Cisco Networking Academy Semester 4

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Cisco Networking Academy Semester 4

• Chapter 2
• WANs

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Table of Contents

• 2.1 WAN Service Providers
• 2.2 WAN Devices
• 2.3 How WANs relate to the OSI Model
• 2.4 WAN Encapsulation Formats
• 2.5 WAN Link Options

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WAN Services

• A WAN is a Data Communications Network operating
  beyond a LAN's geographic scope.
• You must subscribe to a WAN service provider,
  such as a regional Bell operating company (RBOC)
  to use WAN carrier network services.
• A WAN connects the locations of an organization
  to
• each other
• locations of other organizations
• external services (such as databases)
• remote user

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WAN Services

• A WAN uses data links, such as Integrated
  Services Digital Network (ISDN) and Frame
  wide-area geographies
• WANs carry many types of traffic, such as
• voice
• data
• video
• WAN technologies function at three layers of the
  OSI model
• physical
• data link
• Network

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WAN Services

• Telephone and data services are the most commonly
  used WAN services.
• Telephone and data services are connected from
  the building POP to the WAN provider's central
  office (CO).
• The CO is the local telephone company office to
  which all local loops in that area connect
• The services offered by the WAN provider are of 3
  main types
• Call setup (also called signalling)
• Time Division Multiplexing (TDM)
• Frame Relay

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WAN Services

• Call setup (also called signalling)
• Sets up and clears calls between telephone users.
  Most commonly used call setup is Signaling System
  7 (SS7)
• Time Division Multiplexing (TDM)
• Information from many sources has bandwidth
  allocation on a single medium. Basic telephone
  service and ISDN use TDM circuits.
• Frame Relay
• Data contained in frames shares bandwidth with
  other WAN Frame Relay subscribers. Uses
  statistical multiplexing (STDM)

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CPE, demarc, "last mile", CO switch, toll network

• The most commonly used terms associated with the
  main parts of WAN services
• Customer premises equipment (CPE) -- Devices
  physically located on the subscriber's premises.
• Demarcation (or demarc) -- The point at which the
  CPE ends and the local loop portion of the
  service begins. Often occurs at the POP of a
  building.
• Local loop (or "last-mile") -- Cabling (usually
  copper wiring) that extends from the demarc into
  the WAN service provider's central office.
• CO switch -- A switching facility that provides
  the nearest point of presence for the provider's
  WAN service.
• Toll network -- The collective switches and
  facilities (called trunks) inside the WAN
  provider's cloud.

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CPE, demarc, "last mile", CO switch, toll network
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CPE, demarc, "last mile", CO switch, toll network

• A key interface is between the data terminal
  equipment (DTE) and the data circuit-terminating
  equipment (DCE).
• Typically, the DTE is the router, and the DCE is
  the device used to convert the user data from the
  DTE into a form acceptable to the WAN service's
  facility (eg. MODEM, CSU/DSU, TA/NT1).
• The WAN path between the DTEs is called the
• link
• circuit
• channel
• line
• The DTE/DCE interface describes the physical
  layer standards. It uses various protocols (such
  as HSSI and V.35) that establish the codes that
  DTEs and DCEs use to communicate with each other.

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WAN Virtual Circuits

• A virtual circuit is a pathway through a
  packet-switched network that appears to be a
  dedicated, physically-connected circuit (as
  opposed to an actual, physical, circuit-switched
  pathway through a network).
• Virtual circuits are connection oriented
• Two types of virtual circuits exist
• switched virtual circuits (SVCs)
• permanent virtual circuits (PVCs).
• In a PVC, the customer and the carrier have
  negotiated the endpoints and characteristics of
  the virtual circuit ahead of time, and they are
  constantly available.
• The end points and a stated bandwidth called a
  Committed Information Rate (CIR) constitute a
  PVC, which is defined to the frame relay network
  devices
• In a SVC, the virtual circuit is available only
  "on-demand".
• circuit establishment, data transfer, and circuit
  termination.

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PVC and SVC

• SVCs are used in situations where data
  transmission between devices is sporadic.
• Disadvantage increased bandwidth due to the
  circuit establishment and termination phases
• Advantage decreased costs compare with constant
  virtual-circuit availability.
• A PVC is a permanently established virtual
  circuit that consists of one mode
• data transfer.
• PVCs are used in situations where data transfer
  between devices is constant.
• Advantage PVCs decreased bandwidth use because
  there are no establishment and termination phases
• Disadvantage increased costs due to constant
  availability.

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WAN Line Types
OC-768 now exists running at 40Gbps
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Fundamental WAN Devices

• The router is the essential WAN device, but it is
  also considered a LAN device.
• It offers many services, including LAN and WAN
  interface ports
• WAN switches connect to WAN bandwidth for voice,
  data, and video communication.
• Modems interface voice-grade services (telephone
  lines). They include
• CSUs/ DSUs devices that interface T1/E1 lines
• TA/NT1 devices that interface ISDN services.
• Communication servers concentrate dial-in and
  dial-out user communication.

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Routers and WAN Switches

• Routers provide interfaces for a wide range of
  links and subnetworks at a wide range of speeds.
• Routers are active and intelligent network
  devices and can participate in managing the
  network by
• providing dynamic control over resources
• supporting the tasks and goals for networks such
  as
• Connectivity
• Reliable performance
• Management control
• Flexibility
• Security
• A WAN switch is a multiport networking device
  that operates at the data link layer of the OSI
  reference model. A WAN switch typically switches
  traffic such as
• Frame Relay
• X.25
• Switched Multimegabit Data Service (SMDS)

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Routers and WAN Switches
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Describe modems on a WAN

• A device that interprets digital and analog
  signals by modulating and demodulating the
  signal, which enables data to be transmitted over
  voice-grade telephone lines.
• At the source, digital signals are converted to a
  form suitable for transmission over analog
  communication facilities. That is digital signals
  are converted into analog signals. At the
  destination, these analog signals are returned to
  their digital form.

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CSU/DSUs on a WAN

• A CSU/DSU is
• A digital-interface device that connects a T1/E1
• Sometimes two separate digital devices
• Sometimes its integrated into the router
• Adapts the physical interface on a DTE device
  (such as a terminal or router) to the interface
  of a DCE device (such as a switch) in a
  switched-carrier network

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ISDN Terminal Adapters on a WAN

• An ISDN Terminal Adapter (TA) is a device used to
  connect ISDN Basic Rate Interface (BRI)
  connections to other interfaces
• Its is an adapter that allows non ISDN devices
  (terminals or routers) to communicate on an ISDN
  network
• The ISDN TA can be either a standalone device or
  a board inside the TE2.

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Organizations that deal with WAN Standards

• WANs use the OSI model layered approach to
  encapsulation, just as LANs do
• WANs mainly focus on the physical and data-link
  layers
• Physical layer includes delivery of data
• Data-link requirements include addressing, flow
  control, encapsulations
• WAN standards are defined and managed by
• International Telecommunication
  Union-Telecommunication Standardization Sector
  (ITU-T)
• International Organization for Standardization
  (ISO)
• Internet Engineering Task Force (IETF)
• Electronic Industries Association (EIA)/
  Telecommunications Industries Association (TIA)

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WAN Physical Layer Standards

• WAN physical-layer protocols describe how to
  provide electrical, mechanical, operational, and
  functional connections for WAN services.
• Also describes the interface between the DTE and
  the DCE

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WAN Physical Layer Standards

• Physical layer standards define the rules for the
  DTE/DCE interface
• EIA/TIA-232 developed by TIA/EIA, supports
  signal speeds of up to 64kbps, formerly called
  RS-232
• EIA/TIA-449 a faster version of EIA/TIA-232 (up
  to 2 Mbps), capable of longer cable runs.
• EIA/TIA-612/613 A standard describing HSSI,
  which provides access to services at T3 (45
  Mbps), E3 (34 Mbps), SONET (51.84 Mbps) rates.
• V.35 An ITU-T standard describing a
  synchronous, physical-layer protocol used for
  communications between a network access device
  and a packet network. For speeds up to 48kbps
• X.21 -- An ITU-T standard for serial
  communications over synchronous digital lines.

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Name and describe 6 data-link encapsulations

• The WAN data link layer defines how data is
  encapsulated for transmission to remote sites
• Frame Relay uses simplified encapsulation with
  no error correction over high-quality digital
  facilities. A very fast protocol compared to the
  other WAN protocols.
• Point-to-Point Protocol (PPP) developed by the
  IETF. PPP contains a protocol field to identify
  the network-layer protocol.
• ISDN a set of digital services that transmits
  voice and data over existing phone lines.
• Link Access Procedure, Balanced (LAPB) For
  packet-switched networks used to encapsulate
  packets at Layer 2 of the X.25 stack. Provides
  reliability and flow control on a point-to-point
  basis.
• Cisco/IETF Used to encapsulate Frame Relay
  traffic. The Cisco option is proprietary and can
  be used only between Cisco routers.
• High-Level Data Link Control (HDLC) an ISO
  standard, HDLC not compatible between different
  vendors because of the way each vendor has chosen
  to implement it. HDLC supports both
  point-to-point and multipoint configurations.

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Serial line frame fields

• The two most common point-to-point WAN
  encapsulations are HDLC and PPP
• All the serial line encapsulations share a common
  frame format, which has the following fields
• The choice of encapsulation protocol depends on
  the WAN technology and the communicating
  equipment.

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PPP and HDLC

• PPP is a standard serial-line encapsulation
  method
• This protocol can check for link quality during
  connection establishment.
• Provides authentication through Password
  Authentication Protocol (PAP) and Challenge
  Handshake Authentication Protocol (CHAP).
• HDLC is Cisco's default encapsulation for serial
  lines
• No windowing or flow control
• Address field is 11111111, just like PPP
• A proprietary type code is inserted in the frame
  which means that HDLC framing is not
  interoperable with other vendors' equipment.
• Used when both ends of a dedicated-line
  connection are routers running Cisco IOS

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Two basic WAN link options

• Dedicated lines are physical circuits that
  involve no switching
• Switched lines are broken up into 2 categories
• Circuit-switched A physical circuit is
  established for the duration of the data transfer
• Packet-switched Packets may take different
  physical routes through the cloud on the way to
  the destination

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Dedicated Lines

• Dedicated lines, also called leased lines,
  provide full-time service. Typically are used to
  carry
• Data
• Voice
• Video
• Generally provide core or backbone connectivity
  between major sites or campuses, as well as
  LAN-to-LAN connectivity.
• The following are required for dedicated line
  connections
• A router port
• CSU / DSU
• An actual circuit from the service provider.
• Most important dedicated lines are T1, E1, and J1
  depending on where in the world you are located

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Leased Lines

• Leased lines are a form of dedicated lines.
• Dedicated lines also are referred to as
  point-to-point links because their established
  path is permanent and fixed for each remote
  network reached through the carrier facilities.
• Connections are made using the router's
  synchronous serial ports with typical bandwidth
  use of up to 2 Mbps (E1) available through the
  use of a CSU/DSU.
• Point-to-point links provide a single,
  pre-established WAN communications path from the
  subscriber through a carrier network (such as a
  telephone company), to a remote network
• The service provider reserves point-to-point
  links for the private use of the customer.
• Point-to-point is used for direct physical links
  or for virtual links consisting of multiple
  physical links.

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Packet-Switched Connections

• Network devices share a (PVC) permanent virtual
  circuit to transport packets from a source to a
  destination across a carrier network,
• Switched networks can carry variable-size frames
  or fixed-size cells.
• The most common packet-switched network type is
  Frame Relay. Others include X.25 and SMDS

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Frame Relay

• Designed to be used over high-speed, high quality
  digital facilities
• Does not offer much error checking or
  reliability, but expects upper-layer protocols to
  attend to these issues
• Connect multiple network devices on a multipoint
  WAN
• Frame Relay access is typically at 56 kbps, 64
  kbps, or 1.544 Mbps
• Each site can be connected to every other by a
  virtual circuit.
• Frame Relay service is offered through a PVC.
• A data-link connection identifier (DLCI)
  identifies a PVC
• The DLCI number is a local identifier between the
  DTE and the DCE
• The DLCI identifies the logical circuit between
  the source and destination devices.

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Frame Relay

• Two common topologies can be used in a Frame
  Relay solution
• Fully meshed topology Every Frame Relay network
  device has a PVC to every other device on the
  multipoint WAN.
• Partially meshed topology also often called a
  star topology or hub-and-spokes topology. In a
  partially meshed topology, not every device on
  the Frame Relay cloud has a PVC to every other
  device.

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Circuit-switched connections

• A dedicated physical circuit is established,
  maintained, and terminated through a carrier
  network for each communication session.
• Operates much like a normal telephone call
• Connections from one site to another are brought
  up when needed and generally require low
  bandwidth
• ISDN connections are limited to 64 or 128 kbps
• Used primarily
• to connect remote users and mobile users to
  corporate LANs
• as backup lines for higher-speed circuits like
  Frame Relay and T1 lines.

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ISDN

• ISDN BRI operates mostly over the copper
  twisted-pair telephone wiring in place today.
• ISDN BRI delivers a total bandwidth of a 144 kbps
  line into three separate channels.
• Two of the channels, called B (bearer) channels,
  operate at 64 kbps and are used to carry voice or
  data traffic.
• The third channel, the D (delta) channel, is a
  16-kbps signalling channel used to carry
  instructions that tell the telephone network how
  to handle each of the B channels.
• ISDN BRI often is referred to as 2BD.

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Cisco Networking AcademyWAN Design

• Semester 4, Chapter 3

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Table of Contents
Go There!

• WAN Design Requirements

• Gathering Analyzing Requirements

Go There!

• The Three-Layer WAN model

Go There!

• WAN Layer Functions

Go There!
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WAN Design Requirements
Table of Contents
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Network Demand

• WANs need to be developed to meet the following
  requirements
• Optimize WAN bandwidth
• Minimize cost
• Maximize the effective service to end users

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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.

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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

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Overriding Goal in WAN Design
Minimize Cost While Increasing Network
Availability
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Gathering Analyzing Requirements
Table of Contents
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Factors Affecting Design

• Environmental Variables
• Where are all the nodes?
• Performance Constraints
• What level of reliability? Host/client speeds?
  Traffic throughput?
• Networking Variables
• Whats the topology? What is the traffics
  characteristics?

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Traffic Characterization

• Types of Traffic
• Voice/fax
• Client/Server data
• Messaging
• File transfers
• Batch data
• Network overhead
• Multimedia

• Traffic Characteristics
• Peak Avg. Volumes
• Connectivity volume flows
• Connection orientation
• Latency tolerance
• Network availability tolerance
• Error rate tolerance
• Priority
• Protocol type

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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.

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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

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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.

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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.

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The Three-LayerWAN Model
Table of Contents
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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.

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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 in overall management of the
  network

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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

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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

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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

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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

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WAN Layer Functions
Table of Contents
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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
• Blocking local traffic access to the core

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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

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Access Layer Functions

• Workgroup User Access to the Network
• Isolation of Broadcast Traffic
• Shared and Switched Bandwidth
• MAC-layer filtering
• Microsegmentation

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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.

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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.

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Table of Contents
End Slide Show