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LAN Topologies and Standards
Networks and Protocols
Prepared by: TGK First Prepared on: Last Modified on:
Quality checked by: Copyright 2009 Asia Pacific Institute of Information Technology
Networks and Protocols
LAN Topologies and Standards
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Topic & Structure of the lesson
LAN Topologies (Bus, Star, Ring, Mesh, and Tree)Characteristics of TopologiesLAN Standards (IEEE 802.x Series)
Networks and Protocols
LAN Topologies and Standards
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Learning Outcomes
At the end of this module, YOU should be able to:
• Explain the WAN technologies – Cellular Network, Satellite Network, and Wireless Network
Networks and Protocols
LAN Topologies and Standards
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Key Terms you must be able to use
If you have mastered this topic, you should be able to use the following terms correctly in your assignments and exams:
• Bus Topology• Star Topology• Ring Topology• Mesh Topology • Tree Topology• Characteristics of Topologies• LAN Standards
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LAN Topologies and Standards
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Main Teaching Points
• Communication pattern
• Expansion of networks
• Physical outlook of networks
• Logical operations of networks
• Network components and connectivity
• Medium access control and techniques
• IEEE 802 standards committee and working groups
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LAN Topologies and Standards
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Bus Topology
• Connected in a row along a single cable, trunk, backbone or segment
• Communication on a bus
• Sending the signal
• Signal propagates along cable(s)
• A terminator absorbs the signal at the end
• Only one computer can access wire at any one time
• The more PC’s attached, more traffic generated
• Bus is a PASSIVE topology
• PC only listens for traffic
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LAN Topologies and Standards
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• Signal bounce occurs if ends of bus not terminated
• Terminators attached to each end. Every cable end
must be attached to something
• Generally a 50 Ohm resistor is used as terminator
• LAN expansion - bus topology
• Barrel connector
• Repeater - boosts signal (regenerate/amplify)
Bus Topology
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Bus Topology
• Data sent to all computers, but only destination accepts
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Bus Topology
• Terminators absorb ‘free’ signals
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Bus Topology
• Unplugged cable not terminated will take down the
network
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Bus Topology
• Connectors can be used to combine cable segments
• Connectors can be used to combine cable segments
Weakened signal
Regenerated signal
Repeater
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Bus Topology
• CSMA/CD (Contention Method) - Carrier Sense Multiple
Access /Collision Detection:
• also called listen-before talk
• used with bus topology
• part of Ethernet standard 802.3
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LAN Topologies and Standards
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Star Topology
• Each segment attached to centralized component, called
a Hub
• If the hub fails, the network goes down
• The hub is the central connector; not the central
controller
• Simple Star topology:
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Star Topology
• Hub is the central point in a Star topology
Hub
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Ring Topology
• Signal travels around a ring
• Travels in one direction
• Signal boosted (regenerated) by each computer as signal
passes through (computer acts as repeater)
• Generally uses Token Passing
• Simple ring network showing logical ring:
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LAN Topologies and Standards
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Ring Topology
• A computer grabs the token and passes it around the
ring:
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Data
Data
• IEEE 802.5 standard for ring access protocol allows priority
levels to be set for tokens and messages. (Problem - one
station with high priority messages can monopolize network)
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LAN Topologies and Standards
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Ring Topology
• FDDI - standard for high speed ring LAN, using optic
fiber.
• Also uses token passing protocol. Some differences to
maximize efficiency
• Multiple tokens can be circulated because station
transmits free token immediately after transmits
message
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LAN Topologies and Standards
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Mesh Topology
• The advantages of a mesh topology is that the two nodes
are using the entire capacity of the link exclusively
• In terms of robustness, a mesh topology network can
withstand the destruction of anyone of its components
without incapacitating the entire network
• Due to its nature, the mesh network physically prevents
any intrusion on the information sent
• Total number links required:- n(n-1)/2
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LAN Topologies and Standards
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Mesh Topology
• Due to its nature, the mesh network physically prevents
any intrusion on the information sent
• Total number links required:- n(n-1)/2
• To connect all its nodes together, a mesh topology
would require n(n-1)/2 wires, or channels
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Mesh Topology
• This number increases exponentially when new nodes
are added to the network
• Each node itself would, then, be equipped with n-1 I/O
ports to connect itself to the network
• The disadvantage of the mesh topology is, simply, the
amount of cabling itself
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LAN Topologies and Standards
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Tree Topology
• Addition of new networks to a bus topology would be
hard
• A tree topology, however, is an extension of the bus
• In a tree, the trunk is usually a high capacity device or
connection which facilitates data transmission amongst
the branches
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LAN Topologies and Standards
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Tree Topology
• The advantage of a tree topology is usually that the
privacy of transmissions are isolated in a particular
branch
• Also, if a particular branch is incapacitated, the trunk and
the other branches may still function
• The disadvantage is naturally the fault isolation
• Should a transmission fails to be sent, a fault detection
exercise may have to cover the entire distance of the
cabling
• The trunk of the tree must also be properly configured to
be robust
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LAN Topologies and Standards
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The physical topology of a network is the layout or actual
appearance of the cabling scheme used on a network
The logical topology of a network describes how the data
flows through the physical topology
Point-to-point (PTP) topology connects two nodes
directly together - Mesh
Multipoint topologies link three or more devices
together through a single communication - Star, Bus,
Ring, Hybrid
Characteristics of Topologies
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LAN Topologies and Standards
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LAN Standards
• The IEEE 802 Committee
• IEEE has multiple standards committees
• LAN standards are set by the IEEE 802 Standards
Committee
• Working Groups of the 802 Standards Committee create
individual standards
• 802.3 for Ethernet Standards
• 802.5 for Token-Ring LAN Standards
• 802.11 for Radio and Infrared Wireless LANs
• Are there others not listed above?...
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LAN Standards
• Project 802 produced recommendations covering:
• Topology, speed, and data link protocol (Bus, Ring,
CSMA/CD, Token passing)
• Medium - coax, twisted pair, fiber optic cable
• Addressing: (Local access 16 bit address, Unique
International 48 bit)
• The following diagram illustrates where the IEEE 802.
standards relates to the ISO - Open Systems
Interconnect(OSI) model:
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PHYSICALMEDIA
CSMA/CD
BUS TOPOLOGY RING TOPOLOGY
TOKEN BUS
BASEBAND/BROADBANDCOAX,
UNSHIELDEDTWISTED PAIR
BROADBAND COAX
OPTIC FIBRE
TOKEN RING TOKEN RING
SHIELDEDTWISTED PAIR
OPTIC FIBRE
802.3 802.4 802.5 FDDI (ANSI)
LAN Standards
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Quick Review Question
1. Describe the advantages and disadvantages of the various LAN topologies highlighted.
2. Discuss the importance of the IEEE 802 standards committee towards the networks used today and which do you think is important for the near future.
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Follow Up Assignment
Carry out a research on which LAN topology is most commonly used in LANs today and subsequently, discuss the relationship between the topology you have identified with the efforts of the IEEE 802 standards committee if applicable. Should the chosen topology be of a proprietary standard, you have to discuss the origins of it and the functionality/operations.
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LAN Topologies and Standards
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Q & A
Question and Answer Session