Wide Area Networks

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Wide Area Networks

• Presented by
• Heather Harrison
• Crystal Crow
• Jennifer Miller
• Jennifer Robertson

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Chapter 13 Overview

• WAN terminology and topology
• Functions of the data link layer
• WAN data link protocols
• Functions of the network layer
• Network routing
• Differences

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WAN Terminology

• Link
• End-to-end routing
• Path
• Hop
• Store-and-forward
• Session
• Packet switching

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WAN Network Topologies

• Primary Network Topologies
• Ring
• Bus
• Star
• Bus with spurs

• Other ways
• Hierarchical
• Interconnected
• Combination of both

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Hierarchical Network

• Also known as a tree structure, it contains one
  root node. Several nodes at the secondary level
  are connected to the root. Each of these nodes
  can have a number of cascaded nodes attached.
  This type of network closely resembles corporate
  organizational charts, as shown in the diagram on
  the next slide.

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• The network generally mirrors the information
  flow pattern in the corporation. Information
  flowing from a district in one division to a
  district in a different division would need to go
  through the root node. This topology allows for
  a great deal of network control.

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Interconnected (Plex) Network

• This topology provides a high degree of
  flexibility because many paths are available.
  Meaning less congestion.
• The performance of an interconnected system is
  generally quite good because of direct linkage
  with large amounts of data being passed between
  nodes.
• This method is also cost effective because the
  topology is capable of the shortest, least
  expensive configuration.

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Combination Networks

• Two different topologies combined into one can
  sometimes be called a Backbone Network.
• The backbone nodes are dedicated to message
  transfer and data communication, while other
  nodes are dedicated to data processing and data
  communication.
• In a widely distributed system this is
  advantageous, because of the reduction of number
  of hops, length of the path, and congestion
  problems.

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Combination Networks Contd

• Backbone networks are appearing more often in LAN
  technology, as well, the fiber data distributed
  interface (FDDI) LAN operates at 100 Mbps, can
  span up to 125 miles, and uses a token-ring
  passing ring architecture.

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WAN Data Link Control Protocols

• Two Primary Methods in a LAN
• Token passing
• Carrier Sense with multiple access and collision
  detection (CSMA/CD)
• Two Primary Methods in a WAN
• Synchronous
• Asynchronous

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Bit Synchronous Protocols

• Synchronous data link control (SDLC) from IBM in
  1972 (first one)
• Advanced data communications control procedure
  (ADCCP) an ANSI standard data link protocol
  (often pronounced addcap)
• High level data link control (HDLC), a standard
  of the International Standards Organization (ISO)
• Link Access Procedure balanced (LAPB),
  designated as the data link protocol for X.25
  packet distribution networks.

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The HDLC Frame

• The basic unit of transmission in the HDLC is the
  frame.

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Number Sent and Number Received

• The control field contains two 3 bit fields know
  as the number sent and number received
  sub-fields.
• The Nr field is used to acknowledge receipts of
  messages.
• The Ns and Nr fields can both be 7 bits long.

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WAN Network Layer Function

• The OSI network layer performs three major
  functions
• Routing
• Network control
• Congestion control
• These function are the same on both LANs and
  WANs.

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Message Routing In A WAN

• Message routing is one of the functions of the
  network layer on both LAN and WAN systems.
• WANs are much slower than a LAN.
• WANs use different message routing methods than
  do LANs.

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Centralized Routing Determination

• In centralized routing one node is designated as
  the network routing manager.
• Disadvantages
• Congestion
• Large amount of CPU is required.

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Distributed Routing Determination

• Static routing
• Weighted routing
• Adaptive routing
• Broadcast routing

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Static Routing

• The purest form of static routing involves always
  using one particular path between two nodes if a
  link in that path is down, then communication
  between those nodes is impossible.

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Weighted Routing

• When multiple paths exist, some implementations
  use weighted routing, in which each path is
  weighted according to perceived use.

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Adaptive Routing

• Adaptive routing, occasionally called dynamic
  routing, attempts to select the quickest or best
  current route for the message or session.
• Not very efficient and can cause messages to be
  shuffled to more nodes than necessary, thereby
  adding to network congestion.
• Biggest advantage simplicity

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Broadcast Routing

• Quickest and Best
• The message is broadcast to all stations and only
  the station to which the message is addressed
  accepts it.

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Packet Distribution Networks

• Introduced in 1964 by Paul Baran of the Rand
  Corp.
• A PDN is a packet-switching WAN variously called
  an X.25 network, a value-added network (VAN), or
  a public data network.

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PDN Disadvantages

• Users must compete each other for circuits
• Message traffic interferes with delivery
• Large numbers of data packets can be expensive
• Inability to make changes to applications

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X.25 vs. Frame Relay

• X.25 is a product of 1970s
• Limits transmission speed to 64 Kbps
• Not suited for voice or video
• Frame Relay supports speeds up to 2 Mbps and has
  congestion control capabilities

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Comparing WANS LANS

• Distance is the primary difference
• Other features are
• Topology
• Data link protocol
• Routing algorithm, media, ownership, and
  transmission speed

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Topology, Protocols, and Routing

• LANs are typically bus, ring, or star topologies,
  or a combination. WANs are typically
  hierarchical or interconnected
• LAN protocols are usually CSMA/CD or token
  passing. WAN protocols are bit synchronous such
  as HDLC
• LAN routing is broadcast. WAN routing varies
  with conditions

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Media and Ownership

• LAN media is usually a single medium type, WAN
  media is often a variety
• LANs are almost always privately controlled. WAN
  equipment is owned by user

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Interconnection

• Differences in transmission speed, protocols,
  media, and data codes must be reconciled for
  interconnection

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Heathers Question

• What are a couple of advantages of hierarchical
  network topologies?

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Jennifer Robertsons Question

• What are the disadvantages of a Centralized
  Routing Determination?

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Jennifer Millers Question

• List the FOUR primary ways messages are routed

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Crystal Crows Question

• What are the factors that differ between LANs and
  WANs aside from distance?