Mike's PBX Cookbook

VoIP Standards


ITU-T Standards and Recommendations

H.323 V2Packet-based mutlimedia communications systems
H.225.0Call signalling protocols and media stream packetization for packet-based multimedia (includes Q.931 and RAS)
H.225.0 Annex GGatekeeper to gatekeeper (inter-domain) communications
H.245Control protocol for multimedia communications
H.235Security and encryption for H-series multimedia terminals
H.450.xSupplementary services for multimedia:
1. Generic functional protocol for the support of supplementary services in H.323
2. Call transfer
3. Diversion
4. Hold
5. Park & pickup
6. Call waiting
7. Message waiting indication
H.323 Annex DReal-time fax using T.38
H.323 Annex ECall connection over UDP
H.323 Annex FSingle-use device
T.38Procedures for real-time group 3 facsimile communications over IP networks
T.120 seriesData protocols for multimendia conferencing

IETF RFCs and Drafts

RFC 2543SIP: Session initiation protocol
RFC 2327SDP: Session description protocol
Internet DraftSAP: Session announcement protocol

Gateway Control


H.GCPProposed recommendations for gateway control protocol


Internet DraftMGCP: Media gateway control protocol
Internet DraftMEGACO protocol
DraftSGCP: Simple gateway control protocol
Internet DraftIPDC: IP device control

Media Transport


RFC 1889RTP: Real-time transport protocol
RFC 1889RTCP: Real-time transport control protocol
RFC 2326RTSP: Real-time streaming protocol

Media Encoding


Standard  AlgorithmBit Rate (Kbit/s)Typical end-to-end delay (ms)Resultant Voice Quality
G.711PCM48, 56, 64<<1Excellent
G.723.1MPE/ACELP5.3, 6.367-97Good(6.3), Fair(5.3)
annex A
G.722Sub-band ADPCM48, 56, 64<<2Good
G.726ADPCM16,24,32,4060Good(40), Fair(24)
G.727AEDPCM16, 24, 32, 4060Good(40), Fair (24)


Standard AlgorithmBit Rate (Kbit/s)Picture Quality
H.261Discrete cosine transform (DCT) with motion compensationpx64 (p=# of ISDN B channels)Low
H.263Improved version of H.261VariousMedium

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