Topology and Access Methods

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Topology and Access Methods

• Chapter Six

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Simple LAN Topologies

• Physical topology
• Physical layout of a network

• Bus topology consists of a single cablecalled a
  bus connecting all nodes on a network without
  intervening connectivity devices

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Bus

• Linear Bus
• Simplest
• Most common for small networks
• Thinnet (Ethernet 10Base2)
• 10 Mbps
• CSMA/CD

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Communication

• Sender specifies destination address
• Break data into packets
• Place packets onto cable
• Only destination accepts data

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Bus Topology

• Advantages
• Simple and reliable
• Cabling inexpensive
• Less cable

• Disadvantages
• Heavy traffic slows down network
• Cable break brings down network
• Problems difficult to find
• Time divide amongst computers
• Only one can send at a time

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Simple LAN Topologies

• Terminators stop signals after they have reached
  their destination
• Signal bounce
• Phenomenon in which signals travel endlessly
  between the two ends of a bus network

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Cable Problems

• Cable Failure
• Break in cable
• Leads to signal bounce
• Signal Attenuation

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Passive vs. Active Topology

• Passive
• Computer only listen for data
• Active
• Computers regenerate and move signal

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Simple LAN Topologies

• Ring topology
• Each node is connected to the two nearest nodes
  so the entire network forms a circle
• Active topology
• Each workstation transmits data
• Each workstation functions as a repeater

Typical ring network
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Ring Topology

• Connect in a circle
• Read or regenerate data
• Very fast
• Token traverses 200m 10,000 times a second

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Token Passing Scheme

• Tokens travels around ring
• Sender add receiver address and data
• Receiver sends message back to sender
• Sender Puts token back on ring

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Typical Ring Network

• IEEE 802.5
• 4 to 16 Mbps or 100Mbps
• UTP or STP
• Needs a hub creates ring in hub
• Physical Star/Logical Ring

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Typical Ring Topology

• Fiber Distributed Data Interface (FDDI)
• 100Mbps
• 500 nodes
• 60 miles
• 2 Physical Ring/Logical Ring

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Ring Topology

• Advantages
• Equal access by all computers
• Many users network performance still good

• Disadvantages
• Single computer failure network down
• Difficult to find problems
• Adding or removing computers disrupts network

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Simple LAN Topologies

• Star topology
• Every node on the network is connected through a
  central device

Typical star topology network
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Active Hub - Repeaters

• Strengthen the signal
• Regenerates signal

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Hubs

• Logical center of an Ethernet LAN
• Collect all of the cables together
• Active Hub acts as a repeater

• 10/100 - 74.00 470.00

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Star Topology

• Requires a central hub
• More wiring
• Central point of failure
• One cable break does not bring down network

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Typical Star Network

• IEEE 802.3 10Base T, 100Base T, 1000Base T
• 10 Mbps, 100 Mbps, 1Gbps
• Physical star
• Logical bus
• RJ45 connectors to UTP

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Hubs

• Active Hubs
• Regenerate signal when signal is received
• Needs power
• Passive Hubs
• Central connection point
• Wiring Panel
• Punch down block

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Star Topology

• Advantages
• Easy to add new computers
• Network can be monitored and problems found
• Single computer failure does not bring down
  network

• Disadvantages
• Central hub fails, network down
• More cable, more expensive

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Hybrid LAN Topologies

• Hybrid topology
• Complex combination of the simple physical
  topologies
• Star-wired ring
• Star-wired topologies use physical layout of a
  star in conjunction with token ring-passing data
  transmission method

Star-wired ring topology network
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Hybrid LAN Topologies

• Star-wired bus
• In a star-wired bus topology, groups of
  workstations are star-connected to hubs and then
  networked via a single bus

Star-wired bus network topology
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Hybrid LAN Topologies

• Hierarchical
• Uses layers to separate devices by their priority
  or function
• Old PBCC

Hierarchical ring topology
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Enterprise-Wide Topologies

• Enterprise
• An entire organization
• Backbone networks
• Serial backbone
• Distributed backbone
• Collapsed backbone
• Parallel backbone

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Serial Backbone

• Serial backbone
• Two or more hubs connected to each other by a
  single cable
• Daisy-Chained
• Daisy chain is linked series of devices

Daisy-chained star-wired bus topology
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Distributed backbone

• A number of hubs connected to a series of central
  hubs, switches, or routers in a hierarchy

Simple distributed backbone network
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Enterprise-wide Topologies
Distributed backbone connecting multiple LANs
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Routers

• Subdivide network using logical address
• Best Path
• Dynamic Routing
• Distance-vector algorithm number of hobs
• Link-state algorithm network traffic,
  connection speed, other costs
• Works only with routable protocols
• Slower than bridges or repeaters
• Does not retransmit broadcast traffic

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Routers

• Each port has its own unique IP address.

• 10/100
• 1,100.00 2,400.00

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Really Big Routers

• Mega Gitabits
• Cisco 12016 Gigabit Switch Router (GBS)
• 10 Gbps

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Collapsed backbone

• Uses a router or switch as the single central
  connection point for multiple sub-networks

Collapsed backbone network
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Parallel Backbone

• This variation on collapsed backbone arrangement
  consists of more than one connection from the
  central router or switch to each network segment

Parallel backbone network
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Enterprise-wide Topologies

• Mesh networks
• Routers are interconnected with other routers
  with at least two pathways connecting each router

Example of a mesh network
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Mesh Topology

• Ever computer is connected to every other
  computer
• Fault tolerant
• Expensive