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This chapter is from the book

This chapter is from the book

Selecting a WAN Technology (2.2)

Corporate networks can be interconnected using private WAN infrastructures and public WAN infrastructures. This section discusses both types of infrastructures.

WAN Link Connection Options (

There are several WAN access connection options that ISPs can use to connect the local loop to the enterprise edge. These WAN access options differ in technology, speed, and cost. Each has distinct advantages and disadvantages. Familiarity with these technologies is an important part of network design.

As summarized in Figure 2-10, an enterprise can get WAN access over a

  • Private WAN infrastructure: Service providers may offer dedicated point-to-point leased lines, circuit-switched links, such as PSTN or ISDN, and packet-switched links, such as Ethernet WAN, ATM, or Frame Relay.
  • Public WAN infrastructure: Service provider may offer broadband Internet access using digital subscriber line (DSL), cable, and satellite access. Broadband connection options are typically used to connect small offices and telecommuting employees to a corporate site over the Internet. Data traveling between corporate sites over the public WAN infrastructure should be protected using VPNs.

    Figure 2-10

    Figure 2-10 WAN Access Options

    The topology in Figure 2-11 illustrates some of these WAN access technologies.

    Figure 2-11

    Figure 2-11 WAN Access Technologies

Service Provider Network Infrastructure (

When a WAN service provider receives data from a client at a site, it must forward the data to the remote site for final delivery to the recipient. In some cases, the remote site may be connected to the same service provider as the originating site. In other cases, the remote site may be connected to a different ISP, and the originating ISP must pass the data to the connecting ISP.

Long-range communications are usually those connections between ISPs or between branch offices in very large companies.

Service provider networks are complex. They consist mostly of high-bandwidth fiber-optic media, using either the Synchronous Optical Networking (SONET) or Synchronous Digital Hierarchy (SDH) standard. These standards define how to transfer multiple data, voice, and video traffic over optical fiber using lasers or light-emitting diodes (LEDs) over great distances.

A newer fiber-optic media development for long-range communications is called dense wavelength-division multiplexing (DWDM). DWDM multiplies the amount of bandwidth that a single strand of fiber can support. As illustrated in Figure 2-12, DWDM assigns incoming signals specific color wavelengths. These signals are transmitted over the fiber-optic cable to the end device, which then separates the traffic accordingly.

Figure 2-12

Figure 2-12 DWDM Concept

DWDM circuits are used in all modern submarine communications cable systems and other long-haul circuits.

Specifically, DWDM

  • Enables bidirectional communications over one strand of fiber
  • Assigns incoming optical signals to specific wavelengths of light (i.e., frequencies)
  • Each channel is capable of carrying a 10-Gbps multiplexed signal
  • Can multiplex more than 80 different channels of data (i.e., wavelengths) onto a single fiber
  • Can amplify these wavelengths to boost the signal strength
  • Supports SONET and SDH standards
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