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35 Cards in this Set
- Front
- Back
Traditonal Model
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-Structured systems analysis and design process
--Network analysis phase: Meet with users determining needs and apps; Estimate data traffic on each part of network; Designing circuits needed; obtains cost estimates --Implementation phase: Building and implementing the network; Takes place a year or two later |
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Tradional Model Inadequacies
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-Rapidly changing technology of computers, networking devices and the circuits; More powerful devices, faster circuits
-Rapidly growing network traffic; Difficulty of estimating demand; growth requires shorter planning periods -Dramatic change in cost balance; Before: Equipment cost; Now: staff;Minimize staff time using standardized equipment |
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"Building Block" Network Model
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-Simpler than traditional
Key concept: use few standard components; ensure ample capacity without extensive traffic analysis -Few types of devices, over and over, narrow product choice but deep redundancy; yields easily managed network |
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Building Block Cycling Method
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-Needs analysis
-Technology design -Cost assessment |
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Building Block - Needs Analysis
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-Understand current and future needs
-Classify users and applications as typical or high volume -Identify specific technology needs |
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Technology Design Phase of Building-Block Design (BBD)
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-Examine available, off the shelf technologies
-Assess which meets user needs -Provide more capacity to keep ahead of growth (or questions) -Clients and servers -Circuits and devices |
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Cost Assessment Phase of Building-Block Design
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-Consider the relative cost of technology
-Off the shelf -Request for Proposal (RFP) |
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BBD Needs Analysis Goals
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-Understand why the network is being built, users, and applications supported
-Why poor performance? -Enable new applications? -Upgrade, replace equipment? -Standardize equipment; vendor or protocol? -Goals differ depending: LAN and BN built with organizational ownership, design in over-capacity -MAN/WAN rely on leased equipment and circuits, design at capacity; lease additional circuits as required |
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Baselining (Needs Analysis)
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-Gain understanding of operations; apps, systems, and messages
-Most projects involve upgrades: good understanding of needs exists -Provides baseline for future needs -Baseline provides picture of Sequence of operations, processing times, Work volumes, Current network, Existing cost, User/management needs |
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Needs Analysis Objective
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-Define geographic scope of network
-Define apps and users using network The goal: -Produce logical network design describing network elements needed to meet organization’s needs -Specifies no technologies nor products at this stage -Focuses on functionality (e.g., high speed access network) |
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Needs Analysis Steps
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Break the network into three conceptual parts (based on their geographic and logical scope):
1-Access layer: closest to the user; often a LAN 2-Distribution layer: connects access layer to the rest of the network; often a backbone network 3-Core layer: connects different parts of distribution layer together; often a WAN -Identify basic constraints: --Technical --Legacy (infrastructure practicalities) |
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Logical Design Process
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-Start with highest level; WAN connecting locations
-Draw individual locations connected to WAN -Gather characteristics of the environment; Legal requirements, regulations, building codes -Baseline infrastructure -Use characterization -Categorize needs |
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Logical Design Deliverables
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-Set of logical network diagrams showing: Applications, Circuits, Clients, Severs
-Categorized as “typical” or “high volume” -No physical elements specified |
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Technology Design
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-Development of a physical network designs
-Specify the computers: Clients and servers -New apps and upgrades called for or anticipated -Specify circuits and devices (routers, gateways) to connect the computers |
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Designing Clients and Servers
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-Use Building block approach standard units
-Allocate “base level” client computers to “typical” users -Allocate “base level” servers to typical applications -Assign “advanced” computers to “high volume” users and servers -Beware of the definition for a “typical” unit |
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Designing Circuits & Devices
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-Decide fundamental technology and protocols e.g., Ethernet, T1, TCP/IP
-Perform capacity planning, size and type network circuits for each type of network (LAN, BN, WAN) e.g., 10 Mbps, 100 Mbps, 1000 Mbps -Assess current and future “circuit loading” -Amount of data transmitted -Focus on average or peak circuit traffic -Estimate size and type of “standard” and “advanced” circuits for each LAN, BN, WAN -Should “standard” LAN circuit be shared or switched, 100Base-T, or 1 Gbe |
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Estimateing Circuit Traffic
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-Average traffic: total characters transmitted per day per circuit
-Peak traffic: maximum number of characters transmitted per two second interval -Message volume: Count current messages in network: multiply with growth rate -Use analyzers -Precision not major concern due to stair-step nature of communication circuit (lease another line, or upgrade to 1Gbe) |
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Capacity Building Dilemma
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-Upgrading costs 50-80% more
-Majority complains about being under capacity -Most organizations intentionally overbuild -Rapid growth in demand, 5-50% annual growth factor, sometimes 100% -Turnpike effect: efficient, good service leads to heavy use |
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Network Design Tools
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-Used in the technology design process
First step: Enter a diagram of the existing network -Created from scratch (as required by some tools), or -Discovered automatically (by some tools) -Add information about the expected network traffic -Demand may be accomplished through simulation models -Analyze estimated delays and throughput -Modify design, rerun simulations |
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Simulation
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-Mathematical technique modeling network behavior
-Network behaves as under real conditions -Simulates applications and users generating traffic and responding to messages -Can track: Number of packets, delays experienced at each point in the network -May be tailored -Enter parameter values specific to network at hand (e.g., Computer A generates 3 packets per second) -Highlight potential trouble spots -Offer design suggestions in overcoming problems |
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Technical Design Deliverables
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-Set of physical network designs
-General specifications for the hardware and software -Alternative designs to analyze of cost vs performance -Crucial design issue: selection of network circuits and devices -Networks now are upgrades -Entirely new networks; important to define clients’ computers with care due to large portion of total cost |
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Cost Assessment
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-Evaluation of costs of
--various physical network --design alternatives --analysis of many factors: ---Circuit costs and 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 management ---Test and maintenance costs for monitoring equipment and supporting onsite repairs ---Operations costs to run the network |
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Request for Proposal (RFP)
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-Detailed specification of equipment, software, and services desired from vendors
-Items may be categorized as mandatory, important, or desirable -Some RFPs may simply list requirements with no specific equipment -Ask vendor to provide their proposed design (if asked), specific items, and best prices -Allows apple to apple comparisons of numerous vendor responses |
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RFP Outline
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-Background Information: Organizational profile; Overview of current network; Overview of new network; Goals of the new network
-Network Requirements: Choice 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 designs -Service Requirements: Implementation time plan; Training courses and materials; Support services (e.g., spare parts on site); Reliability and performance guarantees -Bidding Process: Time schedule for the bidding process; Ground rules; Bid evaluation criteria; Availability of additional information -Information Required from Vendor: Vendor corporate profile; Experience with similar networks; Hardware and software benchmarks; Reference list |
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Designing for Network Performance
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-Managed networks: use managed devices that assist with network management through monitoring; Policy-based management
-Network circuits:Traffic analysis, Service level agreements -Network devices: Device latency and device memory, Load Balancing -Minimizing network traffic: Content caching and content delivery |
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Managed Networks
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Network that uses managed devices
Managed device: Switches and routers, Monitors traffic flows, Monitors its status and other devices connected to, Records various data on messages it processes, Sends 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 serious based on thresholds -Requires both hardware and software; Hardware: monitor, collect, transmit; Software: store, organize, analyze |
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Network Management Software
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-Application layer protocols defining type of information collected and format of control messages
-Simple Network Management Protocol (SNMP: Developed for Internet and LANs Components of SNMP Agent: collects device info and responds requests from the manager; Management Information Base (MIB): database at device stored by the agent Network Management Station (NMS): Access MIB, sends control messages to agent Common Management Interface Protocol (CMIP: Developed for OSI type networks |
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SNMP
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-Remote Monitoring (RMON): Enables remote monitoring of SNMP devices; Provide network wide monitoring info to the manager (rather than device wide info); No need to look at individual devices
-Reduces network management traffic; Collects info on various layers (data link, network, application layer) Provides a clear picture of types of traffic; collects statistics based on IP addresses; Enables manager to observe any host-host traffic -Problems with SNMP: Limited functionality; security; vendor extensions |
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Policy-Based Management
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Enables managers to set priority policies for traffic (to take effect when congested)
Example: Manager: order processing to have the highest priority Software: configure devices using QoS capabilities in ATM, TCP/IP, etc to give this application the highest priority Expected to become more important |
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Network Service-Level Agreements
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-Established between organizations and common carrier and ISPs
-Specify the exact type of performance that common carrier will provide -Availability: 99% can be down 3.65 days per year with no penalty; 99.9% can be down 8.76 hours per year with no penalty; “Five nines” is 99.999% uptime -Includes maximum response time and other parameters -Specify penalties if the desired performance is not provided |
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Network Device Performance Factors
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-Device latency is delay imposed by device in processing messages
-Device memory is size of memory in device -Load Balancing is capability in sharing the network load -Capacity management |
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Device Latency Perspectives
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-Delay imposed by device in processing messages
-High latency device; takes long time Low latency device: faster Wire speed: fastest device operating as fast as the circuits they connect (virtually no delays) Key element affecting latency: Computer processor in the device More important for networks with heavy traffic High latency devices may cause long traffic backups Less Important in low traffic networks Packets arrive less frequently and less backup delays |
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Device Memory Perspectives
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Goes hand-in-hand with latency
If a high-latency device, backed-up packets to be stored in memory; Otherwise they will be lost and to be retransmitted, causing more, unnecessary traffic High-latency devices need more memory Also important for servers More memory means more files can be stored in memory Requests processed more quickly, often faster than hard disks |
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Load Balancing
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-To ensure that a request is handled immediately by a free server in the server farm or clusters
-Network’s load balancer device: Handles all requests; selects an appropriate server based on some sequence(round-robin, etc.,); If server crashes, no requests are sent to that server |
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Content Delivery Providers
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-Special type of Internet service provided by “content delivery providers (CDPs)”
-A CDP stores Web files for its customers closer to the customer’s potential web page users -Akamai, a CDP, operates 10,000 servers located near busiest NAPs and MAEs -Servers contain most commonly requested web info for some busiest sites like yahoo.com -When a user access a CDP’s website, a software in user’s server looks for an Akamai server (closer to the user) -Akamai server sends the user the static files, the Akamai’s customer’s server sends the user the dynamic files of the site |