flow:

SBC reuses existing connection - example port 5070 = transport port and Via port
UAC:5070   <--INV--       SBC
UAC:5070   --200 OK--> SBC - Contact with different contact port - example 5060
SBC creates new connection to port 5060 if allowed by endpoint
UAC:5060   <--INV--       SBC

If Contact port = Via port, there is no problem and a new connection is not created.

SBC reuses existing connection - example port 5070 = transport port and Via port
UAC:5070   <--INV--    SBC
UAC:5070   --200 OK--> SBC - Contact port = Via Port = Transport port
SBC uses existing connection
UAC:5070   <--INV--    SBC

Cause

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