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What's the Story with Dial-Up Connections?

Dial-up connections are made using plain old telephone service (POTS) and a modem. A POTS line, as the name indicates, is a regular telephone line. You might have noticed that telephone lines excel at carrying sounds. That implies that when you use a POTS line to establish a data connection, you need some device that converts your computer's digital signals to sounds. That device is a modem. You might have heard those soundsa collection of rapid pulses of whistles and beepsif you have ever picked up an incoming fax call.

Now that you know what a modem and a POTS line are, it's time to take a look at how they work together. Then you see how to decide whether they are for you and, if they are, how to configure a dial-up connection on your computer.

How Does It Work?

How does it work? An excellent question! The beginning of this chapter tells you about some of the differences in ISPs and how they really serve different markets within the Internet. Some of those ISPs that function as residential on-ramps would have to support dial-up connectivity to the Internet. Think about it this way: Cable network operators want you to access the Internet using their cable network, whereas local telephone companies want you to use their telephone lines. Independent ISPs (those that aren't a cable or telephone company) are at a distinct disadvantage when it comes to connecting your home to their network.

Independent ISPs have been consolidating (translation: going out of business) at a frightening pace. They still exist and still serve a useful purpose. Such ISPs rely upon your home's telephone line as a way to connect you to their network. To support this, they buy hundreds of modems and install them in a series so when you dial the main telephone number, your call is routed to the next available modem in the pool.

The modems would need to be connected to the telephone company's network. Instead of buying hundreds of POTS lines, it's better to buy trunk lines. A trunk line is a generic term for a high-capacity telecommunications line that can carry multiple dial-up sessions simultaneously. These modems aren't connected to a computer; they are connected to a network. After you prove your identity as a paying customer (by correctly responding to the ID and password challenge), you have free run of the network.

Figures 13-2 and 13-3 show you how this type of Internet access works.

As you can see from comparing Figures 13-2 and 13-3, no permanent connection exists between your computer and the Internet. Instead, there is a physical link between your computer and your local telephone company's switch. That switch makes a temporary physical connection to your ISP when you initiate a dial-up session. The dial-up session is indicated with lightning bolts.

You have two main choices with respect to modems. Modems have become so inexpensive that they are frequently built into today's computers. Internal modems require only that you plug a modular telephone cord into a telephone jack and then configure your dial-up connection. If you have an older computer or bought a new computer that didn't have a modem built in, you can add an external one. Setting up an external modem is only slightly more complicated than setting up an internal modem. You need to plug it into an electrical outlet, cable it to your computer using, and then connect it to the modular telephone jack. Later, this chapter walks you through configuring a dial-up connection logically on your computer.

Dial-Up Today

One of the questions that must be running through your mind is "In this era of residential broadband service, does anybody really still use dial-up technology to access the Internet?" That's a fair question.

Dial-up technologies used to be the only game in town. If you wanted to make a data connection to the Internet from home, you were smiling and dialing. Over time, the quality of the connection increased greatly from just a few hundred bits per second (bps) to about 56,000 bps. That's about where it has stalled.

Remember: You are using a telephone line that was only designed for carrying voice signals, so there is a finite amount of bandwidth available. Over time, modems became capable of processing up to 115,200 bps, which is great over voice-grade telephone lines, but still paltry in comparison to the performance offered by other dedicated transmission technologies.

Modems that communicate over POTS lines are restricted to just 56,000 bps because a POTS line can only carry 64,000 bps. You need some of that capacity for managing the connection, so the theoretical maximum throughput of a modem is 56,000 bps. Modems that transmit at any rate greater than 56,000 bps use compression to reduce the number of bits that need to be sent. Thus, more data gets sent per second even though the modem still only transmits at 56,000 bps.

The other drawback to dial-up service might seem trivial. Still, it is worth mentioning. The process of initiating a communications session can take a little while, although certainly a matter of seconds, not minutes. Think about that. While dedicated connections are always on, with dial-up you have to actually dial the receiving end, wait for the receiving modem to answer, and then negotiate how fast the two modems can talk. All that can occur in less than a minute, but you must suffer that wait every time you want to connect.

When All Else Fails…

…there are still good old modems and POTS lines! Modems and POTS lines are still used in areas where dedicated Internet access technologies aren't available. Let's face it: Cable companies still don't have the same global reach of wire-based telephone companies. Some neighborhoods are just too sparsely populated to make it worthwhile for cable companies to extend their networks there. For such neighborhoods, modems and POTS lines are still the only game in town.

Even if Cable Is Available…

…there might still be a use for modems and POTS lines. Even in neighborhoods where cable companies have built a network, modems and POTS lines might play a role. You see, not every cable company has built a network capable of transmitting and receiving data.

The original cable TV networks were designed just to send signals to their customers. In areas where there is only a one-way network, cable companies offer a service known as an asymmetric cable service. Connecting to the Internet via an asymmetric cable solution requires you to use a modem and POTS line as your uplink and the cable as the downlink. As Figure 13-4 shows, you transmit to the Internet using the modem and POTS line and receive via the cable.

This solution might seem a bit awkward, but it actually makes a lot of sense. Asymmetric service was conceived as a cost-effective way of providing cable-based Internet access without incurring the cost of upgrading the cable network to two-way capability. The asymmetry is in the performance capabilities of the two connections. Cable service is high bandwidth; sometimes as fast as 1 million bps per second on the connection to your home. Dial-up is slow in comparison and is frequently hard pressed to hit more than 50,000 bps in actual throughput.

That might seem like a tragic mismatch of technologies until you stop and think about your Internet usage habits. You open a browser and type in a tiny little command to access a website. That command might be as simple as typing http://www.cisco.com in your browser's address bar. That paltry amount of data easily fits inside just one packet. However, you receive an entire web page filled with lots of information and pretty pictures. Depending on where you go on the Internet, it is possible that the one packet you sent results in the receipt of hundreds of packets. In other words, the nature of web browsing is asymmetric, so why not build a network that way?

The bottom line with dial-up technologies is this: Their best days are behind them but they are not dead yet! Until broadband technologies become as widely installed as telephones, there continues to be a need for modems and POTS lines.