f the current SIP trunk offerings in the market include TLS as an option. Hopefully this situation will change. Chapter 7: Design and Implementation Considerations 121 Back-to-Back User Agent (B2BUA) A B2BUA (such as the CUBE) terminates and reoriginates all calls before they enter your network. All SIP traffic passes through the SIP stack on the B2BUA twice (on ingress and egress) SO that all malformed or rogue packets are dropped. SIP Normalization There are certain numbers, names, or other internal information you might want to popu- late informative displays on the endpoints in your network. When these calls exit over the SIP trunk to external destinations, you might not want all this information to remain in the SIP messaging, especially non-DID numbers used by your organization. You can use SIP normalization features to insert, delete, or change this kind of information in the SIP messaging on your border element. Examples 7-3, 7-4, and 7-5 show how SIP normalization can be used on the CUBE to mod- ify the From header in an INVITE to a gateway@ip-address format and to add the phone-context=gateway field to the To header of the INVITE. Example 7-3 shows the commands needed for the configuration; Example 7-4 shows the original SIP INVITE; and Example 7-5 shows the resulting INVITE after normalization has been applied. Example 7-3 SIP Normalizations Commands voice service voip sip-profiles 1 voice class sip-profiles 1 request INVITE sip-header From modify "(<.*:)(.*@)" "\1gateway@" request INVITE sip-header To modify "<(.*)>" "<\1; phone-context=gateway>" Example 7-4 Original SIP INVITE INVITE sip:22220000205060 SIP/2.0 Via: SIP/2.0/UDP 9.13.24.6:5060;branch=z9hG4bK1AD9E2 Remote-Party- ID:"sipp"<sip:sipp@9.13.24.6>;party=calling;screen=no;privacy=off II From: "sipp"<sip:sipp@9.13.24.6>;tag=23C3F840-99A To: <sip:2222000020@9.13.24.7> Date: Thu, 30 Aug 2007 07:04:36 GMT Example 7-5 Normalized SIP INVITE INVITE sip: 22220000205070 SIP/2.0 Via: SIP/2.0/UDP 1.13.24.7:5060;branch=z9hG4bK1191BFD Remote-Party-ID: - "s