RCSe TLS/TCP Re-Use Connections

In an RCSe environment the sip-interface reuse-connections option is used to make the Oracle Communications Session Border Controller retain the TCP/TLS connection established by the endpoint during the registration for all subsequent messages to that endpoint, essentially providing for a persistent connection between the Oracle Communications Session Border Controller and the user equipment (UE).

Field experience uncovered an implementation deficiency associated with these persistent connections particularly within RCSe deployments. The basic scenario is as follows:

The UE registers in a TLS realm on SBC1. SBC1 stores the IP:Port from VIA (and Contact) as alias of the currently established connection.
The UE transits to another realm/sip-port (same or different Oracle Communications Session Border Controller) without previously unregistering or closing the TCP connection with the TLS sip-port on SBC1.
UE goes back to the TLS realm in SBC1 and establishes a new connection — same source IP as in Step 1, but a different port as in Step 1.

The problem arises at Step 3. If the Oracle Communications Session Border Controller has not detected that the TLS connection established in Step 1 has been effectively terminated, it will not update the alias connection to that established in Step 3, but instead continue to attempt to use the Step 1 connection.

This means that the next message from the core side to the UE will fail, since the Oracle Communications Session Border Controller will attempt to send the message of the dead TLS connection — that is using the IP address:port pair passed in Step 1.

All communications to this UE will fail until it sends the next message to the Oracle Communications Session Border Controller, when the alias connection will be update to the TLS connection in Step 3.

To resolve this issue, the Oracle Communications Session Border Controller needs to always update the alias table when it receives a new inbound connection on the configured sip-interface.

Option Configuration Guidelines

The following table lists the full range of options that pertain to TLS/TCP Connection reuse with an emphasis on use in RCSe environments.

Option	Connection Behavior
reuse-connections	Use/retain first inbound connection until explicitly closed
reuse-connections=latest	Use the last inbound connection, update the alias for each new connection
reuse-connections=no	Establish new connection at each UE access
NOT CONFIGURED	Equivalent to reuse-connections=no