Transcript H.323
© Copyright Ezenia Inc, 2000 Multimedia conferencing standards There are two standards associated with Multimedia Conferencing. H.320 applies to connections across Wide Area Networks. H.323 applies to connections across Local Area Networks. Review Questions H.323 Standards H.320 Beginning Help 1 © Copyright Ezenia Inc, 2000 H.320 conferences H.320 is an umbrella standard linking into other standards where necessary. Many standards exist that are relevant to a multimedia conference. The H.320 standard defines how a multimedia conference running over Wide Area (specifically ISDN) should operate. Many of the individual standards are common to both the WAN and LAN environments. The major difference is in the area of signaling and control. WAN environments are connection based; those in the LAN are connectionless. Previous • What other standards are under the H.320 Umbrella? Beginning Help 2 © Copyright Ezenia Inc, 2000 H.320 conferences H.320 Video H.261 H.263 Data T.120 Audio G.711 G.722 G.728 Multiplexing H.221 Control signaling H.242 H.243 Network Interfaces V.xx X.xx I.xx Line Protocols I.361 I.363 I.400 Previous Beginning Click on the box to find out more about these standards Help 3 © Copyright Ezenia Inc, 2000 H.323 standards H.323 acts as the umbrella standard linking into other standards where necessary. Release 1 - 1996; Release 2 – 1998 ; Release 3 - 1999 Multimedia conferencing over IP LANs uses standards from many organisations, some within ISO and some not, the specific standard H.323 is predominantly used to identify those standards that are relevant. Those listed on the next page are not a complete set, but the ones most likely to be of immediate relevance in configuring and using the Encounter products. • Previous What other standards are under the H.323 Umbrella? Beginning Help 4 © Copyright Ezenia Inc, 2000 H.323 standards H.323 Video Data Audio H.261 T.120 G.711 H.263 G.722 G.723 G.728 Control signaling H.225 H.244 H.450.x Security H.235 Network Network Interfaces Protocols 8802 TCP V.xx UDP X.xx IP I.xx Previous Beginning Click on the box to find out more about these standards Help 5 © Copyright Ezenia Inc, 2000 Video Standards There are 2 standards for video encoding used for Multimedia Conferencing. The standards control such factors as how the signal is compressed and digitised for transmission, the quality of the picture and how frequently the screen will be refreshed. But remember, the higher the picture quality, and the more frequent the refresh rate, the higher the bandwidth requirement. H.261 H.263 Multimedia Standards Beginning Help 6 © Copyright Ezenia Inc, 2000 H.261 This is the older video encoding standard, but the most widely supported. The choice of refresh rates and image format allows choices to be made balancing bandwidth and picture quality. There are two defined image formats: Common Intermediate Format (CIF), which is 352 pixels by 288 lines Quarter CIF (QCIF), which is 176 pixels by144 lines H.261 supports the following refresh rates: Previous 30, 15, 10 and 7.5 times per second This standard is the default for all H.323 traffic and all endpoints must be able to support at least this video mode Beginning Help 7 © Copyright Ezenia Inc, 2000 H.263 This is the newer video standard. It offers improved video coding and decoding, with higher quality options (4CIF has 4 times the picture element count of CIF), and greater refresh options. There are five defined image formats: CIF and QCIF (as for H.261) 16CIF - 1408 pixels by 1152 lines 4CIF - 702 pixels by 576 lines SQCIF - 128 pixels by 96 lines H.263 supports the following refresh rates: Previous 30, 15, 10, 7.5, 6, 5, 4, 3, 2, 1 times per second For some applications a high quality image with very slow refresh will be desirable, while others would prefer rapid refresh at the expense of quality. H.263 is not directly compatible with H.261. Beginning Help 8 © Copyright Ezenia Inc, 2000 Audio standards G.711 G.722 G.723 G.728 There are more variations of audio standards than there are of video, but there is only limited flexibility within each standard. It is possible to inter-work these standards providing a device on the network translates the codes. Each encoding standard relies on an analogue to digital technique called Pulse Coded Modulation (PCM), of which there are two standard methods of operating - A-law is used mainly in North America, and m-law is used mainly in Europe. Some encoding standards support both techniques, some only one. Where both are supported within the standard, the endpoints must be compatible with the chosen technique. Multimedia Standards Beginning Help 9 © Copyright Ezenia Inc, 2000 G.711 This is the most common audio standard used within both H.320 and H.323. G.711 encodes 3.1 KHz audio range using pulse code modulation. G.711 audio is transmitted at 48kbps or 56kbps in H.320, and 64 kbps in H.323. This is the default standard applied to H.323 endpoints, regardless of what other standards they can support, they must support G.711. Previous Beginning Help 10 © Copyright Ezenia Inc, 2000 G.722 G.722 encodes 7.0 KHz audio range based on sub-bands (it divides the total frequency band into higher and lower bands called sub-bands). It only transmits the change in an input signal, instead of the whole signal. G.722 audio is transmitted at 48kbps or 56kbps in H.320, and 64 kbps in H.323. Previous Beginning Help 11 © Copyright Ezenia Inc, 2000 G.723 G723 is also known as IP Audio and is often used in H.323 networks. It provides audio quality like the Mobile Phone standard, and not normal telephone standard sound quality. G.723 encodes 3.0 KHz audio range and is transmitted at 5.3kbps or 6.3kbps. Previous Beginning Help 12 © Copyright Ezenia Inc, 2000 G.728 G.728 is an audio coding algorithm that takes 128K pulse code modulated data and transmits it at 16kbps. It is frequently used in low-speed conferences since it makes more of the transfer rate bandwidth available for video. It is used widely within H.320 networks for this reason. Previous Beginning Help 13 © Copyright Ezenia Inc, 2000 Control standards There are two significant control protocols used within H.323, H225 and H.245. H.225 is used for control signalling during the initial call set up between Gatekeeper and endpoint. H.245 is then used for control signalling during the conference itself. Another set of standards were introduced with H.323 Release 2. These are the H.450 family of protocols which add a range of additional services to H.323. Previous H.450.x H.225 H.245 Beginning Help 14 © Copyright Ezenia Inc, 2000 H.225 H.225 is the principle “language”of the Gatekeeper. A Gatekeeper has a range of special functions to fulfill, and so requires a special language of it’s own. H.225 also uses another standard protocol, Q.931. Previous H.225 RAS / Q.931 Click here to find out more about these standards Beginning Help 15 © Copyright Ezenia Inc, 2000 H.225 RAS The three prime functions of H.225 are those of endpoint Registration, Admission and Status. Each of these functions is performed as a separate step within H.225. The Gatekeeper sends “keep alive” messages to endpoints while it is processing RAS requests. Registration Admission Status Previous Beginning Help 16 © Copyright Ezenia Inc, 2000 Q.931 Q.931 is one of the common call signaling protocols used in Wide Area Networks – it is used extensively in ISDN. In H.323, Q.931 is used to establish a connection between an endpoint and the Gatekeeper, and between one endpoint and another. Previous Beginning Help 17 © Copyright Ezenia Inc, 2000 H.225 Registration Any endpoint that wishes to take part in a conference must Register with a Gatekeeper. When an endpoint attached to a LAN is started it will automatically send a message looking for a Gatekeeper to register with. There can only be one Gatekeeper that is “allowed” to accept that registration. Once an endpoint is registered it will periodically send an update message to the Gatekeeper to maintain it’s registration. Previous Beginning • What does the Gatekeeper do with the registration information? Help 18 © Copyright Ezenia Inc, 2000 H.225 Registration The Gatekeeper will use the information gained during registration to build a “translation” table. This will include learning the name allocated to each endpoint as well as it’s network (IP) address. A Gatekeeper can be set to accept any address, or set to only accept specific addresses. An endpoint could be set to register with any Gatekeeper, or a specific Gatekeeper. To build a zone (in a multi-gatekeeper system), requires that one or other device is correctly configured. In a large network it will be easiest to configure the Gatekeepers. Previous Beginning Help 19 © Copyright Ezenia Inc, 2000 H.225 Admission Before a conference can commence the Gatekeeper will have to give permission. The originating endpoint will request a connection by specifying with whom it wishes to communicate and the amount of bandwidth it requires. The Gatekeeper will permit the connection providing 1. Security conditions are satisfied (e.g. valid user, valid destination, etc.). 2. Sufficient bandwidth exists. If sufficient bandwidth does not exist, then the Gatekeeper can negotiate with the endpoint to attempt to agree a lower value providing the endpoint supports such an option. Previous Beginning • How does admission happen? Help 20 © Copyright Ezenia Inc, 2000 H.225 Admission Is he allowed to? Is there enough capacity? Can we agree on capacity? Previous Beginning Help 21 © Copyright Ezenia Inc, 2000 H.225 Status The Gatekeeper will monitor the status of all registered endpoints and connections, by sending and receiving “Keep Alive” messages. The prime purpose of this is to ensure that registered endpoints remain available. An endpoint should de-register when finished, but may not. To allow for this the Gatekeeper regularly contacts each endpoint to see that they are still operational. An endpoint that fails to respond is removed from the registered list. Similarly the endpoints are required to report periodically to the Gatekeeper for the duration of a call. If an endpoint fails to report for four consecutive times the call is assumed to have ended and the Gatekeeper will send Disconnect messages to both endpoints and release the network resources. How does this happen? Previous Beginning Help 22 © Copyright Ezenia Inc, 2000 H.225 Status No reply from Harry, so I’ll de-register him. Mary’s still active, so she can stay registered Previous Beginning Help 23 © Copyright Ezenia Inc, 2000 H.245 Connections need to be set-up for a specific conference, monitored to ensure they are functional, and then cleared at the end of the conference. This is the function of the H.245 standard. H.245 Control Previous Audio Beginning Video Help 24 © Copyright Ezenia Inc, 2000 Security standards H.235 is a security protocol which was introduced into H.323 at release 2. It provides the following facilities to ensure that conferences can be more tightly controlled. By authenticating users, it can control who can join the conference. H.235 can enforce endpoint integrity which forces endpoints to be associated with Participants. It can ensure data stream privacy by using a pseudo encryption technique. Using a technique, known as non-repudiation, which checks that the caller is who they say they are, it can Previous ensure that callers are billed correctly. Beginning Many multimedia endpoints do not currently support H.235. Help 25 © Copyright Ezenia Inc, 2000 H.450.x Introduced into H.323 at release 2, H450.x protocols facilitate the use of several supplementary services in the H.323 environment. H.450.1 is the signalling protocol which controls the operation of the other protocols. H.450.2 provides call transfer facilities, which allow callers to be answered by one endpoint and then transferred to another. Previous H.450.3 allows calls to be diverted to other endpoints for answering. H.450 is intended primarily for telephony applications (VoIP) and so not all multimedia endpoints support it. Beginning Help 26 © Copyright Ezenia Inc, 2000 Multimedia Conferencing Standards Review Question 1 The H.323 standard is used over Wide Area Networks only. True False Multimedia Standards Beginning Review that information again Move on to the next question Help 27 © Copyright Ezenia Inc, 2000 Wrong Answer H.320 is the Multimedia conferencing standard for WANs. H.323 is used over any network that uses IP as it’s transport protocol. This could be a LAN or a WAN network. Multimedia Standards Beginning Review that information again Move on to the next question Help 28 © Copyright Ezenia Inc, 2000 Correct Answer Well done H.323 is used over any network that uses IP as it’s transport protocol. This could be a LAN or a WAN network. Multimedia Standards Beginning Review that information again Move on to the next question Help 29 © Copyright Ezenia Inc, 2000 Multimedia Conferencing Standards Review Question 2 Which of the following standards are used for conference control, between endpoints,once they have registered with the Gatekeeper. H.225 H.245 Q.931 RAS Multimedia Standards Beginning Review that information again Move on to the next question Help 30 © Copyright Ezenia Inc, 2000 Wrong Answer H.225 is the protocol used by the Gatekeeper to communicate with endpoints. H.245 is used to control the conference traffic between endpoints. Multimedia Standards Beginning Review that information again Move on to the next question Help 31 © Copyright Ezenia Inc, 2000 Wrong Answer Q.931 is part of the H.225 protocol, used by the Gatekeeper to communicate with endpoints. H.245 is used to control the conference traffic between endpoints. Multimedia Standards Beginning Review that information again Move on to the next question Help 32 © Copyright Ezenia Inc, 2000 Wrong Answer RAS is part of the H.225 protocol, used by the Gatekeeper to communicate with endpoints. H.245 is used to control the conference traffic between endpoints. Multimedia Standards Beginning Review that information again Move on to the next question Help 33 © Copyright Ezenia Inc, 2000 Correct Answer Well done H.245 is used to control the conference traffic between endpoints. Multimedia Standards Beginning Review that information again Move on to the next question Help 34 © Copyright Ezenia Inc, 2000 Multimedia Conferencing Standards Review Question 3 As a minimum, an H.323 endpoint must support the H.263 video standard. True False Multimedia Standards Beginning Review that information again Move on to the next question Help 35 © Copyright Ezenia Inc, 2000 Wrong Answer H.263 is the newer video standard, offering more efficient compression, or higher image quality. An H.323 endpoint must support H.261, as a minimum. Multimedia Standards Beginning Review that information again Move on to the next question Help 36 © Copyright Ezenia Inc, 2000 Correct Answer Well done An H.323 endpoint must support H.261, as a minimum. Multimedia Standards Beginning Review that information again Move on to the next question Help 37 © Copyright Ezenia Inc, 2000 Multimedia Conferencing Standards Review Question 4 Which of the following audio standards are most widely used in H.323? G.711 and G.722 G.711 and G.723 G.711 and G.728 G.723 and G.728 Multimedia Standards Beginning Review that information again Move on to the next question Help 38 © Copyright Ezenia Inc, 2000 Wrong Answer G.711 is the most commonly used audio standard in both H.320 and H.323. G.722 is not widely used in H.323. G.711 and G.723 are the most commonly used audio standards in H.323. Multimedia Standards Beginning Review that information again Move on to the next question Help 39 © Copyright Ezenia Inc, 2000 Wrong Answer G.711 and G.728 are the most commonly used audio standards in both H.320. G.711 and G.723 are the most commonly used audio standards in H.323. Multimedia Standards Beginning Review that information again Move on to the next question Help 40 © Copyright Ezenia Inc, 2000 Wrong Answer G.723 is widely used in H.323. G.728 is widely used in H.320. G.711 and G.723 are the most commonly used audio standards in H.323. Multimedia Standards Beginning Review that information again Move on to the next question Help 41 © Copyright Ezenia Inc, 2000 Correct Answer Well done G.711 and G.723 are the most commonly used audio standards in H.323. Multimedia Standards Beginning Review that information again Move on to the next question Help 42 © Copyright Ezenia Inc, 2000 Multimedia Conferencing Standards Review Question 5 Which of the following standards was introduced in Release 2 of the H.323 Standard? H.225 H.235 H.245 Multimedia Standards Beginning Review that information again Help 43 © Copyright Ezenia Inc, 2000 Wrong Answer H.225 is the protocol used by the Gatekeeper, and has been part of H.323 since release 1 of the standard. H.235 was introduced to provide enhanced security in H.323, release 2. Multimedia Standards Beginning Review that information again Help 44 © Copyright Ezenia Inc, 2000 Wrong Answer H.245 is the protocol used by endpoints for conference control, once they have registered with the Gatekeeper and has been part of H.323 since release 1 of the standard. H.235 was introduced to provide enhanced security in H.323, release 2. Multimedia Standards Beginning Review that information again Help 45 © Copyright Ezenia Inc, 2000 Correct Answer Well done H.235 was introduced to provide enhanced security in H.323, release 2. Multimedia Standards Beginning Review that information again Help 46