Hardware Reference
In-Depth Information
Figure 16.4. 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 1-4 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, 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 connect to the Internet, your ISP shares a small chunk of
that 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 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 large networks and university campuses. Pricing information falls into the
“if-you-have-to-ask-you-can't-afford-it” category.
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 makes
installing a higher-capacity service and growing into it—rather than constantly upgrading the link—
more economical than ever.
Comparing High-Speed Internet Access
One way of making sense out of the confusing morass of plans available from cable modem, DSL,
fixed wireless Internet, and satellite vendors is to calculate the average cost per Mbps of data
downloaded ($/Mbps). You can calculate this figure yourself by dividing the service cost per month
by the rated or average speed of the service:
Cost ($) / Speed (Mbps) = $/Mbps
You can use this formula with any broadband or dial-up service to find the best values. Note that this
simple calculation doesn't take into account the cost of any required equipment, such as modems,
filters, satellite dishes, and so on. If you must pay extra for equipment or installation upfront, divide
