Business Data Communications and Networking - Chapter 9: Metropolitan and Wide Area Networks

Business Data Communications and Networking 8th Edition Jerry Fitzgerald and Alan DennisJohn Wiley & Sons, Inc Prof. M. UlemaManhattan CollegeComputer Information Systems1Copyright 2005 John Wiley & Sons, IncChapter 9Metropolitan and Wide Area Networks 2Copyright 2005 John Wiley & Sons, IncOutlineIntroductionCircuit Switched NetworksDedicated Circuit NetworksPacket Switched NetworksVirtual Private NetworksBest practice MAN/WAN designImproving MAN and WAN Performance3Copyright 2005 John Wiley & Sons, IncIntroductionMetropolitan area networks (MANs)Span from 3 to 30 miles and connect backbone networks (BNs) and LANsWide area networks (WANs)Connect BNs and MANs across longer distances, often hundreds of miles or moreTypically built by using leased circuits from common carriers such as AT&TMost organizations cannot afford to build their own MANs and WANs,4Copyright 2005 John Wiley & Sons, IncIntroduction (Cont.)Focus of the Chapter Examine MAN/WAN architectures and technologies from a network manager point of viewFocus on services offered by common carriers (in North America), and how they can be used to build networksRegulation of servicesFederal Communications Commission (FCC) in the USCanadian Radio Television and Telecomm Commission (CRTC) in CanadaPublic Utilities Commission (PUC) in each stateCommon CarriersLocal Exchange Carriers (Less) like Verizon, Bell SouthInterexchange Carriers (IXCs) like AT&T5Copyright 2005 John Wiley & Sons, IncServices Used by MANs/WANsCircuit Switched Network ServicesDedicated Circuit Networks ServicesPacket Switched Networks ServicesVirtual Private Networks Services6Copyright 2005 John Wiley & Sons, IncCircuit Switched ServicesOldest and simplest MAN/WAN approachUses the Public Switched Telephone Network (PSTN)i.e., telephone networksProvided by common carriers like AT&T and AmeritechBasic types in use today:POTS (Plain Old Telephone Service)Via use of modems to dial-up and connect to ISPsISDN (Integrated Services Digital Network )7Copyright 2005 John Wiley & Sons, IncBasic Architecture of Circuit Switched ServicesSimpler design: What happens inside of network is hidden from the user“Cloud” architectureA computer using modem dials the number of a another computer and creates a temporary circuitWhen session is completed, circuit is disconnected.Can be expensive (connection and traffic based payment)8Copyright 2005 John Wiley & Sons, IncPOTS based Circuit Switched ServicesUse regular dial-up phone lines and a modemModem used to call another modemOnce a connection is made, data transfer beginsCommonly used to connect to the Internet by calling an ISP’s access pointWide Area Telephone Services (WATS)Wholesale long distance services used for both voice and dataUsers buy so many hours of call time per month (e.g., 100 hours per month) for one fixed rate9Copyright 2005 John Wiley & Sons, IncISDN based Circuit Switched ServicesCombines voice, video, and data over the same digital circuit Sometimes called narrowband ISDNProvides digital dial-up lines (each requires):An “ISDN modem” which sends digital transmissions is usedAlso called: Terminal Adapter (TA)An ISDN Network Terminator (NT-1 or NT-2)Each NT needs a unique Service Profile Identifier (SPID)Acceptance has been slowLack of standardization, different interpretations. and relatively high costISDN: I Still Don’t Know10Copyright 2005 John Wiley & Sons, IncTypes of ISDN ServicesBasic rate interface (BRI)Basic access service or 2B+DTwo 64 Kbps bearer ‘B’ channels (for voice or data)One 16 Kbps control signaling ‘D’ channelCan be installed over existing telephones lines (if less than 3.5 miles)Requires BRI specific end connectionsPrimary rate interface (PRI)Primary access service or 23B+DTwenty three 64 Kbps ‘B’ channelsOne 64 Kbps ‘D’ channel (basically T-1 service)Requires T1 like special circuit11Copyright 2005 John Wiley & Sons, IncBroadband ISDNA circuit-switched service but it uses ATM to move dataBackwardly compatible with ISDN.B-ISDN services offered:Full duplex channel at 155.2 MbpsFull duplex channel at 622.08 MbpsAsymmetrical service with two simplex channels (Upstream: 155.2 Mbps, downstream: 622.08 Mbps)12Copyright 2005 John Wiley & Sons, IncCircuit Switched ServicesSimple, flexible, and inexpensive When not used intensivelyMain problems Varying qualityEach connection goes through the regular telephone network on a different circuit,Low Data transmission ratesUp to 56 Kbps for POTS, and up to 1.5 Mbps for ISDNAn alternativeUse a private dedicated circuitLeased from a common carrier for the user’s exclusive use 24 hrs/day, 7 days/week13Copyright 2005 John Wiley & Sons, IncDedicated CircuitsLeased full duplex circuits from common carriersUsed to create point to point links between organizational locationsRouters and switches used to connect these locations together to form a networkBilled at a flat fee per month (with unlimited use of the circuit)Require more care in network designBasic dedicated circuit architecturesRing, star, and meshDedicated Circuit ServicesT carrier servicesSynchronous Optical Network (SONET) services14Copyright 2005 John Wiley & Sons, IncBasic Architecture of Dedicated Circuit ServicesEquipment installed at the end of dedicated circuitsCSU/DSU: Channel Service Unit / Data Service UnitWAN equivalent of a NIC in a LANMay also include multiplexers>>>>>> Fig 9.2 goes here15Copyright 2005 John Wiley & Sons, IncRing ArchitectureReliabilityMessages can be rerouted around the failed link (Data can flow in both directions (full-duplex circuits))With the expense of dramatically reduced performancePerformanceMessages need to travel through many nodes before reaching their destination16Copyright 2005 John Wiley & Sons, IncStar ArchitectureEasy to manageCentral computer routes all messages in the networkReliabilityFailure of central computer brings the network downFailure of any circuit or computer affects one site onlyPerformanceCentral computer becomes a bottleneck under high trafficcentral routing computer17Copyright 2005 John Wiley & Sons, IncMesh ArchitecturesFull meshExpensive, seldom usedCombine performance benefits of ring and star networksUse decentralized routing, with each computer performing its own routingImpact of losing a circuit is minimal (because of the alternate routes)More expensive than setting up a star or ring network. Setting up alternate routes between computersPartial meshMore practical18Copyright 2005 John Wiley & Sons, IncT-Carrier ServicesMost commonly used dedicated digital circuits in North America Units of the T-hierarchyDS-0 (64 Kbps); Basic unitT-1 (a.k.a. DS-1) (1.544 Mbps)Allows 24 simultaneous 64 Kbps channels which transport data or voice messages using PCMT-2 (6.312 Mbps) multiplexes 4 T-1 circuitsT-3 (44.376 Mbps); 28 T-1 capacityT-4 (274.176 Mbps); 178 T-1 capacity (672 DS-0 channels)Fractional T-1, (FT-1) offers a portion of a T-119Copyright 2005 John Wiley & Sons, IncT-Carrier Digital HierarchyT-Carrier Designation DS Designation Data RateT-1T-2T-3T-4DS-0DS-1DS-2DS-3DS-4 64 kbps1.544 Mbps6.312 Mbps33.375 Mbps274.176 Mbps20Copyright 2005 John Wiley & Sons, IncSynchronous Optical Network (SONET)ANSI standard for optical fiber transmission in Gbps rangeSimilar to ITU-T-based, synchronous digital hierarchy (SDH)SDH and SONET can be easily interconnectedSONET hierarchy Begins with OC-1 (optical carrier level 1) at 51.84 MbpsEach succeeding SONET hierarchy rate is defined as a multiple of OC-1 21Copyright 2005 John Wiley & Sons, IncSONET Digital Hierarchy SONET Designation SDH Designation Data RateOC-1OC-3OC-9OC-12OC-18OC24OC-36OC-48OC-192STM-1STM-3STM-4STM-6STM-8STM-12STM-1651.84 Mbps155.52 Mbps466.56 Mbps622.08 Mbps933.12 Mbps1.244 Gbps1.866 Gbps2.488 Gbps9.952 Gbps22Copyright 2005 John Wiley & Sons, IncPacket Switched ServicesIn both circuit switched and dedicated servicesA circuit established between two computersSolely assigned for use only between these two computersData transmission provided only between these two computersNo other transmission possible until the circuit is closedPacket switched servicesEnable multiple connections to exist simultaneously between computers over the same physical circuitsUser pays a fixed fee for the connection to the network plus charges for packets transmitted23Copyright 2005 John Wiley & Sons, IncBasic Architecture of Packet Switched ServicesPoint-of-Presence (POP)leased dedicated circuitsUsers buy a connection into the common carrier network, and connect via a PADPacket assembly/ disassembly device (PAD).Owned by the customer or the common carrier24Copyright 2005 John Wiley & Sons, IncPacket SwitchingInterleave packets from separate messages for transmissionMost data communications consists of short burst of dataPacket switching takes advantage of this burstinessInterleaving bursts from many users to maximize the use of the shared network>>>>> Fig 9.10 goes here25Copyright 2005 John Wiley & Sons, IncPacket Routing MethodsDescribe which intermediate devices the data is routed throughConnectionless (Datagram)Adds a destination and sequence number to each packetIndividual packets can follow different routesPackets reassembled at destination (by using their sequence numbers)Connection Oriented (Virtual Circuit (VC))Establishes an end-to-end circuit between the sender and receiver (before the packets sent) All packets for that transmission take the same route over the virtual circuit establishedSame physical circuit can carry many VCs26Copyright 2005 John Wiley & Sons, IncTypes of Virtual CircuitsPermanent Virtual Circuit (PVCs) Established for long duration (days or weeks)Changed only by the network managerMore commonly usedPacket switched networks using PVCs behave like a dedicated circuit networksSwitched Virtual Circuit (SVC)Established dynamically on a per call basisDisconnected when the call ends27Copyright 2005 John Wiley & Sons, IncData Rates of Virtual CircuitsUsers specify the rates per PVC via negotiationsCommitted information rate (CIR)Guaranteed by the service provider Packets sent at rates exceeding the CIR are marked discard eligible (DE), Discarded if the network becomes overloadedMaximum allowable rate (MAR)Sends data only when the extra capacity is available28Copyright 2005 John Wiley & Sons, IncPacket Switched Service ProtocolsX.25Asynchronous Transfer Mode (ATM)Frame RelaySwitched Multimegabit Data Service (SMDS)Ethernet/IP packet networks29Copyright 2005 John Wiley & Sons, IncX.25Oldest packet switched serviceA standard developed by ITU-TOffers SVC and PVC servicesUses LAPB and PLP protocols at the data link and network layers, respectivelyRequires protocol translations at PADs (for those users who use different protocols at their LANs)A reliable protocol (it performs error control and retransmits bad packets)Widely used in Europe Not in widespread use in North AmericaLow data rates (64 Kbps) (available now at 2.048 Mbps)30Copyright 2005 John Wiley & Sons, IncAsynchronous Transfer Mode (ATM)Newer than X.25; also standardizedATM in MAN/WAN similar to ATM technology discussed for BNsSimilar to X.25Provides packet switching serviceDifferent than X.25: Operating characteristicsPerforms encapsulation (no translation) of packetsProvides no error control (an unreliable protocol)Provides extensive QoS informationScaleable (easy to multiplex ATM circuits onto much faster ones)31Copyright 2005 John Wiley & Sons, IncError Control in X.25 vs. ATMError control in ATM is handled typically the transport layer (providing end-to-end communications)ACKs sent immediately by each nodeACKs sent by final destination32Copyright 2005 John Wiley & Sons, IncATM FeaturesUses fixed length, 53 byte “cells”5 bytes of overhead and 48 bytes of user dataMore suitable for real time transmissions.Provides extensive QoS information Enables setting of precise priorities among different types of transmissions (i.e. voice, video & e-mail)Data RatesSame rates as SONET: 51.8, 466.5, 622.08 MpbsNew versions: T1 ATM (1.5 Mbps), T3 ATM (45 Mbps)33Copyright 2005 John Wiley & Sons, IncFrame RelayAnother standardized technologyFaster than X.25 but slower than ATMEncapsulates packetsPackets delivered unchanged through the networkUnreliable, like ATMUp to the end-points to control the errorsNO QoS support (under development)Common CIR speeds: 56, 128, 256, 384 Kbps, 1.5, 2, and 45 Mbps34Copyright 2005 John Wiley & Sons, IncSMDSA non-standardized technologyDeveloped by Telcordia for local phone companiesUnreliable, like ATMEncapsulates packetsOriginally developed for MANs, but could be used for WANs as wellTransmission speeds offered: 56 Kbps to 45 MbpsUncertain futureNot standardized; competition from FR, ATM, and others35Copyright 2005 John Wiley & Sons, IncEthernet/IP Packet NetworksOffer Ethernet/IP packet services for building MAN/WAN networks Gigabit Ethernet fiber optic networks (bypassing common carrier network)Currently offer CIR speeds from 1 Mbps to 1 Gbps at 1/4 the cost of more traditional servicesNo need to translate LAN protocol (Ethernet/IP) to the protocol used in MAN/WAN servicesX.25, ATM, Frame Relay and SMDS use different protocols requiring translation from/to LAN protocolsEmerging technology; expect changes36Copyright 2005 John Wiley & Sons, IncVirtual Private NetworksProvides equivalent of a private packet switched network over public InternetUse PVCs (tunnels) that run over the Internet Appear to the user as private networks Encapsulate the packets sent over these tunnelsUsing special protocols that also encrypt the IP packets they encloseProvides low cost and flexibility Uses Internet; Can be setup quicklyDisadvantages of VPNs:Unpredictability of Internet traffic Lack of standards for Internet-based VPNs, so that not all vendor equipment and services are compatible37Copyright 2005 John Wiley & Sons, IncInternetVPN TunnelVPN TunnelVPNDeviceBackboneBackboneOfficeOfficeVPNDeviceVPNDeviceTelephoneLineISPEmployee’sHomeAccessServerVPN ArchitectureVPN is transparent to the users, ISP, and the Internet as a whole; It appears to be simply a stream of packets moving across the Internetleased circuits38Copyright 2005 John Wiley & Sons, IncATMIPL2TPPPPIPTCPInternetVPN TunnelVPNDeviceTelephone LineISPEmployee’sHomeAccessServerSMTPPacket in transmission through the InternetPPPIPTCPSMTPPPPIPTCPSMTPBackbonePacket from the client computerPacket from the VPNOutgoing packets from the VPN are sent through specially designed routers or switches.VPN Encapsulation of PacketsVPNDeviceAccessServerL2TP: Layer 2 Tunneling Protocol(An emerging VPN Layer-2 access protocol)39Copyright 2005 John Wiley & Sons, IncVPN TypesIntranet VPNProvides virtual circuits between organization offices over the InternetExtranet VPNSame as an intranet VPN except that the VPN connects several different organizations, e.g., customers and suppliers, over the InternetAccess VPNEnables employees to access an organization's networks from remote locations40Copyright 2005 John Wiley & Sons, IncMAN/WAN Design PracticesDifficult to recommend best practicesServices, not products, being boughtFast changing environment with introduction of new technologies and services from non-traditional companiesFactors usedEffective data rates and costReliabilityNetwork integrationDesign PracticesStart with flexible packet switched serviceMove to dedicated circuit services, once stabilizedMay use both: packet switched services as backup41Copyright 2005 John Wiley & Sons, IncMAN/WAN Services>>>>>>>>>Fig 9-15 goes here42Copyright 2005 John Wiley & Sons, IncRecommendations for the Best MAN/WAN Practices>>>>>>>>>Fig 9-16 goes here43Copyright 2005 John Wiley & Sons, IncImproving MAN/WAN PerformanceHandled in the same way as improving LAN performance By checking the devices in the network, By upgrading the circuits between computersBy changing the demand placed on the network44Copyright 2005 John Wiley & Sons, IncImproving Device PerformanceUpgrade the devices (routers) and computers that connect backbones to the WAN Select devices with lower “latency”Time it takes in converting input packets to output packetsExamine the routing protocol (static or dynamic)Dynamic routingIncreases performance in networks with many possible routes from one computer to anotherBetter suited for “bursty” trafficImposes an overhead cost (additional traffic)Reduces overall network capacityShould not exceed 20%45Copyright 2005 John Wiley & Sons, IncImproving Circuit CapacityAnalyze the traffic to find the circuits approaching capacityUpgrade overused circuitsDowngrade underused circuits to save costExamine why circuits are overusedCaused by traffic between certain locationsAdd additional circuits between these locations Capacity okay generally, but not meeting peak demand Add a circuit switched or packet switched service that is only used when demand exceeds capacityCaused by a faulty circuit somewhere in the networkReplace and/or repair the circuit Make sure that circuits are operating properly 46Copyright 2005 John Wiley & Sons, IncReducing Network DemandDetermine impact on networkRequire a network impact statement for all new application softwareUse data compression of all data in the networkShift network usage From peak or high cost times to lower demand or lower cost timese.g., transmit reports from retail stores to headquarters after the stores close Redesign the networkMove data closer to applications and people who use themUse distributed databases to spread traffic across47Copyright 2005 John Wiley & Sons, IncImplications for ManagementChanging role of networking and telecom managersIncreased and mostly digitized data transmission causing the merger of these positionsChanging technologyIncreasing dominance of VPNs, Frame Relay and Ethernet/IP Decreasing cots of setting up MANs/WANsChanging vendor profilesFrom telecom vendors to vendors with Ethernet and Internet experiences48Copyright 2005 John Wiley & Sons, IncCopyright 2005 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein. 49Copyright 2005 John Wiley & Sons, Inc