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H.323 and Associated Protocols
H.323 Protocol Explained
H.323 is a set of standards for real-time communication over IP networks, such as the internet. It was developed by the International Telecommunication Union (ITU) in the late 1990s as a way to enable voice, video, and data communication over IP networks.
H.323 is a suite of protocols that includes a number of different components, including −
H.225 − This protocol is used for signaling, which is the process of establishing and maintaining communication sessions. H.225 uses the Remote Procedure Call (RPC) model to send and receive messages between devices.
H.245 − This protocol is used for control, which is the process of managing the communication session. H.245 allows devices to exchange information about capabilities and to negotiate the parameters of the session.
RAS − The Registration, Admission, and Status (RAS) protocol is used to establish and maintain connections between devices. It allows devices to register with a gatekeeper, which is a central server that manages the communication sessions.
RTP − Real-time Transport Protocol (RTP) is used to transmit the actual media data, such as audio and video, between devices. RTP is a packet-based protocol that breaks the media stream into packets for transmission over the network.
H.323 is widely used in a variety of applications, including voice over IP (VoIP), video conferencing, and streaming media. It is supported by many media players and servers, and it is often used in conjunction with other protocols, such as Session Initiation Protocol (SIP), to deliver audio and video content over the internet.
Elements of H.323
H.323 is a set of standards for real-time communication over IP networks, and it includes a number of different elements, including −
Terminals − H.323 terminals are devices that are capable of participating in H.323 communication sessions. Examples of H.323 terminals include telephones, video conferencing systems, and media players.
Gateways − H.323 gateways are devices that enable communication between H.323 systems and other types of communication systems, such as the public switched telephone network (PSTN) or ISDN (Integrated Services Digital Network).
Gatekeepers − H.323 gatekeepers are servers that manage the communication sessions between H.323 devices. They are responsible for routing calls, controlling access to the network, and providing other services.
Multipoint − Control units (MCUs) − H.323 MCUs are devices that enable communication between multiple H.323 devices in a conference. They are responsible for managing the communication session and for controlling the distribution of media data between the devices.
Protocols − H.323 includes a number of different protocols that are used to establish and maintain communication sessions. These include H.225, H.245, and RAS for signaling and control, and RTP for the transmission of media data.
Overall, H.323 is a complex system that includes a variety of different elements and protocols that work together to enable real-time communication over IP networks.
A Call with the Help of H.323 Protocol
Here is an example of how a call might be established using the H.323 protocol −
The calling device sends an H.225 setup message to the called device. This message includes the destination address of the called device and any other necessary information, such as the caller's identity and the desired media capabilities.
The called device responds with an H.225 alerting message, which indicates that the call has been received and is being processed.
The calling device and called device exchange H.245 messages to negotiate the parameters of the call, such as the codecs to be used and the bandwidth requirements.
If a gatekeeper is involved in the call, the calling and called devices send RAS messages to the gatekeeper to register and request admission to the network.
Once the call has been established, the devices exchange RTP packets to transmit the actual media data, such as audio and video.
When the call is finished, the devices send H.225 messages to tear down the call and release the resources.
Overall, the H.323 protocol is used to establish and maintain communication sessions between devices, and it includes a number of different protocols and message types that are used to negotiate the parameters of the call and to transmit the media data.
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