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DSL vs. T-1
Current Market Deployment
Digital Subscriber Line (DSL) is a digital dedicated service that uses high
bandwidth to bring voice, data, video, teleconferencing, and the Internet to
your business. It has many flavors. So you will need to decide which flavor
is most suitable for your business. It is an "always on" service with speedy
Internet access. Files can be downloaded and uploaded (depending on the
flavor of DSL you choose) at speeds that cannot be attained with an ordinary
56K modem, This new technology is currently being deployed widely, and is
available in most regions.
T-1 is a member of the T-carrier system. T-carrier is a communications
system used for carrying voice and data transmissions in a digital format.
T-1 was developed in the 1960's to meet the needs of businesses having
multiple users on a system requiring fast speed and broad bandwidth. For a
fixed monthly rate, businesses with 20 or more users can communicate via
both voice and data.
T-1 provides high speed, point-to-point digital transmission line (up to
1.544 Mbps). It is widely deployed and readily available in most regions. It
is currently the most common way that large companies connect their LAN to
the rest of the world.
How DSL and T-1 Work
A DSL Modem and an ethernet card for your PC are required for DSL service.
The DSL modem enables you to hook up your PC to the phone line. DSL uses
high bandwidth to allow voice, data, video, teleconferencing, and Internet
access on your ordinary copper wire lines behind your walls. There is only
one path for carrying voice, video and data. It is an "always on" service
with speedy Internet access that is not "shared" with other subscribers.
There are many flavors of DSL. Two flavors are being used widely by SMBs:
Symmetric DSL (SDSL) and Asymmetric DSL (ADSL). The difference between them
is their ability to carry data in upstream (i.e., upload) and downstream
(i.e., download) directions. SDSL uses upstream and downstream capacity to
carry data in both directions. ADSL delivers higher speed downstream
service, and slower speed upstream service. If users at a business spend
more time downloading files than uploading files, then ADSL is a good choice
since pages can be downloaded faster.
T-1 uses pulse code modulation and time-division multiplexing to deliver
voice and data information simultaneously. T-1 is a digital transmission
service that can be divided into 24 voice channels for carrying voice and
data. The entire 1.544 Mbps bandwidth, or any portion of this, can be used
as a single high-speed data channel. A T-1 line can carry both data and
voice signals on the same line with the data part of the line continuously
connected. It is best suited for large networks where 20 or more users are
accessing the Internet at the same time.
T-1 is a dedicated leased digital line. T-1 digital circuits are used to
connect a voice Private Branch Exchange (PBX) to the telephone company's
central office (CO). On the data side, T-1 is used to connect the LANs of
two geographically distant offices.
Distance Requirements
DSL is a distance sensitive. What that means is that your business must be
located within 18,000 feet from the telephone company's central office (CO)
to get service. The closer your business is located from the CO, the faster
you can download files.
T-1 has no specific distance requirements. In fact, for remote areas it is
an excellent solution.
Speed and Bandwidth
Speed and bandwidth are very important considerations when choosing a
service. Speed refers to data transmission rate. Bandwidth is the capacity
to carry data. Both are measured in bits per second. DSL's data rates range
from 128 Kbps to an ultra-fast 8 Mbps or even more (i.e., Very high-bit-rate
DSL), depending on the DSL flavor you choose. This ability to flexibly grow
to higher levels of bandwidth makes it an excellent solution for many SMBs.
Frame Relay's voice and data rates range from 56 Kbps to 45 Mbps.
Installation: Wiring
DSL is easily installed on the ordinary twisted-pair copper wire currently
behind the walls at your business. In some cases, DSL may require a
different jack and, occasionally, new wiring. The telephone company can
complete the wiring for you, you can do it yourself, or you can hire an
independent contractor.
T-1 can be installed on twisted pair copper wire,
fiber optics, coaxial cable, digital microwave or infrared lighting. If
fiber optics is used as the medium, you'll need to supply backup power
(i.e., electricity) at your site. Without this, you will risk losing your
service in the event of a power failure.
Switched Service: T-1
T-1 is a dedicated services, used exclusively by the particular business
leasing the service. It is also a switched services. Switched service is a
circuit for which the endpoints may vary with each usage. The circuit is
provided by a common carrier, which is routed through a switched network,
providing circuit switching between public end users. There are two types of
switched technology: circuit switched and packet switched. In a switched
circuit, a call is established only for as long as needed and then the
session is disconnected. Frame relay is a packet switched service.
Fractional T-1
If your business doesn't need the full 1.544Mbps connection, you can select
a portion of the T-1bandwidth. This is called fractional T-1. You can get
fractional T-1 and then flexibly grow to the full 1.544Mbps as your network
expands or as your needs change. This will be cheaper than leasing the full
T-1.
Applications
DSL is used for high-speed Internet access. It is also used for carrying
voice, data and video at fast rates. Users can download and upload large
files very quickly, with privacy and security. Video conferencing can also
be accomplished. Using DSL, you can set up an email or web server.
T-1 lines are high-capacity lines used to carry voice
and data, and access the Internet. These lines are also used to connect
individual networks to the Internet. T-1 circuits are frequently used to
link remote LANs. Also, T-1 can be used to bring Centrex service from the
telephone company's central office (CO) to your business. Centrex is a
telephone company central office-based service provided by a local service
provider (i.e. your local telephone company). Centrex, brought to you by
T-1, can route and switch your calls. It can give you PBX-like enhanced
services such as conference calling, call forwarding, caller Id, and other
vertical features. Using Centrex, you can save money since you don't need
phone operators, administrators, and other resources needed to manage your
phone lines; and, another plus is that you do not need to use on-site
switching equipment. With Centrex, via T-1, some of the automated features
that you can get are as follows:
Direct Inward Dialing.
Direct Outward Dialing.
Automatic Identification of dialed calls.
Required Equipment
For DSL, a splitter is usually required, depending on
the flavor of DSL you want, or the type of DSL available in your area. G-Lite
DSL does not require a splitter. A DSL modem and an Ethernet card are also
required for installation.
Unlike your analog telephone line, your DSL line does not draw its current
from your local service provider central office. You'll need an
Uninterruptible Power Supply (UPS) to ensure continuous service in the event
of a power failure.
DSL use requires that your computer have a Peripheral Component Interconnect
(PCI) slot for installing the PCI. PCI adaptor cards may also be necessary
to combine an Ethernet interface to your PC with DSL modem functions.
A T-1 line requires a special, dedicated circuit from the phone company.
All T-1lines require that a Channel Service Unit (CSU) be connected between
your Data Terminal Equipment (DTE), i.e., a personal computer, and the T-1
line. A CSU serves both as a surge protector (to protect your equipment from
voltage anomalies such as lightning) and a monitor of the line itself.
A CSU is used to connect Non Data Terminal Equipment to a T-1 line. If your
DTE doesn't provide a "T-1 Out" for a CSU, then a combined DSU/CSU will be
required. Many of these devices include sophisticated performance monitoring
and diagnostic capabilities. For full T-1 service, you must provide a
Channel Service Unit (CSU).
Cost and Value Considerations
DSl is a very affordable and cost-effective service based upon a flat rate.
Since cost is not based upon usage, you can use this service any time for as
long as you want without incurring any usage charges. It is easily and
inexpensively installed. In fact, you may be able to install it yourself.
However, you will need to purchase a DSL modem, a splitter and an
Uninterruptible Power Supply when installing service. When selecting DSL,
you should determine which flavor of DSL is best for your business. This
decision will affect the price of DSL installation and service.
For businesses that need the high-end flavors of DSL with very large
bandwidth and ultra fast speeds, techniques are currently being developed
that will lower costs for installation, deployment, testing and maintenance
of these high-speed services. By reducing or eliminating the need for
additional central office switching equipment, these new products can also
cut the deployment time for these new high-end services.
T-1 is a very fast (10 times faster than ISDN) leased service and this may
come at a premium, but it provides a cost-effective solution for many
businesses. Setup and installation will probably be your biggest
out-of-pocket expenditure. T-1 is an excellent solution for companies that
can initially use fractional T-1.
