SIP Transport Selection

With this feature enabled, when the Oracle® Enterprise 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® Enterprise Session Border Controller falls back to UDP and transmits the message. When the option is not present, the Oracle® Enterprise 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® Enterprise 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® Enterprise Session Border Controller first tries to send it over TCP. If the SIP endpoint does not support TCP, however, then the Oracle® Enterprise Session Border Controller falls back to UDP and tries the request again.
To enable SIP Transport Selection:

In Superuser mode, type configure terminal and press Enter.
```
ORACLE# configure terminal
```
Type session-router and press Enter to access the session-router path.
```
ORACLE(configure)# session-router
```
Type sip-interface and press Enter. The system prompt changes to let you know that you can begin configuring individual parameters.
```
ORACLE(session-router)# sip-interface
```
options—Set the options parameter by typing options, a Space, the option name max-udp-length=X (where X is the maximum UDP length you want to set), and then press Enter.
```
ORACLE(sip-interface)# options +max-udp-length=900
```
If you type options max-udp-length=X, you will overwrite any previously configured options. In order to append the new option to the sip-interface’s options list, you must prepend the new option with a plus sign as shown in the previous example.
options—Set the options parameter by typing options, a Space, the option name udp-fallback, and then press Enter.
```
ORACLE(sip-interface)# options +udp-fallback
```
If you type options udp-fallback, you will overwrite any previously configured options. In order to append the new option to the sip-interface’s options list, you must prepend the new option with a plus sign as shown in the previous example.
Save and activate your configuration.