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Glossar Application-Sharing (T120) Application Sharing (T120) enables conference participants simultaneous access and editing of the same document (e.g. a Word or Excel file). However application sharing is generally understood as the possibility of showing an electronic document / presentation (PDF, PPS) at a remote end. H.239 as part of the H.323 protocol is used for this purpose. If the remote end is not equipped with an H.239compatible codec, the possibility of content streaming exists. The remote viewer can then watch presentation streaming on an Internet connected computer. Another variant of application sharing is to use VCindependent software, such as VNC or Netmeeting, which is installed on the presentation computer and allows remote participants to view or edit a document via a browser or client.
ARP The ARP (address resolution protocol) is part of the TCP / IP protocol suite used to convert an IP address into a physical address such as an Ethernet address.
ID Multimedia Services
Class of Service (CoS) With the help of «Class of Service» technology network traffic can controlled. To this end, groups containing similar data streams are formed. A service priority is assigned to each group. Unlike QoS, CoS does not guarantee service quality, it only provides «best-effort». However CoS is easier to adapt to network change.
CODECs CODECs, short for compressor/decompressor can be implemented in software, hardware, or a combination of both. Many desktop videoconferencing systems use hardware codecs designed as a separate chip in the corresponding plug-in card. This requires at least one plug-in card (ISA or PCI) to which the video camera, audio unit and ISDN S0 cable are attached. The card assumes the tasks of coding and decoding. For desktop video conferencing systems which are connected to a PC via USB, encoding takes place on the device itself, while decoding takes place on the PC processor. This technique, due to minimal hardware requirements, unlike software CODECs, where all audio and video compression (up to a factor 1:1000) as well as signal coding according to corresponding standard (H.320/H.323) is done by the computer processor, does not reduce computer performance. In most case the computer can be used without any additional installations. During a video conference hardware CODECs assures system performance for both you and your conference partner.
Desktop conference system Workstation with fully integrated video conference system. With a software installation (eg. SCOPIA Desktop) you are able to connect to other H323 capable software clients and H323 capable room systems.
DHCP DHCP (dynamic host configuration protocol) belongs to the TCP/IP protocol family and is used for assigning dynamic IP addresses to network devices. With dynamic addressing, a device can have a different IP address every time it connects to the network.
DNS DNS is short for Domain Name System (or Service or Server), an Internet service that translates domain names into IP addresses or vice versa. Because domain names are alphabetic, they›re easier to remember. Internet however is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.
Duplex Full-duplex refers to the transmission of network or voice data, in two directions simultaneously. For example, a telephone is a full-duplex device because both parties can talk at once. In contrast, a walkie-talkie is a half-duplex device because only one party can transmit at a time. E.164 E.164 is the international public telecommunication numbering plan. An E.164 number uniquely identifies a public network termination point and typically consists of three fields, CC (country code), NDC (national destination code), and SN (subscriber number), up to 15 digits in total.
Gatekeeper A gatekeeper serves the purpose of Call Admission Control, security and translation services from E.164 IDs (commonly a phone number) to IP addresses in an H.323 telephony network. A gatekeeper can also deny access or limit the number of simultaneous connections to prevent
network congestion. In addition, the gatekeeper records fees due and allocates them to network and service partners and also provides bandwidth management within the Quality of Service (QoS) framework.
Gateway A gateway is a node on a network that serves as an entrance to another network by protocol conversion. In enterprises, the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. In homes, the gateway is the ISP that connects the user to the internet. A gateway can also be used to connect LAN and WAN. It fully «understands» both protocols and is an addressable network node in both environments. Complete conversion involves translation of addresses and formats, code conversion, the buffering of data packets, packet acknowledgment and flow control as well as speed adjustment. Due to the complete processing of all communication layers, the gateway often effects higher functionality than shareable standard protocols in regard to terminal emulation, graphics capability, program-toprogram communication, file transfer, and number of simultaneous sessions possible. The disadvantage is the limitation to two different protocols, requiring n x (n-1)/2 gateways when using n protocols (quadratic increase!) which makes the logical network structure considerably more costly and confusing.
H.239 H.239 is part of the H.323 protocol family. Practical importance of this recommendation is its setting forth a way to have multiple video channels (e.g. one for conferencing, another for presentation) within a single session (call).
H.264 / MPEG-4 AVC H.264/MPEG-4 AVC is a standard for highly effective video compression. The intent of the H.264/AVC project was to create a standard capable of providing good video quality for mobile as well as TV and HD application at substantially lower bit rates than previous standards (e.g. half or less the bit rate of MPEG-2, H.263, or MPEG4 Part 2). H.264 is the ITU term for this standard while ISO/ IEC MPEG termed it MPEG-4 /AVC (Advanced Video Coding), part 10 of the MPEG-4-standards (MPEG-4/Part 10, ISO/ IEC 14496-10).
The fourCCs used for the standard are «AVC1», «DAVC», «H264», «X264» and «VSSH». The Matroska Codec ID is «V_MPEG4/ISO/AVC». The standardized file / container format is MP4. Text from Wikipedia →
H.320 H.320 is an umbrella recommendation by the ITU-T for running Multimedia (Audio/Video/Data) over ISDN based networks. The main protocols in this suite are H.221, H.230, H.242 (end to end signalization), audio codecs such as G.711, and video codecs such as H.261 and H.263. H320 is the standard for narrow-band visual telephone systems and terminal equipment (ISDN), typical for videoconferencing and videophone services. This is a connection-oriented protocol.
While H.323 excels at providing basic telephony functionality and interoperability, H.323’s strength lies in multimedia communication functionality designed specifically for IP networks.
H.323-Terminals Terminals in an H.323 network are the most fundamental elements in any H.323 system, as those are the devices that the end user would normally encounter. They might exist in the form of a simple IP phone or a powerful high-definition videoconferencing system.
H.324 H.324 is an ITU-T recommendation for voice, video and data transmission over narrow band networks (e.g. analog phone lines).
H.321 An ITU standard for videoconferencing over ATM and Broadband ISDN networks. This is a connection-oriented protocol.
HD High Definition - television (or HDTV) is a digital television broadcasting system with higher resolution than traditional television systems (standard-definition TV, or SDTV).
H.322 An ITU standard for videoconferencing over local area networks (LANs) that can guarantee bandwidth, such as Isochronous Ethernet. This is a package-oriented protocol.
HDTV is digital broadcasting with a minimum resolution of 720p. HD setup for video conferencing includes at least one HD camera - a HD enabled codec (e.g. Tandberg C60) and a HD-enabled projector resp. screen. HDTV broadcast systems are identified with three major parameters: Frame size in pixels is defined as number of horizontal pixels × number of vertical pixels, for example 1280 × 720 or 1920 × 1080. Often the number of horizontal pixels is implied from context and is omitted. Scanning system is identified with the letter p for progressive scanning or i for interlaced scanning.
H.323 H.323 is an umbrella recommendation from the ITU under the title of «Packet-based Multimedia Communications Systems» that defines the protocols to provide audio-visual communication sessions on any packet network. The H.323 standard addresses call signaling and control, multimedia transport and control, and bandwidth control for point-to-point and multi-point conferences. It is widely implemented by voice and videoconferencing equipment manufacturers, is used within various Internet real-time applications such as GnuGK and NetMeeting and is widely deployed worldwide by service providers and enterprises for both voice and video services over Internet Protocol (IP) networks. It is a part of the ITU-T H.32x series of protocols, which also address multimedia communications over Integrated Services Digital Network (ISDN), Public Switched Telephone Network (PSTN) or Signaling System 7 (SS7), and 3G mobile networks.
If all three parameters are used, they are specified in the following form: [frame size][scanning system][frame or field rate] or [frame size]/[frame or field rate][scanning system]. Often, frame size or frame rate can be dropped if its value is implied from context. In this case the remaining numeric parameter is specified first, followed by the scanning system. Examples: 1. 1080i60 = 1080p/30 notation identifies interlaced scanning format with 30 frames (60 fields) per second, each frame being 1,920 pixels wide and 1,080 pixels high.
2. 1080p24 = 1080p/24 = 1920 × 1080 pixels per image and 24 frames (images) per second 3. 720p50 = 720p/50 = 1280 × 720 pixels per image and 50 frames (images) per second Text from Wikipedia →
ILS (NetMeeting) Internet Locator Server (ILS) is a dynamic directory solution for NetMeeting. ILS supports LDAP conferencing servers and directory servers. ILS is used to enable NetMeeting users to locate each other on Internet or corporate intranets. These servers create a directory of NetMeeting users. The IL-server converts an email address, or computer name into the corresponding IP address.
ITU ITU is the leading United Nations agency for information and communication technology issues and is responsible for global standardization of telecommunication services ITU →
LDAP LDAP (lightweight directory access protocol) is a TCP/IP protocol that email and other programs use to look up information from a server. As a protocol, LDAP does not define how programs work on either the client or server side. It defines the «language» used for client programs to talk to servers (and servers to servers, too) i.e. a specific correlation between names and their internal interpretation.
MAC In computer networking, a Media Access Control address (MAC address) is a unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification, and used in the Media Access Control protocol sublayer. If assigned by the manufacturer, a MAC address usually encodes the manufacturer›s registered identification number. It may also be known as an Ethernet Hardware Address (EHA), hardware address, adapter address, or physical address.
MCU (Multipoint Conference Unit) Multipoint Conferencing Unit (MCU) is a device that manages a multipoint conference by connecting the multiple sites and stations in the same videoconference. The MCU can be used in conjunction with a Gateway to connect H.320 and H.324 videoconference end-points. The MCU combines video, audio and data streams from multiple conference end-points into one multi-location, interactive session.
Multicast Multipoint Conferencing Unit (MCU) is a device that manages a multipoint conference by connecting the multiple sites and stations in the same videoconference. The MCU can be used in conjunction with a Gateway to connect H.320 and H.324 videoconference end-points. The MCU combines video, audio and data streams from multiple conference end-points into one multi-location, interactive session.
NTSC NTSC, named for the National Television System Committee is the analog television system used in most of the Americas, Japan, South Korea, Taiwan, Burma, and some Pacific island nations and territories. Image size is 640 x 480 pixels at a frame rate of 30 frames (images) per second, or 60 fields per second.
PAL The PAL (Phase Alternating Line) is the TV standard used in Germany and many other countries. Image size is 768 x 576 pixels and frame rate is at 25fps or 50 fields per second.
PCM Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a numeric (usually binary) code. The process is repeated periodically with the sampling rate (e.g. G.711 8 bit and 8 kHz sampling rate)
Proxy Proxy actually means substitute. It is the general principle of local data caching whereby object data of various services, such as HTTP, FTP, Gopher and WAIS
are cached and related requests from the local database are quickly answered (caching) or forwarded (proxying).
QoS - Quality of Service Quality of Service is a networking term that specifies a guaranteed throughput level. One of the biggest advantages of ATM over competing technologies such as Frame Relay and Fast Ethernet, is that it supports QoS levels. This allows ATM providers to guarantee to their customers that end-to-end latency will not exceed a specified level.
RTP RTP (real time protocol) is an Internet protocol standard that specifies a way for programs to manage the realtime UDP transmission, of multimedia data over either unicast or multicast network services. RTP combines its data transport with a control protocol (RTCP), which makes it possible to monitor data delivery for large multicast networks. Monitoring allows the receiver to detect if there is any packet loss and to compensate for any delay jitter.
SIP The Session Initiation Protocol (SIP) is an IETF-defined signaling protocol, widely used for controlling multimedia communication sessions such as voice and video calls over Internet Protocol (IP). The protocol can be used for creating, modifying and terminating two-party (unicast) or multiparty (multicast) sessions consisting of one or several media streams. The modification can involve changing addresses or ports, inviting more participants, and adding or deleting media streams. Other feasible application examples include video conferencing, streaming multimedia distribution, instant messaging, presence information, file transfer and online games. Text von Wikipedia → The SIP standard is little bit more open than H323 and therefore more and more seen in the video conferece enviroment.
T.120 T.120 is an umbrella standard that encompasses a series of communication and application standards. The ITU T.120 standard is composed of a suite of communication
and application layer protocols developed and approved by the international computer and telecommunications industries. These protocols enable developers to create compatible products and services for real-time, multipoint data connections and conferencing. T.120-based applications let many users participate in conferencing sessions over different types of networks and connections. Depending on the type of T.120 product, users can: Make connections. • Transmit and receive data. • Collaborate using compatible data conferencing features, such as application sharing, conferencing white board, and file transfer. The following standards and components make up the T.120 infrastructure.
T.120 Data protocols for multimedia conferencing which provide an overview of the T.120 series
T.121 This standard provides a generic application template (GAT), which specifies a common set of guidelines for building application protocols. To ensure application consistency, T.121 is a required standard for products developed under T.120.
T.122 The T.122 standard defines the multipoint services that enable one or more participants to send data as part of a conference. These multipoint services are implemented by T.125, which provides the mechanism for transporting the data. Together, the T.122 and T.125 standards make up the T.120 Multipoint Communication Services (MCS).
T.123 The T.123 standard is responsible for transporting and sequencing data, and for controlling the flow of data across networks, including connect, disconnect, send, and receive functions. For data transport, T.123 defines a series of network interface profiles. T.123 also provides an error-correcting mechanism that ensures accurate and reliable data delivery. T.123 Annex B also defines the protocol for secure data conferencing.
T.124 Generic Conference Control (GCC): The definition of the application protocol supporting reservations and basic conference control services for multipoint teleconferences.
T.125 This standard specifies how data is transmitted within a conference. T.125 defines the private and broadcast channels that transport the data and ensures accurate and efficient communication among multiple users. T.125 implements the multipoint services defined by T.122.
T.126 Multipoint still-image and annotation protocol: Definitions for collaborative data sharing, image sharing, graphic display information, and image exchange in a multipoint conference.
T.127 This standard defines how files are transferred simultaneously among conference participants. T.127 enables one or more files to be selected and transmitted in compressed or uncompressed form to all or selected participants during a conference.
T.128 This standard defines how application sharing orders are transmitted.
TCP The Transmission Control Protocol (TCP) is one of the core protocols of the Internet Protocol Suite. TCP provides reliable, ordered delivery of a stream of bytes from a program on one computer to another program on another computer. Besides the Web, other common applications of TCP include e-mail and file transfer. Among its other management tasks, TCP controls segment size, flow control, the rate at which data is exchanged, and network traffic congestion.
UDP The User Datagram Protocol (UDP) is one of the core members of the Internet Protocol Suite. UDP, a connectionless protocol, describes unsecured data
transmission, i.e. there is no confirmation of correctly transmitted packets.
VGA VGA (Video Graphics Array) is a standard for computer graphic cards. In graphic mode resolution is 640 x 480 pixels at 16 colors or 320 x 300 pixels with 256 colors. The more advanced SVGA features 800 x 600 pixels and XGA offers 1024 x 768 pixels.
VNC VNC, acronym for Virtual Network Computing, software provides cross-platform support allowing remote control between different types of computers. To use VNC you must have a network TCP/IP connection, a VNC server and a VNC viewer to connect to the computer running the VNC server. The open source version of VNC has been freely available since 1998, and more than 20 million copies of the software have been downloaded.
Voice-activated Voice-activated calls in a multipoint conference always show the image of the currently speaking participant. Since voice-activation calls for lots of speaker experience, ideally, such conferences are moderated. By contrast, continuous presence mode is where all conference participants can be seen. The screen is divided into 4-16 squares, depending on the number of participants.
Zone A zone is an administrative concept on a gatekeeper. Within the same zone, all necessary video conferencing equipment is grouped together under one name or number (zone name, zone number).
Christopher Sauder Engeler ID.MMS-VC Multimedia Services Videoconferencing & Collaboration HG D21 / HCI D253 ETH Zurich Telefon: +41 44 633 41 20
[email protected] www.vc.ethz.ch →
