601 Assignment 8 & Discussion 8

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601Assignment8Chapter9_IntroductiontoMetropolitanAreaNetworksandWideAreaNetworks.ppt
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Chapter Nine

Introduction to Metropolitan Area Networks and Wide Area Networks

Data Communications and Computer Networks: A Business User’s Approach

Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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After reading this chapter,
you should be able to:

  • Distinguish local area networks, metropolitan area networks, and wide area networks from each other
  • Identify the characteristics of metropolitan area networks and compare to LANs and WANs
  • Describe how circuit-switched, datagram packet-switched, and virtual circuit packet-switched networks work
  • Identify the differences between connection-oriented and connectionless networks

Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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After reading this chapter,
you should be able to:

  • Describe the differences between centralized and distributed routing
  • Describe the differences between static and adaptive routing
  • Document the main characteristics of flooding and use hop count and hop limit in a simple example
  • Discuss the basic concepts of network congestion, including quality of service

Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Introduction

  • As we have seen, a local area network covers a room, a building or a campus.
  • A metropolitan area network (MAN) covers a city or a region of a city.
  • A wide area network (WAN) covers multiple cities, states, countries, and even the solar system.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Metropolitan Area Network Basics

  • MANs borrow technologies from LANs and WANs.
  • MANs support high-speed disaster recovery systems, real-time transaction backup systems, interconnections between corporate data centers and Internet service providers, and government, business, medicine, and education high-speed interconnections.
  • Almost exclusively fiber optic systems

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Metropolitan Area Network Basics

  • MANs have very high transfer speeds
  • MANs can recover from network faults very quickly (failover time)
  • MANs are very often a ring topology (not a star-wired ring)
  • Some MANs can be provisioned dynamically

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Metropolitan Area Network Basics

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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SONET versus Ethernet MANs

  • Most MANs are SONET network built of multiple rings (for failover purposes)
  • SONET is well-proven but complex, fairly expensive, and cannot be provisioned dynamically.
  • SONET is based upon T-1 rates and does not fit nicely into 1 Mbps, 10 Mbps, 100 Mbps, 1000 Mbps chunks, like Ethernet systems do.
  • Ethernet MANs generally have high failover times

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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SONET versus Ethernet MANs

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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SONET versus Ethernet MANs

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Metro Ethernet

  • One of the latest forms of the metropolitan area network is metro Ethernet
  • Metro Ethernet is a service in which the provider creates a door-to-door Ethernet connection between two locations
  • For example, you may connect your business with a second business using a point-to-point Ethernet connection (Figure 9-4a)

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Metro Ethernet

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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Metro Ethernet

  • You may also connect your business with multiple businesses using a connection similar to a large local area network (Figure 9-4b)
  • Thus, by simply sending out one packet, multiple companies may receive the data
  • Neat thing about metro Ethernet is the way it seamlessly connects with a company’s internal Ethernet network(s)

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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Metro Ethernet

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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Wide Area Network Basics

  • WANs used to be characterized with slow, noisy lines.
  • Today WANs are very high speed with very low error rates.
  • WANs usually follow a mesh topology.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Wide Area Network Basics

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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Wide Area Network Basics

  • A station is a device that interfaces a user to a network.
  • A node is a device that allows one or more stations to access the physical network and is a transfer point for passing information through a network.
  • A node is often a computer, a router, or a telephone switch.
  • The sub-network or physical network is the underlying connection of nodes and telecommunication links.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Wide Area Network Basics

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Types of Network Structures

  • Circuit switched network - a sub-network in which a dedicated circuit is established between sender and receiver and all data passes over this circuit.
  • The telephone system is a common example.
  • The connection is dedicated until one party or another terminates the connection.
  • AT&T announced end of 2009 that they will begin phasing out their switched networks

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Types of Network Structures

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Types of Network Structures

  • Packet switched network - a network in which all data messages are transmitted using fixed-sized packages, called packets.
  • More efficient use of a telecommunications line since packets from multiple sources can share the medium.
  • One form of packet switched network is the datagram. With a datagram, each packet is on its own and may follow its own path.
  • Virtual circuit packet switched network create a logical path through the subnet and all packets from one connection follow this path.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Types of Network Structures

  • Broadcast network - a network typically found in local area networks but occasionally found in wide area networks.
  • A workstation transmits its data and all other workstations “connected” to the network hear the data. Only the workstation(s) with the proper address will accept the data.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Summary of Network Structures

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Connection-oriented versus Connectionless

  • The network structure is the underlying physical component of a network. What about the software or application that uses the network?
  • A network application can be either connection-oriented or connectionless.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Connection-oriented versus Connectionless

  • A connection-oriented application requires both sender and receiver to create a connection before any data is transferred.
  • Applications such as large file transfers and sensitive transactions such as banking and business are typically connection-oriented.
  • A connectionless application does not create a connection first but simply sends the data. Electronic mail is a common example.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Connection-oriented versus Connectionless

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Connection-oriented versus Connectionless

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Connection-oriented versus Connectionless

  • A connection-oriented application can operate over both a circuit switched network or a packet switched network.
  • A connectionless application can also operate over both a circuit switched network or a packet switched network but a packet switched network may be more efficient.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing

  • Each node in a WAN is a router that accepts an input packet, examines the destination address, and forwards the packet on to a particular telecommunications line.
  • How does a router decide which line to transmit on?
  • A router must select the one transmission line that will best provide a path to the destination and in an optimal manner.
  • Often many possible routes exist between sender and receiver.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing

  • The communications network with its nodes and telecommunication links is essentially a weighted network graph.
  • The edges, or telecommunication links, between nodes, have a cost associated with them.
  • The cost could be a delay cost, a queue size cost, a limiting speed, or simply a dollar amount for using that link.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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Routing

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing

  • The routing method, or algorithm, chosen to move packets through a network should be:
  • Optimal, so the least cost can be found
  • Fair, so all packets are treated equally
  • Robust, in case link or node failures occur and the network has to reroute traffic.
  • Not too robust so that the chosen paths do not oscillate too quickly between troubled spots.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Least Cost Routing Algorithm

  • Dijkstra’s least cost algorithm finds all possible paths between two locations.
  • By identifying all possible paths, it also identifies the least cost path.
  • The algorithm can be applied to determine the least cost path between any pair of nodes.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Least Cost Routing Algorithm

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Flooding Routing

  • When a packet arrives at a node, the node sends a copy of the packet out every link except the link the packet arrived on.
  • Traffic grows very quickly when every node floods the packet.
  • To limit uncontrolled growth, each packet has a hop count. Every time a packet hops, its hop count is incremented. When a packet’s hop count equals a global hop limit, the packet is discarded.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Flooding Routing

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Flooding Routing

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Centralized Routing

  • One routing table is kept at a “central” node.
  • Whenever a node needs a routing decision, the central node is consulted.
  • To survive central node failure, the routing table should be kept at a backup location.
  • The central node should be designed to support a high amount of traffic consisting of routing requests.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Centralized Routing

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Distributed Routing

  • Each node maintains its own routing table.
  • No central site holds a global table.
  • Somehow each node has to share information with other nodes so that the individual routing tables can be created.
  • Possible problem with individual routing tables holding inaccurate information.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Distributed Routing

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Adaptive Routing versus Static Routing

  • With adaptive routing, routing tables can change to reflect changes in the network
  • Static routing does not allow the routing tables to change.
  • Static routing is simpler but does not adapt to network congestion or failures.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing Examples - RIP

  • Routing Information Protocol (RIP) - First routing protocol used on the Internet.
  • A form of distance vector routing. It was adaptive and distributed
  • Each node kept its own table and exchanged routing information with its neighbors.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing Examples - RIP

  • Suppose that Router A has connections to four networks (123, 234, 345, and 789) and has the following current routing table:
  •  Network Hop Cost Next Router
  • 123 8 B
  • 234 5 C
  • 345 6 C
  • 789 10 D

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing Examples - RIP

  • Now suppose Router D sends out the following routing information (note that Router D did not send Next Router information, since each router will determine that information for itself): 
  • Network Hop Cost
  • 123 4
  • 345 5
  • 567 7
  • 789 10

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing Examples - RIP

  • Router A will look at each entry in Router D’s table and make the following decisions:
  • 1. Router D says Network 123 is 4 hops away (from Router D). Since Router D is 1 hop away from Router A, Network 123 is actually 5 hops away from Router A. That is better than the current entry of 8 hops in Router A’s table, so Router A will update the entry for Network 123.
  • 2. Router D says Network 345 is 5 hops away. Add one hop to get to Router D and Network 345 is 6 hops away. That is currently the same hop count as shown in Router A’s table for Network 345, so Router A will not update its table.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing Examples - RIP

  • Router A will look at each entry in Router D’s table and make the following decisions:
  • 3. Router D says Network 567 is 7 hops away. Add 1 hop to get to Router D, giving 8 hops. Since Router A has no information about Network 567, Router A will add this entry to its table. And since the information is coming from Router D, Router A’s Next Router entry for network 567 is set to D.
  • 4. Router D says Network 789 is 10 hops away. Add 1 hop to get to Router D. The value of 11 hops is worse than the value currently in Router A’s table. Since Router A currently has information from Router D, and Router D is now saying it takes more hops to get to Network 789, then Router A has to use this information.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing Examples - RIP

  • Router A’s updated routing table will thus look like the following: 
  • Network Hop Cost Next Router
  • 123 5 D
  • 234 5 C
  • 345 6 C
  • 567 8 D
  • 789 11 D

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Routing Examples - OSPF

  • Open Shortest Path First (OSPF) - Second routing protocol used on the Internet
  • A form of link state routing
  • It too was adaptive and distributed but more complicated than RIP and performed much better

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Network Congestion

  • When a network or a part of a network becomes so saturated with data packets that packet transfer is noticeably impeded, network congestion occurs.
  • What can cause network congestion? Node and link failures; high amounts of traffic; improper network planning.
  • When serious congestion occurs buffers overflow and packets are lost.

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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Network Congestion

  • What can we do to reduce or eliminate network congestion?
  • An application can observe its own traffic and notice if packets are disappearing. If so, there may be congestion. This is called implicit congestion control.
  • The network can inform its applications that congestion has occurred and the applications can take action. This is called explicit congestion control.

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Congestion Avoidance

  • Before making a connection, user requests how much bandwidth is needed, or if connection needs to be real-time
  • Network checks to see if it can satisfy user request
  • If user request can be satisfied, connection is established
  • If a user does not need a high bandwidth or real-time, a simpler, cheaper connection is created
  • This is often called connection admission control
  • Asynchronous transfer mode is a very good example of this (Chapter Eleven)

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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WANs In Action: The Smartphone

  • The network structure that support cell phones and smartphones is growing more complex every day
  • All phones within transmission distance of a cell tower are participating in a broadcast network

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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WANs In Action: The Smartphone

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

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WANs In Action: The Smartphone

  • Once your data/signal reaches the cell tower, the data becomes part of a packet-switched network within the telephone company
  • If the data moves from the telephone company into the Internet, then your data is passed from one packet switched network to another

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Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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Summary

  • A metropolitan area network is fast, fiber-based, has very small failover times, and is often dynamically provisional
  • Early MANs were SONET-based, but Ethernet-based MANs are becoming very popular
  • SONET-based MANs are rings, while Ethernet-based MANs are meshes
  • Metro Ethernet is a popular form of MAN

Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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Summary (continued)

  • Wide area networks cover states, countries, the world
  • User connects to a station and the station interfaces to a network node
  • A WAN cloud is based upon nodes (routers/switches) and high-speed links
  • WANs can be circuit-switched (fading away) or packet switched (datagram and virtual circuit)
  • RIP and OSPF are two routing protocols

Data Communications and Computer Networks: A Business User's Approach, Eighth Edition

© 2016. Cengage Learning. All Rights Reserved.

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