Chapter 16. Dedicated Connections

SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE

Leased Lines

Asynchronous Transfer Mode ( ATM )

The Importance of Frame Relay and the X.25 Interface

The preceding chapter covered some of the dial-up solutions you can use to connect your LAN to a wide area network (WAN), or to connect branch offices to your LAN. In this chapter you will learn about the dedicated techniques that have typically been used to connect business locations so that large data transfers can take place. Some are traditional approaches that still have a place in today's network environment. T1 lines (digital leased lines), ATM, and Frame Relay are not going to be relegated to history anytime soon. Indeed, ATM and Frame Relay have continued to adapt to today's networking environment by providing a fast transport for other better known protocols, such as IP. These types of connections are normally used in situations in which a large bandwidth and reliability of the connection are the most important considering factors.

Note

One technology that has been considered as a major contender for the past decade for access to the corporate network by a home user is ISDN (Integrated Services Digital Network). This technology was developed to offer up to 128Kbps (provided by two separate 64Kbps bearer channels, along with a separate control channel. This describes the Basic Rate Interface (BRI) ISDN service that is the most popular version. A higher-rate version called the Primary Rate Interface (PRI) offers 23 bearer channels to carry data. However, ISDN comes at a higher price than many of today's available options, and the conditioning, testing, and configuration for an ISDN line can be quite time-consuming . ISDN was developed a decade ago when the concept of high-rate transmissions across an analog telephone line was considered to be the high-tech solution at that time.

In the next two chapters you will learn about other technologies, such as digital subscriber lines (xDSL) and cable modems, that can be used to connect remote users to your network with a larger bandwidth than can be accomplished by using a dial-up modem and an ordinary telephone line. Although many network administrators consider these technologies to be targeted toward a home user, they can be employed inexpensively to allow you to connect low-volume traffic from home workers as well as branch offices.

Note

While ISDN seems to be falling by the wayside, DSL and cable modem access actually offer superior service in bandwidth compared to ISDN, in most instances. DSL service, if it is within the allowable distance from your phone company's office, provides a reliable service that can serve many branch office needs, at a fraction of the cost of a dedicated line. For users who work at home (which is now becoming realized as a boon for businesses), it is also much less expensive than ISDN. One important factor to remember is that most xDSL and cable modem connections offer a larger bandwidth for downloading than uploading. For xDSL customers, you will find that most telcos can offer a wide variety of services that are not geared toward home users, and can give you the same bandwidth for both uploads and downloads.