WAN Design

							    Chabot College
Cisco Networking Academy


      WAN Design

     Semester 4, Chapter 3
Table of Contents

 Go There!   WAN Design Requirements


 Go There!   Gathering & Analyzing
             Requirements

 Go There!   The Three-Layer WAN model


 Go There!   WAN Layer Functions
 WAN Design
Requirements


 Table of Contents
Network Demand

 WANs need to be developed to meet the
 following requirements:
   Optimize WAN bandwidth

   Minimize cost

   Maximize the effective service to end users
Network Demand

 LANs & shared media networks are being
 overtaxed because...
   Network cost continues to escalate

   Network usage has increased

    Application requirements increasingly demand more network
     services (i.e., “push” “technologies)
    Increased use of enterprise servers
    The number on intra- and extranets continues to rise
 LANs connected through WANs is expected to
 increase WAN traffic 300% in the next 5 years.
LAN/WAN Integration

 LANs and WANs, previously logically
 separated, must now be fully integrated for
 seamless performance.
 The LAN/WAN network (or corporate internet)
 now must be able to handle...
   Voice traffic (VoIP)

   Bandwidth intensive multimedia applications

      Video conferencing
      On-line training
    Increased business critical data access
Overriding Goal in WAN Design




     Minimize Cost While
     Increasing Network
         Availability
Gathering & Analyzing
    Requirements


     Table of Contents
Factors Affecting Design

 Environmental Variables
   Where are all the nodes?

 Performance Constraints
   What level of reliability? Host/client speeds? Traffic

    throughput?
 Networking Variables
   What’s the topology? What is the traffic’s characteristics?

 Traffic Characterization is critical to successful
 WAN design and implementation, but it is
 seldom done.
Traffic Characterization
 Types of Traffic        Traffic Characteristics
   Voice/fax              Peak & Avg. Volumes

   Client/Server data     Connectivity & volume flows

   Messaging              Connection orientation

   File transfers         Latency tolerance

   Batch data             Network availability tolerance

   Network overhead       Error rate tolerance

   Multimedia             Priority

                           Protocol type

                           Avg. packet length & MTUs
Gathering User Requirements

 In general, users primarily want application
 availability in their networks. This includes...
   Response Time -- time between entry of a command and

    execution of the command
   Throughput-intensive apps. -- such as file-transfers and

    batch operations scheduled during low traffic periods
   Reliability -- some apps require nearly 100% uptime such

    as NASDAQ and emergency services.
Assessing User Requirements

 Three methods to assess user needs:
   User community profiles--determine the needs of various

    user groups within the organization; crucial 1st step
   Interviews, focus groups, and surveys--used to establish a
    baseline for building the network
   Human factors tests--most expensive & time consuming of

    the three; sampling of users interacting with the network
    from a controlled lab environment to determine user
    tolerance to various levels of service
Factors That Affect Availability

            Throughput
            Response Time
            Access to Services

 You can increase availability by adding more
 resources (i.e. bandwidth, servers, etc.), but
 this drives up cost
 Network design seeks to provide the greatest
 availability for the least cost.
Analyzing Requirements

 Sensitivity Testing
  Evaluate how a network will behave under certain

   conditions.
  Involves breaking stable links and observing the results

      how is traffic rerouted
      speed of convergence
      is connectivity lost?
      is some traffic sensitive to the break?
    Increase traffic loads to media saturation point and observe
     results.
The Three-Layer
  WAN Model


  Table of Contents
The Importance of Layers

 Designing networks using the OSI model
   Allows the network to be designed in layers

   Uses layers to simplify the tasks required for

    internetworking
   Design elements can be replicated as the network grows

 Therefore, networks should be designed using
 a hierarchical model.
   Unfortunately, most networks are thrown together into a
    mesh (“a mess!”) with little or no vision of future needs.
Benefits of Hierarchical Design
 Scalability
   allows for future growth without sacrificing control or functionality

 Ease of Implementation
   logically constructed layers specify the functions of each layer

 Ease of troubleshooting
   well-defined functions at each layer aid in the isolation of problems

 Predictability
   behavior of functional layers can be estimated and planned for

 Protocol support
   allows easier implementation of future technologies because the
    network has been logically constructed
 Manageability
   All the above aids net. admin. in overall management of the network
The Hierarchical Design Model

 The three layers are...
   Core layer--provides transport between remote sites

   Distribution layer--provides policy-based connectivity

   Access layer--provides workgroup/user access to network
Core Layer

 Fast WAN connections between remote sites
 Core links are normally point-to-point with no host

  devices
 Core services include:

    T1/T3
    Frame Relay
    ATM
    SMDS
Distribution Layer

 Provides WAN services to multiple LANs
 Usually the campus backbone

 Uses Fast Ethernet (or Gigabit Ethernet)

 Used on large sites to interconnect buildings
Access Layer
 Usually a LAN or group of LANs
 Gives access to specific users and workgroups

 This layer is where all hosts (including servers) are attached to
  the network
 We study the design of this layer in Semester 3, LAN Design
WAN Layer Functions


    Table of Contents
Core Layer Functions

 Optimize Transport Between
 Remote Sites
  Redundant paths to guard against circuit

   outages
  Provide load sharing and rapid

   convergence when link states change
  Efficient use of bandwidth by...

     Implementing scalable routing protocols and
     Blocking local traffic access to the core
Distribution Layer Functions

 Policy-Based Connectivity
  Boundary definition & packet manipulation

  Control access to services of the core layer and other

   distribution layer routers
  VLAN routing

  Address aggregation (i.e., subnets) & route optimization

  ACLs and other security measures
Access Layer Functions

 Workgroup & User Access to the Network
  Isolation of Broadcast Traffic

  Shared and Switched Bandwidth

  MAC-layer filtering

  Microsegmentation
Other Hierarchical Options
 One-Layer Design
  Only a few remote sites
   need to be connected
  Servers are placed in farms
   or in each workgroup to
   reduce traffic on the
   backbone

 Two-Layer Design
   WAN link is used to
    interconnect separate sites
   Link does not have to be
    dedicated. An alternative
    would be ISDN.
Hierarchical Design Advantages
 Controlling data traffic patterns through
 source/destination network layer addressing
   A packet only needs to travel up the hierarchy as far as it needs to

    find the destination.
   With good design, most traffic would be contained in the access

    layer with users accessing their workgroup servers
 Server Placement
   Enterprise Servers needed by all workgroups should be placed in the
    Distribution Layer (e.g. email, DNS, etc.)
   Workgroup Servers needed by a unique set of users should be
    placed in the Access Layer, preferably in the same broadcast
    domain as the users.
Table of Contents




 End Slide Show