vice as part of the SIP trunk service to ensure UNI compliance regardless of the enterprise equipment. In some cases, especially for larger enterprises, both exist, and there is a pair of border elements at the enterprise edge, one side owned by the service provider (CPE), the other by the enterprise. This is separate from the SBC that always exists at the service provider edge and is a shared device among many SIP trunk customers. The SIPConnect forum has been established by a consortium of members as an industry organization to focus on specifying and defining the SP UNI as a standard to ease some of interconnecting and interoperability issues currently still experienced. Codec Choice Codec choice was briefly discussed previously in this chapter in the "Transcoding" sec- tion. Transcoding is one of the demarcation features you might want to deploy in your network to normalize codec use at the border of your network to the choices you have engineered your network for, independent of the codec choices on the SIP trunk or those chosen by the offnet destination of the call. Newer wideband codecs, such as G.722, can be used in your network but might not yet be available on SIP trunks services. The choice 110 SIP Trunking of SIP delayed offer or early offer also has some influence over what codecs can be cho- sen for any particular call. To control the use of codecs on your network to comply either with bandwidth engi- neering (call admission control) or with other enterprise policies, you have the follow- ing choices: Allow calls with inappropriate or incompatible codecs to fail. Involve a transcoder to resolve calls with incompatible codecs and to change incom- ing codecs to those you prefer to use on your network. Configure features to control codec negotiation and filtering in SIP call setups as the call passes through the border element. Fault Isolation In traditional TDM PSTN access, the PSTN gateway terminated the TDM connection from the provider's network and originated a VoIP connection inside your enterpris