• SIPv2 - Session Initiation Protocol version 2 (RFC 3261, 3262, 3263, 3264)
• SIP proxy redundancy - Dynamic via DNS SRV, A records
• Reregistration with primary SIP proxy server
• SIP support in NAT networks (including STUN)
• SIPFrag (RFC 3420)
• Secure (encrypted) calling via prestandard Implementation of Secure RTP
• Codec name assignment
• Voice algorithms:
• G.711 (A-law and mu-law)
• G.726 (16/24/32/40 kbps)
• G.729 A
• G.723.1 (6.3 kbps, 5.3 kbps)
• Dynamic payload support
• Adjustable audio frames per packet
• DTMF - Dual-tone multifrequency, in-band and out-of-band (RFC 2833) (SIP INFO)
• Flexible dial plan support with interdigit timers
• IP address/URI dialing support
• Call progress tone generation
• Jitter buffer - Adaptive
• Frame loss concealment
• VAD - Voice activity detection with silence suppression
• Attenuation/gain adjustments
• VMWI - Voicemail waiting indicator via NOTIFY, SUBSCRIBE
• Caller ID support (name and number)
• Third-party call control (RFC 3725)
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