H.225.0
Encyclopedia
H.225.0 is part of the H.323
family of telecommunication
protocols
.
The main objective of H.225.0 is the definition of messages and procedures for:
The Message Encoding is performed by utilizing Q.931
User-to-User information elements to convey H.225 messages. The messages themselves are encoded according to the Packed Encoding Rules
(PER) of ASN.1.
The structure of H.225 follows the Q.931 standard as seen in the table below.
H.323
H.323 is a recommendation from the ITU Telecommunication Standardization Sector that defines the protocols to provide audio-visual communication sessions on any packet network...
family of telecommunication
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
protocols
Communications protocol
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
.
The main objective of H.225.0 is the definition of messages and procedures for:
- Call Signaling: establish, control and end an H.323H.323H.323 is a recommendation from the ITU Telecommunication Standardization Sector that defines the protocols to provide audio-visual communication sessions on any packet network...
call. The call signaling of H.225.0 is based on the call setup procedures for ISDN, Recommendation Q.931Q.931ITU-T Recommendation Q.931 is ISDN's connection control protocol, roughly comparable to TCP in the Internet Protocol stack. Q.931 doesn't provide flow control or perform retransmission, since the underlying layers are assumed to be reliable and the circuit-oriented nature of ISDN allocates...
.
- RAS Signaling Function: perform registration, admission, bandwidth changes, status and disengage procedures between endpoints and an H.323 GatekeeperH.323 GatekeeperAn H.323 Gatekeeper serves the purpose of Call Admission Control and translation services from E.164 IDs to IP addresses in an H.323 telephony network. Gatekeepers can be combined with a gateway function to proxy H.323 calls and are sometimes referred to as Session Border Controllers...
. The RAS signaling function uses a separate channel (RASRegistration, Admission and StatusH.323 defines packet-based multimedia communications systems that use a RAS channel to carry messages used in the H.323 Gatekeeper discovery and endpoint registration processes...
channel). This set of messages is called Registration, Admission and Status (RASRegistration, Admission and StatusH.323 defines packet-based multimedia communications systems that use a RAS channel to carry messages used in the H.323 Gatekeeper discovery and endpoint registration processes...
).
- Additionally, H.225.0 defines media packetization using RTPReal-time Transport ProtocolThe Real-time Transport Protocol defines a standardized packet format for delivering audio and video over IP networks. RTP is used extensively in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applications, television services and...
for traditional codecs like G.711, H.261 and H.263. Newer ITU recommendations for media compression/signaling refer to RFCRequest for CommentsIn computer network engineering, a Request for Comments is a memorandum published by the Internet Engineering Task Force describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems.Through the Internet Society, engineers and...
s for packetization (e.g. H.264 utilizes the single NAL unit mode of RFC 3984 in H.323 as defined in H.241H.241H.241 is a Recommendation from the ITU Telecommunication Standardization Sector that defines extended video procedures and control signals for H.300-series terminals, including H.323 and H.320....
).
The Message Encoding is performed by utilizing Q.931
Q.931
ITU-T Recommendation Q.931 is ISDN's connection control protocol, roughly comparable to TCP in the Internet Protocol stack. Q.931 doesn't provide flow control or perform retransmission, since the underlying layers are assumed to be reliable and the circuit-oriented nature of ISDN allocates...
User-to-User information elements to convey H.225 messages. The messages themselves are encoded according to the Packed Encoding Rules
Packed Encoding Rules
Packed encoding rules are ASN.1 encoding rules for producing a compact transfer syntax for data structures described in ASN.1, defined in 1994....
(PER) of ASN.1.
The structure of H.225 follows the Q.931 standard as seen in the table below.
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