Transcript LAN Topologies and Standards

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