Computer Networks

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Computer Networks

• Chapter 9

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Objectives

• Compare and contrast bus, ring, and star network
  topologies
• Describe packet routing across local and wide
  area networks
• Compare and contrast token passing and CSMA/CD
  media access control protocols
• Describe network hardware devices, including
  network interface units, bridges, routers, and
  switches
• Describe the OSI network model, the TCP/IP
  protocol suite, and IEEE network standards

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Chapter Topics
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Network Topology

• Network topology
• the spatial organization of network devices
• the physical routing of network cabling
• the flow of messages from one network node to
  another

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Network Topology

• Topology Types
• Point-to-Point transmission the line is laid
  over the shortest path and connected directly to
  both nodes. Used for small networks.
• Shared connections smaller shared links are
  connected to larger shared links. Used for larger
  networks.

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Network Topology
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Network Topology

• Shared Connections
• Store and Forward - interconnected system of end
  nodes and transfer points used to route data
  among end nodes.

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Network Topology
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Network Topology

• Network Topology
• Logical topology refers to the path that
  messages traverse as they travel from node to
  node.
• Physical topology refers to the physical
  placement of cables and device connections to
  those cables.

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Network Topology

• Topologies
• Star
• Bus
• Ring

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Network Topology

• Star Topology
• uses a central node to which all other nodes are
  connected
• the central node can be a transfer point
• Advantage simple wiring
• Disadvantage the failure of the hub disables the
  entire network

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Network Topology
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Network Topology

• Bus Topology
• Connects each node to a common transmission line
• Transmitted messages travel from a node across
  the common transmission line
• Advantages simple wiring and low susceptibility
  to failure

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Network Topology
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Network Topology

• Ring Topology
• Connects each network node to two
• nodes and the entire network forms a closed
• loop
• Advantages long maximum network length
• and low susceptibility to noise and distortion

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Network Topology

• Ring Topology
• Disadvantages
• susceptibility to failure
• difficulty adding, deleting and moving nodes

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Network Topology
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Network Topology
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Network Topology
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Addressing and Routing

• Local Area Network a network covering a floor
  or building.
• Wide Area Network a network a network that
  spans large physical distances, such as multiple
  buildings, cities, regions, or continents.

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Addressing and Routing

• Local Area Network Routing
• Each time a node is started, it sends a message
  announcing its presence and its address to the
  nearest nodes
• Each hub and router maintains a table of node
  addresses and transmission lines or connections
  ports and uses that table to make routing
  decisions

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Addressing and Routing
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Addressing and Routing

• Wide Area Network Routing
• Each router knows
• The addresses and physical locations of its own
  nodes
• Other nearby routers
• Groups of addresses that they control
• Default destination for messages to the addresses
  that it does not know

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Media Access Control

• Methods for dealing with collisions
• Carrier Sense Multiple Access/Collision Detection
  (CSMA/CD)
• Token Passing

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Media Access Control

• Carrier Sense Multiple Access/Collision
• Detection (bus topology)
• a node that wants to transmit listens (carrier
  sense) until no traffic is detected
• the node then transmits its message

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Media Access Control

• CMSA/CD (cont.)
• the node listens during and immediately after its
  transmission. If abnormally high signal levels
  are heard, which is a collision detection, then
  the node ceases transmission
• if a collision is detected, the node waits for a
  random time interval and then retransmits its
  message

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Media Access Control
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Media Access Control

• Token Passing (ring topology)
• a token is passed from node to node
• only the node with the token can pass a message
• Advantage simplicity
• Disadvantage inefficient use of data
• transfer capacity

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Network Hardware
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Technology Focus
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OSI Network Layers

• Open Systems Interconnection (OSI)
• Model
• A conceptual model for network hardware and
  software developed by the International Standards
  Organization

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OSI Network Layers
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OSI Network Layers

• Presentation Layer ensures that data
  transmitted by one network node is correctly
  interpreted by the other network node
• Session Layer establishes and manages
  communication sessions
• Transport Layer formats messages into packets
  suitable for transmission over the network

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OSI Network Layers

• Network Layer routes packet to their proper
  destination
• Data Link Layer interface between network
  software and hardware
• Physical Layer the layer at which communication
  between devices actually takes place

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TCP/IP

• Transmission Control Protocol/Internet
• Protocol (TCP/IP)
• Protocol used by private networks to transmit
  data over the Internet. TCP establishes and
  manages communication sessions. IP provides
  packet routing and forwarding services to higher
  network layers.

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TCP/IP
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Network Standards

• IEEE 802 telecommunication and network standards
  developed by the Institute of Electrical and
  Electronic Engineers (IEEE).
• Standards describe network hardware, transmission
  media, transmission methods and protocols.

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Network Standards
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Technology Focus
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Technology Focus
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Summary

• Network topology refers to the spatial
  organization of network devices, the physical
  routing of network cabling and the flow of
  messages from one network node to another.
• LANs are interconnected to form WANs.
• A media access control (MAC) protocol specifies
  rules for accessing a shared transmission medium.
• Network hardware devices include NIUs, hubs,
  bridges, routers, and switches.

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Summary

• The Open Systems Interconnection (OSI) model is
  an ISO conceptual model that divides network
  architecture into seven layers.
• TCP/IP is the core Internet protocol suite.
• The IEEE 802 standards cover many types of
  networks.