Business Data Communications and Networking - Chapter 12: Network Design

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 12Network Design 2Copyright 2005 John Wiley & Sons, IncOutlineIntroductionTraditional Network DesignBuilding Block Network DesignNeeds AnalysisTechnology DesignCost AssessmentDesigning for Network Performance3Copyright 2005 John Wiley & Sons, IncTraditional Network DesignA structured systems analysis and design processNetwork analysis phase Meeting with users to determine the needs and applicationsEstimating data traffic on each part of the networkDesigning circuits needed to support this traffic and obtains cost estimatesImplementation phase:Building and implementing the networkTakes place a year or two laterWorks well for static and slowly evolving networks (although costly and time consuming)4Copyright 2005 John Wiley & Sons, IncInadequacy of Traditional DesignForces making the traditional design approach less appropriate for many of today’s networks:Rapidly changing technology of computers, networking devices and the circuitsMore powerful devices, much faster circuitsRapidly growing network trafficDifficulty of estimating demand and growthShorter planning periods (3 years)Dramatic change in the balance of costsBefore: Equipment; now: staffDesign goal: Minimize the staff time to operate (not the hardware costs)E.g., use similar standardized equipment for the ease of management5Copyright 2005 John Wiley & Sons, IncBuilding Block Network DesignA simpler new approachKey concept:Networks that use a few standard components are cheaper (in the long run) than the networks that use many different componentsStart with a few standard components with ample capacity (without extensive traffic analysis)Called: narrow and deep (few types of devices, used over and over)Result: simpler design process, easily managed networkPhases of designNeeds analysis, Technology design, and Cost assessmentCycles through, refining the outcome of each phase6Copyright 2005 John Wiley & Sons, IncPhases of Building Block DesignNeeds analysisUnderstand current and future needsClassify users and applications as typical or high volume Identify specific technology needsTechnology design Examine available technologies and ask which ones meet the needsIn case of difficulty in determining traffic needs, use more capacity (easy to grow)Cost assessmentConsider the relative cost of technology7Copyright 2005 John Wiley & Sons, IncBuilding Block Network DesignCycles through all three phases, refining the outcome of each phase8Copyright 2005 John Wiley & Sons, IncReaching a Final Network DesignProcess of cycling through all three design phases is repeated until a final design is decided on.9Copyright 2005 John Wiley & Sons, IncNeeds AnalysisTo understand why the network is being built and what users and applications it will supportTo improve poor performance?To enable new applications?To upgrade, replace old equipment? orTo standardize equipment (one type, one protocol, etc)Goals differ depending on the networkLAN and BN (everything owned by the organization)Design over capacityLittle additional cost after the initial costMAN/WAN (mostly rely on leased circuits)Design under capacity Lease additional circuits if necessary10Copyright 2005 John Wiley & Sons, IncBaseliningGain an understanding of the current operations (applications and messages)Most projects today involve upgrades and not new network designs: A good understanding of the needs already existProvides baselining against future needsClear picture of Sequence of operations, processing times, Work volumesCurrent networkExisting costUser/management needs11Copyright 2005 John Wiley & Sons, IncObjective of Needs AnalysisObjectivesDefine the geographic scope of the networkDefine applications and users that will use the networkThe goal: To produce a logical network design thatDescribes what network elements will be needed to meet the organization’s needsSpecifies no technologies nor products at this stageFocuses on functionality (e.g., high speed access network)12Copyright 2005 John Wiley & Sons, IncFirst Step in Needs AnalysisBreak the network into three conceptual parts (based on their geographic and logical scope):Access layerLies closest to the user; often a LANDistribution layer Connects the access layer to the rest of the network; often a backbone networkCore layer Connects the different parts of the distribution layer together; often a WANNot all layers present in all networksSmall networks may not have a distribution layer13Copyright 2005 John Wiley & Sons, IncNext Step in Needs AnalysisIdentify basic technical constraint at each layerExamples: If access layer is A MAN; then users need to use dial up linesA LAN; no need to use T1 linesIdentify constraints imposed by the current network infrastructureExample: adding a new building to an existing office complex that use 100Base-TProbably choose the same for new building14Copyright 2005 John Wiley & Sons, IncDesign ProcessStart with the highest levelBegin by drawing a WAN connecting locationsNext draw individual locations connected to WAN Usually a series of diagrams, one for each locationGather information and characteristics of the environmentLegal requirements, regulations, building codes15Copyright 2005 John Wiley & Sons, IncGeographic ScopeMore complex, has its own core layerDial-up access16Copyright 2005 John Wiley & Sons, IncApplication SystemsBaseliningReview the applications currently used on the network and Identify their location so they can be connected to the planned networkInclude applications expected to be added to the networkReview long and short range plansAlso identify the hardware and software requirements and protocol type for each applicationHTTP over TCP/IP; Windows file access17Copyright 2005 John Wiley & Sons, IncNetwork UsersAssess the number and type of users that will generate network trafficMuch network traffic comes from Internet use (i.e., e-mail and WWW)In the past, application systems accounted for the majority of network trafficFuture network upgrades will require understanding of the use of new applicationsEffect of video on network traffic18Copyright 2005 John Wiley & Sons, IncCategorizing Network NeedsAssess the traffic generated in each segment (for each application and user) Based on an estimate of the relative magnitude of network needs (i.e. typical vs. high volume)Can be problematic, but the goal is a relative understanding of network needsE.g, multimedia applications: high volumeOrganize network requirements intoMandatory, Desirable, and Wish-list requirementsEnables development of a minimum level containing mandatory requirements (if cost is a constraint)19Copyright 2005 John Wiley & Sons, IncDeliverablesA set of logical network diagrams showingApplicationsCircuitsClientsSeversCategorized as “typical” or “high volume”Just a conceptual plan for the networkNo physical elements specified20Copyright 2005 John Wiley & Sons, IncLogical Network Design21Copyright 2005 John Wiley & Sons, IncTechnology DesignDevelopment of a physical network (or set of possible designs)Specify the computers (Clients and servers) needed to support applications and usersNew computersUpgradesSpecify circuits and devices (routers, gateways) to connect the computers22Copyright 2005 John Wiley & Sons, IncDesigning Clients and ServersSpecification of the computers needed in terms of standard unitsAllocate “base level” client computers to “typical” users Allocate “base level” servers to typical applicationsAssign “advanced” computers to “high volume” users and serversBeware of the definition for a “typical” unitKeeps changing as hardware costs continue to fall, and capabilities/capacities continue to increase23Copyright 2005 John Wiley & Sons, IncDesigning Circuits and DevicesDeciding on the fundamental technology and protocolse.g., Ethernet, ATM, TCP/IPChoosing the capacity each circuit will operate ate.g., 10 Mbps, 100 Mbps, 1000 MbpsRequires capacity planningAssess current and future “circuit loading” Amount of data to be transmitted on a circuitFocus on either average or peak circuit trafficIdeal: Peak trafficEstimate size and type of “standard” and “advanced” circuits for each LAN, BN, WANShould “standard” LAN circuit be 10Base-T or higher24Copyright 2005 John Wiley & Sons, IncEstimating Circuit TrafficAverage traffic: Estimate total characters transmitted per day per circuitPeak trafficEstimate maximum number of characters transmitted per two second intervalEstimating Message volumeCount messages in a current network and multiply it with a growth rateUse analyzers if an existing networkPrecision not a major concernStair step nature of communication circuit (lease another line, or upgrade to 100Base-T)Uncertainty to project future needs25Copyright 2005 John Wiley & Sons, IncCapacity Overbuilding DilemmaCost of extra capacity vs. Cost of upgrading a networkUpgrading costs 50-80% more (than building it right at the first time)Majority complains about being under capacity, not over capacityMost organizations intentionally overbuildRapid growth in demand5-50% annual growth factor, sometimes 100%Difficulty in accurate predictionMost end up using overcapacity within 3 yearsTurnpike effect: when the network is efficient and provides good service, it becomes heavily used26Copyright 2005 John Wiley & Sons, IncNetwork Design ToolsUsed mostly in the technology design processFirst step: Enter a diagram of the existing networkCreated from scratch (as required by some tools), orDiscovered automatically (by some tools)Once the diagram is completeAdd information about the expected network traffic andSee if the expected level of traffic can be supportedMay be accomplished through simulation models Once simulation is completeExamine results to see estimated delays and throughputChange the design if necessary and rerun simulations27Copyright 2005 John Wiley & Sons, IncSimulationA mathematical technique used to model the behavior of a networkOnce modeled, the network behaves as it would under real conditionsSimulates applications and users generating traffic and responding to messages Can track: Number of packets, delays experienced at each point in the networkMay be tailoredEnter parameter values specific to network at hand (e.g., Computer A generates 3 packets per second)May also highlight potential trouble spotsOffer suggestions in overcoming problemsIncrease a circuit speed from T1 to T328Copyright 2005 John Wiley & Sons, IncDeliverablesA set of physical network designsGeneral specifications for the hardware and software requiredSeveral alternative designs to do cost-benefit analysisThe crucial issue:Design of the network circuits and devicesA new network designed from scratchImportant to define clients computers with careA major part of the total cost29Copyright 2005 John Wiley & Sons, IncPhysical Network DesignA switched 10/100Base-T collapsed backbone30Copyright 2005 John Wiley & Sons, IncCost AssessmentAssessment of the costs of various physical network design alternativesComplex process; many factors; consider:Circuit costs (leased circuits and purchased cabling)Internetworking devices (switches and routers)Hardware costs (servers, hubs, NICs & UPSs)Software costs (network operating systems, application software and middleware)Network management costs including special hardware, software, and training needed for network managementTest and maintenance costs for monitoring equipment and supporting onsite repairsOperations costs to run the network31Copyright 2005 John Wiley & Sons, IncRequest for Proposal (RFP)Used before making large network purchasesSpecify what equipment, software, and services desiredItems may be categorized as mandatory, important, or desirableSome RFPs may simply list requirements (no specific equipment)Ask vendor to provide their proposed design (if asked), specific items, and best prices32Copyright 2005 John Wiley & Sons, IncOutline for Request for ProposalsBackground InformationOrganizational profile; Overview of current network; Overview of new network; Goals of the new networkNetwork RequirementsChoice sets of possible network designs (hardware, software, circuits); Mandatory, desirable, and wish list items, Security and control requirements; Response time requirements; Guidelines for proposing new network designsService RequirementsImplementation time plan; Training courses and materials; Support services (e.g., spare parts on site); Reliability and performance guaranteesBidding ProcessTime schedule for the bidding process; Ground rules; Bid evaluation criteria; Availability of additional informationInformation Required from VendorVendor corporate profile; Experience with similar networks; Hardware and software benchmarks; Reference list33Copyright 2005 John Wiley & Sons, IncVendor Selection ProcessEvaluate submitted proposals against specific criteriaSelect winner(s) based on criteriaMulti-vendor selectionsProvide better performanceUnlikely that one vendor makes the best in all categoriesTend to be less expensiveUnlikely that one vendor has the cheapest in all categoriesMore difficult to manageIf not working properly, each vendor blame each other for the problem34Copyright 2005 John Wiley & Sons, IncSelling the Proposal to ManagementObtaining the support of senior management for the proposed designNetwork treated as cost centerKeys gaining acceptanceSpeak their language and present the design in terms of easily understandable issuesMake a business case by focusing on organizational needs and goals such asComparing the growth in network use with the growth in the network budgetAvoid focusing on technical issues such as upgrading to gigabit EthernetFocus on network reliabilityMission critical applications must be always available35Copyright 2005 John Wiley & Sons, IncDeliverablesAn RFPIssued to potential vendors.Revised set of physical network diagramsDone after the vendor(s) selectedFinal technology designSelected components (exact products and costs)Business caseTo support the network designExpressed in terms of business objectives36Copyright 2005 John Wiley & Sons, IncDesigning for Network PerformanceSeveral higher level concepts used to design network for the best performanceManaged networksNetwork management software and standardsPolicy-based managementNetwork circuitsTraffic analysisService level agreementsNetwork devicesDevice latency and device memoryLoad BalancingMinimizing network trafficContent caching and content Delivery37Copyright 2005 John Wiley & Sons, IncManaged NetworksNetwork that uses managed devicesManaged device: standard devices that can (in addition to performing its basic functions (switching and routing))Monitors traffic flows, Monitors its status and other devices connected toRecords various data on messages it processesSends these data to manager’s computer (on a request)Sends alarms if a critical situation detected (such as a failing device, or unusual increase in traffic)Problems detected and reported by devices themselves before problems become seriousRequires both hardware and softwareHardware: monitor, collect, transmitSoftware: store, organize, analyze38Copyright 2005 John Wiley & Sons, IncNetwork Management SoftwareDevice (point) management softwareProvide specific information about a deviceConfiguration, traffic, error conditions, etcSystem management softwareaka, enterprise management softwareProvide analysis device info to diagnose patternsPrevents alarm storms (for a failure on a circuit, many connected devices sending alarms)Software analyze these and correlates them and generates a single alarm to the managerApplication management softwareMonitor applications based on device infoFocus on delays and application layer packets39Copyright 2005 John Wiley & Sons, IncDevice Management Software>>>>> Fig 12.7 goes here40Copyright 2005 John Wiley & Sons, IncSystem Management Software>>>>> Fig 12.8 goes here41Copyright 2005 John Wiley & Sons, IncNetwork Management StandardsApplication layer protocols defining type of information collected and format of control messagesSimple Network Management Protocol (SNMP)Developed for Internet and LANsComponents of SNMP Agent: collects device info and responds requests from the managerManagement Information Base (MIB): database at device stored by the agentNetwork Management Station (NMS): Access MIB, sends control messages to agentCommon Management Interface Protocol (CMIP)Developed for OSI type networks42Copyright 2005 John Wiley & Sons, IncMore on SNMPRemote Monitoring (RMON)Enables remote monitoring of SNMP devicesProvide network wide monitoring info to the manager (rather than device wide info)No need to look at individual devices Reduces network management trafficCollects info on various layers (data link, network, application layer)Provides a clear picture of types of trafficAlso collects statistics based on IP addressesEnables manager to observe any host-host traffic Problems with SNMPLimited functionality; security; vendor extensions43Copyright 2005 John Wiley & Sons, IncMore on SNMP>>>> Fig 12.9 goes here44Copyright 2005 John Wiley & Sons, IncPolicy-Based ManagementEnables managers to set priority policies for traffic (to take effect when congested)Example:Manager: order processing to have the highest prioritySoftware: configure devices using QoS capabilities in ATM, TCP/IP, etc to give this application the highest priorityExpected to become more important45Copyright 2005 John Wiley & Sons, IncNetwork CircuitsPlay a critical role in designing network for maximum performanceImportant to size the circuit and place them to match the trafficAreas of concern:Circuit loading and capacity planning (already discussed before)Traffic analysis, and Service level agreementsespecially for MAN and WAN46Copyright 2005 John Wiley & Sons, IncTraffic AnalysisPerformed to pinpoint why some circuits are heavily used>>>>>> Fig 12.10 goes hereExample: Toronto-NY circuit overloadedImmediate reaction: upgrade/add another circuit between Toronto-NYReason for the overload: NY-LA trafficIdeal solution: new circuit directly between LA and NY47Copyright 2005 John Wiley & Sons, IncService Level AgreementsEstablished between organizations and common carrier and ISPsSpecify the exact type of performance that common carrier will provideAvailability99%  can be down 3.65 days per year with no penalty 99.9%  can be down 8.76 hours per year with no penaltyAlso includes maximum response time and other parametersSpecify penalties if the desired performance is not provided48Copyright 2005 John Wiley & Sons, IncNetwork DevicesNetwork devices from different vendors provide different capabilitiesSome faster, some more reliable, etc,.Factors important in network performanceDevice latencyDelay imposed by device in processing messagesDevice memorySize of memory in deviceLoad BalancingCapability in sharing the network load49Copyright 2005 John Wiley & Sons, IncDevice LatencyDelay imposed by device in processing messagesHigh latency device; takes long timeLow latency device: fasterWire speed: fastest device operating as fast as the circuits they connect (virtually no delays)Key element affecting latency:Computer processor in the deviceMore important for networks with heavy trafficHigh latency devices may cause long traffic backupsLess Important in low traffic networksPackets arrive less frequently and less backup delays50Copyright 2005 John Wiley & Sons, IncDevice MemoryGo hand-in-hand with latencyIf a high-latency device, backed-up packets to be stored in memory; Otherwise they will be lost and be retransmitted More, unnecessary traffic high-latency devices need more memoryAlso important for serversMore memory means more files can be stored in memory Requests processed more quicklyFaster than hard disks51Copyright 2005 John Wiley & Sons, IncLoad BalancingTo ensure that a request is handled immediately by a free server in the server farm>>>> Fig 12.11 goes hereLoad balancer:Handles all requests; selects an appropriate server based on some sequence(round-robin, etc.,)If server crashes, no requests are sent to that server52Copyright 2005 John Wiley & Sons, IncMinimizing Network TrafficAnother approach in improving network performanceAttempts to move most commonly used data closer to user  reduces traffic elsewhereProviding servers with duplicate copies at points closer to usersApproaches in reducing trafficContent caching Content delivery53Copyright 2005 John Wiley & Sons, IncContent CachingBasic idea: Store other people’s WEB data closer to your usersInstall a content engine (aka, cache engine) close to your Internet connectionInstall special content management software on the router OperationsStores requests and responses (mostly static files)Examines each outgoing request; if it requires a file already in cache, it responds immediately (without going to the requested site) Stores contents form most commonly accessed sites (updates them frequently)Must operate at wire speeds (otherwise degrade performance)Reduces traffic between Internet and Organization  less circuits to lease54Copyright 2005 John Wiley & Sons, IncNetwork with Content Engine>>>> Fig 12.12 goes here55Copyright 2005 John Wiley & Sons, IncContent DeliveryA special type of Internet service provided by “content delivery providers (CDPs)”A CDP stores Web files for its client closer to the client’s potential usersAkamai, a CDP, operates 10,000 servers located near busiest NAPs and MAEsServers contain most commonly requested web info for some busiest sites like yahoo.comWhen a user access a client’s site, a software in client’s server looks for an Akamai server (closer to the user)Akamai server sends the static files, the client’s server sends the dynamic files of the site56Copyright 2005 John Wiley & Sons, IncNetwork with Content Delivery>>> Fig 12.14 goes hereUser: in Singapore:Requests a web page from yahoo.comClient: Yahoo.com server farm located in CaliforniaResponds with a dynamic page with static files are directed to be pulled from Akamai’s server in Singapore57Copyright 2005 John Wiley & Sons, IncBenefits of Content DeliveryUsers of the client subscribed to AkamaiMuch faster response time (because many parts of the requested page will come form a nearby Akamai server)Client organization subscribed to AkamaiLess traffic for its servers  Need not spend as much on its server farm  Need less capacity on its circuits to InternetISPs providing service to usersLess traffic flows through their networks (unpaid traffic due to peering)58Copyright 2005 John Wiley & Sons, IncImplications for ManagementDevelop strong relationships with only few vendorsUse a building block approach in designing networksUse a few common, standardized technologies everywhere in the network Purchase technologies that will provide strong network management capabilitiesCost to operate is now much more expensive than the cost to purchaseUse powerful design and management toolsSaves money in the long run 59Copyright 2005 John Wiley & Sons, IncCopyright 2005 John Wiley & Sons, Inc. 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