Leased Lines

For users with high bandwidth requirements (and deep pockets), dedicated leased lines provide digital service between two locations at speeds that can far exceed ISDN and are as fast or faster than DSL or cable modem. A leased line is a permanent 24-hour connection to a particular location that can be changed only by the telephone company. Businesses use leased lines to connect LANs in remote locations or to connect to the Internet through a service provider. Leased lines are available at various speeds, as described in the following sections.

T-1 and T-3 Connections

To connect networks in distant locations, networks that must support a large number of Internet users, or especially organizations that will be hosting their own Internet services, a T-1 connection might be a wise investment. A T-1 is a digital connection running at about 1.5Mbps. This is more than 10 times faster than an ISDN link and is more than double the speed of most fast DSL connections. A T-1 can be split (or fractioned), depending on how it is to be used. It can be split into 24 individual 64Kbps lines or left as a single high-capacity pipeline. Some ISPs allow you to lease any portion of a T-1 connection that you want (in 64Kbps increments). SBC (formerly Ameritech), for example, offers a flexible T-1 service it calls DS1; it's available at full bandwidth or in various fractional sizes. Figure 17.5 shows how a T-1 line is fractioned.

Figure 17.5. Full T-1 service uses all 24 lines (each one is 64Kbps) as a single pipeline; a fractional T-1 service of 256Kbps could use slots 14 only, for example.

An individual user of the Internet interacts with a T-1 line only indirectly. No matter how you're accessing the Internet (dialup modem, ISDN, DSL, cable modem, DirecWAY, StarBand, or fixed-base wireless), your ISP typically will have a connection to one or more T-1 or T-3 lines, which connect to the backbone of the Internet. This connection to the backbone is sometimes referred to as a point of presence (PoP). When you make your connection to the Internet, your ISP shares a small chunk of that T-1 pipe with you. Depending on how many other users are accessing the Internet at your ISP or elsewhere, you might experience very fast to slow throughput, even if your modem connection speed remains constant. It's a bit like splitting up a pizza into smaller and smaller slices to accommodate more people at a party: The more users of a high-speed connection, the slower each individual part of it will be. To keep user connections fast while growing, ISPs add full or fractional T-1 lines to their points of presence. Or, they might switch from a T-1 connection to the even faster T-3 if available.

Note

Equivalent in throughput to approximately 28 T-1 lines, a T-3 connection runs at 45Mbps and is suitable for use by very large networks and university campuses. Pricing information falls into the "if-you-have-to-ask-you-can't-afford-it" category.

If your Internet connection is on a corporate LAN or your office is located in a downtown building, your relationship to a T-1 line might be much closer. If your building or office is connected directly to a T-1, you're sharing the capacity of that line with just a relatively few other users rather than with the hundreds or thousands of dialup users a normal ISP is hosting at one time. Full or fractional T-1 lines are being added to more and more apartments and office buildings in major cities to allow residents and workers faster Internet access. In these cases, a LAN connection to the T-1 is usually provided, so your Internet access device is a network card, rather than a modem or ISDN terminal adapter.

With the rise of the Internet and the demand for high-speed data access for networks, the price of T-1 links in the United States has fallen drastically since the late 1990s, although you will still pay in the hundreds of dollars for typical service offerings. T-1 service can be acquired from either your local telco or third-party firms. Fractional T-1 or burstable T-1 (which allows you to have differing levels of bandwidth up to the entire T-1 1.5Mbps depending on demand) costs less than full T-1 service. For a large organization that requires a lot of bandwidth, the lower cost of T-1 services today make installing a higher-capacity service and growing into itrather than constantly upgrading the linkmore economical than ever. Although the speed of T-1 links resembles the maximum rates available with DSL or cable modem service, most types of T-1 service provide constant bandwidth (unlike cable modems) and bypass the potentially severe problems of trying to retrofit old phone lines with digital service (unlike DSL).

Comparing Conventional High-speed Services

Some telcos who formerly posted pricing for ISDN, T-1, or other high-end telecommunications services now have a "call us" button on their websites because pricing is complicated by many factors, including

• Location (state and locality because telephone companies are regulated public utilities)

• Fixed and variable costs

• Usage

• Installation costs

• Your needs

Be sure to consider hardware and usage costs when you price services, and (for items such as ISDN terminal adapters and network cards) compare the official offerings with products available elsewhere. If you decide to provide some of the equipment yourself, find out whose responsibility repairs become. Some companies provide lower-cost "value" pricing for services in which you agree to configure the hardware yourself and maintain it. If you have knowledgeable staffers who can handle routers and other network configuration, you can save money every month, but if not, go with the full-service option.