IWF Codec Renegotiation for Audio Sessions

For calls requiring interworking between SIP and H.323, there can be several instances for audio sessions when a mid-call codec change is necessary. These are some examples of when the codec used for voice transportation is necessary:

• Sessions between analog FAX machines that start as regular voice calls but then must use a codec that is fax-signalling tolerant (like transparent G.711) when FAX tones are detected; detection takes place after the call has been answered. The case of modem calls is similar.
• An established call is redirected in one carrier’s network either to a different enduser or to a media server. In this case, the party to which the call is redirected might not support the codec used in the redirection. If request for a codec change is carried out at the signalling level, the call can proceed with the party to which the call was redirected.
• Endusers might want to change codecs when they suffer low voice quality.

Both SIP and H.323 provide mechanisms for changing codecs during a call: SIP uses the ReINVITE, and H.323 uses the H.245 Request Mode. Using the option called processRequestModeForIWF=all either in an H.323 interface (stack) or an H.323 session agent configuration, you can enable the Oracle® Enterprise Session Border Controller to interwork SIP ReINVITE and H.245 Request Mode requests.

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