System information

 CLIP/CLIR
 DTMF generation
 Call-Forward on out-of-service
 Codec transcoding
 Advanced statistics support
 NAT traversal of signaling
 NAT traversal of media
 SIP Session timers
 RTP Timers and media timeout
 Blind SIP Registration
 Late Codec Negotiation
 Multiple SIP registrations per user account
 Can act as an SBC
 Max Session Setting
 Manage Presence
 Detailed call logs
 SIP/SIMPLE
 SIP Reinvites
 SIP-H.323 protocol conversion
 Class 4 features
 Class 5 features
 RFC 2543 compatibility
 RFC 3261 compatibility
 RFC 2976 The SIP INFO Method
 RFC 3262 Reliability of Provisional Responses in Session Initiation
 RFC 2617 HTTP Authentication
 RFC 3263 Locating SIP Servers
 RFC 3265 Specific Event Notification
 RFC 3420 Internet Media Type message/sipfrag
 RFC 3515 Refer Method
 RFC 3311 UPDATE Method
 RFC 3581 Symmetric Response Routing
 RFC 3842 Message Summary and Message Waiting Indication Event Package
 RFC 3891 "Replaces" Header
 RFC 3325 Private Extensions to the Session Initiation
 RFC 2778 A Model for Presence and Instant Messaging