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					               LAN Structures and Data Traffic




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Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Agenda
  Types and structures of LAN
  LAN Data Traffic
  LAN Performance
  Congestion and Congestion Controls
  Congestion control in TCP




Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Mesh Topology

       Fully connected




                                 3 lines : 2 ports per machine

Michael Chai; Behrouz Forouzan              08/09/2011           Staffordshire University
                                                                 School of Computing
              IADCN - Week 8
              Mesh Topology

         Fully connected




                          6 lines : 3 ports per machine

Michael Chai; Behrouz Forouzan         08/09/2011         Staffordshire University
                                                          School of Computing
              IADCN - Week 8
              Mesh Topology

       Fully connected




                                              10 lines : 4 ports per
                                              machine

    Not a practical system for LANs.

Michael Chai; Behrouz Forouzan   08/09/2011          Staffordshire University
                                                     School of Computing
              IADCN - Week 8
              Star Topology

       STAR




Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Ring Topology

       RING




Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Bus Topology

       BUS




Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Data Traffic
  The main focus of congestion control and quality
   of service is data traffic
  In congestion control we try to avoid traffic
   congestion
  In quality of service, we try to create an
   appropriate environment for the traffic




Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Types of Traffic Profile




Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Congestion
  Congestion occurs when load on the network is
   higher than the network capacity
  Reasons for congestion
      – Retransmission on noisy media caused by verification
        mechanisms (e.g. TCP)
      – Simply too many concurrent requests (many users)
      – “Bursty” applications may make many requests quickly
    Congestion control uses mechanisms and
     techniques to control the congestion and keep
     the load below the capacity
Michael Chai; Behrouz Forouzan   08/09/2011      Staffordshire University
                                                 School of Computing
              IADCN - Week 8
              Congestion (Cont’)




                                    Figure 24.3 Queues in a router
      Congestion occurs when
      i.  Packet arrival > packet processing
      ii. Packet departure <packet processing


Michael Chai; Behrouz Forouzan    08/09/2011            Staffordshire University
                                                        School of Computing
              IADCN - Week 8
              Network Performance
    Two main factors
      – Delay
      – Throughput
  Delay is composed of propagation delay and
   processing delay
  Delay increases dramatically once the load
   reaches the network capacity
  Throughput is the number packets passing
   through a network in a unit of time

Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Network Performance (Cont’)




Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Congestion Control
    Congestion control refers to techniques and
     mechanisms that can either:
      – prevent congestion, before it happens
      – remove congestion, after it has happened
    Congestion control mechanisms into two broad
     categories:
      – open-loop congestion control (prevention)
      – closed-loop congestion control (removal)




Michael Chai; Behrouz Forouzan   08/09/2011         Staffordshire University
                                                    School of Computing
              IADCN - Week 8
              Congestion Control

prevention                                    Removal




Michael Chai; Behrouz Forouzan   08/09/2011     Staffordshire University
                                                School of Computing
              IADCN - Week 8
              Congestion control & avoidance
  TCP uses a “sliding window” flow control protocol
  Receiver specifies the amount of additional
   received data that it is willing to buffer for the
   connection
  Sender can send only up to that amount of data
   before it must wait for some reply
  Acknowledgments are used by senders to infer
   network conditions
  Coupled with timers, this alters the behaviour of
   the flow of data
Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing
              IADCN - Week 8
              Networking and Research
    Enhancing TCP to
      –   reliably handle loss
      –   minimize errors
      –   manage congestion
      –   go fast in very high-speed environments
  are ongoing areas of research
  and areas of standards development
  As a result, there are many TCP congestion
   related algorithms and standards

Michael Chai; Behrouz Forouzan   08/09/2011         Staffordshire University
                                                    School of Computing
              IADCN - Week 8
              Summary
    There are some common network structures/topologies
      – Star, bus and tree topologies in LANs
      – Ring and mesh topologies in WANs
    The characteristics of the data traffic in the network
     depend on the applications
    Congestion controls are used for controlling the amount
     of traffic flow in the network to keep the traffic below the
     network capacity
    TCP avoids congestion through slow start and additive
     increase, and multiplicative decrease


Michael Chai; Behrouz Forouzan      08/09/2011        Staffordshire University
                                                      School of Computing
              IADCN - Week 8
              References and reading
    TCP Congestion Control (John Kristoff 2002)
     http://condor.depaul.edu/~jkristof/technotes/cong
     estion.pdf
    Transmission Control Protocol (Wikipedia)
     http://en.wikipedia.org/wiki/Transmission_Control
     _Protocol
    Congestion Control Overview
     http://users.ecs.soton.ac.uk/sqc/EL336/CNL-
     11.pdf

Michael Chai; Behrouz Forouzan   08/09/2011   Staffordshire University
                                              School of Computing

				
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