Chapter 1 – Sections & Objectives

• 1.1 WAN Technologies Overview
  • Explain WAN access technologies available to small to medium-sized business networks.
• 1.2 Selecting a WAN Technology
  • Select WAN access technologies to satisfy business requirements.

1.1 WAN Technologies Overview

Purpose of WANs

• WANs connect LANs
• WANs are used to connect remote sites to the enterprise network.
• WANs connect home users to the Internet.
• Enterprise networks are using security and privacy solutions over the Internet to connect remote sites and users.

Common WAN topologies are:

• Point-to-Point – Typically a dedicated leased-line connection such as T1/E1
• Hub-and-Spoke – A single-homed, point-to-multipoint topology where a single interface on the hub router can be shared with multiple spoke routers through the use of virtual interfaces
• Full Mesh – Each router has a connection to every other router; requires a large number of virtual interfaces
• Dual-homed – Provides redundancy for a single-homed, hub-and-spoke topology by providing a second hub to connect to spoke routers
• As businesses grow, the topologies and WAN strategies change:
  • Small Office – These businesses typically consist of one LAN at one location that connects to the Internet through a broadband technology.
  • Campus Network – A small- to medium-sized business with one location and multiple LANs uses specialized equipment and technologies to connect to the Internet.
  • Branch Networks – As the business grows, it adds more branch offices, each with its own campus network. WAN contracts to connect the remote networks are negotiated.
  • Distributed Network – A multinational business has a network distributed across the globe. These businesses have complex WAN strategies to securely connect to regional offices, branch offices, partners, and telecommuters.

WAN Technologies Overview WAN Operations

• • WAN operations focus primarily on the physical layer (OSI Layer 1) and the data link layer (OSI Layer 2).
    • Layer 1 protocols describe how to provide electrical, mechanical, operational, and functional connections
    • Layer 2 protocols define how data is encapsulated
  • WAN Terms include:
    • Customer Premises Equipment (CPE) – owned by the business or leased from the service provider.
    • Data Communications Equipment (DCE) – provides an interface to connect subscribers to a communication link on the WAN cloud.
    • Data Terminal Equipment (DTE) – connects to the local loop through the DCE.
    • Demarcation Point – separates customer equipment from service provider equipment and is the place where the responsibility for the connection changes from the user to the service provider.
    • Local Loop – cable that connects the CPE to the CO of the service provider (last mile).
    • Central Office (CO) – local service provider facility or building that connects the CPE to the provider network.
    • Toll network – all the cabling and equipment inside the WAN provider network.

• WAN devices include:
  • • Dialup modem – legacy WAN technology that converts digital signals into voice frequencies to be transmitted over the analog lines of the public telephone network.
    • Access server – legacy WAN technology that coordinates dial-in and dial-out user communications.
    • Broadband modem – used with high-speed DSL or cable Internet service
    • CSU/DSU – used to convert digital, leased-line signals into frames that the LAN can interpret and vice versa.
    • WAN switch – multiport internetworking device used in service provider networks
    • Router – provides internetworking and WAN access interface ports to connect to the service provider network
    • Core router/Multilayer switch – resides within the backbone of the WAN, supports multiple interfaces, and forwards IP packets at full line speed

  

• WANs can operate as circuit-switched or packet-switched networks:
  • Circuit-switched Networks – establish a dedicated circuit between source and destination before the users may communicate, such as making a telephone call
  • Packet-Switched Networks – split traffic into packets that are routed over a shared network and do not require a dedicated circuit between source and destination

1.2 Selecting a WAN Technology

WAN Services

Two way that a business can get WAN access:

• • Private WAN Infrastructure
    – The business negotiates for dedicated or switched WAN access with a service provider.
  • Public WAN Infrastructure
    – WAN access is achieved through the Internet using broadband connections. VPNs secure the connections.

• • This topology illustrates some of these WAN access technologies.

Private WAN Infrastructures

• • • Dialup
      • Advantages:
        • Simplicity
        • Quality
        • Availability
      • Disadvantages:
        • Cost
        • Limited flexibility

• ISDN
  • Sample ISDN Topology
  • ISDN BRI
  • ISDN PRI
• Frame Relay
  • • PVCs carry both voice and data traffic.
    • PVCs are uniquely identified by a data-link connection identifier (DLCI).
    • PVCs and DLCIs ensure bidirectional communication from one DTE device to another.
    • R1 uses DLCI 102 to reach R2 while R2 uses DLCI 201 to reach R1.

  

• ATM
  • Built on a cell-based architecture, rather than on a frame-based architecture. ATM cells are always a fixed length of 53 bytes.
• Ethernet WANFeatures and Benefits of Ethernet WAN include:
  • Reduced expenses and administration
  • Easy integration with existing networks
  • Enhanced business productivity
  • Service providers now offer Ethernet WAN service using fiber-optic cabling.
  • Known as Metropolitan Ethernet (MetroE), Ethernet over MPLS (EoMPLS), and Virtual Private LAN Service (VPLS).

  

  Note: Commonly used to replace the traditional Frame Relay and ATM WAN links.

• MPLSMultiprotocol Label Switching (MPLS) is a multiprotocol high-performance WAN technology that directs data from one router to the next, based on short path labels rather than IP network addresses.

  

• VSATVery small aperture terminal (VSAT) – a solution that creates a private WAN using satellite communications.

  

Public WAN Infrastructures

• DSL
  • • Always-on connection technology that uses existing twisted-pair telephone lines to transport high-bandwidth data, and provides IP services to subscribers.
    • A DSL modem converts an Ethernet signal from the user device to a DSL signal, which is transmitted to the central office.

  

• Cable
  • • Network access is available from some cable television networks.
    • Cable modems provide an always-on connection and a simple installation.

  

• Wireless
  • • New developments in broadband wireless technology:
    • Municipal Wi-Fi – Many cities have begun setting up municipal wireless
    • WiMAX – Worldwide Interoperability for Microwave Access (WiMAX) is a new technology that is just beginning to come into use.
    • Satellite Internet – Typically used by rural users where cable and DSL are not available.

  

• 3G/4GCommon cellular industry terms include:
  • • 3G/4G Wireless – Abbreviation for 3rd generation and 4th generation cellular access. These technologies support wireless Internet access.
    • Long-Term Evolution (LTE) – A newer and faster technology, considered to be part of the 4th generation (4G) technology.

  

  • Public WANs rely on VPNs for securing data between private networks as it crosses a public network, such as the Internet.
  • Benefits:
    • Cost savings
    • Security
    • Scalability
    • Compatibility with broadband technology
  • Two types of VPN:
    • Site-to-site VPNs
      
    • Remote-access VPNs
      

Selecting WAN Services

Answer the following questions when choosing a WAN Connection:

1.3 Summary

Summary

• WAN access standards operate at Layers 1 and 2 of the OSI model.
• Permanent, dedicated point-to-point connections are provided by using leased lines.
• Private WAN connections include:
  • Dialup
  • ISDN
  • Frame Relay
  • ATM
  • Metro Ethernet
  • MPLS
  • VSAT
• Public WAN connections include:
  • DSL
  • Cable
  • Wireless
  • Cellular
• Security over public infrastructure connections can be provided by using remote-access or site-to-site Virtual Private Networks (VPNs).

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