ls and Codecs Best practices in the area of protocol choices include the following: Use SIP end-to-end in your network if you can. Interoperability is easier and more flexible on SIP-to-SIP connections than translating to other protocols. If adhering to the previous guideline is not possible, use a SBC to interoperate H.323 with your SIP trunk. Use RFC-2833 dual-tone multi-frequency (DTMF) relay throughout your network if possible. If not possible, make sure you understand where in your network transla- tions occur between out-of-band signaling methods (such as the traditional H.323 methods) and RFC-2833, which travels in the media stream. The device (such as a call agent on an SBC) that does this conversion must have access to both the signaling and the media streams to do SO. Investigate RFC-2833 DTMF payload type value assignments on your own call agents, endpoints, applications, and the values used by the SP. Conversion or inter- working between these values might need to be configured on your border element to ensure proper interoperation of calls. Using T.38 fax relay for fax over IP transmission is technically a more robust method of faxing and works better than other methods where available. But it is not avail- able on all networks and to all endpoints SO that fax passthrough (or fax via G.711) is still widely used as it interoperates easier and with more endpoints. If the provider offers T.38, investigate if failover to G.711 fax is offered as a secondary call negotia- tion service to connect calls to destinations that might not yet support T.38. Consider keeping fax on TDM trunks for a while longer if this is a critical part of your business. Similar to the previous point, keep modem, point-of-sale (POS), and telecommunica- tions devices for the deaf (TDD) traffic on TDM trunks for the time being. SIP trunk technology is not ready to carry these traffic types in a reliable and pre- dictable manner. Seriously consider getting G.711 service on your SIP trunk. Although it uses more bandwidth than G.729, i