Network Design

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Network Design

• WAN/LAN Design
• Three Layer
• Two Layer
• One Layer

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Network Design

• Benefits of hierarchical design model
• Scalability
• Ease of implementation
• Ease of troubleshooting
• Predictability
• Protocol support
• Manageability

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Scalability

• Networks that follow the hierarchical model
• can grow much larger without sacrificing control
  or manageability because
• functionality is localised and
• potential problems can be recognised more easily.
  
• An example of a very large-scale hierarchical
  network design is the Public Switched Telephone
  Network.

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Ease of implementation

• A hierarchical design assigns clear functionality
  to each layer, thereby making network
  implementation easier.

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Ease of troubleshooting

• Because the functions of the individual layers
  are well defined, the isolation of problems in
  the network is less complicated.
• Temporarily segmenting the network to reduce the
  scope of a problem also is easier.

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Predictability

• The behaviour of a network using functional
  layers is much more predictable,
• makes capacity planning for growth considerably
  easier
• this design approach also facilitates modelling
  of network performance for analytical purposes.

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Protocol support

• The mixing of current and future applications and
  protocols will be much easier on networks that
  follow the principles of hierarchical design
  because the underlying infrastructure is already
  logically organised.

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Manageability

• All of the listed benefits contribute to greater
  manageability of the network.

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Hierarchical Design
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Core layer

• Provides fast wide-area connections between
  geographically remote sites, tying a number of
  campus networks together in a corporate or
  enterprise WAN.
• Core links are usually point-to-point, and there
  are rarely any hosts in the core layer.
• Core services are typically leased from a telecom
  service provider (for example, T1/E1, Frame
  Relay, and so on).

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Core Layer

• Optimised transport between remote sites
• Redundant paths
• Load sharing
• Rapid convergence
• Efficient use of bandwidth

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Distribution layer

• Refers to the distribution of network services to
  multiple LANs within a campus network
  environment.
• This layer is where the campus backbone network
  is found, typically based on Fast Ethernet.
• This layer is implemented on sites that are large
  and is used to interconnect buildings.

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Distribution Layer

• Provides policy-based connectivity
• Control access to services
• Define path metrics
• Control network advertisements

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Access layer

• Usually a LAN or a group of LANs, typically
  Ethernet or Token Ring, that provide users with
  frontline access to network services.
• The access layer is where almost all hosts are
  attached to the network, including servers of all
  kinds and user workstations.

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Access layer

• Connects workgroups to backbone
• Provide logical segmentation
• Group users with common interest
• Isolate broadband traffic from the workgroup

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WAN connectivity

• Different WAN technologies can be used to access
  WAN core, e.g.
• Frame Relay
• ISDN
• xDSL

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Enterprise Servers
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Workgroup Servers
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LAN Design
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A System Approach to Network Design

• Requirements analysis
• Flow Analysis
• Logical Design
• Technology choices
• Interconnection mechanisms
• Network Management and security
• Physical Design
• Addressing and Routing

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Logical design Technology Choices

• Background
• Establishing Design Goals
• Developing Criteria for Technology Evaluation
• Making Technology Choices for the Design

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Logical design Technology Choices Background

• Input from previous stages
• Requirements specifications
• Application,
• user and
• host requirements
• flow information
• Capacity plan
• Service plan and
• Performance characteristics

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Logical design Technology Choices - Background

• Determine your design goals for the network
• Translate these goals into evaluation criteria
  for making technology choices
• Determine interconnection strategy
• Integrate security and network management into
  the design

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Design

• OutcomeA set of diagrams used to
• Prepare the environment for the network
• Ordering equipment
• Deploying cable
• Writing the transition plan for any existing
  network

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Establishing Design Goals

• Common design goals
• Minimizing network deployment and/or operation
  cost
• Maximizing one or more network performance
  characteristics
• Ease of use and manageability
• Optimising security
• Adaptability to new and changing user needs

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Cost/Performance Graph
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Design Goals

• Prioritise goals
• One primary
• One or more secondary
• Wish list
• You will face Constraints
• E.g. cost

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Criteria for technology evaluation

• Starting point
• Design goals
• Flow specification
• Capacity planning
• Service planning
• Standards based and commonly available
• Commercial off the shelf (COTS) network products

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Criteria for technology evaluation

• Maximizing performance
• Meet or exceed
• Expected capacity,
• Delay and/or
• Reliability
• Maximizing reliability
• Redundancy in the network

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Criteria for technology evaluation

• Adaptability
• Support dynamic behaviour
• Rapid reconfiguration of
• User groups
• Address assignment
• Routing,
• And location adds/drops to/from network
• Example use a service provider for WAN
  connection VPNs!

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Criteria for technology evaluation

• Flowspec
• Capacity Plan
• Minimizing cost (design goal)
• Service Plan
• Maximizing performance (design goal)
• Adaptability (design goal)

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Criteria for technology evaluation

• Characteristics of technologies
• Non-broadcast multiple access (NBMA) capability
• Broadcast capability
• Performance upgrade paths
• Flow considerations
• Meeting capacity and service plans requirements

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Criteria for technology evaluation

• NBMA ATM, Frame Relay, HiPPI
• Broadcast LAN technologies Ethernet, Token ring,
  FDDI (using ARP, RARP)
• NBMA vs Broadcast technology
• Native broadcast support
• Connection support connection oriented/connection
  less

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Criteria for technology evaluation

• Functions and features of technology
• Adapting to a lack of communications
  infrastructure
• Use of wireless techniques protocols
• Adapting to the mobility of users or their
  resources
• Wireless networks, multiple access points
  protocols
• Adapting to users/applications that have strict
  performance requirements
• For asymmetric flows, technology should optimize
  directionality of flow

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Criteria

• NBMA technologies do not inherently have a
  broadcast mechanism
• NBMA flexible handling of broadcast
• Use hierarchies
• Background broadcast traffic will be less than 2
  of the capacity of the technology e.g. 200 Kb/s
  for 10Mb/s Ethernet

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Criteria

• Upgrade paths
• NICs supporting multiple bit rates
• Cable types
• Distances
• SONET 51.84 Mb/s to 9.953 Gb/s
• Ethernet 10 Mb/s to 1 Gb/s
• FDDI 100 Mb/s to 1 Gb/s
• Frame Relay 56 Kb/s to 45 Mb/s
• ATM 1.5 Mb/s to 622 Mb/s

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Criteria

• Scalability
• Backbone flows
• Use scaling depending on the hierarchy
• Hierarchy lt 41 scaling factor 1
• Hierarchy 41 to 61 scaling factor 1.5
• Hierarchy 71 to 91 scaling factor 2

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Criteria

• Flow considerations
• Capacity planning and
• Service planning will be used in the selection of
  technology

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Next Week

• Logical Design Interconnection Mechanisms
• Logical Design Network Management and Security