LAN Topologies, Access methodsLearning ObjectivesNetwork TopologiesBus TopologyAdvantages of Bus TopologyRing TopologyAdvantages of Ring TopologyDisadvantages of Ring TopologyStar TopologyAdvantages of Star TopologyDisadvantages of Star TopologyLAN Access MethodsEthernetEthernet (CSMA/CD)Ethernet (IEEE 802.3) standardsSlide 1610Base-2 Ethernet10Base-T EthernetEthernet frameToken Ring (IEEE 802.5)Token Ring operationFDDI (Fiber Distributed Data Interface)Summary QuestionsSlide 24Slide 251LAN Topologies, Access methods(Week 1, Wednesday 1/10/2007)© Abdou Illia, Spring 20072Learning ObjectivesDescribe LAN topologiesDescribe major LAN access methods (Ethernet, Token ring, and FDDI)3Network TopologiesPhysical topology is different than Logical topologyPhysical topology = Shape of the networkHow computers connect to each other in the network Logical topologyHow actually messages are transmitted in the LANThree main topologiesBus Ring StarTopologies differ in terms of:Cost (both to install and maintain)Performance and Reliability4Bus TopologyBuilt by connecting nodes (PCs or Servers) to a Bus using patch cableTerminators signal the physical end to the segment10Base2 & 10Base5 Ethernet are the most prevalent bus networks.Patch cable5Advantages of Bus TopologyWorks well for small networksRelatively inexpensive to implementDisadvantage of Bus TopologyPotential for congestion with network traffic6Ring TopologyLogical network arrangementNodes (workstations and servers) attached at points around the ringData goes around the ring from node to nodeImplemented using a MAU (Multistation Access Unit)7Advantages of Ring TopologyWell-suited for transmitting signals over long distances on a LANEnables reliable communication8Disadvantages of Ring TopologyExpensiveNot used as widely as bus topologyFewer equipment optionsFewer options for expansion to high-speed communication9Star TopologyMost common physical network designMultiple nodes attached to a central wiring point10Advantages of Star TopologyLow startup costsOffers opportunities for expansionMost popular topology in use; wide variety of equipment available11Disadvantages ofStar TopologySingle point of failure (Hub, etc.)Requires more cable than Bus topology12LAN Access MethodsAccess Method = Set of rules governing how computers access the networkEthernetIEEE 802.3 specificationsToken ringIEEE 802.5 specificationsFDDI (Fiber Distributed Data Interface)ANSI X3T9.5 (High-speed variation of token ring)Most Common Access methods used in LANIEEE = Institute of Electrical and Electronic Engineers13EthernetMany Ethernet (IEEE 802.3) standardsUses CSMA/CD access method for data transmission on a networkCSMA/CD* :1) All computers (“carriers”) listen (“sense”) for traffic on the LAN2) If no traffic, computer that wishes to transmit may transmit3) If collision occurs, computers must wait a random amount of time4) The computer with smallest random number send again first.* Carrier Sense Multiple Access with Collision Detection14Ethernet (CSMA/CD)CSMA/CD rules are:Carrier Sense Multiple Access (CSMA)1) If a NIC wishes to transmit, it must listen for trafficIf there is no traffic, the NIC may transmitIf there is traffic, the NIC must wait until there is no trafficCollision Detection (CD)2) If there is a collision (by two or more stations transmitting at the same time),All NICs stop transmitting and wait for a random amount of timeThe first NIC that finishes its wait may transmitbut only if there is no traffic!If there is traffic, the NIC must wait until there is no trafficCollision Detection (CD)3) If there are multiple collisions,The random wait is increased each timeAfter 16 attempts to transmit, the sending NIC discards the frameSource: Panko (2002:116)15Ethernet (IEEE 802.3) standards802.3CSMA/CD802.3Ethernet802.3uFast Ethernet802.3zGigabit Ethernet10Base-210Base-510Base-T10Broad-36100Base-TX100Base-FX100Base-T41000Base-SX1000Base-LX1000Base-CX1000Base-CX+ New 10Gbps standard10Base-2Speed:10 MbpsSignal type:Baseband transmissionDistance:185 meters- Speed: 10 Mbps- Signal type: Baseband w coaxial cable- Distance: 185 meters/segment- No more than 30 nodes (computers, printers, etc.) per segment- Nodes must be spaced at least 0.5 meters apart10Base-210Base-5Speed:10 MbpsSignal type:Baseband transmissionDistance:500 meters- Speed: 10 Mbps- Signal type: Baseband w coax. cable- Distance: 500 meters/segment- No more than 100 nodes per segment- Nodes must be spaced at least 2.5 meters intervals10Base-5Thick Ethernet or ThicknetThin Ethernet or Thinnet16Ethernet (IEEE 802.3) standards10Base-TSpeed:10 MbpsSignal type:Baseband transmissionMedium:Twisted Pair- Speed: 10 Mbps- Signal type: Baseband- Distance: 100 meters between the Hub/Switch and the node- No more than 1024 nodes per Hub/Switch- Star topology: physical star, logical bus- Uses CAT3 or better UTP with RJ-45 connectors10Base-Thttp://grouper.ieee.org/groups/802/index.htmlhttp://standards.ieee.org/getieee802/802.3.html100Base-TX: Two Twisted-pairs of Category 5 UTP or STP100Base-FX: Fiber-optic cabling using 2-strand cable100Base-T4: Four Twisted-pairs of Category 3,4, or 5 UTP1000Base-CX: Uses special shielded cable called Twinaxial cable1000Base-LX: Uses single-mode Fiber-optic cable (5 km)1000Base-T: Four Twisted-pairs of Category 5 UTP in full-duplex802.3CSMA/CD802.3Ethernet802.3uFast Ethernet802.3zGigabit Ethernet10Base-210Base-510Base-T10Broad-36100Base-TX100Base-FX100Base-T41000Base-SX1000Base-LX1000Base-CX1000Base-CX+ New 10Gbps standard1710Base-2 EthernetNote: 1 meter = 3.28 feet10Base-2 follows a Physical bus topology and a Logical bus topologyNo need for Hub/Switch to implement 10Base-2 or 10Base-5Source: Berg (1998:170-172)1810Base-T Ethernet BridgeNICNICNICNICNICNIC- Speed: 10 Mbps- Signal type: Baseband- Distance: 100 meters between the Hub/Switch and the node- No more than 1024 nodes per Hub/Switch- Star topology: physical star, logical bus- Uses CAT3 or better UTP with RJ-45 connectors10Base-Tor Switch19Ethernet framePreamble: used for synchronization between stationsSOF (Start Of Frame): Signal the receiving station that the next field is comingDestination Address: Receiver’s MAC addressSource Address: Sender’s MAC addressLength: Number of bytes in the Data field (Length used if number < 1518)Type:
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