Chapter Five Physical and Logical Topologies. Simple Physical Topologies What does physical topology mean? The physical layout of the network nodes Bus,

Chapter FiveChapter FivePhysical and Logical Physical and Logical

TopologiesTopologies

Simple Physical TopologiesSimple Physical Topologies

What does physical topology mean?What does physical topology mean?The physical layout of the network nodesThe physical layout of the network nodesBus, Ring, & StarBus, Ring, & Star

What does logical topology mean?What does logical topology mean?Network transmission methodsNetwork transmission methodsEthernet, Token Ring, LocalTalk, FDDI, Ethernet, Token Ring, LocalTalk, FDDI, ATMATM


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 network Each node is connected to the two nearest nodes so the entire network

forms a circleforms a circle One method for passing data on ring networks is One method for passing data on ring networks is token passingtoken passing Three byte token used to pass dataThree byte token used to pass data

Active topologyActive topology Each workstation transmits dataEach workstation transmits data

Figure 5-3: A typical

ring network


Token passing process:Token passing process: Computer ready to transmitComputer ready to transmit Computer picks up the token packetComputer picks up the token packet Adds control and data information plus the destination Adds control and data information plus the destination

node’s address node’s address (the token is now a data frame)(the token is now a data frame) The token is then passed to the next nodeThe token is then passed to the next node Once received by the destination, an Once received by the destination, an

acknowledgment is sent to the originating nodeacknowledgment is sent to the originating node After the originating node receives the After the originating node receives the

acknowledgement, it releases a new free token which acknowledgement, it releases a new free token which is sent down the ringis sent down the ring


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 methodconjunction with token ring-passing data transmission method Fault tolerance of star – reliability of token passingFault tolerance of star – reliability of token passing

Figure 5-5: A star-

wired ring topology network

Hybrid Physical TopologiesHybrid Physical TopologiesStar-wired busStar-wired bus

In a In a star-wired bus topologystar-wired bus topology, groups of workstations are star-connected to hubs and then , groups of workstations are star-connected to hubs and then networked via a single busnetworked via a single bus

More expensive that star or busMore expensive that star or bus Basis for modern Ethernet networksBasis for modern Ethernet networks

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 Drawback – Large # of hubs may affect transmission integrityDrawback – Large # of hubs may affect transmission integrity

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 networks (commonly fiber, but Backbone networks (commonly fiber, but may be CAT5 wiring)may be CAT5 wiring) Serial backboneSerial backbone Distributed backboneDistributed backbone Collapsed backboneCollapsed backbone Parallel backboneParallel backbone


Serial backbone (identical to daisy-chained networks)Serial backbone (identical to daisy-chained networks) Two or more hubs connected to each other by a single cableTwo or more hubs connected to each other by a single cable Not suitable for large networksNot suitable for large networks

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 connection point Uses a router or switch as the single central connection point

for multiple subnetworks (subnetworks may be different types)for multiple subnetworks (subnetworks may be different types)

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, Routers are interconnected with other routers, with at least two pathways connecting with at least two pathways connecting

each routereach router InternetInternet

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 telecommunication providerpoints that are leased from a telecommunication 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 transmitted Refers to the way in which data are transmitted between nodesbetween nodes

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

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

Examples include: Ethernet, Token Ring, Examples include: Ethernet, Token Ring, LocalTalk, FDDI, and ATMLocalTalk, FDDI, and ATM

SwitchingSwitchingComponent of network’s logical topology that Component of network’s logical topology that determines how connections are createddetermines how connections are created between between nodesnodes Circuit switchingCircuit switching

Connection is established between two network nodes before they Connection is established between two network nodes before they begin transmitting databegin transmitting dataMonopolized bandwidth between two nodes (not efficient)Monopolized bandwidth between two nodes (not efficient)PC - ISPPC - ISP

Message switchingMessage switchingEstablishes connection between two devices, transfers information Establishes connection between two devices, transfers information to second device, and then breaks connectionto second device, and then breaks connectionE-mail systemsE-mail systems

Packet switchingPacket switchingBreaks data into packets before they are transmittedBreaks data into packets before they are transmittedEthernet and FDDI (including the Internet)Ethernet and FDDI (including the Internet)

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 transmissiontransmissionCollision rate > 5% is unusualCollision rate > 5% is unusual

JammingJammingPart of CSMA/CD in which, upon detection of collision, Part of CSMA/CD in which, upon detection of collision, station station issues special 32-bit sequenceissues special 32-bit sequence to indicate to all nodes 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 has suffered a collision and should be considered faultyshould 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 If to long, cannot identify collisions accuratelyIf to long, cannot identify collisions accurately

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 modelNewer Ethernet model that enables multiple nodes to 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

* Increase the effective bandwidth of a network segment

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

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

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

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

Sometimes called Sometimes called LLC (Logical Link Control) frameLLC (Logical Link Control) frame In Novell’s lingo, this frame is called In Novell’s lingo, 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 type (NetWare 3.12-)Original NetWare frame type (NetWare 3.12-)Also called:Also called: 802.3 Raw802.3 Raw Ethernet 802.3 frameEthernet 802.3 frame Rarely used anymoreRarely used anymore

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 SNAPAdaptation of IEEE 802.3 and Ethernet IIAdaptation of IEEE 802.3 and Ethernet IISNAP stands for SNAP stands for Sub-Network Access ProtocolSub-Network Access ProtocolOrganization ID (OUI) – identifies network typeOrganization ID (OUI) – identifies network typeRarely used on current networksRarely used on current networks

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 – coax or twisted-pair – coax or twisted-pair

Connectivity devicesConnectivity devices – less expensive than – less expensive than comparable Token Ring or LocalTalkcomparable Token Ring or LocalTalk

Number of stationsNumber of stations – 10BaseT/100BaseTX – 10BaseT/100BaseTX limited to 1024limited to 1024

SpeedSpeed – 10/100 Mbps, 1 and 10 Gbps (soon) – 10/100 Mbps, 1 and 10 Gbps (soon)

ScalabilityScalability – easily expandable – easily expandable

TopologyTopology – 10BaseT/100BaseTX use star-wired – 10BaseT/100BaseTX use star-wired bus hybrid topology (highly fault tolerant)bus hybrid topology (highly fault tolerant)

LocalTalkLocalTalk

Logical topology designed by Apple Computer, Logical topology designed by Apple Computer, Inc.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) Similar to CSMA/CD, except node signals intent Similar to CSMA/CD, except node signals intent

before it actually doesbefore it actually does

A A teleconnectorteleconnector is a transceiver used on a is a transceiver used on a LocalTalk networkLocalTalk network

Macintosh 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

network, network, similar to MAUsimilar to MAU but more flexible and but more flexible and allows easier management of nodesallows easier management of nodes

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 – shielded/unshielded twisted pair – shielded/unshielded twisted pair

Connectivity devicesConnectivity devices – more expensive – more expensive than Ethernetthan Ethernet

Number of stationsNumber of stations – 255 STP – 72 UTP – 255 STP – 72 UTP

SpeedSpeed – 4/16/100 Mbps – 4/16/100 Mbps

Scalability Scalability – Easily daisy-chain MAUs– Easily daisy-chain MAUs

TopologyTopology – Star-wired ring topology – Star-wired ring topology (highly fault-tolerant)(highly fault-tolerant)

Fiber Distributed Data Interface (FDDI)Fiber Distributed Data Interface (FDDI)Logical topology whose standard was originally specified by ANSI in mid-1980s and later Logical topology whose standard was originally specified by ANSI in mid-1980s and later refined by ISOrefined by ISODouble ring of multimode or single mode fiber to transmit dataDouble ring of multimode or single mode fiber to transmit data

Figure 5-30: A FDDI network

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

Describes both a network access method & a Describes both a network access method & a multiplexing techniquemultiplexing techniqueLogical topology that relies on a Logical topology that relies on a fixed packet sizefixed packet size to to achieve data transfer rates up to 9,953 Mbpsachieve data transfer rates up to 9,953 MbpsTypically used on WANsTypically used on WANs

The fixed packet in ATM is called a The fixed packet in ATM is called a cellcellA unique aspect of ATM technology is that it relies A unique aspect of ATM technology is that it relies on on virtual circuitsvirtual circuits Connections between network nodes logically appear Connections between network nodes logically appear

to be direct, dedicated links between the two nodesto be direct, dedicated links between the two nodes

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

ATM uses circuit switching, which allows ATM to ATM uses circuit switching, which allows ATM to guarantee a specific guarantee a specific quality of service (QoS)quality of service (QoS)QoS – standard that specifies that data will be QoS – standard that specifies that data will be delivered within a certain period of time after the delivered within a certain period of time after the transmissiontransmission

ATM technology can be integrated with Ethernet or ATM technology can be integrated with Ethernet or Token Ring networks through the use of Token Ring networks through the use of LAN LAN Emulation (LANE)Emulation (LANE)ATM is very expensiveATM is very expensiveGigabit Ethernet is a better choiceGigabit Ethernet is a better choice

Documents

Chapter Five Physical and Logical Topologies. Simple Physical Topologies What does physical topology mean? The physical layout of the network nodes Bus,