Payload Type Handling

The Oracle® Enterprise Session Border Controller supports the RTP NTE for telephony events such as transport of DTMF digits and hook flash. Using RTP NTE, endpoints perform per-call negotiation of the DTMF transfer method and negotiate payload type value for the RTP NTE packets.

Although most endpoints use payload type number 101, the RTP payload type formats can become asymmetrical when being interworked between SIP and H.323 because there is no default standard and endpoints use different types. This means that the payload type negotiated on one side of the Oracle® Enterprise Session Border Controller, and that ends up being used for the call, might not be the same payload type negotiated on the other side of the Oracle® Enterprise Session Border Controller. And while certain endpoints handle the asymmetry well, others do not.

Consider the simplified example of an IWF call initiated in SIP and translated to H.323. In this scenario, the SIP endpoint negotiates the payload type 106 with the Oracle® Enterprise Session Border Controller. And despite the fact that the H.323 endpoint negotiates payload type 101, the Oracle® Enterprise Session Border Controller returns type 106 and the call proceeds using type 106.

However, you can enable forced symmetric payload type handling so the Oracle® Enterprise Session Border Controller changes the payload type of RFC 2833 packets to avoid using asymmetrical payload types.

For H.323 session agents and H.323 interfaces (stacks), you can configure an option that forces symmetric payload type use. The Oracle® Enterprise Session Border Controller can detect when the payload types negotiated by the SIP and H.323 endpoints are symmetrical and when they are not. When it detects asymmetrical payload type use, the Oracle® Enterprise Session Border Controller forces the remote endpoint to use the RFC 2833 payload type you configure in the SIP interface.