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ISDN vs. DSL
Current Market Deployment Integrated Services Digital Network (ISDN) is a dedicated digital
service that, like DSL, brings voice, video and data packets to your
business. However, there are characteristic differences from DSL. ISDN is
slower than DSL, but faster than a 56K modem. Unlike DSL that is an "always
on" service, ISDN is a dial-up service. It also has a special channel that
is used for switching. If your business requires the special characteristics
of ISDN, then ISDN is an excellent choice. It has been widely deployed since
the 1980s, and is available in most regions.
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. It is predicted that it will surpass ISDN for
usage.
How ISDN and DSL Work
ISDN is a switched digital dial-up service. It combines video, voice and
data on a single access line. Basic Rate (BRI) ISDN is generally for home
use and has three channels. Primary Rate Interface (PRI) ISDN is the
business version of ISDN and has 24 channels, or paths. It uses 23 B
channels for carrying voice, video and data on the same copper wire. Channel
24, the D channel, is used for carrying low speed data communications,
switching, and signaling. This signaling is what produces the ringing of the
phone, busy signals, alarm signals, and other non-voice functions. ISDN
cannot transmit video or data to analog lines. Some of your customers may
need special ISDN equipment to receive certain data files sent by your
business.
Unlike ISDN, DSL is an "always on" digital service. To connect, you never
have to dial-up. There is only one path for carrying voice, video and data.
There are two flavors of DSL that are widely being used today: 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 your business spend more time
downloading files than uploading files, you may choose ADSL since you can
download pages faster.
Distance Requirements
Both DSL and ISDN are 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 either service. The closer your business is
located from the CO, the faster you can download files.
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. PRI ISDN can deliver
data at rates from 128 Kbps to 384 Kbps. DSL, with its many flavors, offers
much faster rates and more bandwidth for downloading files. DSLs data rates
range from 128 Kbps to 8Mbps, depending on the DSL flavor you choose.
Installation: Wiring
Both ISDN and DSL work over the ordinary twisted pair copper wires that are
located behind your walls. For DSL, your service provider may need to
install new wire depending on the type of DSL flavor you want. Generally,
ISDN installations do not require wiring upgrades.
Dial-Up and Always-On Service
ISDN is a dial-up service. To make your connection to the Internet, you must
dial a phone number. The connection is ended when the caller hangs up. There
is a version of ISDN that is always connected without dial-up. It is called
Always On/Direct ISDN (AO/DI). If you are interested, you will have to buy
both an AO/DI modem and a Dial-Up Networking Patch for Windows. You will
also need to use a service provider that supports AO/DI.
DSL does not require a dial-up. Once your business has installed DSL, your
service is "always on" and youre always connected.
Applications
Both ISDN and DSL are used for carrying voice, data and video at fast rates.
They are both used to access the Internet, and download/upload large files
quickly. Video conferencing can also be accomplished with both services.
Special ISDN Uses
If any of the following applications are practical for your business, then
you may wish to consider choosing ISDN over DSL.
Back up for Frame Relay.
Receiving the calling party numbers at large call
centers.
Backing up LAN-to-LAN connections.
Backing up dedicated, private lines in case the
private lines fail.
Remote access use.
Transmission of circuit data or packet-switched
data (by using the D channel).
Credit card approval or similar transactions (by
using the D channel).
Emerging Technologies: New DSL Products
Many new and exciting DSL products will be introduced into the marketplace
soon. These products may be particularly suitable to your needs. Here's some
examples of developing DSL products:
Network-based backup of computer files and
network-based security packages such as auto-detection intrusion.
Voice-over DSL services.
Required Equipment
ISDN
Unlike DSL, ISDN does not require a special modem. However, if you are going
to use ISDN for high-speed Internet access for data and video transmissions,
you'll need a terminal adaptor to connect the line to your PC. If your
network users are "sharing" the dedicated line in your network,
you'll need
an ISDN router.
For PCs, the UART chip for the PCs serial port should support ISDNs speeds.
If it does, you can use an internal ISDN card or external ISDN terminal
equipment. If it does NOT, you'll need to consider an internal ISDN card to
bypass the slower PC port. If you are using Windows 3.1 or Windows for
Workgroups, you'll need to make sure your ISDN terminal equipment includes an
ISDN-compatible dialer.
For Macs, youll need an internal ISDN card or external ISDN terminal
equipment. MacOS 7.5.3 (and earlier) requires installation of the SerialDMA
driver for faster throughput when using external ISDN terminal equipment.
DSL
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. Youll 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.
Cost and Value Considerations
ISDN is a premium service based on usage. Costs will vary, depending on your
own particular use. ISDN routers may need to be installed. Setup and
installation will probably be your biggest out-of-pocket expenditure. If you
are building a fairly large network, ISDN may be a good choice for your
business. An alternative to ISDN with a very large bandwidth is Asymmetric
Digital Subscriber Line (ADSL).
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.
