H.323 Liane Tarouco Leandro Bertholdo
Standard entities • Telecommunications standards are set by the United Nations agency, International Telecommunications Union (ITU) • The ITU has developed the H, G and T Series of standards • Internet Engineering Task Force (IETF) defines stadards for the Internet • IETF has developed Real-Time Protocol (RTP), Real-Time Control Protocol (RTCP) & Resource Reservation Protocol (RSVP). • Products that adhere to these standards allow users to participate in a conference, regardless of their platform.
Available Transport Media. • ISDN, LAN, WAN, Internet, ADSL (Asynchronous Digital Subscriber Lines) and VPN, (Virtual Private Networks) are the popular transport media used in desktop video conferencing. • The worldwide availability of the Internet has virtually stopped the use of POTS (Plain Old Telephone Service) as a direct means of connecting video conferencing systems. • However, the forthcoming media-enabled 3G mobile phone has caused the creation of a derivative of the H.324 POTS standard in the form of 3G-324M as well as next generation Gateways to transcode the new protocols.
ISDN • There are two available ISDN connections • Basic Rate Interface (BRI) • Primary Rate Interface (PRI). • Essentially, a BRI provides two 64kbps B-channels and one 16kbps D-channel whilst a PRI in Europe provides 30 x 64kbps B-channels and one 64kbps D-channel.
ISDN • ISDN connections usually aggregate the BRI and share the same number for both B channels. Known as ISDN-2, this provides a line speed of 128kbps is typically used in a desktop conference over ISDN. • For increased bandwidth, ISDN-6 provides a line speed of 384kbps and is typically used in room-based conferences over ISDN. • With ISDN-6, the sequence in which the lines are aggregated must be known and adhered too! Furthermore, if the connection is going to use some form of 'switch', this must be configured to pass both voice and data!
ISDN for multipoint conference • To hold a multipoint conference over ISDN, participants use a Multipoint Control Unit (MCU), that connects and manages all the ISDN lines. • This can be either a separate MCU or an endpoint with an embedded H.320 multipoint capability
H.320 • H.320 is the ITU standard for ISDN conferencing and includes: • Audio: G.711, G.722, G.722.1, G.728 • Video: H.264, H.263, H.261 • Data: H.239, T.120 • Control: H.221, H.231, H.242, H.243
Local Area Network (LAN) or Intranet and Wide Area Network (WAN). • LANs and WANs use TCP/IP protocol and the H.323 standard defines how to assemble the audio, video, data and control (AVDC) information into an IP packet.
DHCP • Most companies use DHCP and allocate dynamic IP addresses to PC's. • Therefore, in order to correctly identify a user, the H.323 endpoints are usually registered with a Gatekeeper and 'called' into a conference by their H.323 alias. • The Gatekeeper translates the alias into the corresponding IP address. • Another method of identifying H.323 users is for them to register their presence using Light Directory Access Protocol (LDAP) with a Directory Service such as Microsoft's Site Server ILS or Windows 2003 Active Directory.
Multipoint conference • To hold a multipoint conference over IP, H.323 systems require some form of Multipoint Conference Server (MCS). • This is also referred to as an H.323 Multipoint Control Unit (H.323 MCU), which is not the same as an H.320 MCU;
Lan & WAN • H.323 is the ITU standard for LAN conferencing and includes: • Audio: G.711, G.722, G.722.1, G.723.1, G.728, G.729 • Video: H.264, H.263, H.261 • Data: H.239, T.120 • Control: H.225, H.245
Cellular Networks. • The cellular phone network is a readily available form of wireless multimedia delivery and with the forthcoming media-enabled 3G mobile phone or Personal Digital Assistants, PDAs, that support the CDMA2000 or WCDMA Air Interface, there is sufficient bandwidth to enable IP-based multipoint audio and video conferencing to existing desktop video conferencing systems when used in-conjunction with next generation Gateways and MCU's that also support these new protocols.
Cellular networks • 3G-324M is an extension by the 3rd Generation Partner Project (3GPP) and 3rd Generation Partner Project2 (3GPP2) to the ITU H.324M standard for 3G mobile phone conferencing and includes: • Audio: G.722.2 (AMR-WB), G.723.1 • Video: MPEG-4, but not H.264 • Control: H.223 A/B, H.245
Internet, VPN & ADSL. • Like LANs, the Internet, VPNs and ADSL are other forms of TCP/IP networks and hence can be used as a transport media in desktop conferencing systems. • What the users must do is to get their Internet Service Provider (ISP) to provide them with a fixed IP address
Directory services • Alternatively, users can register their presence using LDAP with a Directory Service such as Microsoft's Site Server ILS or Windows 2003 Active Directory. This is how you determine the address of the machine that you want to conference with. Obviously, speed is limited to that of the slowest link, but most ISPs now support ISDN Dial-up at 128kbps or V.92 modems at 56kbps
Internet • H.323 is the ITU standard used for Internet conferencing and includes: • Audio: G.723.1, G.722.1, G.728 • Video: H.264, H.263, H.261 • Data: H.239, T.120 • Control: H.225, H.245
Video standards • H.261 - video codec for audiovisual services at p x 64Kbps. • H.263 - video codec for narrow telecommunications channels at < 64 Kbps. • H.264/AVC - a new video codec standard offering major improvements image quality.
Image size • QCIF is Quarter Common Intermediate Format and represents a 176x144 pixel image. • This is the minimum size that must be supported to be H.320 compliant. • CIF is the optional full- screen H.320 video image of 352x288 pixels and requires considerably more computing capability. • Note: whilst this is termed full-screen, it is nowhere near the size of a typical PC screen (1024x768) pixels or that of a UNIX workstation (1280x1024) pixels.
Video and PC Window Sizes • NTSC - National Television Standards Committee, used in USA, Canada & Japan. 640 x 480 pixels. • PAL - Phase Alternation by Line, used in Europe (except France), Africa & Middle East. 768 x 576 pixels.
Video and PC Window Sizes • CIF - Common Intermediate Format; optional for both H.261 & H.263, 352 x 288 pixels. • QCIF - Quarter Common Intermediate Format; required by both H.261 & H.263, 176 x 144 pixels. • SQCIF - Sub Quarter Common Intermediate Format; used by 3G mobiles MPEG4 video and H.263, 88 x 72 pixels.
Video and PC Window Sizes • SXGA - 1280 x 1024 pixels - used by high end graphics workstations. • XGA - 1024 x 768 pixels - typical PC or laptop resolution. • SVGA - 800 x 600 pixels. • VGA - 640 x 480 pixels.
H.264 • Ratified in late 2003, this new codec standard was a development between the ITU and ISO/IEC Joint Video Team, (JVT) and is known as H.264 (ITU name) or ISO/IEC 14496-10/MPEG-4 AVC (ISO/IEC name). • This new standard surpasses H.261 and H.263 in terms of video quality, effective compression and resilience to transmission losses, giving it the potential to halve the required bandwidth for digital video services over the Internet or 3G Wireless networks. H.264 is likely to be used in applications such as Video Conferencing, Video Streaming, Mobile devices, Tele-Medicine etc. Current 3G mobiles use a derivate of MPEG-4, but not H.264.
Audio standards • G.711 - Pulse Code Modulation of voice frequencies (PCM), were 3.1 kHz analogue audio is encoded into a 48, 56 or 64 kbps stream. Used when no other standard is equally supported. • G.722 - 7 kHz audio encoded into a 48, 56 or 64 kbps stream. Provides high quality, but takes bandwidth. • G.722.1 - 7 kHz audio encoded at 24 and 32 kbps for hands-free operation in systems with low frame loss. • G.722.2 - Coding of speech at around 16 kbps using Adaptive Multi-Rate Wideband, AMR-WB. Five mandatory modes, 6.60, 8.85, 12.65, 15.85 and 23.85 kbps. • G.723.1 - 3.4 kHz dual rate speech codec for telecommunications at 5.3 kbps & 6.4 kbps.
Audio standards • G.728 - 3.4 kHz Low Delay Code Excited Linear Prediction (LD-CELP) were 3.4 kHz analogue audio is encoded into a 16 kbps stream. This standard provides good quality results at low bitrates. • G.729 A/B - 3.4 kHz speech codec that provides near toll quality audio encoded into an 8 kbps stream using the AS-CELP method. Annex A is a reduced complexity codec and Annex B supports silence suppression and comfort-noise generation.
Data standards • T.120 - defines protocols and services for multimedia conferencing. • T.121 - Generic Application Template (GAT). Defines a template as a guide for developers in managing T.120 resources. • T.122 - defines Multipoint Communication Services (MCS) available to developers. • T.123 - defines Network Specific Data protocol for multimedia conferencing. • T.124 - defines Generic Conference Control (GCC), mandatory for 'group' conferences. • T.125 - defines MCS data transmission protocol.
Data standards • T.126 - Multipoint Still Image and Annotation protocol. Defines the protocol used to provide interoperability with graphics data in applications such as whiteboarding, annotated image exchange, screen sharing and remote apps control. • T.127 - Multipoint Binary File Transfer protocol. Defines the protocol used to support binary file transfer within a conference. • T.128 - defines Multipoint Application Sharing protocol (also known as T.SHARE) • T.134 - defines Multimedia Application Text Conversation protocol (also known as T.CHAT).
Data standards • T.135 - User-to-reservation system transactions within T.120 conferencing. • T.136 - Remote device control application protocol. • T.137 - Virtual meeting room management - services & protocol. • T.140 - Protocol for multimedia application text conversation.
Control standards • H.221 - defines the transmission frame structure for audovisual teleservices in channels of 64 to 1920 Kbps; used in H.320 • H.223 - specifies a packet-orientated multiplexing protocol for low bit rate multimedia communications; Annex A & B handles light and medium error prone channels of the mobile extension as used in 3G-324M. • H.224 - defines real-time control protocol for simplex applications using the H.221 LSD, HSD and HLP channels. • H.225 - defines the multiplexing transmission formats for media stream packetisation & synchronisation on a non-guaranteed QoS LAN.
Control standards • H.231 - specifies multipoint control units used to bridge three or more H.320 systems together in a conference. • H.233 - Confidentiality systems for audiovisual services, used by H.320 devices. • H.234 - Encryption key management and authentication system for audiovisual services, used by H.320 devices. • H.235 - Security and encryption for H.323 and other H.245 based multimedia terminals.
Control standards • H.239 - defines role management and additional media channels for H.300-Series multimedia terminals. How data and web-enabled collaboration work in parallel with video in a conference, allowing endpoints that support H.239 to receive and transit multiple, separate media streams - typically voice, video and data collaboration. • H.241 - defines extended video procedures and control signals for H.300-Series multimedia terminal. • H.242 - defines the control procedures and protocol for establishing communications between audiovisual terminals on digital channels up to 2 Mbps; used by H.320.
Control standards • H.243 - defines the control procedures and protocol for establishing communications between three or more audiovisual terminals - H.320 multipoint conferences. • H.245 - defines the control procedures and protocol for H.323 & H.324 multimedia communications. • H.246 - Interworking of H-Series multimedia terminal. • H.248 - Gateway Control Protocol. • H.281 - defines the procedures and protocol for far end camera control (FECC) in H.320 calls.
Control standards • H.282 - Remote device control protocol for multimedia applications. • H.283 - Remote device control logical channel transport. • H.350 - Storing and retrieving video and voice over IP information from enterprise directories.
Numbers & names • E.164 Number - (User Number). A numeric string given to an H.323 endpoint. If this endpoint registers with a Gatekeeper, then the Gatekeeper can translate the E.164 Number into the endpoints IP address. • H.323 Alias - A logical name given to an H.323 endpoint. If this endpoint registers with a Gatekeeper, then the Gatekeeper can translate the H.323 Alias into the endpoints IP address.
Q.931 • Q.931 - Signalling protocol for establishing and terminating calls.
Evolution • H.323 was first approved in February 1996, the same month that the first SIP draft was published • •Designed to operate over IP networks • •Today, H.323 is the most widely deployed standards-based voice and videoconferencing standard for packet-switched networks, with literally billions of minutes of billable traffic every month • •ITU-T now considering work on H.323v6
What is H.323 • H.323* is a multimedia conferencing protocol, which includes voice, video, and data conferencing, for use over packet-switched networks * H.323 is “ITU-T Recommendation H.323: Packet-based multimedia communications systems”
Elements of an H.323 System • •Terminals • •Multipoint Control Units (MCUs) • •Gateways • •Gatekeeper • •Border Elements Endpoints
Terminals • Video phones • IVR devices • Voicemail Systems • “Soft phones” (e.g., NetMeeting®)
Terminals • H.323 Terminals are the endpoints on the LAN that provide real-time two way communications. • The H.323 standard states that all H.323 Terminals must support voice, with video and data being optional. • Hence the basic form of an H.323 Terminal is the IP Phone; however most H.323 Terminals are Video Conferencing Systems.
Terminals • The H.323 standard specifies what modes must be supported so that all these endpoints can work together. • H.323 Terminals must support • H.245 protocol to control channel usage and capabilities; • Q.931 protocol for call setup and signalling; • RAS (Registration/Admission/Status) protocol to communicate with the Gatekeeper and • RTP/RTCP protocol to sequence audio and video packets.
Terminal identification • When initiating an H.323 Video Conference, we need some means of identifying the User or H.323 Endpoint that we wish to conference with. • The thought of having to remember IP addresses is daunting enough; but the use of DHCP to dynamically allocate the IP address of an endpoint means that this method is impractical. • Hence the concept of a Dial Plan and the use of an H.323 User Number registered to a Gatekeeper. • A Dial Plan is simply a method of allocating a unique number to an H.323 Endpoint.
H.323 User Number • This number is referred to as the H.323 User Number and when registered with a Gatekeeper, we have a means of translating this User Number into an IP address. • The H.323 User Number is often loosely referred to as the E.164 Number.
MCUs • Responsible for managing multipoint conferences (two or more endpoints engaged in a conference) • The MCU contains a Multipoint Controller (MC) that manages the call signaling and may optionally have Multipoint Processors (MPs) to handle media mixing, switching, or other media processing
Multipoint Control Units (MCUs): • To allow three or more participants into a conference, most H.323 systems usually require a Multipoint Conference Server (MCS). • This is also referred to as an H.323 Multipoint Control Unit (H.323 MCU). • This is not the same as an H.320 MCU; hence it is important to be clear about what you mean when using the term MCU
MCU • The H.323 MCU's basic function is to maintain all the audio, video, data and control streams between all the participants in the conference. • Whilst most H.323 MCU's, such as the mcu-15v or mcu-xx cards with the viaIP are hardware based, VCON have introduced the VCON Conference Bridge™, VCB that provides a basic software MCU capable of allowing Ad-Hoc Conferencing in both Continuous Presence or Voice-Activated Switching modes.
MCU • The main components of an H.323 MCU are • MC - multipoint controller • MP - multipoint processor (optional) • The MC is the conference controller and handles H.245 negotiations between all terminals to determine common capabilities for audio and video processing.
MCU: MC & MP • The MC also controls conference resources such as multicasting. • Most H.323 systems support IP multicast and use this to send just one audio and one video stream to the other participants. • The MC does not actually deal directly with any of the audio, video and data streams. • This is left to the MP, which does all the audio mixing, data distribution and video switching/mixing of the bits. It also provides the conversion between different codecs and bit rates.
MCU: MC & MP • Both the MC and MP functions can exist in one unit or as part of other H.323 components. • Most H.323 MCU's work in conjunction with, or include a Gatekeeper functionality.
MCU - H.320 • H.320 conferences are essentially a point-to-point connection and need to use an H.320 MCU to link and manage all the ISDN lines in order to hold a conference with three or more participants.
Endpoint with Embedded MCU • An alternative to using a dedicated MCU for small conferences involving 3 or 4 participants is to equip one of the endpoints with an embedded multipoint capability. • The Polycom VSX 7000s has an embedded multipoint options that supports itself and up to 3 other sites in a Voice-Activated or Continuous Presence session. • Furthermore, the VSX 7000s has both BRI or PRI ISDN options that when used in conjunction with the multipoint capability, allows mixed-mode operation between both ISDN and IP networks. In a simplistic manner, it also acts like a Gateway, bridging between the other 2 or 3 ISDN and IP endpoints.