What is DSL?
General
Frequently Asked Questions
What is
DSL?
DSL (sometimes referred to as xDSL) stands for Digital Subscriber Line.
It is a high-speed, dedicated, digital line from your home to the telephone
company's central office, and runs over normal copper telephone lines already
in place.
DSL is a new way to use your regular phone lines to transfer and deliver
data at a very high rate of speed. It works like an existing slow dial-up modem,
only without the slow dial-up part. With DSL you are always connected directly
to the Internet with your own secure, dedicated line.
With some phone carriers or companies, DSL also provides a separate channel for
voice phone conversations, which means that analog calls (voice, fax, etc.) can
be carried at the same time that data is flowing across the line.
- top -
What types of DSL are there?
ADSL (Asymmetric Digital Subscriber Line): Asymmetric means that the download
speed and the upload speed can differ. This type, or flavor, can run up to 6 Mbps
when downloading, and up to 384Kbps when uploading. This differentiation in speeds
makes it perfect for residential or casual users.
SDSL (Symmetric Digital Subscriber Line): Symmetric means that the download
and upload speeds are the same. This flavor of DSL runs up to 1.5 Mbps for both
uploading and downloading. This setup makes SDSL a good choice for businesses
that require high speeds in both directions.
IDSL (ISDN Digital Subscriber Line): This version of DSL combines the regular
DSL formats with ISDN technology. This enables the distance limitations to decrease,
but it lowers the speed as well. IDSL is only available at 144Kbps for both the
upload and download channel. Sometimes, due to distance limitations, IDSL is the
only option available to customers.
HDSL (High-bit-rate Digital Subscriber Line): This DSL type is similar
to SDSL, and also runs up to 1.5 Mbps for it's upload and download channels.
VDSL (Very high-data-rate Digital Subscriber Line): This is not one of
the most common types of DSL, as it generally has large cost associations. The
download channel runs anywhere from 13Mbps to 52Mbps, with an upload channel transfer
rate of 1.5Mbps to 2.3Mbps.
- top -
How do I tell what I'm ordering?
DSL speeds are shown as a combination of two numbers, written like this:
XXX/YYY
The "XXX" portion of this number is the download rate, listed in Kilobits per
second (Kbps). The "YYY" portion is the upload speed, also listed in Kbps. If
a connection was described as 768/128, then is has a download rate of 768, and
an upload of 128.
- top -
How does DSL work?
DSL runs on top of the same copper phone lines that are already in place at all
homes and businesses. Normal voice calls use a small portion of the frequency
range available in the phone line. DSL uses the frequencies above the voice call
range to send data back and forth, without interfering with an ongoing phone call.
The data from the computer is sent along the DSL line to your local phone company's
central office (CO), where it is split off from the normal voice traffic and sent
straight to the Internet.
- top -
How does DSL go so fast?
Voice calls tap very little of the actual potential of copper phone lines. DSL
has the ability to open up the extra room on the standard phone lines, split them
into different "channels", and to use them for data transfer at extremely high
speeds. The connection itself is also set up on a permanent basis, so the delays
and bottlenecks caused by the dial-up process are avoided.
- top -
How fast is it?
DSL delivers speeds up to 1.5 Megabits per second (Mbps), which is up to 25 times
faster than a standard 56 Kbps modem and up to 10 times faster than ISDN.
- top -
How many email accounts do I get?
DSL accounts get one email account. Additional email accounts can be purchased.
- top -
If I have ISDN, can I switch to DSL?
Yes. If the service is available in your area, you can cancel the ISDN line and
use the same wire for DSL.
- top -
Does DSL have distance requirements?
DSL is a distance sensitive technology requiring you to live a certain distance
from the central office (CO). ADSL technology requires that you live within 1.5
miles of the CO. With SDSL, the location must be within 3 - 4 miles of the CO.
IDSL has the longest reach, with a span of 6 - 7 miles, but it also has the slowest
transfer rate. Imbris does not offer IDSL at this time.
- top -
What type of DSL is right for me?
The type if service that you'll want depends on exactly what you plan on doing
with the Internet: business or pleasure.
If you are just a residential or casual user, more focused on browsing web pages,
retrieving email, and downloading files, then download speeds will be far more
important than upload speeds. A DSL connection with a speed of 768/128 or 1.5M/128
would be well suited for this type if user.
If you plan to be doing more business-oriented work, a lot of web site development,
or transferring a large number of files, then you will want a quicker upload speed.
Connections of 384/384, 768/768 or even 1.5MB/384 would be best suited for this
type of connection.
If you are a distance away from the phone company's central office, then Frame
Relay or Wireless may be your only available option.
- top -
What business uses could I have for the Internet?
With DSL, you could provide a multitude of "in-house" resources and tools for
your employees. Such resources include a personal web server, personal email
server, and the ability to use video conferencing.
- top -
What do I need for a DSL connection?
Most of the work is actually done by us. There are a couple of items that you
will need to have in order to use the DSL connection. Click here to view these
prerequisites.
- top -
Is DSL available everywhere?
Imbris is teaming up with national DSL providers in order to have coverage in
all major metropolitan areas of the United States, with many more cities to come.
Even with national coverage, DSL's 'distance sensitivity' requires us to qualify
your specific location.
- top -
Why can't everyone get DSL?
For DSL to be available, two things must occur:
- There must be a special
piece of equipment in the telephone company's central office (CO) that serves
your location. This piece of high cost equipment is called a Digital Subscriber
Line Access Multiplexer, or DSLAM for short. The DSLAM is the device that
receives the digital signals from your DSL router or modem, at your home or
office. At this time, not all CO's have a DSLAM installed and running. As
more and more of our partners deploy DSL, the number of CO's with DSL capabilities
will increase, and so will our coverage.
- If the CO does have
a DSLAM, your home or office must be a certain distance away from it.
DSL is a distance sensitive technology, which means that as your distance
from the central office increases, the number of choices for connection speeds
decreases. Additionally, the condition of the telephone company's copper infrastructure
will also affect your ability to obtain service. If the copper phone wire
type is not sturdy enough, or there are electronic devices deployed on their
phone network, it will limit DSL availability.
Some homes and businesses will
be too far away to qualify for DSL, even if there is a DSLAM in the local central
office. Upcoming technological advances will eliminate some or all of these distance
requirements.
- top -
My phone company says I do not qualify; can I qualify for
Imbris DSL?
Your local phone company will typically offer ADSL, a service that only extends
a signal about 18,000 feet from the central office. Beyond that distance we are
unable to provide DSL service at this time. You may want to explore the possibility
of Imbris Frame Relay or Wireless service.
- top -
What is the qualification process?
When you call Imbris, one of our sales representatives will ask you for your phone
number and address.
Using the phone number, we can determine if the central office (CO) that services
your area has a DSLAM installed and running.
The address will allow us to estimate how far away you are from the CO, which
will determine the speeds that are available for you.
The address and phone number that we request will need to match the listing on
your local telephone company phone bill. Please have this bill handy. Your name
and address must match exactly for DSL to work.
The closer that you live to the central office, the more speeds available for
a DSL connection. Please note that the qualification tools we use to measure
your distance from the central office measure in terms of driving distance, following
the shortest path it would take to get from one place to the other.
Your phone line may actually wind around your neighborhood, increasing the distance
that the connection would have to travel to a much greater length than our original
estimates. The exact measurement of distance comes from the phone company, when
they begin the process of setting up your DSL connection.
- top -
What are the benefits of DSL vs. an Analog connection?
The biggest advantage of DSL over standard analog connections is speed.
Analog lines are simply not made for Internet connections. Analog connections
are forced to use a small portion of the telephone line's available frequencies.
Analog modems also connect by translating digital data into noise. An analog modem
on the other end must take those packets of noise and change them back into readable
digital information. Some information requests must be made over and over again.
- top -
What are the benefits of DSL vs. an ISDN connection?
ISDN takes a large step over regular modem connections by keeping all the data
in a digital state; the same state that the computer transfers data internally.
ISDN is still a dial-up connection, though; the modem must dial out every
time you request information. ISDN is also expensive. Phone companies charge
ISDN calls at an hourly rate, a charge generally matched by the ISP as
well. The amount of time you can spend online is dependant on your finances.
- top -
What are the benefits of DSL vs. a Cable connection?
Cable connections are high-speed connections as well. However, cable systems are
set up as giant local area network, with entire residential blocks able to see
their neighbors. This setup leads to serious security issues, as an experienced
hacker may be able to access unprotected resources on someone else's computer.
Most cable companies also need to upgrade their networks in order to supply a
two-way data connection, and there is little to no availability in business
areas.
- top -
What are the benefits of DSL vs. a Satellite connection?
Satellites often have side benefits, such as an increased number of available
television channels, but have disadvantages when handling Internet connections.
With a normal, land based connection, data travels from point A to point B through
a series of computers, all with response times in the milliseconds. A satellite
connection sends data out through a normal analog line; information being
downloaded is relayed from point A to point B through a series of computers, and
then is shot up thousands of miles in the area to a hovering satellite.
Satellite connections also are difficult to maintain, if the satellite
you are using breaks, it may be a while before service is restored.
- top -
What is NAT?
NAT stands for Network Address Translation. By using NAT, it is possible
for a company to have multiple computers on a TCP/IP network, and still only pay
for one "public" IP address.
Public IPs vs. Private IPs
IP addresses can be grouped in two categories; public and private. The majority
on the IP addresses that are used are public IP's. They can be seen by any computer
that has Internet access.
Private IP addresses have been set up with the sole purpose of giving an internal
network the ability to run over TCP/IP. The IP addresses that are classified as
private will not be recognized by any outside Internet server, so security is
maintained, along with lessening the demand for public IP addresses.
The IP addresses classified as private are 10.1.1.1, 127.0.0.1, and 192.168.1.1.
They can be used by any network without paying for them.
Using NAT
NAT can take the requests made by internal, private, IP addresses, and send them
out through one public IP address. It tags each packet going out with a special
code, which it can then use to determine which computer gets the information.
- top -
What is DHCP?
DHCP stands for Dynamic Host Configuration Protocol. It is used to dynamically
assign IP addresses to computers when they log onto a LAN for the first time.
After the computer logs off, another machine may be assigned that IP, and when
the initial computer logs back onto the network, chances are that it will get
a different IP address.
DHCP makes configuring and controlling mutliple machines very easy. All needed
information, IP address, gateway, DNS servers, is given to the "client" machine
at the time of logon. There is no need to configure each computer individually,
and all changes can be made almost instantaneously.
- top -
What does "routing" mean?
Routing is the process of moving data from one location to another. Using
IP address, TCP/IP is able to route incoming and outgoing data to the correct
computers.
- top -
Routers and NAT
A router is one of the more intelligent pieces of equipment used in Internet services.
Its job is to analyze all data, and determine where that data should
next be sent. For a business, one of the advantages to using a router is through
a function known as NAT.
NAT stands for Network Address Translation, and is used to allow a large
network the ability to have multiple computers on a TCP/IP network, with only
the use of one "public" IP address. A public IP address is one that can be seen
by any computer on the Internet. For Imbris purposes, an example of this is our
"216.18.xxx.yyy" IP addresses. These are given to all of our customers, including
the routed ones. Anyone can "ping" this IP address; it's alive and a functioning
member of the Internet.
The alternative to this is the use of "private" IP addresses. These are addresses
that, due to the design of the TCP/IP protocol, cannot be seen by any other computer
outside of that LAN. Most of these IP addresses begin with "192.168.xx.yy", however
there are variations. Using these types of IP addresses enables anyone to set
up a TCP/IP network, without paying any money for purchasing the addresses.
They are available for everyone, and as such, cannot be seen on the Internet at
all. They're invisible, except to those computers physically connected
to the same LAN.
Putting this all into place, a router, using NAT, can track which information
coming from the one public IP address belongs to which internal private IP address.
Much like an apartment building, all people on the outside can see is the one
IP address, the one building, while on the inside there are a great many other
computers or apartments.
- top -
Ports and the mapping of…
Information is sent on the Internet in multiple ways. A customer can send email,
go to web sites, connect to chat channels, and download information from ftp sites.
All these different types of activity are handled in different ways, on what are
called "ports".
Ports have been set up to help the right information get to where it should
be. For instance, all web traffic is handled on port 80. Customers don't need
to know this, because the browser that they are using already does. All web sites
communicate using this port, so that they don't get confused with other information,
like mail.
If a customer is running a web server, or any server, inside a LAN, there is a
large challenge to be faced. People on the Internet can't get to that site and
computer, because it's using an internal, private IP address that they can't see.
So, even though other people on their network can view the website, the mass of
people on the Internet can't.
In order to overcome this, the router must be set up to allow that traffic,
aimed for that web site, access to that one computer. This is handled through
a process known as port-mapping. The router listens for information
traffic on every port available, but if it's not set up to act on any of that
information, it'll ignore it. With port-mapping, the router will be told that
any information coming in on port 80, the web port, will be sent over to that
one particular machine on the internal network that's running the web server.
Even though the customer's can't see the internal network, the router can, so
it just funnels all information for that port over to the specified computer.
This process can be done for any type of Internet service: web, mail, ftp, chat,
you name it. All that is required is informing the router of exactly how it should
handle this information that it is receiving. The rest is up to the server itself
at the receiving end.
- top -
Can I set up a firewall?
Yes. Routers for business accounts that we distribute come with the capability
of setting up and managing your own firewall. The firewalls are integrated inside
the routers so you can be assured your network will be secure from unwanted traffic.
- top -
I have two computers. Can I hook them both up to DSL?
Yes, although you will need to obtain a "secondary" connection option and provide
the MAC addresses of each networked computer. You may also need to obtain an additional
IP assignment (additional fee), depending on your networking needs. Our
Technical Support staff cannot assist you with networking, however we have a Sales
Engineer available for telephone and on-site consultation on an hourly fee basis.
You would be required to provide your own networking equipment such as a hub and
a network card for each computer. Imbris can assign the primary server its own
IP address with Static IP service and provide a block of IP addresses,
which will allow for simultaneous Internet access.
DSL accounts utilizing DHCP service are provided with free forward and reverse
DNS for each connection purchased. Customers purchasing a block of IP addresses
can choose to provide your own forward and reverse DNS for the IP addresses assigned,
or for an additional fee, Imbris can provide this service for you.
Copyright
© 2000 IMBRIS, Inc., All Rights Reserved
No part of this website may be duplicated or used in any way without prior
consent.