Transcript LAN Topology

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
• Bus LAN Practical Implementations
• Topology: The Ring LAN
• Ring LAN Practical Implementation
• Topology: The Star LAN
• Topology: Mixed Topologies
END OF Chapter
Introduction
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
Printer
Server
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
Advantages of Bus LAN
• 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
Disadvantages of a Bus LAN
• 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
Advantage of Using a Switch
WS2
Switch
WS1
LAN 1
(Collision Domain 1)
WS3
LAN 2
(Collision Domain 2)
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
END OF MODULE
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
Thin coaxial
cable
Terminator
Network
Interface
Card
A Typical Installation
BNC Jack
Thin Coaxial Cable
T Connector
Terminator
Expansion
Slots
Practical Implementation
Source: Black Box
END OF MODULE
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
A Practical Implementation
Source: Black Box
10Base5 Feeder Connection
10Base 5 Feeder Line
10Base2
Clusters
Source: Black Box
END OF MODULE
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
Ring LAN Advantages
• 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
– Gradual decline in performance with
increased load
• A good topology for larger LANs
– Used as a backbone in large enterprise
networks
Ring LAN Disadvantages
• 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
END OF MODULE
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)
Actual Implementation
Hardware
Source:
Black Box
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
An Actual 4 Mbps Token Ring
Implementation
Source: Black Box
An Actual 16 Mbps Token Ring
LAN Implementation
Source: Black Box
An Actual 4 Mbps Token Ring
Implementation
Source: Black Box
Web Research
• Visit
http://www.landfield.com/faqs/LANs/toke
n-ring-faq/ for additional information on
Token-Ring network
• Visit
http://www.networking.ibm.com/tra/trspe
c700.html#34L5201
• Visit www.ibm.com for further information
on Token-Ring products
END OF MODULE
MODULE
Topology: The Star LAN
Star Network
Server
Work
Station
Work
Station
Please note that this
is not a hub but a server.
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
Essential Features of the Physical
and Logical Star Topologies
• 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)
NIC
NIC
NIC
Workstation
Workstation
Workstation
An Actual Implementation of a
Ethernet StarLAN
Source: Black Box
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?
END OF MODULE
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 internetworking
• 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
Hub
Server
AUI
BNC
PC
PC
PC
PC
Star LAN
Server
Bus 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
A More Advanced Mixed
Topology
Bus Network Segment
Bus
Router
Bus
Ring
Backbone
Bus Network Segment
END OF MODULE
END OF MODULE
END OF MODULE
END OF CHAPTER