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Network - University of California_ Santa Cruz

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					                     Department of Computer Engineering
                     University of California at Santa Cruz




Networking Systems (1)


       Hai Tao
                                                      Department of Computer Engineering
                                                      University of California at Santa Cruz



LANs, MANs, and WANs

     LANs (Local area networks)
      •   Extension over a local area typically within a few kilometers
      •   Usually owned by a single organization
      •   High data rate
      •   The number of stations connect to a LAN is usually less than 100
      •   Usually is based on broadcasting channels
      •   Some examples include Ethernet, Token Ring, Fiber Distributed
          Data Interface (FDDI), local ATM (asynchronous transfer mode)
          networks
     MANs (Metropolitan Area Networks)
      • Covers an entire city with LAN technology
      • Shared medium and distributed access control
                                          Department of Computer Engineering
                                          University of California at Santa Cruz



LANs, MANs, and WANs

     WANs (Wide Area Networks)
      • Typically span entire countries
      • Point-to-Point communication
      • Example: Internet
                                                      Department of Computer Engineering
                                                      University of California at Santa Cruz



LANs, WANs, Layers, Protocols, and Services

     Services provides a set of applications for the requesting
      application
     Logically related services are grouped into layers
      • Each layer is a service provider to the layer lying above
     Protocol consists of rules followed by two peers during
      any communications
      • Define protocol data units (PDU) in terms of format (syntax) and
        meaning (semantics)
                                          Department of Computer Engineering
                                          University of California at Santa Cruz



ISO-OSI Reference Model




                 (SearchNetworking.com)
                                                    Department of Computer Engineering
                                                    University of California at Santa Cruz



Layers in ISO-OSI Reference Model

     Physical Layer
      • Transmission method of individual bits over the physical medium
        such as fiber optics, cables, phone lines, etc
      • Concern with modulation, delay, etc
     Data Link Layer
      •   Transmission of data frame (block)
      •   Access protocols to the physical medium
      •   Error and recognition correction
      •   Flow control and block synchronization
                                                     Department of Computer Engineering
                                                     University of California at Santa Cruz



Data Link Layer

     Medium access protocol
       • Multi-access channels
          - Medium access control (MAC) to determine access from competing
             parties
                + Very important in LANs
                + Timed Token Rotation Protocol
                + Carrier Sense Multiple Access with Collision Detection
                  (CSMA/CD)
       • Point-to-Point connection
                                              Department of Computer Engineering
                                              University of California at Santa Cruz



Network Layers

     Transports data packets from one station to another
     Provide services such as addressing, internetworking, error
      handling, congestion control, packet sequencing
     For continuous media data, resource reservation and
      guarantees for through put can be achieved using Quality
      of Service (QoS) parameters
                                                     Department of Computer Engineering
                                                     University of California at Santa Cruz



Transport Layers

      Provides process-to-process connection
      Bridge the gap between the requested transport and the
       provided services from network layers
      Some functionalities include
       • Divide and assemble packets
       • Error handling between process (e.g. TCP)
                                                     Department of Computer Engineering
                                                     University of California at Santa Cruz

Session Layer, Presentation Layer, and Application
Layer
      Session layer - Guarantee the existence of connection
       during a session
       • Point-to-point session
       • Multi-cast session – a connection with many destinations
       • Multi-drop session – a connection with many sources
       Presentation layer – Definition, abstraction, and
       conversion of various data exchange formats
       • Examples: HTTP, TELNET, FTP, POP
      Application Layer – Various applications based on the
       presentation layer (See figure for an example)
                                                     Department of Computer Engineering
                                                     University of California at Santa Cruz



LANs - Ethernet

     Bandwidth increases dramatically: 10Mbps to 100Mbps to
      1GMbps to 10 Gbps
     Bus-based network




                    Three kinds of Ethernet cabling.
                (a) 10Base5, (b) 10Base2, (c) 10Base-T.
                                          Department of Computer Engineering
                                          University of California at Santa Cruz



LANs - Ethernet




        A simple example of switched Ethernet.
                                                     Department of Computer Engineering
                                                     University of California at Santa Cruz



LANs - Ethernet




     Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented.
                                              Department of Computer Engineering
                                              University of California at Santa Cruz



LANs - Ethernet




      (a) A two-station Ethernet. (b) A multistation Ethernet.
                                                     Department of Computer Engineering
                                                     University of California at Santa Cruz



LANs - Ethernet

     Using CSMA/CD protocol to solve the multiple access
      problem
      • Sender station checks the network state (Listen)
      • Only send data when no other stations are transmitting data (Send)
      • When multiple stations send data simultaneously, sending stations
        detect collisions by finding errors in their own data
      • If collision detected, wait for randomly computed time and
        transmit again
                                                     Department of Computer Engineering
                                                     University of California at Santa Cruz



Ethernet and Continuous Media

     Ethernet does not explicitly guarantee end-to-end delay
     To transmit continuous media data on the Ethernet, several
      methods can be used
      • Using fast Ethernet – end-to-end delay can be long if the network
        is congested, using fast Ethernet will solve this problem under
        most situations
      • Dynamic adaptation – Change the data rate of the media data
        according to the network load
      • Dedicated Ethernet for media data – one network for discrete date,
        one network for continuous data
                                                Department of Computer Engineering
                                                University of California at Santa Cruz



LANs – Token Ring

     All stations are connected to a logical ring
     A special bit pattern (3Bytes) called a token circulate in the
      ring
     A sender station will capture the token and break the ring.
      The station sends the data in data frames. Each frame
      include sender address and destination address
     Connect the ring once the transmission is finished
     A multiple priority scheme is used to control the network
      access
                                                      Department of Computer Engineering
                                                      University of California at Santa Cruz



LANs – Local ATM Networks

     Asynchronous Transfer Mode use fixed length packet
      (cell)
     ATM allows systems to operate at higher rate because
      • No error protection or flow control on a link-to-link basis (but can
        be done in higher layers)
      • Operate in connection oriented mode with a setup phase for
        resource reservation
      • Information field is small to reduce the internal buffers in the
        switching nodes
                                                     Department of Computer Engineering
                                                     University of California at Santa Cruz



WANs

    Internet – DARPA experiment in 1973, see table 1 for
     illustration
    Interconnection devices
     • Source and destination are connected by a sequence of
       interconnection devices (packet switches)
     • Packet switches cooperatively compute the path in the network.
       They are called routers in network layer
     • Routing protocols
         - Distance vector – each router keeps tracking and informing its
           neighbors of its distance to each destination. Slow propagation.
         - Link State - Each router determines the identities of its
           neighbors and the associated distance and constructs link state
           packet (LPS). LPS is sent to all all the other routers

				
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