In this lesson,
we're going to cover digital subscriber line connections.
Now, a digital subscriber line or DSL connection
is a family of technologies that provide internet access
by transmitting digital data over the wires
of a local telephone network.
When I first started building networks
back in the late 1990s and early 2000s,
DSL was all the rage.
It was everywhere, because it was relatively inexpensive
and a great way to get high-speed data
to our end users in small offices
and in home office environments.
Now, instead of having to pay for a dedicated lease line
like a T1, which could cost you 1,000 or $2,000 a month,
you could go ahead and get a DSL connection
for 50 or $100 per month.
Now, back in the day, we had three different types of DSL,
and you may still run into some of these these days.
These are ADSL, SDSL, and VDSL.
ADSL stands for Asymmetric DSL.
That means there's going to be a different speed
on the download versus what you're going to get on the upload.
The maximum download speed on an ADSL line
was about eight megabits per second,
according to our current textbooks,
although there were some
that were getting a little bit faster than that.
The upload speed was equivalent
to about a T1 at 1.544 megabits per second.
Now, why do you think it would be okay
to have two different speeds for downloads and uploads?
Well, when you're online, think about it.
Do you do more uploading or downloading?
If you're like most people,
you download a lot more than you upload.
For example, when you're watching this video,
you selected the video with your mouse
and you told the server what you wanted to watch.
You may have sent just a couple of kilobits in size
up to our server, and then we sent you back a video
that was maybe 100, 200, or 300 megabytes in size.
And it's a really large file,
and you're downloading all of that.
So your upload was very, very small,
but your download was a whole lot.
And for most users, they upload very little,
but they download a ton of information.
This is why ADSL decided to maximize the download
and minimize your upload speeds.
Now, on the other hand, if you're somebody
who needed the same upload and download speeds,
you could get a specialty product known
as SDSL or symmetric DSL.
Now, symmetric DSL works just like a typical
lease line connection, like a T1.
With an SDSL connection,
you have an equal upload and download speed.
Now, the problem here is because you're having
equal upload and download speeds,
you are going to have slower speeds overall.
For example, with ADSL,
we said you can have an eight meg download speed
and a one meg or one and a half meg upload speed.
So you have about 10 megs total to work with.
But if you're using SDSL, you can actually reconfigure that,
so you have five megs upload and five megs download,
or four megs upload and four megs download.
Either way, you're going to have equal
upload and download speeds but at a much slower rate
than the total speed you would get
on an asymmetric connection.
Now, because these were more of a specialized product,
they gave you dedicated access,
and you're guaranteed to pretty much get
all that speed all of the time.
Now, if you're dealing with ADSL, on the other hand though,
if there's a lot of people online at a time,
it actually could slow down your speeds,
because ADSL used a shared pipe
for the entire neighborhood
where you are connected to.
Now, ADSL was very, very popular
with home users back in the '90s and early 2000s,
and so it got a lot of funding
from the telecommunication companies,
and that means ADSL speeds quickly increased
and got into the one and a half megabits per second,
and then four megabits per second,
and then eight megabits per second.
And they kept going up from there.
And these days, ADSL is still out in the marketplace
for some more remote areas,
but most people have now moved into cable modems
or fiber modems in larger city environments.
Now, when DSL first started coming out though,
it was very, very slow.
When we started talking about DSL speeds,
it was in the quarter of a meg per second
or 256 kilobits per second of speed.
As advancements came up, we kept getting more
and more towards ADSL and faster and faster modems.
Now, the last type of DSL that we need to mention
is what's known as VDSL or very high bit rate DSL.
Now, this is where you can actually get
very, very high speeds, and you can have downloads
as high as 50 megabits per second or more,
and uploads of about 10 megabits per second or more.
The big limitation here though
was your distance from what is known as the DSLAM.
Now, what is a DSLAM?
Well, the DSLAM is the point of presence
that's owned by the telephone company.
With very high bit rate DSL, you had to be within
about 4,000 feet of that D-S-L-A-M or DSLAM.
And this is less than a mile.
Now, unfortunately, a lot of home and offices
could not get VDSL, because most of them
were outside that 4,000 foot range.
But they were still within the 18,000 foot range
that you would need to get ADSL.
So if you have to be anywhere between 4,000 and 18,000 feet,
you were stuck with ADSL.
But if you were lucky enough
to be within 4,000 feet of the DSLAM,
you could get VDSL and get those really high speeds.
Again though, at this time,
DSL has really declined in popularity,
and you really won't see it
unless you're working in one of the older areas of town,
or if you're working in more rural area of town,
because VDSL and ADSL were installed
over traditional copper phone lines.
And these days, a lot of those copper phone lines
aren't really being serviced and are being taken out
as most things are starting
to move towards fiber optic connections
and voiceover IP services
where we're just using data packets
over the internet to make our phone calls.
And this is why you're going to see a lot more cable
and fiber modems out there
instead of DSL as you move into the field.