Chapter Five Physical and Logical Topologies. Objectives Describe the basic and hybrid LAN physical...

Chapter FiveChapter FivePhysical and Logical Physical and Logical

TopologiesTopologies

ObjectivesObjectives

Describe the basic and hybrid LAN physical Describe the basic and hybrid LAN physical topologies, their uses, advantages, and topologies, their uses, advantages, and disadvantagesdisadvantagesDescribe a variety of enterprise-wide and Describe a variety of enterprise-wide and WAN physical topologies, their uses, WAN physical topologies, their uses, advantages, and disadvantagesadvantages, and disadvantagesCompare the different types of switching used Compare the different types of switching used in data transmissionin data transmissionUnderstand the transmission methods, or Understand the transmission methods, or logical topologies, underlying Ethernet, Token logical topologies, underlying Ethernet, Token Ring, LocalTalk, and FDDI networksRing, LocalTalk, and FDDI networks

Simple Physical TopologiesSimple Physical Topologies

Physical topologyPhysical topology Physical layout of a networkPhysical layout of a network

A A Bus topologyBus topology consists of a single cable—called consists of a single cable—called a a busbus— connecting all nodes on a network without — connecting all nodes on a network without intervening connectivity devicesintervening connectivity devices

Figure 5-1: Bus topology

network


Figure 5-2: A terminated bus network


Ring topologyRing topology Each node is connected to the two nearest nodes so the entire Each node is connected to the two nearest nodes so the entire

network forms a circlenetwork forms a circle One method for passing data on ring networks is One method for passing data on ring networks is token passingtoken passing

Active topologyActive topology Each workstation transmits dataEach workstation transmits data

Figure 5-3: A typical

ring network


Star topologyStar topology Every node on the network is connected through Every node on the network is connected through

a central devicea central device

Figure 5-4: A typical

star topology network

Hybrid Physical TopologiesHybrid Physical Topologies

Hybrid topologyHybrid topology Complex combination of the simple physical topologiesComplex combination of the simple physical topologies

Star-wired ringStar-wired ring Star-wired topologiesStar-wired topologies use physical layout of a star in use physical layout of a star in

conjunction with token ring-passing data transmission conjunction with token ring-passing data transmission methodmethod

Figure 5-5: A star-

wired ring topology network


Star-wired busStar-wired bus In a In a star-wired bus topologystar-wired bus topology, groups of workstations are , groups of workstations are

star-connected to hubs and then networked via a single busstar-connected to hubs and then networked via a single bus

Figure 5-6: A star-wired bus network topology


Daisy-ChainedDaisy-Chained A A Daisy chainDaisy chain is linked series of devices is linked series of devices

Figure 5-7: A daisy-chained

star-wired bus

topology


Hierarchical hybrid topologyHierarchical hybrid topology Uses layers to separate devices by priority or functionUses layers to separate devices by priority or function

Figure 5-8: A hierarchical ring topology

Enterprise-Wide TopologiesEnterprise-Wide Topologies

EnterpriseEnterprise An entire organizationAn entire organization

Backbone networksBackbone networks Serial backboneSerial backbone Distributed backboneDistributed backbone Collapsed backboneCollapsed backbone Parallel backboneParallel backbone


Serial backboneSerial backbone Two or more hubs connected to each other by a single cableTwo or more hubs connected to each other by a single cable

Distributed backboneDistributed backbone Hubs connected to a series of central hubs or routers in a hierarchyHubs connected to a series of central hubs or routers in a hierarchy

Figure 5-9: A simple

distributed backbone network


Figure 5-10: A distributed backbone connecting multiple LANs


Collapsed backboneCollapsed backbone Uses a router or switch as the single central Uses a router or switch as the single central

connection point for multiple subnetworksconnection point for multiple subnetworks

Figure 5-11: A

collapsed backbone network


Parallel BackboneParallel Backbone Collapsed backbone arrangement that consists of more than one Collapsed backbone arrangement that consists of more than one

connection from central router or switch to each network segmentconnection from central router or switch to each network segment

Figure 5-12: A

parallel backbone network


Mesh networksMesh networks Routers are interconnected with other routers, with at least two Routers are interconnected with other routers, with at least two

pathways connecting each routerpathways connecting each router

Figure 5-13: An example of

a mesh network

Wide Area Network (WAN) Wide Area Network (WAN) TopologiesTopologies

Peer-to-peer topologyPeer-to-peer topology WAN with single interconnection points for each locationWAN with single interconnection points for each location Dedicated circuitsDedicated circuits

Continuous physical or logical connections between two access Continuous physical or logical connections between two access points that are leased from a communication providerpoints that are leased from a communication provider

Figure 5-14: A peer-to-peer

WAN


Ring WAN topologyRing WAN topology Each site is connected to two other sites so that entire Each site is connected to two other sites so that entire

WAN forms a ring patternWAN forms a ring pattern

Figure 5-15: A ring-configured WAN


Star WAN topologyStar WAN topology Single site acts as the central connection point for several Single site acts as the central connection point for several

other pointsother points

Figure 5-16: A star-

configured WAN


Mesh WAN topologyMesh WAN topology Many directly interconnected locations forming a complex meshMany directly interconnected locations forming a complex mesh

Figure 5-17: Full-mesh and partial-mesh WANs


Tiered WAN topologyTiered WAN topology Sites connected in star or ring formations are interconnected at Sites connected in star or ring formations are interconnected at

different levels, with interconnection points organized into layersdifferent levels, with interconnection points organized into layers

Figure 5-18: A tiered WAN topology

Logical TopologiesLogical Topologies

Refers to the way in which data are Refers to the way in which data are transmitted between nodestransmitted between nodes

Describes the way:Describes the way: Data are packaged in framesData are packaged in frames Electrical pulses are sent over network’s physical Electrical pulses are sent over network’s physical

mediamedia

Logical topology may also be called Logical topology may also be called network network transport systemtransport system

SwitchingSwitching

Component of network’s logical topology that Component of network’s logical topology that determines how connections are created determines how connections are created between nodesbetween nodes Circuit switchingCircuit switching

Connection is established between two network nodes Connection is established between two network nodes before they begin transmitting databefore they begin transmitting data

Message switchingMessage switchingEstablishes connection between two devices, transfers Establishes connection between two devices, transfers information to second device, and then breaks connectioninformation to second device, and then breaks connection

Packet switchingPacket switchingBreaks data into packets before they are transmittedBreaks data into packets before they are transmitted

EthernetEthernet

Carrier Sense Multiple Access with Collision Carrier Sense Multiple Access with Collision Detection (CSMA/CD)Detection (CSMA/CD) The The access methodaccess method used in Ethernet used in Ethernet CollisionCollision

In Ethernet networks, the interference of one network node’s In Ethernet networks, the interference of one network node’s data transmission with another network node’s data data transmission with another network node’s data transmissiontransmission

JammingJammingPart of CSMA/CD in which, upon detection of collision, Part of CSMA/CD in which, upon detection of collision, station issues special 32-bit sequence to indicate to all nodes station issues special 32-bit sequence to indicate to all nodes on Ethernet segment that its previously transmitted frame on Ethernet segment that its previously transmitted frame has suffered a collision and should be considered faultyhas suffered a collision and should be considered faulty

EthernetEthernet

Figure 5-19: CSMA/CD process

EthernetEthernet

On an Ethernet network, an individual On an Ethernet network, an individual network segment is known as a network segment is known as a collision collision domaindomain Portion of network in which collisions will occur if Portion of network in which collisions will occur if

two nodes transmit data at same timetwo nodes transmit data at same time

Data propagation delayData propagation delay Length of time data take to travel from one point Length of time data take to travel from one point

on the segment to another pointon the segment to another point

EthernetEthernet

Demand priorityDemand priority Method for data transmission used by 100BaseVG Ethernet networksMethod for data transmission used by 100BaseVG Ethernet networks Demand priority requires an Demand priority requires an intelligent hubintelligent hub

Figure 5-20: CSMA/CD versus demand priority

EthernetEthernet

Traditional Ethernet LANs, called Traditional Ethernet LANs, called shared shared EthernetEthernet, supply fixed amount of bandwidth , supply fixed amount of bandwidth that must be shared by all devices on a segmentthat must be shared by all devices on a segmentSwitchSwitch Device that can separate network segments into Device that can separate network segments into

smaller segments, with each segment being smaller segments, with each segment being independent of the others and supporting its own independent of the others and supporting its own traffictraffic

Switched EthernetSwitched Ethernet Newer Ethernet model that enables multiple nodes to Newer Ethernet model that enables multiple nodes to

simultaneously transmit and receive data over logical simultaneously transmit and receive data over logical network segmentsnetwork segments

EthernetEthernet

Figure 5-21: A switched Ethernet network

EthernetEthernet

Gigabit EthernetGigabit Ethernet 1 Gigabit Ethernet1 Gigabit Ethernet

Ethernet standard for networks that achieve 1-Ethernet standard for networks that achieve 1-Gbps maximum throughputGbps maximum throughput

10 Gigabit Ethernet10 Gigabit EthernetStandard currently being defined by IEEE 802.3ae Standard currently being defined by IEEE 802.3ae committeecommittee

Will allow 10-Gbps throughputWill allow 10-Gbps throughput

Will include full-duplexing and multimode fiber Will include full-duplexing and multimode fiber requirementsrequirements

EthernetEthernet

PaddingPadding Bytes added to data portion of an Ethernet frame to Bytes added to data portion of an Ethernet frame to

make sure this field is at least 46 bytes in sizemake sure this field is at least 46 bytes in size

Ethernet frame types:Ethernet frame types: IEEE 802.3 (“Ethernet 802.2” or “LLC”)IEEE 802.3 (“Ethernet 802.2” or “LLC”) Novell proprietary 802.3 frame (or “Ethernet 802.3”)Novell proprietary 802.3 frame (or “Ethernet 802.3”) Ethernet II frameEthernet II frame IEEE 802.3 SNAP frameIEEE 802.3 SNAP frame

IEEE 802.3 (“Ethernet 802.2” or IEEE 802.3 (“Ethernet 802.2” or “LLC”)“LLC”)

Default frame type for versions 4.x and higher of Novell Default frame type for versions 4.x and higher of Novell NetWare network operating systemNetWare network operating system

Sometimes called Sometimes called LLC frameLLC frame In Novell’s lexicon, this frame is called In Novell’s lexicon, this frame is called Ethernet 802.2 frameEthernet 802.2 frame

Figure 5-22: An IEEE 802.3 frame

IEEE 802.3 (“Ethernet 802.2” or IEEE 802.3 (“Ethernet 802.2” or “LLC”)“LLC”)

Service Access Point (SAP)Service Access Point (SAP) Identifies node or internal process that uses LLC Identifies node or internal process that uses LLC

protocolprotocol

Frame Check Sequence (FCS)Frame Check Sequence (FCS) This field ensures that data are received just as This field ensures that data are received just as

they were sentthey were sent

Cyclical Redundancy Check (CRC)Cyclical Redundancy Check (CRC) Algorithm used by FCS field in Ethernet framesAlgorithm used by FCS field in Ethernet frames

Novell Proprietary 802.3 (or Novell Proprietary 802.3 (or “Ethernet 802.3”)“Ethernet 802.3”)

Original NetWare frame typeOriginal NetWare frame typeAlso called:Also called: 802.3 Raw802.3 Raw Ethernet 802.3 frameEthernet 802.3 frame

Figure 5-23: A Novell proprietary 802.3 frame

Ethernet IIEthernet II

Original Ethernet frame type developed by Original Ethernet frame type developed by DEC, Intel and Xerox, before IEEE began DEC, Intel and Xerox, before IEEE began to standardize Ethernetto standardize Ethernet

Figure 5-24: An Ethernet II frame

IEEE 802.3 SNAPIEEE 802.3 SNAP

Adaptation of IEEE 802.3 and Ethernet IIAdaptation of IEEE 802.3 and Ethernet IISNAP stands for Sub-Network Access ProtocolSNAP stands for Sub-Network Access Protocol

Figure 5-25: An IEEE 802.3 SNAP frame

Understanding Frame TypesUnderstanding Frame Types

Learning about networks is analogous to Learning about networks is analogous to learning a foreign language, with the frame type learning a foreign language, with the frame type being the language’s syntaxbeing the language’s syntax Just as you may know the Japanese word for go but Just as you may know the Japanese word for go but

how to use it in a sentence, you may know all about how to use it in a sentence, you may know all about the IPX/SPX protocol but not how devices handle itthe IPX/SPX protocol but not how devices handle it

AutosenseAutosense Feature of modern NICs that enables a NIC to Feature of modern NICs that enables a NIC to

automatically sense what types of frames are running automatically sense what types of frames are running on a network and set itself to that specificationon a network and set itself to that specification

Design Considerations for Ethernet Design Considerations for Ethernet NetworksNetworks

CablingCabling

Connectivity devicesConnectivity devices

Number of stationsNumber of stations

SpeedSpeed

ScalabilityScalability

TopologyTopology

LocalTalkLocalTalk

Logical topology designed by Apple Logical topology designed by Apple Computer, Inc.Computer, Inc.

Uses a transmission method called Uses a transmission method called Carrier Carrier Sense Multiple Access/Collision Sense Multiple Access/Collision Avoidance (CSMA/CA)Avoidance (CSMA/CA)A A teleconnectorteleconnector is a transceiver used on a is a transceiver used on a LocalTalk networkLocalTalk networkMacintosh version of TCP/IP is called Macintosh version of TCP/IP is called MacTCPMacTCP

Token RingToken Ring

Token Ring networks use the token passing Token Ring networks use the token passing routine and a star-ring hybrid physical routine and a star-ring hybrid physical topologytopology

The 100-Mbps Token Ring standard is known The 100-Mbps Token Ring standard is known as as High-Speed Token Ring (HSTR)High-Speed Token Ring (HSTR)

On a Token Ring network, one workstation, On a Token Ring network, one workstation, called the called the active monitoractive monitor, acts as the , acts as the controller for token passingcontroller for token passing


Multistation Access Unit (MAU)Multistation Access Unit (MAU) Regenerates signalsRegenerates signals

Figure 5-26: Interconnected Token Ring MAUs


Control Access Unit (CAU)Control Access Unit (CAU) Connectivity device used on a Token Ring Connectivity device used on a Token Ring

networknetwork

Lobe Attachment Module (LAM)Lobe Attachment Module (LAM) Device that attaches to a CAU to expand the Device that attaches to a CAU to expand the

capacity of that devicecapacity of that device


Token Ring networks with STP cabling may use a Token Ring networks with STP cabling may use a type 1 IBM connectortype 1 IBM connectorA A DB-9 connectorDB-9 connector is another type of connector is another type of connector found on STP Token Ring networksfound on STP Token Ring networks

Figure 5-27: Type 1 IBM and DB-9 Token Ring connectors


Media filterMedia filter Device that enables two types of cables or connectors to be linkedDevice that enables two types of cables or connectors to be linked

Token Ring media filterToken Ring media filter Enables DB-9 cable and type 1 IBM cable to be connectedEnables DB-9 cable and type 1 IBM cable to be connected

Figure 5-28: A Token Ring media filter


Token Ring switchingToken Ring switching Like Ethernet networks, Token Ring networks can take Like Ethernet networks, Token Ring networks can take

advantage of switching to better utilize limited bandwidthadvantage of switching to better utilize limited bandwidth

Token Ring framesToken Ring frames IEEE 802.5 Token Ring frameIEEE 802.5 Token Ring frame IBM Token Ring frameIBM Token Ring frame

Figure 5-29: An IBM Token Ring frame

Design Considerations for Token Design Considerations for Token Ring NetworksRing Networks

CablingCabling

Connectivity devicesConnectivity devices

Number of stationsNumber of stations

SpeedSpeed

ScalabilityScalability

TopologyTopology

Fiber Distributed Data Interface Fiber Distributed Data Interface (FDDI)(FDDI)

Logical topology whose standard was originally specified Logical topology whose standard was originally specified by ANSI in mid-1980s and later refined by ISOby ANSI in mid-1980s and later refined by ISO

Figure 5-30: A FDDI network

Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM)(ATM)

Logical topology that relies on a fixed packet Logical topology that relies on a fixed packet size to achieve data transfer rates up to 9953 size to achieve data transfer rates up to 9953 MbpsMbps

The fixed packet in ATM is called a The fixed packet in ATM is called a cellcell

A unique aspect of ATM technology is that it A unique aspect of ATM technology is that it relies on relies on virtual circuitsvirtual circuits

Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM)(ATM)

ATM uses circuit switching, which allows ATM uses circuit switching, which allows ATM to guarantee a specific ATM to guarantee a specific quality of quality of service (QOS)service (QOS)

ATM technology can be integrated with ATM technology can be integrated with Ethernet or Token Ring networks through the Ethernet or Token Ring networks through the use of use of LAN Emulation (LANE)LAN Emulation (LANE)

Chapter SummaryChapter Summary

A physical topology is the basic layout of a networkA physical topology is the basic layout of a network

Physical topologies are categorized into three Physical topologies are categorized into three fundamental geometric shapes: bus, ring, and starfundamental geometric shapes: bus, ring, and star

Few LANs use the simple physical topologies in Few LANs use the simple physical topologies in their pure formtheir pure form

Hubs that service star-wired bus or star-wired ring Hubs that service star-wired bus or star-wired ring topologies can be daisy-chained to form a more topologies can be daisy-chained to form a more complex hybrid topologycomplex hybrid topology

Hierarchical hybrid topology can designate hubs at Hierarchical hybrid topology can designate hubs at different layers to perform different functionsdifferent layers to perform different functions


Cabling that connects each hub is called the Cabling that connects each hub is called the backbonebackbone

In mesh networks, routers are interconnected with In mesh networks, routers are interconnected with other routers so at least two pathways connect each other routers so at least two pathways connect each nodenode

WAN topologies use LAN and enterprise-wide WAN topologies use LAN and enterprise-wide topologies as building blocks, but add more topologies as building blocks, but add more complexitycomplexity

Network logical topologies encompass a set of rules Network logical topologies encompass a set of rules specifying which data are packaged and transmitted specifying which data are packaged and transmitted over network mediaover network media


Switching is a component of a network’s logical Switching is a component of a network’s logical topology that manages the filtering and forwarding topology that manages the filtering and forwarding of packets between nodes on a networkof packets between nodes on a networkEthernet is a networking technology and is by far Ethernet is a networking technology and is by far the most popular logical topology for LANs todaythe most popular logical topology for LANs todayEthernet follows a network access method called Ethernet follows a network access method called CSMA/CDCSMA/CDOn heavily trafficked Ethernet networks, collisions On heavily trafficked Ethernet networks, collisions are not uncommonare not uncommonA switch is a device that can separate a network A switch is a device that can separate a network into smaller segments, each independent of each into smaller segments, each independent of each other and supporting its own trafficother and supporting its own traffic


Token Ring networks currently run at either 4 or 16 Token Ring networks currently run at either 4 or 16 Mbps, as specified by IEEE 802.5Mbps, as specified by IEEE 802.5

Token Ring networks use the token-passing routine Token Ring networks use the token-passing routine and a star-ring hybrid physical topologyand a star-ring hybrid physical topology

FDDI is a networking standard originally specified by FDDI is a networking standard originally specified by ANSI in mid-1980s and later refined by ISOANSI in mid-1980s and later refined by ISO

ATM relies on a fixed packet size to achieve data ATM relies on a fixed packet size to achieve data transfer rates up to 9953 Mbpstransfer rates up to 9953 Mbps

ATM relies on virtual circuits to determine the ATM relies on virtual circuits to determine the optimal path between sender and receiveroptimal path between sender and receiver

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