SIP Transport Selection
With this feature enabled, when the Oracle Communications Session Border Controller forwards a message larger than the value specified in the maximum UDP length parameter, it attempts to open on outgoing TCP connection to do so. This connection might fail for a number of reasons; for example, an endpoint might not support UDP, or it might be behind a firewall. The UDP fallback option addresses this condition. If it is configured in SIP interfaces associated with an outgoing message and a TCP session cannot be established, the Oracle Communications Session Border Controller falls back to UDP and transmits the message. When the option is not present, the Oracle Communications Session Border Controller’s default behavior is to return the SIP status message 513 Message too Large.
SIP Transport Selection Configuration
You enable this feature per SIP interface by setting options that control the maximum UDP length and allow UDP fallback:
- max-udp-length=X (where X is the maximum length)—Sets the largest UDP packers that the
Oracle Communications Session Border Controller will pass. Packets exceeding this length trigger the establishment of an outgoing TCP session to deliver the packet; this margin is defined in RFC 3261. The system default for the maximum UDP packet length is 1500.
You can set the global SIP configuration’s max-udp-length=X option for global use in your SIP configuration, or you can override it on a per-interface basis by configuring this option in a SIP interface configuration.
- udp-fallback—When a request needs to be sent out on the SIP interface for which you have configured this option, the
Oracle Communications Session Border Controller first tries to send it over TCP. If the SIP endpoint does not support TCP, however, then the
Oracle Communications Session Border Controller falls back to UDP and tries the request again.
To enable SIP Transport Selection: