Different type of standard for IP Telephony

Different type of standard:

 Different type of standard and protocols are employed by the IP telephony. H.323, session initiation protocol (SIP), media gateway to media controller protocol(MGCP) & many more other protocol are based on IP telephony.

4. What is H.323?

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H.323 provides multimedia communication services-real-time audio, video, and data Communications-over packet networks, including Internet protocol (1P)-based networks. It specifies the components, protocols, and procedures providing multimedia communication over packet-based networks

H.323 is a standard produced by the ITU-T Study Group 16

.H.323 is part of a family of ITU-T recommendations called H.32x that provides multimedia communication services over a variety of networks. H.323 can also be applied to multipoint-multimedia communications. Currently the most widely supported IP telephony signaling protocol.

5. The ITU-T H.32x Family:

The H.323 standard is part of the H.32x family of recommendations specified by

ITU-T. The other recommendations of the family specify multimedia communication services over different networks:

(a)H.324 over SCN

(b)H.320 over integrated services digital networks (ISDN)

(c)H.321 and H.310 over broadband integrated services digital networks (B-ISDN)

(d)H.322 over LANs that provide guaranteed QoS

H.323 standard was interoperability with other multimedia-services networks through the use of a gateway. H.323 terminals are compatible with H.324 terminals on SCN and wireless networks, H.310 terminals on B-ISDN, H.320 terminals on ISDN, H.321 terminals on BISDN, and H.322 terminals on guaranteed QoS LANs.

6. H.323 Components:

The H.323 standard specifies four kinds of components, which, when networked together, provide the point-to-point and point-to-multipoint multimedia communication Services:

6.1. Terminals

6.2. Gateways

6.3. Gatekeepers

6.4. Multipoint control units (MCUs)

An H .323 zone is a collection of all terminals, gateways, and MCUs managed by a single gatekeeper. A zone includes at least one terminal and may include gateways or MCUs. A zone has only one gatekeeper. A zone may be independent from network topology.

6.1. Terminals:

H.323 terminal can either be a personal computer (PC) or a stand-alone device, running an H.323 and the multimedia applications. It supports audio communications and can optionally support video or data communications. Because the basic service provided by an H.323 terminal is audio communications, H.323 terminal plays a key role in IP-telephony services.

6.2. Gateways:

A gateway connects two dissimilar networks. An H.323 gateway provides connectivity between an H.323 network and a non-H.323 network. A gateway is not required, however, for communication between two terminals on an H.323 network.

6.3 Gatekeepers:

A gatekeeper can be considered the brain of the H.323 network. It has many functions

Address Translation:

The gatekeeper translates this E.164 telephone number or the alias into the network address for the destination terminal. The destination endpoint can be reached using the network address on the H.323 network.

Admission Control:

The gatekeeper can control the admission of the endpoints into the H.323 Network by using RAS messages, admission request (ARQ), confirm (ACF), and reject (ARJ).

Bandwidth Control:

The gatekeeper provides support for bandwidth control by using the RAS messages, bandwidth request (BRQ), confirm (BCF), and reject (BRJ). If a network manager has specified a threshold for the number of simultaneous connections on the H.323 network, the gatekeeper can refuse to make any more connections once the threshold is reached.

Zone Management:

The gatekeeper provides the above functions address translation, admissions control, and bandwidth control4or terminals, gateways, and MCUs located within its zone of control.

Call-Control Signaling

The gatekeeper can route call-signaling messages between H.323 endpoints using H.225 call signaling message.

Call Authorization

Gatekeeper authorizes the user to setup connection within its zone.

Call Management

The gatekeeper may maintain information about all active H.323 calls. It can control its zone by providing the maintained information.

6.4 Multipoint Control Units:

MCUs provide support for conferences of three or more H.323 terminals. All terminals participating in the conference establish a connection with the MCU. The gatekeepers, gateways, and MCUs are logically separate components of the H.323 standard but can be implemented as a single physical device.

7. Protocols Specified by H.323:

The protocols specified by H.323 are listed below.

7.1 audio CODECs

7.2 video CODECs

7.3 H.225 registration, admission, and status (RAS)

7.4 H .225 call signaling

7.5 H.245 control signaling

7.6 real-time transfer protocol (RTP)

7.7 real-time control protocol (RTCP)

7.1 Audio CODEC

An audio CODEC encodes the audio signal from the microphone for transmission on the transmitting H.323 terminal and decodes the received audio code that is sent to the speaker on the receiving H.323 terminal. Audio is the minimum service provided by the H.323 standard, all H.323 terminals must have at least one audio CODEC support. ITU-T G.711 (audio coding at 64 kbps), G.722 (64, 56, and 48 kbps), G.723.1 (5.3 and 6.3 kbps), G.728 (16 kbps), and G.729 (8 kbps) recommendation are the audio CODEC.

7.2 Video CODEC

A video CODEC encodes video from the camera for transmission on the transmitting H.323 terminal and decodes the received video code that is sent to the video display on the receiving H.323 terminal. The support of video CODECs is optional. ITU-T H.261 is the video CODEC recommendation.

7.3 H.225 Registrations, Admission, and Status (RAS)

RAS is the protocol between endpoints (terminals and gateways) and gatekeepers. RAS is used to perform these tasks

• Gatekeeper discovery (GRQ):
• Endpoint registration
• Endpoint location
• Admission control

Gatekeeper Discovery

The gatekeeper discovery process is used by the H.323 endpoints to determine the gatekeeper with which the endpoint must register.

Endpoint Registration

Registration is a process used by the endpoints to join a zone and inform the gatekeeper of the zone's transport and alias addresses.

Endpoint Location

Endpoint location is a process by which the transport address of an endpoint is determined and given its alias name or E.164 address.

Admission Control

The gatekeeper can control the admission of the endpoints into the H.323 network. It uses RAS messages, admission request (ARQ), confirm (ACF), and reject (ARJ)

7.4 H.225 Call Signaling:

The H.225 call signaling is used to establish a connection between two H.323 endpoints over which the real-time data can be transported. There are the two type of Call Signaling.

 7.4.1 Gatekeeper-Routed Call Signaling

The gatekeeper receives the call-signaling messages on the call signaling channel from one endpoint and routes them to the other endpoint on the call-signaling channel of the other endpoint.

7.4.2 Direct Call Signaling

During the admission confirmation, the gatekeeper indicates that the endpoints

can exchange call-signaling messages directly.

7.5 H.245 Control Signaling

H.245 control signaling consists of the exchange of end-to-end H.245 messages between communicating H.323 endpoints. The H.245 control channel is the logical channel 0 and is permanently open.

7.5.1 Capabilities Exchange

Capabilities exchange is a process using the communicating terminals' exchange messages to provide their transmit and receive capabilities to the peer endpoint.

7.5.2 Logical Channel Signaling

A logical channel carries information from one endpoint to another endpoint (in the case of a point-to-point conference) or multiple endpoints.

7.6 Real-Time Transport Protocol

Real-time transport protocol (RTP) provides end-to-end delivery services of real time audio and video. RTP, together with UDP, provides transport-protocol functionality.H.323 is used to transport data over IP-based networks; RTP is typically used to transport data via the user datagram protocol

7.7Real-Time Transport Control Protocol

Real-time transport control protocol (RTCP) is the counterpart of RTP that provides control services. The primary function of RTCP is to provide feedback on the quality of the data distribution.