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  • 1Petri Vuorimaa 1

    Video conferencing

    Introduction Standards Products Internet telephony Computer Telephony Integration (CTI)

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    Video conferencing can be used for+ Audio-visual communication+ Sharing of documents, tables, pictures, etc.

    Several benefits+ Traveling costs+ Response time+ Better understanding (body language)

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    Two main types:+ Video conferencing rooms+ Video conferencing software

    Video conferencing rooms are for group meetings+ Organization either has it own premises or rents them

    from operator

    Video conferencing software is for personal use

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    Modem, ISDNor LAN



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    Group Meetings

    Two types of video conferences:+ Point-to-point conferences (video telephony)+ Multipoint conferences (group meetings)

    In group meetings, there are two ways to share turns (i.e., floor control):+ Automatic selection (e.g., based on audio)+ Chairman

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    Multipoint Conferences


    Multipoint server

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    Standard Families

    Integrated Services Digital Network - ISDN (H.320)

    Networks supporting QoS (H.310, H.321, and H.322)

    Local area networks - LAN (H.323) Plain old telephone systems - POTS (H.324) Shared workspaces (T.120)

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    Standard families (cont.)

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    Two resolutions:+ Quarter Common Intermediate Format (QCIF): 176 x

    144+ Common Intermediate Format (CIF): 352 x 288

    Frame rates 7.5, 10, 15, or 30 frames per second Motion estimation can be used, but is not


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    Audio codecs

    Three different audio codecs:+ G.711 48-64 Kbps narrow band+ G.722 48-64 Kbps wide band+ G.728 16 Kbps narrow band

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    Different classes

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    Meant for Plain Old Telephone Systems (POTS) H.263 can be used for below 64 Kbps video

    coding+ sub-QCIF (128 x 96), QCIF (176 x 144), CIF (352 x

    288), 4CIF (702 x 576), and 16CIF (1408 x 1152)

    G.723.1 audio codec transmits at 5.3 or 6.3 Kbps

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    H.324 (cont.)

    Can use even 28.8 and 33.3 Kbps modems (V.34) Codecs are better, but quality is worse than H.320

    + H.320 has much more bandwidth than H.324

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    LANs (Internet & Intranet) without QoS support Clients, multipoint servers, gateways and

    gatekeepers Real-time transport protocol (RTP) New audio codec G.729 (8 Kbps)

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    The gateway allows the integration of H.323 networks with other networks

    Tasks:+ transformations between media formats+ transformations between communication protocols+ transformations between audio and video codecs+ connection setup and tear-down

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    Gatekeeper takes care of resource reservations The amount of simultaneous users can be limited Transforms connection requests from outside to

    internal addresses and vice versa

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    Multipoint Server

    Required when three or more clients participate the conference

    Is composed of two parts:+ Multipoint Controller takes care of connections+ Multipoint Processor(s) transform(s) media streams

    Processors can also combine streams:+ Mixing+ Switching

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    Multipoint Server (cont.)

    Videoconferences can be set up in three different ways:+ unicast, multicast, and broadcast

    Three ways of practical implementation:+ centralized, distributed, and hybrid

    In practice H.323 is implemented on top of IP etc. protocols

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    Different alternatives

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    Protocol stack

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    Implements the extra services:+ conformance+ image transfer+ shared workspaces+ file transfer+ multipoint conferences

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    T.120 (cont.)

    T.120 is composed of three layers:+ transport layer+ protocol layer+ application layer

    Transport layer is divided into three levels:+ transport protocol+ multipoint conference+ conference control

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    Transport layer

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    T.120 (cont.)

    Protocol layer is composed of+ image transfer (T.126)+ binary file transfer (T.127)+ share application transfer (T.Share)+ resource reservation (T.RES)

    New standard family T.130 is under development

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    Video conference bridges Video networks Video conference rooms Workstations Gatekeepers Gateways

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    Video conference bridges

    Support primarily H.320 and T.120 standard families

    Allow multipoint video conferencing Support few tens of users Participants either call to the bridge or the bridge

    setups the connections itself

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    Video networks

    Best possible image quality Intended primarily for conferences Uses either ISDN or ATM network

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    Video conference rooms

    Intended for video conferencing Maintained by companies or operators Based on H.320 (ISDN) standard family H.323 (Internet) standard family is coming

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    LAN, ISDN, or modem card Audio and video cards Software (e.g., Microsoft Netmeeting, Picturetel,

    Intel) H.320 most common, but H.323 is coming (client

    software is available)

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    Required by H.323 standard family For example, Intel LANDesk Conferencing

    Manager+ automatic gate keeper+ zone management+ outbound route management+ incoming call routing

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    Intel LiveGateway+ bi-directional connection between H.323 and H.320

    systems+ format transform between H.323 and H.320 systems+ supports also H.320 multipoint server+ four gates in on PC+ either local or gate keeper based administration

    Both Intel LANDesk Conferencing and LiveGateway are Windows NT based

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    Internet telephony

    With suitable hardware and software computers connected to Internet can be used for telephony

    No extra charges, but the quality is not very good Gateways to ordinary telephone network also


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    Internet telephony (cont.)

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    Internet telephony (cont.)

    Some long distance operators use Internet connections for telephony

    Allows the use of compression For example, 64 Kbps -> 2.4 Kbps

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    Calls within organization

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    Public Internet calls

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    Internet telephony products

    Microsoft Netmeeting supports H.323 and T.120 standard families

    Includes H.263 video codec Compatible with Intel and PictureTel products Utilizes Intel Pentium MMX technology Other products include White Pine Software CU-

    SeeMe, IBM Internet Connection Phone, VDOnet VDOPhone

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    Computer Telephony Integration (CTI) integrated computers and telephones

    Brings savings and increases efficiency (invest return time usually under year)

    Several different implementations

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    CTI block diagram

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    CTI applications

    Voice mail (answering service) Automatic call transfer Intelligent call routing and distribution (call

    centers) Voice text (timetable, etc.) Fax requests (information delivered via fax)

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    CTI applications (cont.)

    Interactive telephone services (reservations, orders, etc.)

    Call records (automatic recognition of customers) Gateways (video conference with standard

    telephone) Call management (automatic dialing)

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    CTI implementations

    CTI can be based on separate server Another alternative is to join telephone directly to

    workstation Video conference, Internet telephony, and CTI

    systems can be integrated

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    Call Center

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    Integrated system

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    CTI standards

    Multi-Vendor Integration Protocol (MVIP) System Computing System Architecture (SCSA) Both are buses connecting different PC cards Buses are used for call traffic within PC

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    PC cards

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    CTI APIs

    Microsoft Telephony Application Programming Interface = TAPI (-93)+ Windows applications

    Novell Telephony Service API = TSAPI (-93)+ Novell servers

    IBM CTI API+ Switches and their interfaces

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    CTI APIs (cont.)

    SCSA framework Sun Java Telephony API = JTAPI

    + Java-framework+ utilizes above mentioned API definitions