Introduction. Video conferencing. Equipment. Systems. Multipoint Conferences. Group Meetings

July 5, 2019 | Author: Arnold Reed | Category: N/A
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Video conferencing • • • • •

Introduction

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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Systems

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Equipment

• Two main types:

Video/audio capture

+ Video conferencing rooms + Video conferencing software

Modem, ISDN or LAN Communication network

• 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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Audio card

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Group Meetings

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Multipoint Conferences

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

Communications network

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

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Standard Families

Standard families (cont.)

• 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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H.320

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Video

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Audio codecs

• Two resolutions:

• Three different audio codecs:

+ Quarter Common Intermediate Format (QCIF): 176 x 144 + Common Intermediate Format (CIF): 352 x 288

+ G.711 48-64 Kbps narrow band + G.722 48-64 Kbps wide band + G.728 16 Kbps narrow band

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

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Different classes

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H.324

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H.324

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H.324 (cont.)

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

• 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

+ 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.323

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H.323 • 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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Gateway • 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

Multipoint Server

• 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

• 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 Petri Vuorimaa

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Multipoint Server (cont.)

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Different alternatives

• 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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Protocol stack

T.120 • Implements the extra services: + conformance + image transfer + shared workspaces + file transfer + multipoint conferences

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T.120 (cont.)

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Transport layer

• 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 Petri Vuorimaa

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T.120 (cont.)

Products

• 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

Video networks

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

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Video conference rooms • • • •

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Workstations

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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Gatekeepers

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Gateways

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

• 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

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

• Both Intel LANDesk Conferencing and LiveGateway are Windows NT based Petri Vuorimaa

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Internet telephony

Internet telephony (cont.)

• 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 available

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Internet telephony (cont.)

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Calls within organization

• 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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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 CUSeeMe, IBM Internet Connection Phone, VDOnet VDOPhone

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CTI

CTI block diagram

• 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 applications

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CTI applications (cont.)

• 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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• 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

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Call Center

• 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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Integrated system

CTI standards • • • •

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PC cards

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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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

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