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					     OSI

  Jacek Ilow
j.ilow@dal.ca
     OSI        1
                    Overview
   Wide Area Networking and Telecommunications
   Standard Organizations
   OSI Model
   WAN Technologies
   Digital Telephony
   QoS
   Summary




                           OSI                    2
                WANs and LANs
   Wide Area Networks                      Local Area Networks
     machines are spread over a               machines are spread over a
      wide geographical region                  “small” geographical region
     comm channels are                        comm channels are privatly
      furnished by a third party                owned
      (telephone company, public               channels are relatively high
      data networks)                            capacity (Mbs)
     channels are of relatively               channels are relatively
      low capacity (tens kbs)                   error-free, BER=10 E-9
     channels are error prone,
      BER=10 E-5




                                   OSI                                     3
          The Telephone Network
   The customer premise equipment
       telephone handsets, modems, PBX
   transmission facilities
       the local (subscriber) loop and the trunk lines
   switching facilities
     the main function is to interconnect and route
     local switching systems (central office)
     tandem switches connect trunks to trunks
     a toll switch that serves the long distance network




                                   OSI                      4
      Virtual Circuits vs Datagrams

                Virtual Circuit                           Datagram
Initial Setup   Required                                  Not applicable
Destination     Only needed during setup;                 Needed in every packet
Address         After setup only short virtualcircuit #
                needed
Error           Transparent to data processing            Explicitly done by data processing
Handling        equipment                                 equipment

End-to-end      Provided by communications subnet         Not provided by communications
flow control                                              subnet

Packet          Messages always passed to data            Messages passed to data processing
sequencing      process equipment in order sent           equipment in order of arrival




                                               OSI                                             5
      Packet vs. Circuit Switching
   Packet switching allows multiple users to share data-
    network facilities and bandwidth, rather than providing
    specific amounts of dedicated bandwidth to each user.
   Traffic passed by packed-switched networks is “bursty”
    and can be aggregated statisticall to maximize the use of
    on-demand bandwidth resources.
   There is much more overhead associated with packet
    switching as compared to circuit switching.
       Conncetionless character of packet switching in
        contradistinction to connection-oriented circuit switching
        allows routing around failed links, whereas in circuit
        switching the entire circuit would need to be switched

                                  OSI                                6
          Driving force for WAN

   More powerful applications have an impact on human
    productivity
   Bandwidth is becoming available to support these
    applications
   Decreased costs to use this bandwidth
   Increased computing power
   Decreased costs of telecomputing will make gigabit-
    based applications cost effective



                             OSI                          7
             Bandwidth requirements of different
                        media types
Media        Transaction        Format   Sampling dimensions          Uncompressed   Compressed
             type                        Pixel, line frame/s          Bit rate       Max bit rate


Speech and   Telephony                   8ksps                        64 kbps        8-32 kbps
music                                    x 8 bit/sample

             Telecon-                    16 ksps                      128 kbps       48-64 kbps
             Ferencing                   x 8 bit/sample

             CD-audio                    44.1 ksps x 16bit / sample   705.6 kbps     128 kbps
Image        Normal           SVGA       640 pixel x 480 line         2.458 Mbits    24 k – 245 kbits
             resolution image            x 8 bit/pixel

                                JPEG     720 pixel x 576 line         6.636 Mbits    104 k – 830 kbits
             Very high                   x 16 bit/pixel
             resolution image
                                         1280 pixel x 1024 line       31.46 Mbits    300 k – 3 Mbits
                                         x 24 bit/pixel

  CIF Common Intermediate Format                          QCIF Quarter CIF
  MPEG Moving Pictures Expert Group                       JPEG Joint photographic experts group
                                                 OSI                                         8
Media        Transaction    Format    Sampling dimensions      Uncompressed Compressed
             type                     Pixel, line frame/s      Bit rate     Max bit rate


Bussines     Videophone     QCIF      176 pixel x 144 line     9.115 Mbps    px64 kbps
Video                       (H.261)   x 12 bit x 30 frame/s                  (p=1,2)

             Telecon-       MPEG4     176 pixel x 144 line     3.04 Mbps     64 kbps
             ferencing      H.320     x 12 bit x 10 frame/s

             Video          CIF       352 pixel x 288 line     36.45 Mbps    mx384 kbps
             conferencing   H.261     x 12 bit x 30 frame/s                  m=1,2,…5

                            MPEG1     352 pixel x 288 line     30.4 Mbps     1.15 M – 3 Mbps
                            PAL       x 12 bit x 25 frame/s
                            NTSC               x 30
Entertain-   VCR            CIF       352 pixel x 240 line     30.4 Mbps     4 Mbps
ment Video                  MPEG2     x 12 bit x 30 frame/s

             Broadcast      MPEG2     720 pixel x 576 line     124.4 Mbits   15 Mbps
             television     PAL       x 12 bit x 25 frame/s
                            NTSC                 30

             High quality   HDTV      1920 pixel x 1080 line   994.3 Mbps    135 Mbps
             television               x 16 bit x 30 frame/s

                            MPEG3     1920 pixel x 1080 line   745.8 Mbps    20 M – 40 Mbps
                                      x 12 bit OSI frame/s
                                               x 30                                    9
               WAN Technologies
   Synchronous Optical Network (SONET) or Synchronous
    Digital Hierarchy (SDH)
       a high-speed synchronous carrier system, based on the use
        of optical fiber technology and a defined digital multiplexing
        hierrarchy
   Frame Relay
       a fast relay service, with minimal network support offering
        bandwidth on demand
   Wireless Systems
       a wide array of wireless systems designed to support
        primarilly voice and low-speed data



                                  OSI                                 10
   Broadband Signaling
       a second-generation signaling technology (based on ISDN
        and SS7) used to setup and tear down virtual circuits
   Asynchronous Transfer Mode
       a high speed virtual circuit with cell relay technology
   Residential Broadband
       video on demand, client-server applications, Internet
        browsing on the local loop




                                   OSI                            11
                      Standards
   Standards are required to govern
     the physical
     electrical
     procedural

characteristics of communication equipment
 The principal disadvantage of standards is that they tend
  to freeze technology
 Standards and Regulation
     Voluntary standards (CCITT and OSI)
     Regulatory standards (FCC and Industry Canada)
     Regulatory use of voluntary standards




                              OSI                         12
               Terms of Reference
   Telecommunications
       the technology of communication-at-a-distancethat permits
        information to be created anywhere and used everywhere
   Communication
       the transfer of information according to agreed conventions
   Standard
       a prescribed set of rules, conditions, or requirements
        concerning definition of terms; classification of components;
        specification of materials, performance, or operations;
        delineation of procedures; or measurement of quality
        describing products and materials
   Communication network
       set of devices, mechanisms, and procedures by which end-
        user equipment attached to the network can exchange
        meaningful information
                                  OSI                                 13
   OSI Standard
       provides conceptual and functional framework which allows
        international teams of experts to work productively and
        independently on standards for each layer of the Ref Model
   Bearer services
       means to convey information between users without
        alteration of the content of the message
   Connection
       a concatenation of transmission channels or
        telecommunication circuits, switching and other functional
        units set up to provide for the transfer of signals between two
        or more points in a telecommunication network, to support a
        single communication




                                  OSI                                14
          Standards Organizations
   CCITT - International Telegraph and Telephone Consultive
    Committee
       committee of the International Telecommunications Union
        (ITU) which itself is a United Nations treaty organization
          Study  groups:Network organization; Tariff and
           accounting principles; Data communications
           networks; Terminals for telematic services;
           Switching and signaling; Transmission performance
           of telephone network and terminals; Transmission
           systems and equipment; Data transmission over the
           telephone network; ISDN
          As of 1993, CCITT is ITU-TSS (Telecommuni-
           cation Standardization Sector) in Geneva
                                  OSI                                15
   IOS - International Organization for Standardization
     international agancy for the development of standards on the
      wide range of subject
     voluntary, non-treaty organization whose members are
      designated bodies of participating nations
   CCITT has primarily been concerned with data
    transmission and communication network issues
       the lower three layers of the OSI architecture.
   ISO has traditionally been concerned with computer
    communications and distributed processing issues,
       layers 4 through 7.
   The merger of the fields of data processing and data
    communications has resulted in considerable overlap in
    the areas of concern of these two organizations.

                                  OSI                           16
    Communications Architecture
   A communications architecture is a structured set of
    software modules that implement the communications
    function.
     The model provides a framework within which standards at
      each layer can be developed systematically and in parallel.
     Communications standards assure a large market and
      therefore promote lower costs through competition and mass
      production.
     Standards promote interoperability; that is, standards
      promote the ability for products from different vendors to
      work together. Interoperability gives purchasers more
      flexibility in equipment selection and promotes distributed
      applications between and among different organizations.

                               OSI                             17
        OSI Reference Model

Application                        AH User Data


Presentation                  PH   AH User Data


  Session                SH   PH   AH User Data

 Transport            TH SH   PH   AH User Data

  Network         NH TH SH    PH   AH User Data

 Data Link     LH NH TH SH    PH   AH User Data        LT

  Physical     LH NH TH SH    PH   AH User Data        LT


                OSI                               18
              OSI Reference Model..

Application                                           Application
                  Service to layer (N+1)
Presentation                                          Presentation
  Session        Layer (N)           Protocol with      Session
                                     peer layer (N)
 Transport                                             Transport
                  Service to layer (N-1)
  Network                                               Network
 Data Link                                             Data Link
  Physical                   Comm Path                  Physical

                               OSI                           19
             OSI Network Service
   Independence of the underlying communications facility:
        Network users need not be aware of the details of the
        subnetwork facilities used.
   End-to-end transfer:
        All routing and relaying are performed by the network-
        service provider and are not of concern to the network-
        service user.
   Transparency:
       The network service does not restrict the content, format, or
        coding of user data.




                                  OSI                               20
           OSI Network Service...
   Quality of service selection:
       The network-service user has some ability to request a
        given quality of service.
   User addressing:
       A system of addressing (NSAP addressing) is used that
        allows network-service users to refer unambiguously to one
        another.
   The essential requirement for internetworking is that the
    two communicating end users are presented with the
    same network service; that is, they employ the same set of
    network-service primitives and parameters.


                                 OSI                             21

				
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