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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