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INFO 331 Computer Networking Technology II Network Design Intro Glenn Booker Network Design Through the Kurose text we’ve covered The application, transport, network, & link layers Wireless and multimedia technologies Security Network management Not bad!

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INFO 331Computer Networking Technology II

Network Design Intro

Glenn Booker

Network Design

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Network Design

  • Through the Kurose text we’ve covered

    • The application, transport, network, & link layers

    • Wireless and multimedia technologies

    • Security

    • Network management

  • Not bad!

  • So how does all this come together to help create a network?

Network Design

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Network Design

  • Ok, that’s not a small question – we’ll just tickle the surface (not even scratch!)

  • Main resources for this section are:

    • McCabe, James D. (2003). Network Analysis, Architecture & Design (2nd Ed.). San Francisco: Morgan Kaufmann Publishers. [Chapters 1-5, 10]

    • Teare, Diane. (2004). CCDA Self-Study: Designing for Cisco Internetworking Solutions (DESGN). Indianapolis: Cisco Press.

Network Design

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Network Design Objective

  • Ultimately, our network design must answer some pretty basic questions

    • What stuff do we get for the network?

    • How do we connect it all?

    • How do we have to configure it to work right?

  • Traditionally this meant mostly capacity planning – having enough bandwidth to keep data moving

    • May be effective, but result in over engineering

Network Design

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Network Design Objective

  • And while some uses of the network will need a lot of bandwidth (multimedia), we may also need to address:

    • Security

      • Considering both internal and external threats

    • Possible wireless connectivity

    • Reliability and/or availability

      • Like speed for a car, how much are you willing to afford?

Network Design

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Network Design Phases

  • Designing a network is typically broken into three sections:

    • Determine requirements

    • Define the overall architecture

    • Choose technology and specific devices

(McCabe, 2003)

Network Design

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Systems Methodology

  • There’s lots of room for refining these sections (Teare, 2004)

    • Identify customer requirements

    • Characterize the existing network

    • Design topology

    • Plan the implementation

    • Build a pilot network

    • Document the design

    • Implement the design, and monitor its use

Network Design

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Two Main Principles

  • For a network design to work well, we need to balance between

    • Hierarchy – how much network traffic flows connect in tiers of organization

      • Like tiers on an org chart, hierarchy provides separation and structure for the network

    • Interconnectivity – offsets hierarchy by allowing connections between levels of the design, often to improve performance between them

Network Design

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Two Main Principles

(McCabe, 2003)

Network Design

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Plan Ahead!

  • The 80/20 rule applies here

    • 80% of the cost of a network is its operation and support

    • Only 20% is the cost of designing and implementing it

  • So plan for easy operation, maintenance, and upgrade of the network

Network Design

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Requirements? Booooring!

  • Yes, determining the requirements for a network probably isn’t as much fun as shopping for really expensive hardware

    • And that may be why many networks are poorly designed – no one bothered to think through their requirements!

    • Many people will jump to a specific technology or hardware solution, without fully considering other options – the obvious solution may not be the best one

Network Design

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  • We need to develop the low level design and the higher level architecture, and understand the environment in which they operate

  • We also need to prove that the design we’ve chosen is ‘just right’ (Southey, 1837)

    • Is that $2 million network backbone really enough to meet our needs?

    • How do we know $500,000 wouldn’t have been good enough?

Network Design

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  • Part of this process is managing the customer’s expectations

    • They may expect a much simpler or more expensive solution than is really needed

    • Showing analysis of different design options, technologies, or architectures can help prove you have the best solution

Network Design

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  • We need to use a systems approach for understanding the network

    • The system goes far beyond the network hardware, software, etc.

    • Also includes understanding the users, applications or services, and external environment

  • How do these need to interact?

  • What does the rest of the organization expect from the network?

Network Design

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  • Consider how devices communicate

Images from (McCabe, 2003) unless noted otherwise

Network Design

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  • What services are expected from the network?

    • Typical performance levels might include capacity, delay time, reliability

      • Providing 1.5 Mb/s peak capacity to a remote user

      • Guaranteeing a maximum round-trip delay of 100 ms to servers in a server farm

    • Functions include security, accounting, scheduling, management

      • Defining a security or privacy level for a group of users or an organization

Network Design

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  • Service requirements could include the QoS (quality of service) guarantees (ATM, Intserv, Diffserv, etc.)

    • This connects to network management monitoring of network performance

Network Design

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  • Capacity refers to the ability to transfer data

    • Bandwidth is the theoretical capacity of some part of the network

    • Throughput is the actual capacity, which is less than the bandwidth, due to protocol overhead, network delays, etc.

      • Kind of like hard drive actual capacity is always less than advertised, due to formatting

Network Design

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Requirements Analysis

  • Given these concepts, how do we describe requirements for a network?

  • Need a process to filter or classify requirements

    • Network requirements (often have high, medium, low priorities)

    • Future requirements (planned upgrades)

    • Rejected requirements (remember for future ref.)

    • Informational requirements (ideas, not required)

Network Design

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Requirements Analysis

  • Requirements can come from many aspects of the network system

    • User Requirements

    • Application Requirements

    • Device Requirements

    • Network Requirements

    • Other Requirements

Network Design

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User Requirements

  • User requirements are often qualitative and very high level

    • What is ‘fast enough’ for download? System response (RTT)?

    • How good does video need to be?

    • What’s my budget?

Network Design

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Application Requirements

  • What types of apps are we using?

    • Mission-critical

    • Rate-critical

    • Real-time and/or interactive

  • How sensitive are apps to RMA (reliability, maintainability, availability)?

  • What capacity is needed?

  • What delay time is acceptable?

Network Design

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Application Requirements

  • What groups of apps are being used?

    • Telemetry/command and control - remote devices

    • Visualization and simulation

    • Distributed computing

    • Web development, access, and use

    • Bulk data transport – FTP

    • Teleservice – VOIP, teleconference

    • Operations, admin, maintenance, and provisioning (OAM&P) – DNS, SMTP, SNMP

    • Client-server – ERP, SCM, CRM

Network Design

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Application Requirements

  • Where are the apps located?

  • Are some only used in certain locations?

Network Design

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Device Requirements

  • What kinds of devices are on your network?

    • Generic computing devices include normal PCs, Macs, laptops, handheld computers, workstations

    • Servers include all flavors of server – file, print, app/computation, and backup

    • Specialized devices include extreme servers (supercomputers, massively parallel servers), data collection systems (POS terminals), industry-specific devices, networked devices (cameras, tools), stoplights, ATMs, etc.

Network Design

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Device Requirements

  • Specialized devices are often location-specific

Network Design

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Device Requirements

  • We want an understanding of the device’s performance – its ability to process data from the network

    • Device I/O rates

    • Delay time for performing a given app function

Network Design

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Device Requirements

  • Performance results from many factors

    • Storage performance, that is, flash, disk drive, or tape performance

    • Processor (CPU) performance

    • Memory performance (access times)

    • Bus performance (bus capacity and arbitration efficiency)

    • OS performance (effectiveness of the protocol stack and APIs)

    • Device driver performance

Network Design

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Device Requirements

  • The device locations are also critical

    • Often generic devices can be grouped by their quantity

    • Servers and specialized stuff are shown individually

Network Design

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Network Requirements

  • Network requirements (sounds kinda redundant) are the requirements for interacting with the existing network(s) and network management concerns

  • Most networks have to integrate into an existing network, and plan for the future evolution of the network

Network Design

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Network Requirements

  • Issues with network integration include

    • Scaling dependencies – how will the size of the existing network affect the new one?

      • Will the existing network change structure, or just add on a new wing?

    • Location dependencies – interaction between old and new networks could change the location of key components

    • Performance constraints – existing network could limit performance of the new one

Network Design

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Network Requirements

  • Network, system, and support service dependencies

    • Addressing, security, routing protocols and network management can all be affected by the existing network

  • Interoperability dependencies

    • Changes in technology or media at the interfaces between networks need to be accounted for, as well as QoS guarantees, if any

  • Network obsolescence – do protocols or technologies become obsolete during transition?

Network Design

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Network Requirements

  • Network management and security issues need to be addressed throughout development

    • How will the network be monitored for events?

    • Monitoring for network performance?

      • What is the hierarchy for management data flow?

    • Network configuration?

    • Troubleshoot support?

Network Design

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Network Requirements

  • Security analysis can include the severity (effect) of an attack, and its probability of occurrence

Network Design

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Other Requirements

  • Requirements can come from other outside sources – your customer, legal requirements, larger scale organization (enterprise) requirements, etc.

  • Additional requirements can include

    • Operational suitability – how well can the customer configure and monitor the system?

    • Supportability – how well can the customer maintain the system?

Network Design

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Other Requirements

  • Confidence – what is the data loss rate when the system is running at its required throughput?

  • Financial requirements can include not only the initial system cost, but also ongoing maintenance costs

    • System architecture may be altered to remain within cost constraints

      • This is a good reason to present the customer with design choices, so they see the impact of cost versus performance

  • Network Design

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    Other Requirements

    • Enterprise requirements typically include integration of your network with existing standards for voice, data, or other protocols

    Network Design

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    Requirements Spec and Map

    • A requirements specification is a document which summarizes the requirements for (here) a network

      • Often it becomes a contractual obligation, so assumptions, estimates, etc. should be carefully spelled out

    • Requirements are classified by Status, as noted earlier (core/current, future, rejected, or informational requirement)

    Network Design

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    Requirements Spec and Map

    • Priority can provide additional numeric distinction within a given Status (typically on a 1-3 or 1-5 scale)

    • Sources for Gathering requirements can be identified, or give basis for Deriving it

    • Type is user, app, device, network or other

    Network Design

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    Requirements Spec and Map

    • Requirements Mapping can show graphically where stuff is, what kind of apps are used, and existing connectivity

    Network Design

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    Requirements Analysis Process

    • So, how do we determine what the requirements are for our network?

    • Collect requirements service metrics, and delays to help develop and map requirements

    Network Design

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    Gather and List Requirements

    • A great starting point is the very beginning

    • What initial conditions are you facing?

      • What type of project is this?

        • New network, Modifying an existing network, Analysis of network problems, Outsourcing, Consolidation, Upgrade

      • What is the overall scope of the project?

        • Network size, Number of sites, Distance between sites

    Network Design

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    Initial Conditions

    • Why is the network being designed? What are the goals for its architecture & design?

      • Upgrade technology and/or vendor

      • Improve performance to part or all of network

      • Support new users, applications, or devices

      • Solve perceived problems within system

      • Increase security

      • Support a new capability in system

    Network Design

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    Initial Conditions

    • What project constraints are there?

      • Funding, organizations involved, existing network, facility limitations, schedule, political, etc.

      • Are users receptive to the new network?

    • Are user needs homogeneous, or are there multiple tiers of performance needs?

      • The former is easier to handle, of course

    Network Design

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    Customer and User

    • Customer expectations need to be set quickly

      • What order of magnitude is the project, and does that match what they thought?

      • Better to find out early on if there’s a big gap!

    • Working with users is important, to know how they use the network and what problems they find important

      • Surveys, phone calls, personal meetings, and/or group discussions could be used

    Network Design

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    Customer and User

    • Look for red flags in early discussions

      • Abuse of the term "real-time"

      • Availability as solely a percentage (99.99%)

      • "High performance" without verification or clarification

      • Highly variable, inconsistent requirements

      • Unrealistic expectations from the customer

    • Measure application performance using existing network (if possible) or a test bed

    Network Design

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    Requirements Management

    • The requirements you develop need to be tracked and managed, just like any system’s requirements

      • Identify requirements by some form of ID and short name

      • Need a tool to track requirements, their status, changes, sources, etc.

    • Map location of apps and devices of the existing network

    Network Design

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    Service Metrics

    • Service metrics are characteristics measured or derived from the network

      • Metrics must be configurable, measurable, and verifiable

    • RMA metrics might include

      • Reliability – mean time between failures (MTBFs) and mean time between mission critical failures (MTBCFs)

      • Maintainability – mean time to repair (MTTR)

      • Availability – MTBF, MTBCF, and MTTR

    Network Design

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    Service Metrics

    • Related RMA metrics include

      • Uptime and downtime (percentage of total time)

      • Error and loss rates at various levels, such as packet error rate, bit error rate (BER), cell loss ratio (CLR), cell misinsertion ratio (CMR), frame and packet loss rates

    • Service metrics for capacity include:

      • Data rates – peak data rate, sustained data rate, and minimum data rate

      • Data sizes – burst sizes and durations

    Network Design

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    Service Metrics

    • Service metrics for delay include:

      • End-to-end or round-trip delay

      • Latency

      • Delay variation

    • SNMP or CMIP (Common Management Information Protocol) can be used to configure these metrics, which are kept in the Management Information Base (MIB)

    Network Design

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    Service Metrics

    • MIB Variables often used as service metrics:

      • Bytes in/out (per interface)

      • IP packets in/out (per interface)

      • Dropped ICMP messages per time per interface

      • Service-level agreement (SLA) metrics (per user)

      • Capacity limit

      • Burst tolerance

      • Delay

      • Downtime

    Network Design

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    Metrics Tools

    • Tools for making service metric measurements include

      • Ping, pathchar, traceroute, TCPdump

      • Packet capture utilities: Ethereal, Sniffer, and Etherpeak

    • Then summarize the metrics collection approach

    Network Design

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    Characterizing Behavior

    • Next we can analyze how users and apps use the existing network

    • We could use simulations or models to assess network behavior

      • That’s way beyond the scope here!

    • User behavior is looking for patterns in how people use apps

      • How many users, how frequently, how long per session, how much data they use

    Network Design

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    Characterizing Behavior

    • Application behavior includes looking at how each app uses the network

      • Communication between client/server parts

      • Multicast or broadcast transmissions – how often, how big

    • Focus on the most critical apps (mission critical, real time, interactive, etc.)

    • Models can be simple or complex, as project size and time constraints dictate

    Network Design

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    RMA Requirements

    • Reliability is a common measurement

      • Mean time between mission critical failure (MTBCF) focuses on failures during certain time periods, excluding planned down times

      • Mean time between failure (MTBF) includes failure at any time

    • Maintainability is typically captured with mean time to repair (MTTR)

    Network Design

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    RMA Requirements

    • Availability relates failures to repair time

      • Scheduled maintenance time doesn’t count against availability

    • Uptime and downtime measure those percentages when the system is up or down

      • The upper practical limit is 99.999% uptime, which is 5.3 minutes of downtime per year

      • Uptime of 99.99% is fairly common

      • How many events occur is also important

    Network Design

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    RMA Requirements

    • Thresholds and limits can be defined for RMA measures

      • MTBF is typically a couple thousand hours

      • MTTR may be a few hours

    • Different parts of the system may have different requirements

    Network Design

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    Delay Requirements

    • Various delays can have a strong impact on network requirements

      • Interaction delay (INTD) is how long a user will wait for a response from the system

      • Human response time (HRT) is when a system delay becomes noticable to a user

      • Network propagation delay is how long it takes for a command to cross the network and get the reply

    Network Design

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    Delay Requirements

    • INTD and HRT help distinguish burst from bulk apps

    Network Design

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    Delay Requirements

    • End-to-end and round-trip delays can be network requirements

      • We’ve used ping to get RTT (round trip time)

    • Delay variation can be defined for multimedia apps – typically is 1-2% of end-to-end delay

    Network Design

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    Capacity Requirements

    • Much of the needed capacity of a network derives from key applications that are especially intense in such areas

      • Peak data rate

      • Minimum acceptable data rate

      • Sustained (long term) data rate

    • We need to distinguish apps that CAN use a lot of capacity (if it’s available), versus those that MUST use a lot

    Network Design

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    Data Rates

    • Data rates for an app can be measured at many levels of the protocols

      • App, network, etc.

      • Most TCP apps will take what’s available, but back off when the network gets crowded (why?)

    • Often we may need to identify where the performance bottleneck is located

    • It helps to get a rough idea of typical app performance

    Network Design

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    Data Rates

    • Sometimes a range of values is more helpful

      • Processing credit card info might take 5-10 seconds, and require 100-1000 bytes of data

    • Multimedia rates are well known, and depend on the protocol and level of compression and quality desired

    • Low- and high-performance realms are completely subjective – there are no industry or generic numbers to set them apart

    Network Design

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    Supplemental Performance

    • Other non-functional requirements can be important to a network

    • Operational Suitability is making sure your customer can operate the network once it’s running

      • How often are manual network adjustments needed?

      • How often does network configuration change?

      • How much monitoring is automated?

    Network Design

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    Operational Suitability

    • How many shifts of operators will there be?

    • How well trained are the network operators?

    • How often will hardware changes be needed?

      • What hardware can the operators change?

      • What level of component is an operator expected to be able to change? Chip, board, rack unit, entire rack? (Line-Replaceable Unit, LRU)

    • All of this can result in a Concept of Operations description

    Network Design

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    • Can the network’s level of performance be sustained over time?

    • Is affected by

      • RMA of the architecture and design

      • Workforce, including training and staffing levels

      • System procedures and technical documentation

      • Tools, both ordinary and special

      • Spare and repair parts

    Network Design

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    • Maintenance of a system expects

      • Components are located where they can be maintained without affecting the rest of the system much

      • Spare parts are supplied to allow replacement of failed and soon-failed components

    • Reliability can be formally modeled with reliability block diagrams (RBDs) or failure mode and effect analysis (FMECA)

    Network Design

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    • Workforce should be equivalent to the ones being replaced; or at least as cheap overall

    • Documentation typically includes

      • Technical documentation of the system configuration, design, parts, etc.

      • Maintenance procedures describe routine actions

      • Casualty or corrective procedures describe how to troubleshoot, debug, or otherwise fix basic problems

    Network Design

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    • Tools and test equipment describe what tools are needed to maintain the system

      • How are faults detected?

      • How is performance being monitored?

      • What capabilities will be available to remotely diagnose, reconfigure, or reset components?

    • Stuff breaks and wears out, so spare parts are needed to improve availability

      • How much are you will to invest in parts?

    Network Design

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    • All of this produces a concept for support of a network

      • Important to state assumptions about the knowledge, skills, and availability of support personnel

      • Spares are an ongoing investment – the customer needs to be aware of their cost

    • Often results in at least three tiers of support (onsite, central maintenance, and vendor)

    Network Design

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    Network Design

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    • Confidence is the ability of a network to provide throughput at an acceptable error or loss rate

      • Often thought of at the device or link level, but can also be considered end-to-end

    • Measure by percent of traffic lost during a given time period (e.g. 2% loss up to 1 min)

      • Ping might be used to measure losses

    Network Design

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    Environment-specific Limits

    • What constitutes acceptable performance depends wildly on the industry or particular environment of the network

      • High-performance devices often drive the acceptable thresholds or limits

    • Also consider if predictable or guaranteed performance is important

      • May lead to high QoS requirements, since best effort may not be good enough

    Network Design

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    Map and Spec

    • Then, as mentioned earlier, map out the requirements, and write them in a specification

      • Make sure you and your customer are in agreement on the needs of the network

      • Prioritize requirements, so if something has to give, it’s not critical to your customer

    Network Design

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    Flow Analysis

    • The requirements map is a great place to start analysis of flows in your network

      • We don’t want to model EVERY traffic (data) flow, just the important ones

    • A traffic flow describes data movement, e.g.

      • Source and/or destination addresses

      • Type of information

      • Directionality (bidirectional or unidirectional)

      • Other aspects, such as QoS needs

    Network Design

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    Flow Analysis

    • Later, flows can be broken down into subnet or link level flows

    • A key purpose of flow analysis is to understand the balance between hierarchy and interconnectivity needed

    Network Design

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    Flow Analysis

    • Flows can be individual, or grouped into composites

    • Flows can be critical (and often drive architecture and design)

    Network Design

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    Flow Analysis

    • The requirements spec should be able to define flows by user, app, device, & network

    • Looks for important flows by application, location, user type, device, type of function (multimedia, mission critical)

    • Define capacity (Kbps or Mbps), delay requirements (ms), reliability requirement (%)

    • Map flows geographically

    Network Design

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    Flow Analysis

    Network Design

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    Consolidate Flows

    Network Design

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    Data Sources and Sinks

    • Look for devices (servers, special devices) which generate lots of data (sources) or take in a lot of data (sinks)

    • Consider also WHEN the flows occur – are there specific times that are critical?

    • Consider worst-case and normal-usage scenarios

    Network Design

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    Flow Models

    • Model the flows using common examples

      • Peer-to-peer

      • Client-server

      • Hierarchical client-server

      • Distributed computing

    • These models differ in directionality (or lack thereof), hierarchy, and interconnectivity

    Network Design

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    Peer-to-Peer Flow Model

    • All users or apps are equal

    • Flows are all critical or none are

    • Flows are all equivalent (have same specification)

    Network Design

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    Client-Server Flow Model

    • Requests are small data amounts compared to responses, so these flows are asymmetric toward the clients

    • ERP, video editing, and web apps often follow this model

    Network Design

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    Distributed Computing

    • Behavior varies – inverse client-server, peer-to-peer, hybrid, etc.

    Network Design

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    Flow Prioritization

    • Flows are typically prioritized based on many factors, only a couple of which are technical

      • Capacity, delay, RMA, and/or QoS requirements

      • Security requirements

      • Number of users or apps affected by each flow

      • Business or political objectives, and the impact of the flow on the customer’s business

      • Who pays for it!

    Network Design

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    Flow Specification

    • Like the requirements, the flows can be summarized in a specification of some kind

    • Critical for identifying priorities, in case everyone can’t be happy with your design

    • Balancing flow requirements can be done with a flowspec algorithm

      • Best effort algorithms only consider capacity

      • Predictable flow req’ts consider capacity, delay, and RMA

      • Guaranteed flow req’ts are treated separately

    Network Design

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    Network Architecture

    • Now that we FINALLY have requirements and flows defined, we can consider how all this will affect the architecture of our network

    • The architecture of a house needs many views to understand not only the exterior appearance, but also where the wires run, where the pipes are, ductwork for heating and cooling, etc.

      • Similarly, we need several views of a network

    Network Design

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    Network Architecture

    • Avoid thinking of just the physical components of a network (routers, hubs, etc.)

    • Think of the functions it’s performing (addressing, routing, security, network management, performance) as an integral part of the components

      • E.g. routing or switching can be affected by security

      • So think of functional entities, not just HW

    Network Design

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    Network Architecture

    • Measure network success by how well user, app, and device req’ts are met functionally

      • Also connects easier to traffic flows

      • And scales well to large networks

    • Each function will be defined by a component architecture; combine them to get the overall reference architecture

      • See house analogy a couple slides back

    Network Design

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    Network Architecture

    • The design of a network is more detailed, technology- and location-specific description than its architecture

    • Component architectures describe the hardware and software mechanisms needed to make a type of function work

      • Each component is sort of a subsystem; so we’ll need to understand how they work together

    Network Design

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    Network Functions

    • The key functions are

      • Addressing and routing

      • Network management

      • Performance

      • Security

    • Functions may also include storage and infrastructure, but we’ll focus on other ones

    • Making this work may require trade-offs!

    Network Design

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    Basic Design Rules: Regions

    • Divide the network into regions, based on similar traffic flows

      • Edges (access regions) are where flows start or stop

      • Distribution regions are where flows collect and terminate (app or storage servers)

      • Core (backbone) regions let collections of flows pass through

      • External interfaces (DMZs) collect flows leaving or entering the network from outside

    Network Design

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    • Addressing applies MAC or IP addresses for devices

    • Routing establishes connectivity within and between networks

    • This component architecture defines how user and management flows are forwarded, and how hierarchy & interconnectivity are balanced in subnets

    Network Design

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    • Mechanisms for this architecture could be

      • Addressing: subnetting, supernetting, dynamic vs private addressing, VLANs, IP v4 versus v6, NAT

      • Routing: CIDR, mobile IP, multicast, and various routing protocols (BGP, RIP, etc.), establish routing policies

    • Notice at the architecture level we’re just choosing the types of mechanisms, not deciding exact structures

    Network Design

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    Network Management Arch.

    • This decides how the network will be monitored and managed

    • Types of mechanisms include

      • Monitoring, instrumentation, configuration, security management components, does mgmt data flow in band or out?, how centralized is mgmt?, mgmt capacity needs, duplicate mgmt mechanisms, MIB selection

    Network Design

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    Performance Architecture

    • This component defines how network performance will be established and managed

      • Defines how network resources are allocated to users, apps, and devices

      • Capacity planning, traffic engineering, QoS, access control, SLAs, policies, resource mgmt

      • Balances end-to-end vs per-link prioritization

      • DiffServ vs IntServ

    Network Design

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    Security Architecture

    • How do you protect system resources and data from theft, damage, DoS, and unauthorized access?

      • VPN, encryption, firewalls, routing filters, NAT

      • Threat analysis, physical vs app security

    • Define security zones (cells) for different levels of security

    • Affects how other architectural components can interact with each other

    Network Design

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    Reference Architecture

    • All these components need to be reconciled with each other

      • Can add key req’ts and chosen mechanisms to flow diagram

      • Prioritize mechanisms and how they interact

    • The Reference Architecture is the collection of all the component architectures

    Network Design

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    Reference Architecture

    • Req’ts dictate which components are favored, if any

    Network Design

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    Architectural Models

    • Models for network architecture can be based on topology, flow, or functionality

      • Generally more than one model is needed

      • Often start with topology model and add other(s)

    • Topology models are mainly

      • The WAN/MAN/LAN model – basic hierarchical structure

      • The core/distribution/access model – think of getting videos from CNN

    Network Design

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    Topology Models

    Network Design

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    Flow Models

    • We’ve already seen these (slides 84-87)

      • Peer-to-peer

      • Client-server

      • Hierarchical client-server

      • Distributed-computing

    Network Design

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    Functionality Models

    • These models focus on supporting key functions in the network

      • Service-provider – like an ISP

      • Intranet/Extranet – focus on security and privacy

      • Single-tier/Multi-tier Performance – where flows indicate different levels of performance needs

      • End-to-end Models – where a single flow is critical to understand and fulfill

    • These all require knowing location data

    Network Design

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    Functionality Models

    • Service provider and intranet/ extranet models

    Network Design

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    Functionality Models

    • No cartoon for single- or multi-tier model; could be a combination of the others

    • End-to-end model

    Network Design

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    Applying Models

    • The flow and functional models overlap in focus with the core/distribution/access model

    Network Design

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    System Architecture

    • The network (reference) architecture connects to the rest of the organization

      • Related components and functions may include storage, clients and servers, databases, etc.

    • How much detail outside of networking you include is up to the context of your problem

    Network Design

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    Selecting Technologies

    • After the types of mechanisms in the reference architecture have been selected, we can start choosing more specific design technologies for our network

      • This is where most people start ‘network design’

    • Technologies need to be consistent with the goals of the network

      • What is most important – cost, capacity, QoS, security, manageability…?

    Network Design

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    Selecting Technologies

    • The goals may be different in different parts of the network

    • Consider having a primary goal and one or more secondary goals

    • Consider graphs to show tradeoffs

  • Based on the flow requirements, how do you evaluate candidate technologies?

    • RMA, capacity, cost, performance, supportability, etc. can be your basis for judging technologies

  • Network Design

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    Selecting Technologies

    • Consider a car-buying analogy; if you’re buying a car, you might consider many characteristics to make your choice

      • Cost, performance, appearance, safety, comfort, load capacity, handling, reputation, reliability, etc.

    • Here we look to the flowspec and reference architecture for the relative importance of each desirable characteristic

    Network Design

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    Selecting Technologies

    • Consider also design and configuration issues for technology, not just price-vs-performance

    • For example, many older technologies have built-in ARP capability

      • Ethernet, Token Ring, and FDDI all do this

    • But newer non-broadcast multiple access (NBMA) technologies don’t have this

      • ATM, frame relay, SMDS, HiPPI

    Network Design

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    Selecting Technologies

    • As a result, using NBMA technologies requires separate support for broadcast and multicast

    • Also consider how autonomous systems (AS’s) are being formed and managed

    • What kinds of connections are maintained in the network?

      • Stateless, hard state, or soft state

      • Connections require more work from the network

    Network Design

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    Technology Functions

    • What features and functions will each technology offer to users, apps, and devices?

      • Does it depend on the local infrastructure?

      • Are flows asymmetric, like Web access?

        • HFC and DSL both take advantage of this

      • Are there distance limitations?

        • Affects delay time, buffering, reliability needs, and HW

    Network Design

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    Performance Upgrades

    • How easily can your design be upgraded?

      • Generally focus on capacity, but delay and RMA may be affected too

    • For examples, SONET optical carrier (OC) levels can be easily upped in capacity for ATM or HiPPI

      • SONET Level Rate

      • OC-3 155.52 Mb/s

      • OC-12 622 Mb/s

      • OC-48 2.488 Gb/s

      • OC-192 9.953 Gb/s

      • OC-768 39.812 Gb/s

    Network Design

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    Performance Upgrades

    Network Design

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    Flow Considerations

    • The flow spec should help tell which flows have similar requirements, and which need special consideration for performance, capacity, or other needs

      • Find backbone flows, which collect smaller flows

      • Capacity planning is based on estimating usage, to compare against available technologies

      • Service planning also compares levels of service needed

    Network Design

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    Guidelines for Tech Eval

    • Use combined capacities for best-effort flows (generic Internet), and RMA, capacity, and/or delay requirements for predictable or guaranteed services

      • Guideline 1: If predictable and/or guaranteed requirements are listed in the flow specification (service plan), then either the technology or a combination of technology and supporting protocols or mechanisms must support these requirements. This guideline restricts the selection of candidate technologies to those that can support predictable and/or guaranteed requirements.

    Network Design

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    Guidelines for Tech Eval

    • For examples which are technology-dependent, for predictable service:

      • Quality-of-service levels in ATM

      • Committed information rate levels in frame relay

      • Differentiated service or integrated service levels in IP

    • Guaranteed service gets even messier!

    Network Design

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    Guidelines for Tech Eval

    • Guideline 2: When best-effort, predictable, and/or guaranteed capacities are listed in the flow specification, the selection of technology may also be based on capacity planning for each flow. Capacity planning uses the combined capacities from the flow specification to select candidate technologies, comparing the scalability of each technology to capacity and growth expectations for the network.

    Network Design

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    Guidelines for Tech Eval

    • Specific flows in the flow spec can be mapped to the best technology solution

      • Constraints in terms of RMA, delay, cost or QoS can be used to eliminate technologies

      • Interaction with existing networks needs to be checked for possible conflicts

      • Facility or other large scale issues may need to be addressed too

    Network Design

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    Segmenting the Network

    • Now that we have nailed down technology choices, we can address the detailed structure of the network – how it’s segmented

      • Segmenting focuses technology selection

    • We could do it by geography, groups of users (even virtual), or flow hierarchy

      • Groups of users could belong to different organizations – would that be a problem for security or privacy?

    Network Design

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    Segmenting the Network

    • A geographic example of segmenting

    Network Design

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    Segmenting the Network

    • A user-based view of segmenting

    Network Design

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    Segmenting the Network

    • A flow hierarchy-based example

    Network Design

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    Segmenting the Network

    • Segments can include defining broadcast domains, collision domains, or the scope of autonomous systems (AS’s)

    • Really large networks can be segmented by the type of functions and features involved in each segment (WAN, MAN, LAN, specialized equipment areas, core business areas, etc.)

    Network Design

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    Segmenting the Network

    • Segmenting by types of function and feature

    Network Design

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    Black Box Method

    • Once segments have been defined, we can view each segment as black box(es)

      • Know inputs and outputs, and don’t worry about the inner details yet

      • A segment could have several black boxes

    Network Design

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    Black Box Method

    • Then for each black box, determine the exact technology needs within it

    • This lets us hide irrelevant information, and focus our technology decisions on critical info

    • Naturally we don’t want to have all technology decisions made in a vacuum, or wildly different or incompatible technologies may be chosen

      • Common sense should prevail!

    Network Design

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    • Network design needs to understand and balance requirements from network users, applications, devices, and the external environment

    • Flow analysis helps capture capacity, delay, QoS, reliability, and other critical aspects

    • Then technology choices can be made based on segmenting the network by geography, user, flow spec, or functions provided

    Network Design