Physical and Logical Physical and Logical TopologiesTopologies

Simple Physical TopologiesSimple Physical TopologiesPhysical 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

Simple Physical TopologiesSimple Physical Topologies

Simple Physical TopologiesSimple Physical TopologiesRing 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 passingActive topologyActive topology

Each workstation transmits dataEach workstation transmits data

Simple Physical TopologiesSimple Physical Topologies

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

a central devicea central device

Hybrid Physical TopologiesHybrid Physical Topologies

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

Logical TopologiesLogical Topologies

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

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

Traditional Ethernet LANs, called Traditional Ethernet LANs, called shared shared EthernetEthernet, supply fixed amount of bandwidth that , supply fixed amount of bandwidth that must be shared by all devices on a segmentmust 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 trafficindependent of the others and supporting its own traffic

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 committeecommitteeWill allow 10-Gbps throughputWill allow 10-Gbps throughputWill include full-duplexing and multimode fiber Will include full-duplexing and multimode fiber requirementsrequirements

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

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

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 topologytopologyThe 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

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