One very popular type of digital wide-area network service
is ISDN.
Is stands for Integrated Services Digital Network.
You'll find that ISDN can be delivered
in two different ways.
One of these ways is BRI or Basic Rate Interface.
You may see this referred to as a 2B+D network.
The 2B stands for two 64 kilobit bearer channels or B channels.
This is what the data is sent over an ISDN network.
There's another channel called the D channel.
This is on 16 kilobit per second signaling channel.
As a signaling channel, the D channel
is responsible for setting up the call
and breaking down the call.
And once the call is established,
we can send all of our data over one
or both of the two bearer channels.
For larger ISDN implementations, you
would use a PRI connection or Primary Rate Interface.
This is usually brought into an organization
over a T1 or an E1 line.
A T1 line can support 23 bearer channels and one single D
channel.
And E1 one would support 30 bearer channels and a D channel
along with a separate alarm channel.
You don't usually see ISDN installed
as a sole wide-area network connection these days.
It's often brought in to support traditional public switched
telephone network PBX connections inside
of an organization.
You might also see this used in radio or broadcasting services
where they need to connect two locations very easily.
And they want to support high-quality audio
between those locations.
Some of the more traditional wide-area network connections
may be brought in over a T1 or an E1 line.
T1 stands for T-Carrier Level 1, and it's
a way to connect two locations using
time-division multiplexing.
You commonly see T1 implemented in North America, Japan
and South Korea.
There are 24 channels on a T1 line,
and each channel can support 64 kilobits per second
for a total of 1.544 megabits per second of a line rate
over a T1 connection.
A similar wide-area connection in Europe is the E1.
The E1 is slightly different.
It has 32 channels.
And each channel can support 64 kilobits per channel.
That gives them a total of a 2.048 megabits
per second line rate over E1.
For these legacy wide-area networks,
the next step up from a T1 is a T3.
This stands for T-Carrier Level 3.
You might hear this also referred to as a DS3
or Digital Signal 3.
And its usually brought into your facility
over coax connections that are connecting to the T3 equipment
using these BNC connections.
A T3 provides 28 separate T1 circuits for total line rate
of 44.736 megabits per second.
And in Europe, the E3 combines 16 E1 circuits
for total line rate of 34.368 megabits per second.
Here's a summary of the T1, the E1, the T3 and the E3
wide-area networks.
The T1 is 24 channels at 64 kilobits per second
in each channel providing a line rate of 1.544
megabits per second.
The E1 is 32 channels, also at 64 kilobits
per second each channel, giving you a total line rate
of 2.048 megabits per second.
Moving up to the T3 and E3.
The T3 is 28 T1 circuits, or 672 channels,
providing a total line rate of 44.736 megabits per second.
And the E3 is 16 E1 circuits or 512 total channels for a 34.368
megabit per second line rate.
As carriers moved away from the circuit switch networking of T1
and T3, they moved into more packet-switch networking
with SONET.
SONET it is Synchronous Optical Networking.
And it's often implemented as rings
in a large geographical area.
There are a number of different line rates on SONET networks.
These are usually referenced by optical carrier number or OC
number.
If a SONET network is an OC-3 network, than
it has a line rate of 155.52 megabits per second.
OC-12 is 622 megabits per second.
OC-48 moves up to 2.4 nine gigabits per second.
And an OC-192 SONET network can support
a line rate of almost 10 gigabits per second.
A common type of wide-area network connection
that we might find in our home is
DSL, or what may be more appropriately called
ADSL for Asymmetric Digital Subscriber Line.
This is a wide-area network that allows
us to use our existing telephone lines
as high-speed digital connections.
The reason that DSL is asymmetric
is because the download speed in DSL
is generally much faster than the upload speed.
There's also a distance limitation associated with DSL.
You can't go much farther than about 10,000 feet away
from the central office connection.
The closer you are to the central office,
the higher your line rate will be.
It's common to see DSL advertised
as having about a 52 megabit per second downstream and 16
megabit upstream speeds.
But those speeds will vary depending on how far away you
are from the central office.
If you need to connect locations within a single city,
you might want to consider using metropolitan-area networks
such as Metro Ethernet.
These would be connections that would be in a relatively
close geographical area.
Instead of connecting a T1 line or a T3 line,
you can simply have the provider give you an ethernet connection
on both ends, and you're able to connect to your normal ethernet
equipment.
Inside of your provider's network,
the transport is probably not going to be ethernet.
You may be running ethernet over SDH or MPLS
or even ethernet over DWDM.
A broadband wide-area network connection
is where you are using different frequencies to send data
through that connection.
You could even be using different frequencies
for different data types.
We commonly use broadband when we're
connecting a cable modem to our traditional cable television
networks.
This is a standard known as DOCSIS or Data Over
Cable Service Interface Specification.
Depending on your cable providers implementation
of DOCSIS, you can see throughput
of 4 megabits per second through 250 megabits per second.
And in some areas, they're supporting gigabit speeds
over these cable broadband networks.
What used to be the traditional cable television company
is now also supporting data and voice over the same cable
broadband connection.
There are some places where installing a DSL or cable modem
connection may not be available.
You can then use the existing voice telephone lines
and connect a modem to be able to send
digital signals over these analog voice communication
lines.
These dial-up modems communicate at 56 kilobits
per second over these voice telephone lines.
And internally, the modem can compress some data up
to 320 kilobits per second.
This is obviously a much slower transmission rate
than you'd find with the DSLR or cable modem connections,
and it's difficult to scale.
If you need more connections, you
need to bring in more phone lines and more modems.
Today, we generally see dial-up modems used
with very specific use cases.
Maybe you don't have access to a cable modem or DSL connection.
Or maybe you only need to send a little bit of information only
once a day, and you can simply use the existing telephone line
to send that data.