ice versa Support of H.245 tunneling in Interworking Function (IWF) H.323 Annex-E support for UDP signaling Q.931 port can be specified by SBC H.245 UII to RFC-2833 DTMF interworking Transparent RFC-2833 support Support of call hold using Empty the terminal capabilities set Support of call transfer using the Empty terminal capabilities set Support of conference call using the Empty terminal capabilities set SBC can act in Gatekeeper proxy mode SBC can act as a virtual gateway Q.850 Cause to H.323 Release Complete Reason Chapter 9: Questions to Ask of a Service Provider Offering and an SBC Vendor Codec mapping supported SIP Redirects can be mapped to an H.323 LRQ SIP Info and DTMF UII management capabilities Support of midsession media change Early media support Ringback support for IWF sessions Media release, or antitromboning, for IWF calls Support for Privacy in IWF calls SIP Trunk URI compliancy for IWF calls including trunk group routing Manipulation of SIP headers allowed in IWF calls Other Interworking Support A few more interworking-related issues could not be grouped in the previous sections, which are also critical for your network and good to put into the RFP: DTMF interworking SIP over TCP to SIP over User Diagram Protocol (UDP) interworking IPSEC to non-IPSEC interworking RTP to SRTP interworking IPv4 to IPv6 interworking SIP-T to SIP-T interworking TLS to non-TLS interworking FAX capability: T38 ITU standard fax protocol over IP network Demarcation An SBC separates your internal network from the external network. This is kind of a wall between these two networks. When you connect your UC system via SIP, there is a possi- bility to expose your whole network to the external world. SBC protects you from that risk. You need to check with your SBC vendor about the demarcation issues discussed in the following sections. Topology Hiding The SBC must have the capability to hide your whole IP topology information (at both Layers 3 and 5) when interworking between the public and private interfaces. It should i