CHAPTER LAN Topology

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# CHAPTER LAN Topology - PowerPoint PPT Presentation

CHAPTER LAN Topology. Chapter Objectives. Describe the characteristics of different LAN topologies Bus, ring, star and mixed topologies Compare and contrast the topologies with one another with respect to their relative advantages and disadvantages. Chapter Modules. Topology: The Bus LAN

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Presentation Transcript
Chapter Objectives
• Describe the characteristics of different LAN topologies
• Bus, ring, star and mixed topologies
• Compare and contrast the topologies with one another with respect to their relative advantages and disadvantages
Chapter Modules
• Topology: The Bus LAN
• Bus LAN Practical Implementations
• Topology: The Ring LAN
• Ring LAN Practical Implementation
• Topology: The Star LAN
• Topology: Mixed Topologies

### MODULE

The Bus Topology

Questions
• What are physical and logical topologies?
• What is a collision domain?
• How can the bus network be implemented in practice?
• How is it frequently implemented in practice?
• How could collisions be reduced?
• Is it possible to reduce the danger of a cable breakdown? Explain.
Bus Network

Server

Printer

Peripheral Device

Single Data Bus

Workstation

Workstation

Bus LAN Transmission Logic
• Listen to the bus for traffic
• If no traffic is detected, then transmit
• Otherwise, if the bus is busy with traffic, wait for a random period of time before attempting to transmit again
• Repeated attempts will be made until the bus is found free
Collision of Data
• Two workstations may find the bus free at the same time
• Both would transmit at the same time
• Collision of data occurs
• Both workstations will now wait for a random period of time before attempting to transmit again
• Cabling is simple and easy to install in a local setup
• Based on well established standards
• IEEE 802.3
• Also known as the Ethernet standard
• Sharing of a single data bus
• When the traffic increases the performance deteriorates
• Waiting period may reach unacceptable lengths of time under heavy data traffic
• Cable fault results in the entire LAN becoming inoperative
Solution
• Collision domains are present only when a hub used
• Using switches will eliminate the collision domains

WS2

Switch

WS3

WS1

LAN 2

(Collision Domain 2)

LAN 1

(Collision Domain 1)

Occasional Crossover Traffic

Practical Consideration
• All popular logical bus networks currently implemented using switches
In Summary
• The use of switches in a . network reduces network traffic congestion
• Increases the utilization of the bus network

### MODULE

Bus LAN Practical Implementation: 10Base2

Logical and Physical Topology
• Logical topology
• Logical functioning of a network
• Physical topology
• Physical configuration of a network
• Example:
• For ease of implementation, a logical bus network may be physically configured as a star network
Major Bus Implementation Architectures
• 10Base2
• 10Base5
• 10BaseT
• 100BaseTX
• 1000BaseT
• Although this represents a logical bus topology, it is implemented physically in the form of a star topology
Topologies
• 10Base2 and 10Base5
• Logical bus and Physical bus
• 10BaseT
• Logical bus and Physical star
• 100BaseTx
• Logical bus and physical star
• Fast Ethernet LAN
10Base2
• 10 Mbps LAN
• Based on a well established standard
• Ethernet 802.3 standard
• Configured using thin coaxial cables
• Sometimes called the 10Base2 cables
• Very popular in the past
• In recent times, the popularity has declined
• Due to emergence of fast Ethernet
• Due to the popularity of 100BaseTX
Components for Building a 10Base2 Network

T connector

Network

Interface

Card

Thin coaxial

cable

Terminator

A Typical Installation

BNC Jack

Thin Coaxial Cable

T Connector

Terminator

Expansion

Slots

Practical Implementation

Source: Black Box

### MODULE

Bus LAN Practical Implementation: 10Base5

10Base5
• 10 Mbps
• It is also based on a popular standard known as the Ethernet 802.3 standard
• Thick coaxial cables are used for configuring the network in this case
• The cables are less maneuverable
• In practice, the 10Base5 network is often used as a feeder connection to 10Base2 and/or other types of networks
A Simple Implementation

Vampire Clamp

Thick Coax (10Base5)

Transceiver

Transceiver

15-pin AUI

Connector

Client

Server

10Base5 Feeder Connection

10Base 5 Feeder Line

10Base2

Clusters

Source: Black Box

### MODULE

Topology: The Ring LAN

Questions
• Is there a collision domain in this case?
• How is a ring network implemented in practice?
• Is the ring network technologically superior to the bus network?
• Is a ring or bus LAN used widely in practice?
• Explain
Ring LAN

Peripheral

Device

Printer

Server

WS

WS

WS

Ring LAN : Practical Implementation

Multi-Access Unit (MAU) Or Hub

Server

WS

Physical Star/ Logical Ring

Practical Implementation Considerations of a Ring Network
• Based on a central hub
• Multi-Access Unit (MAU)
• Multi-Station Access Unit (MSAU)
• Logical ring
• Wiring inside the hub
• Physical star
• Resembles in appearance only
• Ring bypass
• Bypass the Non-functioning workstation
Ring LAN

Token

Server

WS

WS

WS

Token carries and delivers the information in the network.

Characteristics of the Ring Transmission Logic
• Data path
• A ring that connects the workstations and the servers
• Transmission logic
• Based on a token that circulates around the ring
• The token carries the data
• Protocol
• The popular IEEE 802.5 standard
• Orderly transmission of data
• Guarantees an opportunity for each workstation to transmit
• Performance deterioration is not as critical as in the case of the bus LAN
• Data traffic congestion is minimized
• A good topology for larger LANs
• Used as a backbone in large enterprise networks
• Difficult to implement the network as a ring
• This drawback is overcome by physically implementing the network in the form of a star
• Relatively higher cost of configuring the ring LAN
Current Status of the Ring LAN
• First introduced to overcome the speed limitation of the older bus networks
• 16 Mbps ring LANs as opposed to the 10 Mbps bus LANs
• Recent advancement in bus LANs in the 100 Mbps speed range
• Resulted in the decline in the popularity of the ring LANs
• However, 100 Mbps Token-Ring products are now available
Questions
• Is there a collision domain in this case?
• How is a ring network implemented in practice?
• Is the ring network technologically superior to the bus network?
• Is a ring or bus LAN used widely in practice?
• Explain

### MODULE

Ring LAN Practical Implementation

Practical Ring LAN Characteristics
• The practical implementation is based on the IEEE 802.5 standard
• The newer Ring LANs operate at a speed of 100 mbps
• Many current Ring LANs operate at 16 Mbps
• The older ring LANs operate at 4 Mbps
• As a hub-based LAN, it is easy to implement and manage
Hardware Required to Implement a Basic Token Ring LAN
• Token-ring NIC
• Cable
• IBM Type 1 or 2 or 3
• UTP as needed by the design
• Multi-station Access Unit (MAU)
• Multi-station Access Unit (MSAU)
• Smart Multi-station Access Unit (SMAU)
A Typical Token Ring LAN Configuration

Special IBM

Connectors

Multi-Station

Access Unit

IBM Type 1

Twisted Pair

9-Pin AUI

Connectors

Client

Client

Server

Web Research
• Visit http://www.landfield.com/faqs/LANs/token-ring-faq/ for additional information on Token-Ring network
• Visit http://www.networking.ibm.com/tra/trspec700.html#34L5201
• Visit www.ibm.com for further information on Token-Ring products

### MODULE

Topology: The Star LAN

Star Network

Server

is not a hub but a server.

Work

Station

Work

Station

Work

Station

Polling: The Functioning of the Logical Star Network
• The server polls each workstation in turn inquiring whether a workstation has information to transmit
• If a workstation has information to transmit:
• the server will obtain the information and deliver it to the intended destination
• Each workstation is given a chance to transmit
Practical Implications of Polling
• Polling works well in the case of a LAN with a single server
• Becomes complicated when there are multiple servers
• Majority of networks are not based on the logical star topology
• They are based on the physical star topology
• Best suited for practical implementation
• Almost all star LANs found in practice conform to the physical star topology
• Many of them operate based on a logical bus topology or a logical ring topology as seen earlier
• Reason for choosing a physical star topology for implementation
• Ease with which a LAN can be built around hubs and managed
Popular Physical Star Implementations
• 10BaseT
• 10 Mbps, Ethernet network
• Uses a hub and twisted pair wires
• 100BaseTx
• 100 Mbps, Fast Ethernet network
• Hubs and twisted pair wires are used
• Higher quality twisted pair wires are used
• Category 5
• 1000BaseT
• 1 Gbps Ethernet
• Switches and twisted pair wire are used
• Higher quality wires are needed such as Cat 5e and above
Actual Implementation Hardware

Network

Cards

Cables

Hub

Source: Black Box

A Typical Star Ethernet LAN Configuration

RJ 45 Connection

Hub

Twisted Pair Wire (10baseT)

Workstation

NIC

NIC

Workstation

NIC

Workstation

NIC

Questions?
• Give the name of one or more networks that could be classified as:
• a logical bus and a physical bus network?
• a logical bus and a physical star network?
• a logical ring and a physical star network?
• a logical star and a physical star network?

### MODULE

Topology: Mixed Topologies

Reason for the Mixed Topology
• Mixed topologies are found in many organizations
• A very large LAN is composed of small LAN segments
• Each segment may be based on a different topology
A Large Mixed Topology Network

Bus LAN

Mainframe

Systems

Ring Backbone

Star

LAN

Ring

LAN

Characteristics of Mixed Topologies
• Mixed topologies result from inter-networking
• Mixed topologies can include network segments of different protocols or of the same protocol
• Interfacing devices
• Hubs, switches, bridges, routers and gateways
A Simple Mixed Topology LAN

Transceiver

Server

Hub

AUI

BNC

PC

PC

PC

PC

Server

Bus LAN

Star LAN

A Simple Mixed Topology LAN Characteristics
• Topologies connected together
• Star and Bus
• Protocol
• Both operate under the Ethernet protocol
• Transceiver
• Interconnects star and bus LANs

Bus Network Segment

Router

Bus

Bus

Bus Network Segment

Ring

Backbone