How does h323 work

For example, the latest version of NetMeeting Version 3. An implementation note for compliant H. The poor interoperability of H. The International Multimedia Teleconferencing Consortium IMTC was set up with the primary goal of ensuring that vendors' products and services are interoperable. IMTC is a non-profit organization with over members that regularly conducts interoperability and compliance testing of products and services.

Profile as a set of implementation guideline for gateway-to-gateway and terminal-to-gateway interoperability. Recently, the iNOW! The iNOW! Profile has also been extended to include interoperability between gatekeepers and other endpoint.

Compliant products and services are certified by IMTC. Several software vendors have developed H. These software modules allow developers of H. Vendors that offer H. Many hardware and software companies have set up their own interoperability labs to test their and other vendors products and services. NetMeeting, a H. The vision of H.

These goals have not yet been achieved. From a business point of view a technology cannot succeed solely on the basis of lower operational costs. It must also provide additional value and performance in the form of ease of use and improved feature set for it to supplant a well-entrenched technology such as PSTN.

Several ITSPs exist today e. Global interoperability is still a problem. Furthermore, the features and quality of service being offered is often inferior to POTS. The first is the lack of interoperability of endpoints especially gateways from different vendors. And the second is the poor scalability of H. As such, it is well positioned to offer services to ITSPs, ISPs, and traditional telephone companies to route their multimedia traffic over its packet-based network. It had earlier signed similar service deals with Priceline.

The quality of video on public networks like the Internet is poor. For example, in IP networks H. Development of more efficient codecs will also play an important role in improving quality.

Enterprise IT managers are also reluctant to deploy H. Security of H. Concerns over privacy has prevented businesses from moving over to H. Part of the problem was resolved with H. However, many products have not implemented the security recommendation. In this section several key developments and trends that are shaping H.

This is the question IP telephony vendors are asking. Analysts often make an analogy between H. Although the share of SIP will increase H. Moreover, the investment in H. SIP and H. The greatest growth in H. Integration and development of new services is also an advantage. Furthermore, H. Small business and home users put more emphasis on quality, value, and features. They are less concerned with interoperability with legacy systems and security.

This is the market where H. Adoption will increase in the coming years as the price-performance ratio improves. This is also the market where SIP can make a significant impact. Version 2. The focus has shifted from LANs to larger networks such as the Internet and the challenges associated with it.

Work is also being done to add mobile communication capability to H. Another initiative is the preparation of an implementation guide for H. Interoperability issues and security are on-going initiatives. For documents on current developments in H.

An analysis of H. An extensive listing of vendors and their products is also maintained at IPTelephony. Multipoint control units MCU are needed when dozens of endpoints participate in a multimedia conference like in a virtual corporate meeting.

Gateways : Used to connect two distinct networks, the H. This distinct network connectivity is established by translating protocols intended for call setup and release, transforming media formats in between various networks and switching details between networks that are interconnected by the gateway.

Gateways are also used in order to enable videoconferencing devices based on H. Gatekeepers : Considered the most vital H. However, if they are available in the network, the endpoints must definitely use their services. MCU deliver support for conferencing three or more H. Gateways allow H. They provide protocol conversion between the devices that are running different types of protocols. For example, the figure below shows a gateway between an H.

They can be used to isolate sections of an H. Gatekeepers are optional nodes that manage endpoints in an H. The endpoints communicate with the gatekeeper using the RAS protocol. Endpoints attempt to register with a gatekeeper on startup. When they wish to communicate with another endpoint, they request admission to initiate a call using a symbolic alias for the endpoint, such as an E.

If the gatekeeper decides that the call can proceed, it returns a destination IP address to the originating endpoint. This IP address may not be the actual address of the destination endpoint, but it may be an intermediate address, such as the address of a proxy or a gatekeeper that routes call signaling.

The Cisco gatekeeper provides H. The Cisco H. An endpoint that detects the failure of its gatekeeper can safely recover from that failure by utilizing an alternate gatekeeper for future requests, including requests for existing calls.

A gateway can only be registered to a single GK at a time. Only one GK is allowed to manage a single zone. The cluster manages up to five similarly configured zones and shares resources between the alternate gatekeepers in the cluster for each zone.

You can define up to zones in a single GK. A calling endpoint can recover from a call setup failure by sending a setup message to one of the alternate endpoints so that it is possible for a call to finish even if a gateway goes down and the gatekeeper is not yet aware of the problem. Cisco supports a maximum of 20 alternates for each endpoint, and any alternates received through registration, admission, and status protocol RAS messages are merged with those entered manually in the gatekeeper command-line interface.

If more than 20 alternates are submitted, the total list of alternates reverts back to Other messages are extended to contain more parameters for added call control. Cost and priority fields are included with each remote zone definition, which ensures that the zones with lower cost are given an advantage over zones with higher cost. Load balancing allows the gatekeeper to move registered H. Border elements BE exchange addressing information and participate in call authorization between the administrative domains.

The BEs are often located with a gatekeeper. The BE can reduce the routing information passed though the network by aggregating address information. Each zone has one gatekeeper that manages all the endpoints in the zone.

Because a zone is, by definition, the area of control of a gatekeeper, the terms "zone name" and "gatekeeper name" are used synonymously in this chapter. Gateways and gatekeepers communicate using the Registration, Admission, and Status RAS protocol for discovery and registration.

When endpoints are brought online, they first attempt to discover their gatekeeper. They discover their gatekeeper either by sending multicast a discovery request or by being configured with the address and, optionally, with the name of the gatekeeper and by sending a unicast discovery request.

Following successful discovery, each endpoint registers with the gatekeeper. The gatekeeper keeps track of which endpoints are online and available to receive calls. In a typical H. For example, in the figure below, both gateways are registered to the same gatekeeper, and the gatekeeper has chosen direct call signaling.

Fast connect allows endpoints to establish media channels without waiting for a separate H. This streamlines the number of messages that are exchanged and the amount of processing that must be done before endpoint connections can be established. A high-level view of the fast-connect procedures within the H. Fast connect is not explicitly configurable. All H. It is assumed that the gateway is capable of sending and receiving fast-connect procedures unless its corresponding dial peer has been configured for the Resource Reservation Protocol RSVP.

RSVP means the quality of service is set by the req-qos command to a value other than the default of best-effort. If the dial peer has been configured for RSVP, traditional "slow" connect procedures are followed, and the endpoint neither attempts to initiate fast connect nor responds to a fast-connect request from its peer.

MCU performs video streams transcoding in order to mix and downscale other participants video in a unique layout for every participants.

This process require a lot of computational elements and resources which makes MCU a very expensive device. Each endpoint or device supporting H. This internet protocol packets routing within networks is established via H. UDP protocols are used to connect endpoints to gateways and gatekeeper and transmit media traffic. TCP transport protocols are only used to establish a call between endpoints and exchange additional features, so called signalling.

Detection process is required for endpoints to find a gatekeeper by its network address and to register on it.

This procedure can be performed automatically if there are several gatekeepers, the endpoint selects gatekeeper to register on by means of multicasting messaging over the networks or manually the gatekeeper's network address is known in advance and set during device configuration. The first variant of gatekeeper detection is more preferable, as the endpoint will be able to switch to another gatekeeper automatically in case of gatekeeper breakdown.

The registration procedure is required to allow endpoints send their addresses to gatekeeper and join its control zone. To establish connection between the endpoints and to exchange media traffic in networks, the following protocols are used:. To terminate connection, the endpoints send a message to the gatekeeper. After that, the channel closes and the connection is terminated.

Audio exchange function is considered the main function of H. Thus, each endpoint should support at least one codec from the G.

Video communications were positioned as secondary in respect to this standard.