802.6 ~ MAN (DQDB) 802.7 ~ Broadband Technical Advisory Group 802.8 ~ Fiber Optic Technical Advisory Group 802.9 ~ Integrated Voice & Data Network 802.10 ~ Internetwork & Security 802.11 ~ Wireless (polling) 802.12 ~ High speed LANs (e.g. 100VG-AnyLAN)
802.6 ~ MAN (DQDB) 802.7 ~ Broadband Technical Advisory Group 802.8 ~ Fiber Optic Technical Advisory Group 802.9 ~ Integrated Voice & Data Network 802.10 ~ Internetwork & Security 802.11 ~ Wireless (polling) 802.12 ~ High speed LANs (e.g. 100VG-AnyLAN)
Carrier sense protocols ~ protocols in which stations listen for a carrier. Example: 1-persistent, p-persistent, nonpersistent CSMA
05/23/13 TJ 2013 - Data Comm. 1CHAPTER TEN (10)CHAPTER TEN (10)LOCAL AREA NETWORK
05/23/13 TJ 2013 - Data Comm. 2Learning ObjectivesLearning Objectives After completing this chapter you will be able to:-– Components of LAN- Topology– Describe Project 802.– Explain IEEE 802.3 (Ethernet), IEEE 802.4 (Token Bus),IEEE 802.5 (Token Ring) network data transports andmedia specifications.– Understand the access methods used in Ethernet andToken Ring.
05/23/13 TJ 2013 - Data Comm. 3Chapter OutlineChapter OutlineIntroductionTopologyProject 802EthernetFast EthernetToken BusToken Ring
05/23/13 TJ 2013 - Data Comm. 4IntroductionIntroductionComputer Network – a set of devices (nodes)connected by communication links creating dataroutes where we share and exchange information.Categories of Network: Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN) Internetworks (internet)
05/23/13 TJ 2013 - Data Comm. 5MANMANDesigned to extend over an entire city.It may be a single network (cable televisionnetwork) or it may be a means of connectinga number of LANs into larger network sothat resources may be shared LAN-to-LANor device-to-device.Example: (Telekom, ASTRO)
05/23/13 TJ 2013 - Data Comm. 7WANWANProvides long-distance transmission of data,voice, image, and video information overlarge geographical areas that may comprisea country, a continent, or even the wholeworld.WAN that is wholly owned by a singlecompany is often referred to as anenterprise network.
05/23/13 TJ 2013 - Data Comm. 9internet vs. Internetinternet vs. Internetinternet ~ two or more networks connectedby the use of internetworking devices suchas routers or gateways.Internet ~ specific worldwide network usingTCP/IP protocol suite.
05/23/13 TJ 2013 - Data Comm. 10Internetwork (internet)Internetwork (internet)
05/23/13 TJ 2013 - Data Comm. 11LANLAN A local area network (LAN) is a data communication systemthat allows a number of independent devices tocommunicate directly with each other in a limitedgeographic area. It is usually privately owned within a single office, buildingor campus of up to a few kilometers in size. It is widely used to connect personal computers andworkstations in home, company offices and factories toshare resources and exchange information. The resources to be shared can include hardware (e.g.printers), software (e.g. application program) or data.
05/23/13 TJ 2013 - Data Comm. 13CharacteristicsCharacteristics LANs are distinguished from other types of networksby their size, transmission technology and topology. They are restricted in size, which means that theworst-case transmission time is bounded and known inadvance. Traditionally, LANs have data rates in the 4 to 100Mbps range, however, newer LANs may operate athigher speeds, up to gigabits/second. Various topologies are possible for broadcast LANs,and the most common are bus, star and ring.
05/23/13 TJ 2013 - Data Comm. 14TopologyTopologyTopology ~ refers to the way network is laidout, either physically or logically.Two or more devices connect to a link; twoor more links form a topology.The topology of a network is the geometricrepresentation of the relationship of all linksand linking devices (nodes) to each other.i.e. mesh, star, bus, ring, tree, hybrid
05/23/13 TJ 2013 - Data Comm. 15Mesh TopologyMesh Topology Every device has a dedicated point-to-point link to every other device. Dedicated means that the link carriestraffic only between the two devices itconnects. A fully connected mesh network hasn(n-1)/2 physical channels to link ndevices. To accommodate that many links,every device on the network musthave n –1 input/output ports. I.e. telephone network
05/23/13 TJ 2013 - Data Comm. 16Mesh Topology (example)Mesh Topology (example) The Big Pond Company has a fullyconnected mesh network consistingof 5 devices. Calculate the totalnumber of cable links needed and thenumber of ports for each device. Solution:– # of links = n(n-1)/2 = 5(4)/2 = 10 links– # of ports per device = n-1 = 5-1 = 4 ports
05/23/13 TJ 2013 - Data Comm. 17Mesh Topology AdvantageMesh Topology Advantage Eliminating traffic problems ~ each connection cancarry its own data load. Robust ~ if one link fails, it does not anticipate theentire system. Privacy or security ~ when every message senttravels along a dedicated link, only the intendedrecipient sees it. Fault identification & isolation easy ~ traffic can berouted to avoid links with suspected problems.
05/23/13 TJ 2013 - Data Comm. 18Mesh Topology DisadvantageMesh Topology DisadvantageThe amount cabling and I/O ports required ~every device must be connected to everyother device.Installation and reconfiguration are difficult.Need a lot of space since bulk of wiringrequired.Expensive ~ the hardware required toconnect each link (I/O ports and cable) areexpensive.
05/23/13 TJ 2013 - Data Comm. 19Star TopologyStar Topology Each device has a dedicatedpoint-to-point link only to acentral controller/ concentrator,usually called a hub. The controller acts as anexchange; if one device wantsto send data to another, it sendsdata to the controller, which thenrelays the data to the otherconnected device. Star topology does not allowdirect traffic between devices. I.e. 10BaseT
05/23/13 TJ 2013 - Data Comm. 20Star Topology AdvantageStar Topology Advantage Less expensive than a mesh topology ~ eachdevice needs only one link and one I/O port toconnect it to any number of others. Easy to install and reconfigure ~ involve only oneconnection between that device and the hub. Robustness ~ if one link fails, only that link isaffected; all other links remain active. Easy fault identification & isolation ~ hub can beused to monitor link problems and bypassdefective links.
05/23/13 TJ 2013 - Data Comm. 21Bus TopologyBus Topology Multipoint configuration, where onelong cable acts as a backbone to linkall the devices in the network. Backbone ~ the major transmissionpath in a network. Nodes are connected to the bus cableby drop lines and taps. A tap is a connector that either splicesinto the main cable or punctures thesheathing of a cable to create acontact with the metallic core. The end of the bus cable, must beterminated with a resistive load orterminating resistors. I.e. 10Base2
05/23/13 TJ 2013 - Data Comm. 22Bus Topology AdvantageBus Topology AdvantageEase of installation ~ backbone cable can belaid along the most efficient path, thenconnected to the nodes by drop lines ofvarious lengths.Cheap ~ Less cabling is needed than meshand star topology
05/23/13 TJ 2013 - Data Comm. 23Bus Topology DisadvantageBus Topology DisadvantageDifficult reconfiguration ~ difficult to add newdevice since require modification orreplacement of the backbone.fault isolation is difficult ~ a fault or break inthe bus cable stops all transmission.
05/23/13 TJ 2013 - Data Comm. 24Ring TopologyRing Topology Each device has a dedicated point-to-point line configuration only withthe two devices on either side of it. A signal is passed along the ring inone direction, from one device todevice, until it reaches itsdestination. Each device in the ringincorporates a repeater; when adevice receives a signal intendedfor another device, its repeaterregenerates the bits and passesthem along. I.e. Token Ring (IEEE 802.5)
05/23/13 TJ 2013 - Data Comm. 25Ring Topology AdvantageRing Topology AdvantageEasy to install and reconfigure ~ eachdevice is linked only to its neighbors. To addor delete a device requires moving only twoconnections.Easy fault identification & isolation ~ adevice capable of issuing an alarm to alertthe network operator to the problem and itslocation.
05/23/13 TJ 2013 - Data Comm. 26Ring Topology DisadvantageRing Topology DisadvantageUnidirectional traffic ~ a break in the ring(disable station) can disable the entirenetwork.Note: this weakness can be solved by usinga dual ring or a switch capable of closing offthe break.– I.e. FDDI (using dual ring)
05/23/13 TJ 2013 - Data Comm. 27Wireless TopologyWireless Topology There’s no topologyfor wireless network. Nodes can beeverywhere but itmust be in the rangethat can be accessbetween the accesspoint. Example: IEEE802.11
05/23/13 TJ 2013 - Data Comm. 28Project 802Project 802 In 1985, the Computer Society of the IEEE starteda project, called Project 802, to set standards toenable intercommunication between equipmentfrom a variety of manufacturers. It covers the first two layers of the OSI model andpart of the third level. Project 802 has split the data link layer into twodifferent sublayers:– Logical link control (LLC)– Media access control (MAC)
05/23/13 TJ 2013 - Data Comm. 29Project 802 & OSI ModelProject 802 & OSI Model
05/23/13 TJ 2013 - Data Comm. 30Logical Link Control (LLC)Logical Link Control (LLC)IEEE 802.2 LLC is the upper sublayer of thedata link layer.The functions include the logical address,control information, and data.
05/23/13 TJ 2013 - Data Comm. 31Medium Access Control (MAC)Medium Access Control (MAC)MAC is the lower layer of the DLL layer.MAC sublayer resolves the contention forthe shared media.It contains the synchronization, flag, flow,and error control specifications necessary tomove information from one place to another,as well as the physical address of the nextstation to receive and route a packet.
05/23/13 TJ 2013 - Data Comm. 32ArchitectureArchitectureIEEE 802 are subdivided into severalfunctions, identified by:– a number• 802.1 ~ internetworking• 802.2 ~ LLC– The MAC module• 802.3 ~ CSMA/CD (Ethernet)• 802.4 ~ Token Bus• 802.5 ~ Token Ring• Others (802.6 ~ DQDB, 802.11 ~ Polling)
05/23/13 TJ 2013 - Data Comm. 34IEEE 802.1~ InternetworkingIEEE 802.1~ InternetworkingThe section of project 802 devoted tointernetworking issues in LANs and MANs.It seeks to resolve the incompatibilitiesbetween network architectures withoutrequiring modifications in existingaddressing, access, and error recoverymechanisms, among others.
05/23/13 TJ 2013 - Data Comm. 35802.2 ~LLC802.2 ~LLCIEEE 802.2 LLC is the upper sublayer of thedata link layer.The functions include the logical address,control information, and data.
05/23/13 TJ 2013 - Data Comm. 36IEEE 802.3IEEE 802.3It supports a LAN standard originallydeveloped by Xerox and later extended by ajoint venture between Digital EquipmentCorporation, Intel Corporation and Xerox.This was called Ethernet and the accessmethod used is CSMA/CD.IEEE 802.3 therefore is known as Ethernetor CSMA/CD.
05/23/13 TJ 2013 - Data Comm. 37IEEE 802.3 CategoriesIEEE 802.3 Categories IEEE 802.3 defines two categories:– Baseband ~ base specifies digital signal– Broadband ~ broad specifies analog signal IEEE divides the baseband category into severaldifferent standards:– 1Base5, 10Base5, 10Base2, 10BaseT, 100BaseT IEEE defines only one specification for thebroadband catergory:– 10Broad36
05/23/13 TJ 2013 - Data Comm. 38IEEE 802.3 CategoriesIEEE 802.3 Categories 1Base5, 10Base2, 100BaseT, 10Broad36 The first number (1,10,100) indicates the data ratein Mbps. The base or broad indicates type of signal. The last number or letter (1,2,5,T) indicates themaximum cable length or the type of cable. The maximum cable length restriction can bechanged using network devices such as repeatersor bridges.
05/23/13 TJ 2013 - Data Comm. 39IEEE 802.3 Access MechanismIEEE 802.3 Access Mechanism Whenever multiple users have unregulated access to asingle line, there is a danger of signals overlapping anddestroying each other. Such overlaps, which turn the signals into unusablenoise, are called collisions. As traffic increases on a multiple-access link, so docollisions. A LAN therefore needs a mechanism to coordinatetraffic, minimize the number of collision occur, andmaximize the number of frames that are deliveredsuccessfully.
05/23/13 TJ 2013 - Data Comm. 41IEEE 802.3 Access MechanismIEEE 802.3 Access Mechanism The access mechanismused in an Ethernet is calledCarrier Sense MultipleAccess with CollisionDetection (CSMA/CD). CSMA/CD is the result of anevolution from MultipleAccess (MA) to CarrierSense Multiple Access(CSMA), and finally toCSMA/CD.
05/23/13 TJ 2013 - Data Comm. 42Multiple Access (MA)Multiple Access (MA) The original design was MA method in which everyworkstation had equal access to a link. There was no provision for traffic coordination. Access to the line was open to any node at any time. Any station wishing to transmit did so, then relied onacknowledgements to verify that the transmitted framehad not been destroyed by other traffic on the line. The examples of algorithms for allocating a multipleaccess channel is ALOHA.
05/23/13 TJ 2013 - Data Comm. 43CSMACSMA In Carrier Sense Multiple Access (CSMA) system, anyworkstation wishing to transmit must first listen for existingtraffic on the line. Carrier Sense ~ a device listens by checking for a voltage. If no voltage is detected, the line is considered idle and thetransmission is initiated. CSMA cuts down on the number of collisions but does noteliminate them. Collisions can still occur, if another station has transmittedtoo recently for its signal to have reached the listeningstation, the listener assumes the line is idle and introducesits own signal onto the line.
05/23/13 TJ 2013 - Data Comm. 44CSMA/CDCSMA/CDIn CSMA/CD the station wishing to transmit firstlistens to make certain the link is free, thentransmits data, then listens again.During the data transmission, the stationchecks the line for the extremely high voltagesthat indicate a collision.If a collision is detected, the station quits thecurrent transmission and waits a predeterminedamount of time for the line to clear, then sendsits data again.
05/23/13 TJ 2013 - Data Comm. 45IEEE 802.3 Frame FormatIEEE 802.3 Frame FormatIEEE 802.3 specifies one type of framecontaining seven fields:– Preamble ~ alert the receiving system of incoming frameand synchronize input timing– Start Frame Delimiter (SFD) ~ starts signal thebeginning of the frame– Destination Address (DA) ~ physical address– Source Address (SA) ~ physical address– Length/type of PDU– 802.2 frame/PDU/Data and padding/payload– CRC ~ error detection
05/23/13 TJ 2013 - Data Comm. 46MAC Frame FormatMAC Frame Format
05/23/13 TJ 2013 - Data Comm. 47ImplementationImplementation Although the Project 802 standard focuses on the data linklayer of the OSI model, it also defines some physicalspecifications for each of the protocols defined in the MAClayer. In the 802.3 standard, IEEE defines the types of cable,connections, and signals that are to be used in eachEthernet implementations. All Ethernet LANs are configured as logical buses, althoughthey may be physically implemented in bus or startopologies. Each frame is transmitted to every station on the link butread only by the station to which it is addressed.
05/23/13 TJ 2013 - Data Comm. 4810BASE5: Thick Ethernet10BASE5: Thick Ethernet The 1stof the physical standards defined in the IEEE 802.3 modelis called 10Base5 or Thick Ethernet or Thicknet. The name derives from the size of the cable, which is roughly thesize of garden hose and too stiff to bend with your hands. It’s a bus topology LAN that uses baseband signalling and has amaximum segment length of 500 meters. Using networking devices such as repeaters or bridges the totallength of the bus should not exceed 2500 meters (5 segments) toreduce collisions.
05/23/13 TJ 2013 - Data Comm. 4910BASE5 (cont…)10BASE5 (cont…)The standard demands that each separatedfrom each neighbor by 2.5 meters (200 stationsper segment and 1000 stations total)The physical connectors and cables utilized by10Base5 include coaxial cable, networkinterface cards, transceivers, and attachmentunit interface (AUI) cables and terminators.Coaxial cable– RG-8 (Radio Government) cable is a thick coaxialcable that provides the backbone.
05/23/13 TJ 2013 - Data Comm. 5110BASE5 (cont…)10BASE5 (cont…)Transceiver– Each station is attached by an AUI cable to anintermediary device called medium interface unit(MAU) or transceiver (transmitter-receiver).– It performs the CSMA/CD function of checking forvoltages and collisions on the line and may containa small buffer.– It also serves as the connector that attaches astation to the thick coaxial cable itself via a tap.
05/23/13 TJ 2013 - Data Comm. 5210BASE5 (cont…)10BASE5 (cont…)
05/23/13 TJ 2013 - Data Comm. 5310BASE5 (cont…)10BASE5 (cont…) AUI Cables– Each station is linked to its corresponding transceiver by anattachment unit interface (AUI), also called a transceivercable.– An AUI is a 15-wire cable with plugs that performs thephysical layer interface functions between the station and thetransceiver.– Each end of an AUI terminates in a DB-15 (15 pin) connector.– One connector plugs into a port on the NIC, the other into aport on the transceiver.– AUIs are restricted to a maximum length of 50 meters,allowing for some flexibility in placement stations relative tothe 10Base5 backbone cable.
05/23/13 TJ 2013 - Data Comm. 5410BASE5 (cont…)10BASE5 (cont…) Transceiver Tap– Each transceiver contains a connecting mechanism called atap because it allows the transceiver to tap into the line at anypoint.– The tap is a thick cable-sized well with a metal spike in thecenter.– The spike is attached to wires inside the transceiver.– When the cable is pressed into the well, the spike pierces thejacket and sheathing the layers and makes an electricalconnection between the transceiver and the cable.– This kind of connector is often called the vampire tap becauseit bites the cable.
05/23/13 TJ 2013 - Data Comm. 5510BASE5 (cont…)10BASE5 (cont…)Terminator– Terminators are required for bus topologies whereone main cable acts as a backbone with branchesto several devices.– Located at the end in bus cabling.– If the main cable is left unterminated, any signaltransmitted over the line echoes back and interfereswith the original signal.– A terminator absorbs the wave at the end andeliminates echo-back.
05/23/13 TJ 2013 - Data Comm. 5610BASE5 (cont…)10BASE5 (cont…)
05/23/13 TJ 2013 - Data Comm. 5710Base2: Thin Ethernet10Base2: Thin Ethernet The 2ndEthernet implementation defined by the IEEE802 series called 10Base2, thin Ethernet, thinnet,cheapnet, cheapernet, thinwire Ethernet. It provides an inexpensive alternative to 10Base5Ethernet, with the same data rate. Like 10Base5, 10Base2 is also bus topology LAN. The advantages of thinnet are reduced cost and easeof installation. (The cable is lighter weight and moreflexible than that used in Thicknet) The disadvantages are shorter range (185 meters) andsmaller capacity (30 stations/segment).
05/23/13 TJ 2013 - Data Comm. 5810Base2 (cont…)10Base2 (cont…)The connectors and cables utilized are NICs,thin coaxial cable, BNC-T connectors andterminators.NIC– The NICs in a thinnet system provide all of the samefunctionality as those in the thicknet system, plusthe functions of the transceivers.– It does not only provide the station with an addressbut also checks for voltages on the link.
05/23/13 TJ 2013 - Data Comm. 5910Base2 (cont…)10Base2 (cont…)
05/23/13 TJ 2013 - Data Comm. 6010Base2 (cont…)10Base2 (cont…) Thin coaxial cable– The cable required to implement the 10Base2 standard isRG-58.– These cables are relatively easy to install and move around. BNC-T– The BNC-T connector is a T-shaped device with three ports:one for the NIC and one each for the input and output ends ofthe cable. Terminator– 50-ohm is used to absorbs the wave at the end andeliminates the echo-back.
05/23/13 TJ 2013 - Data Comm. 6110BaseT: Twisted Pair Ethernet10BaseT: Twisted Pair Ethernet The most popular standard defined in the IEEE 802.3series. Physically a star-topology LAN, but logically is a bus-topology. It uses unshielded twisted pair cable (UTP CAT-3 orCAT-5) It supports data rate of 10Mbps and has a maximumlength (hub to station) of 100 meters.
05/23/13 TJ 2013 - Data Comm. 6210BaseT (cont…)10BaseT (cont…) It places all of its networking operations in an intelligenthub with a port for each station. Stations are linked into the hub by four-pair RJ-45cable (8-wire UTP) terminating at each end in a male-type connector much like telephone jack. The hub sends out any transmitted frame to all of itsconnected stations. Logic in the NIC assures that the only station to openand read a given frame is the station to which thatframe is addressed.
05/23/13 TJ 2013 - Data Comm. 6310BaseT (cont…)10BaseT (cont…)
05/23/13 TJ 2013 - Data Comm. 64Other Ethernet NetworksOther Ethernet NetworksDuring the last decade, there has been anevolution in Ethernet Networks.Several new schemes have been devised toimprove the performance and the speed ofEthernet LANS.Some of the efforts are:– Switched Ethernet– Fast Ethernet– Gigabit Ethernet
05/23/13 TJ 2013 - Data Comm. 65Switched EthernetSwitched Ethernet An attempt to improve the performance of 10BaseTEthernet. 10BaseT is a shared media network, which means that theentire media is involved in each transmission. This is because the topology, though physically a star, islogically a bus. When a station sends a frame to a hub, the frame is sentout all ports (interfaces) and every station will receive it. In this situation, only one station can send a frame at anytime. If two stations try to send frames simultaneously, there is acollision.
05/23/13 TJ 2013 - Data Comm. 6610BaseT Example10BaseT ExampleStation A is sending a frame to station E. The frame isreceived by the hub and is sent to every station. All ofthe cabling in the system involved in this transmission.Another way to think about this is that one transmissionuses the entire capacity of 10Mbps; if one station usesit, no other station can.AEDCFB
05/23/13 TJ 2013 - Data Comm. 67Switched Ethernet (cont…)Switched Ethernet (cont…) If we replace the hub with a switch, a device that canrecognize the destination address and can route the frameto the port to which the destination station is connected, therest of the media are not involved in the transmissionprocess. This means that the switch can receive another frame fromanother station at the same time and can route this frame toits own final destination. In this way, theoretically, there is no collision. Using a switch, instead of hub, we can theoreticallyincrease the capacity of a network with N devices to N x 10Mbps because the two pairs of UTP for full-duplexcommunications.
05/23/13 TJ 2013 - Data Comm. 68Switched Ethernet ExampleSwitched Ethernet ExampleStation A is sending a frame to station E. The frame isreceived by the hub and sent to station E. Only stationE receives the frame, so the rest of the media is freefor another transmission. Station B can also send aframe to station D without any collision.AEDCFB
05/23/13 TJ 2013 - Data Comm. 69Fast Ethernet (IEEE 802.3u)Fast Ethernet (IEEE 802.3u)Fast Ethernet is a version of Ethernet operatesat 100 Mbps data rate.There is no change in the frame format and theaccess method (CSMA/CD).The only two changes in the MAC layer are thedata rate and the collision domain.The data rate is increased by a factor of 10; thecollision domain is decreased by a factor of 10.
05/23/13 TJ 2013 - Data Comm. 70Fast Ethernet (cont…)Fast Ethernet (cont…)In the physical layer, the specificationdeveloped for Fast Ethernet is a star topologysimilar to 10Base-T; however, to match thephysical layer to different resources available,IEEE has designed two categories of FastEthernet:– 100Base-X (2 cables between the station to hub)• 100Base-TX (2 pairs of UTP or STP)• 100Base-FX (2 optical fibers)– 100Base-T4 (4 pairs of UTP)
05/23/13 TJ 2013 - Data Comm. 71100Base-TX100Base-TXIt uses two category 5 UTP or STP cables toconnect a station to the hub.One pair is used to carry frames from thestation to the hub and the other to carry fromthe hub to the station (1 pair for transmission, 1pair for reception).The distance between the station and the hub(or switch) should be less than 100 meters.
05/23/13 TJ 2013 - Data Comm. 72100Base-FX100Base-FXIt uses two optical fibers (either multimode fiberor single mode fiber), one to carry frames fromthe station to the hub, and the other from thehub to the station (1 for transmission, 1 forreception).The distance between the station and the hubshould be less than 412 meters for multimodehalf duplex, 2 km for multimode full duplex and20 km for single mode fiber.
05/23/13 TJ 2013 - Data Comm. 73100Base-T4100Base-T4It uses 4 pairs of UTP between the station tothe hub (2 pairs for transmission and two pairsfor reception).A length of 4-pair UTP must not more than 100meters between the NIC in the station and theport in the 100Base-T4 hub.The physical layer implementation for 100base-T4 varies significantly from the physical layerdefinition of 10baseT.
05/23/13 TJ 2013 - Data Comm. 74100Base-T4 (cont…)100Base-T4 (cont…)It achieves its speed by dividing a 100 Mbpsdata stream into three 33 Mbps streams.These 3 streams are sent over 3 pairs of UTP.A 4thpair is used for collision detection.No data is sent on the 4thpair; instead, a hubuses it to signal a station when a collisionoccurs.
05/23/13 TJ 2013 - Data Comm. 75Gigabit EthernetGigabit Ethernet The migration from 10 Mbps to 100 Mbps encouragedthe IEEE 802.3 committee to design gigabit Ethernet,which has data rate of 1000 Mbps or 1 Gbps. The MAC layer and the access method remain thesame, but the collision domain is reduced. The physical layer ~ the transmission media and theencoding system, however, changes. It is mainly designed to use optical fiber, although theprotocol does not eliminate the use of twisted paircables.
05/23/13 TJ 2013 - Data Comm. 76Gigabit Ethernet (cont…)Gigabit Ethernet (cont…)It usually serves as a backbone to connect FastEthernet networks.Four implementation has been designed forGigabit Ethernet:– 1000Base-LX (multimode FO, max 550 meters)– 1000Base-SX (multi, max 550 m or single, 5 km)– 1000Base-CX (STP, max 25 meters)– 1000Base-T (UTP, max 25 meters)
05/23/13 TJ 2013 - Data Comm. 77TOKEN BUS (IEEE 802.4)TOKEN BUS (IEEE 802.4) It combines features of Ethernet and Token Ring. It combines the physical configuration of Ethernet (a bustopology) and the collision free (predictable delay) featureof Token Ring. Token Bus is a physical bus that operates as a logical ringusing tokens. Stations are logically organized into a ring. A token is passed among stations, if a station wants tosend data, it must wait and capture token. Token bus is limited to factory automation and processcontrol and has no commercial application in datacommunication.
05/23/13 TJ 2013 - Data Comm. 78Token Ring (IEEE 802.5)Token Ring (IEEE 802.5)A LAN using a ring topology and token-passingmethod.A control station creates a special entity on thenetwork called a token and passes it around thenetwork ring.A token is a simple placeholder frame that ispassed from station to station around the ring.A station may send data only when it haspossession of the token.
05/23/13 TJ 2013 - Data Comm. 79Token Ring: Access MethodToken Ring: Access Method Token Ring use the access method called tokenpassing. Token passing is an example of deterministic protocol. It solves collision problem in CSMA/CD. 2 types of token- Free token (no data)- Busy token (with data) Token moves in one way circling the ring and only onetoken at a time.
05/23/13 TJ 2013 - Data Comm. 80A token is passed from NIC to NIC in sequence untilit encounters a station with data to send.When the token reaches a station on the network thathas something to transmit, it “captures” (keep the tokenin its network board) the token, changes the status ofthe token to busy.It then sends data frame.This data frame proceeds around the ring, beingregenerated by each station.Token Ring: Access Method (cont…)Token Ring: Access Method (cont…)
05/23/13 TJ 2013 - Data Comm. 81Token Ring: Access MethodToken Ring: Access Method Each intermediate station examines the destinationaddress, finds that the frame is addressed toanother station, and relays it to its neighbor. The intended recipient recognizes its own address,copies the message, checks for errors, andchanges four bits in the last byte of the frame toindicate address recognized and frame copied. The full packet then continues around the ring untilit returns to the station that sent it.
05/23/13 TJ 2013 - Data Comm. 82The sender receives the frame and recognizesitself in the source address field.It then examines the address-recognized bits.If they are set, it knows the frame wasreceived.The sender then discards the used data andreleases the token back to the ring.Token Ring: Access MethodToken Ring: Access Method