CSCI1412 - Topologies and Protocols

CSCI1412Lecture 18Networks 4Topologies and ProtocolsDr John Cowell

phones off (please)1OverviewNetwork topologiesring, star, bus and mesh topologiescombined topologiesCommunication protocolsmessage switchingLANEthernet, Token RingMANFDDI, DQDBWANATM, ISDN2Network Topologies3Network TopologiesTopology means physical layout of a networkissues of:hardwarecabling, deskingsoftwareprotocol, applicationsEach workstation attached to network is known as a nodeTypes of Networksring, star, bus, mesh/distributedcombined4Ring NetworksRing must be maintained at all timesnetwork crashes if break in cable ring

5Higher speeds available at costCan be inflexible in wiringAddition/deletion cause problemsStar NetworksServer dependent - often a mainframeGood central controlRobust - no problems if cable/node breaks

6Large amounts of cable(Common) Bus NetworksAlso known as multidropEach node has a feed to the busEasy to add new nodesCan be inflexible - limits to cable lengthCoax connectors cause problems only used with 10 MHz Ethernet

7Mesh NetworksFully connected networkUsed in WANs, not LANsNo competition for common linesfast connectionsWasteful of connectivity potential

8Combined Topologies

9Combined Topologies 2Combinations of topologies are commondynamically grown networksCommon bus - backboneLANs cope with most usersoccasional access to mainframe is sufficientBridges convert between protocols10Communication Protocols11ProtocolsSet of rules governing communication issuesa standardIEEE define the 802 protocol standardsDifferent protocols exist for different geographical area topologies LANsEthernet (802.3), Token Bus (802.4), Token Ring (802.5), Wireless - WiFi (802.11[a|b|g|n])MANFDDI (802.5), DQDB (802.6)WANsATM, ISDN, Frame Relay12Connection StrategiesCircuit switchedpermanent circuit established for call durationMessage switcheda message is sent from node to nodemessage is stored temporarily at intermediate nodes problem if message is too long for buffersecurity issuesPacket switched - 2 typesdatagram and virtual circuit

13Packet SwitchingPacket switched - 2 typesdatagrameach packet transmitted separately (e.g. TCP/IP)connectionless servicevirtual circuitprotocols establish a circuit, used for all packets (e.g. ATM)segments may be shared with other virtual circuitsconnection orientedThere are possible routes between A and Feach packet may have new routepacket 1: A B Fpacket 2: A C E F(could arrive last of three)packet 3: A C F14LAN ProtocolsEthernet and Token Ring 15EthernetNode connects to bus cable via a transceiverSending Network interface card receives a frame from PCTransceiver says when cable clearframe is put onto cable by transceivertransceiver listens for collision (CSMA/CD)if collision occurs, waits random time, then tries againReceiving Transceiver monitors all trafficall incoming frames address field are readif for node, bits are sent to NICNIC does error checkPC executes network software to move frame from NIC to memory for further processing16Ethernet Cable SpecificationsThe 802.3 standard specifies limitsmaximum backbone lengthmaximum number of nodes attachedcommon data rates17Max distanceCable TypeBackbonebetween nodes Data Rate10 BASE 550 ohm coax,50010 MbpsThick10 mm diameter10 BASE 250 ohm coax, 18510 MbpsThin5 mm diameter10 BASE-TUTP10010 Mbpsstar topology100 BASE-TUTP100100 MbpsFast1000 BASE-TUTP1001000 MbpsGigabit EthernetDistance limitations10 BASE 5 was limited to 500 metressignals degrade in copper cableUsed repeaters (amplifiers) to join 500 meter sections together maximum of four repeaters (between two nodes)the limit comes from the collision detection protocolif the transceiver hears a collision, it must still have part of frame to transmit, in order to abandon itminimum frame size of 64 bytesmaximum frame size to prevent network hoggingFaster Ethernet reduces cable lengthe.g. 100 base T limited to 100 metre cables from central switch/hub18Token RingUsed widely in industryoriginally developed by IBMtime critical applicationsData rates of 1 Mbps, 4 Mbps, 16 MbpsNodes are connected in a ring topologyA token (special frame) is constantly circlingIf network breaks, token disappears need to restart (reboot) networkavoid this with wire centre hubstar topology, logical ring

19Sending Data on Token RingNode wishing to send frame waits for token if token is free, it is replaced with data frameFrame travels around ringeach node reads destination addressdestination nodecopies frameresets status bitsputs frame back on ringtransmitting noderemoves frame from ringcreates a new token, and puts it on ringwaits a period before next grabbing tokenprevents hogging

20Token Ring FeaturesUnlike Ethernet, collisions cannot occura node must wait until the token is freeit is possible to calculate the maximum time that will pass before any node will be able to transmitno wasted bandwidth from collisionsToken ring uses a sophisticated priority schemenodes can be assigned different prioritiesonly nodes with high priority can seize the tokenIf a sending device fails, its token may continue to circulate forever and lock the networkspecial monitor nodes can detect such a situation21MAN ProtocolsFDDI and DQDB22Fibre Distributed Data InterfaceFDDI is essentially Token Ring over fibrecovered by the same IEEE 802.5 standardno electromagnetic interferencebetter securityfaster data rates100 Mbps around 200 Km ring with 200 nodesToken is put back onto the ring immediately after a frame is transmittedCapacity much greater than Token RingRecently a CDDI (Copper Distributed Data Interface) standard has also emerged23Distributed Queue Dual BusAttributed to the PhD thesis of Robert Newman (Uni. Western Australia)IEEE 802.6 is an exampleHigh speed MAN (2 - 300 Mbps)Range up to 34 miles.Two parallel cables, if one breaks the signal can switch to the other bus.Highly resistance to cable damage

24WAN ProtocolsISDN, ATM & 10GbE25Integrated Services Digital NetworkNow largely replaced by broadband technologies

ISDN is digital network available over telephoneintegrates voice & non-voice transmissionBasic installation uses three separate channels2 B channels = 64 Kbps - data channelsD channel = 16 Kbps - control channelcan also used for telemetryremote (water/electricity) meter reading, alarm systemsthe three channels share time on a cabletime-division multiplexingIndustry installation uses thirty B channels + D26Asynchronous Transfer ModeATM is a very fast packet-switched protocol100 Mbps or greater, up to gigabits per second!Uses small fixed-size packets53 octets (5 header, 48 payload)very similar to DQDBConnection orientedevery packet with same destination travels same routevirtual circuit number in headerrequires dedicated routersCRC in header allows error checking at network nodesProtocol optimised for multimediaWill probably be replaced by Gigabit Ethernet technologies for new implementations2710 GbE10 Gigabit Ethernet10 times as fast as Gb Ethernetretains Ethernet frame formatOver 1.2 million ports shipped in 2008Different standards availableE.g. 10 GBASE-SR short range, 26m-85m. Low cost.E.g. 10 GBASE-LR range up to 10km, but 25lm often achievable. FibreLAN PHY, etcCopper10GBaseT, etcGreatest distance between hosts currently 80 km (10GBASE-ZR), but this is a de-facto standard only (not part of IEEE802)Seehttp://en.wikipedia.org/wiki/10_gigabit_Ethernethttp://www.ieee802.org/3/10GBT/public/nov03/10GBASE-T_tutorial.pdf28SummaryNetwork topologiesring, star, bus and mesh topologiescombined topologiesCommunication protocolsmessage switchingLANEthernet, Token RingMANFDDI, DQDBWANATM, ISDN29