Chapter Network Topologies and Related Protocols © Nanda Ganesan, Ph.D.

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 Workstation Server Peripheral Device Printer Single Data Bus

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 –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 WS1 WS3 Switch LAN 1 (Collision Domain 1) 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

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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 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 Thin coaxial cable T connector Terminator Network Interface Card

A Typical Installation Expansion Slots T Connector Thin Coaxial Cable Terminator BNC Jack

Practical Implementation Source: Black Box

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MODULE Bus LAN Practical Implementation: 10Base5

10Base5 10 Mbps It is also based on a popular standard known as the Ethernet 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 Transceiver ClientServer Vampire Clamp 15-pin AUI Connector Thick Coax (10Base5)

A Practical Implementation Source: Black Box

10Base5 Feeder Connection 10Base 5 Feeder Line Source: Black Box 10Base2 Clusters

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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 Server WS Printer Peripheral Device

Ring LAN : Practical Implementation Multi-Access Unit (MAU) Or Hub Physical Star/ Logical Ring ServerWS

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 Server WS Token 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 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 available100 Mbps Token-Ring

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 star LAN used widely in practice? –Explain

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MODULE Ring LAN Practical Implementation

Practical Ring LAN Characteristics The practical implementation is based on the IEEE 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 Multi-Station Access Unit Client Server IBM Type 1 Twisted Pair 9-Pin AUI Connectors Special IBM Connectors

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 ring-faq/ for additional information on Token- Ring network ring-faq/ Visit html#34L html#34L5201 Visit for further information on Token-Ring productswww.ibm.com

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MODULE Topology: The Star LAN

Star Network Server Work Station Work Station Work Station Please note that this is not a hub but a server.

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 BaseT –1 Gbps Ethernet –Switches and twisted pair wire are used –Higher quality wires are needed such as Cat 5e and above

Actual Implementation Hardware Hub Cables Network Cards Source: Black Box

A Typical Star Ethernet LAN Configuration Workstation NIC Hub RJ 45 Connection Twisted Pair Wire (10baseT)

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?

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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 Mainframe Systems Ring Backbone Bus LAN Ring LAN Star 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 Hub PC Server PC Transceiver Star LAN Bus LAN BNC AUI

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 Router Ring Backbone Bus Bus Network Segment

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