Telcos or service providers offer leased lines with different speeds.
However, you as a customer conscious pick some arbitrary speed.
The speeds of lease lines follow the standards of older technology.
In the US it's called the carrier system and in other parts of the world it's called the EE carrier
system.
This comes originally from Alexander Graham Bell and the way that analog voice is digitized.
So as an example, when you speak, it's an analog signal and you're sending sound waves through the
air.
But that gets digitized using something called the Nyquist Theorem.
And your analog voice is converted into a 64 kilobits per second stream using a technology called Time
Division multiplexing.
A single voice call in most parts of the world using older technology, such as ISDN, use a 64 kilobits
per second.
In the US, you'll typically find 56 kilobits per second when bonded together.
Speeds can be increased.
So as an example, a popular one is a PT one, which consists of 2464 kilobits per second sessions,
plus eight kilobits per second for overhead in a single connection or single lease line, which provides
1.54 megabits per second.
Don't worry too much about the details, but for example, a zero or digital signal level of zero provides
64 kilobits per second.
A T1 consists of 2464 kilobits per second sessions plus eight kilobits per second overhead, giving
you 1.54 megabits per second.
So this is 24 D zeros plus eight kilobits overhead, giving you at1 speed of 1.54 megabits per second.
That's a standard used in the US.
In Europe, as an example, we have an E one rather than at1, which gives you just over two megabits
per second.
So 2.048 and that consists of 32 D zeros or 3264 kilobits per second.
Channels Ideas zero or digital signal level zero is a 64 kilobits per second channel.
A T1 consists of 24 channels each providing 64 kilobits per second.
Some other US examples.
at2 is for t one lines provide six megabits per second at3 is 20 8t1 lines providing 48 megabits per
second.
at4 consists of 168 T1 lines, giving you 274 megabits per second.
In Europe, an E one is just over two megabits per second.
E two is eight megabits per second.
E three is 34 megabits per second and an E four is 140 megabits per second.
If you're going to remember any 1at1 is 1.54 four megabits per second and an E one is 2.048 megabits
per second.
So the CSU DSU, which is acting as the DCE, is using, clocking to control when the router sends data
and it also is configured for the relevant speed of the connection.
So the DCI controls the speed of the serial connection and the router is controlled by the clocking
signals that it receives from the DCE.
The CQ tells Router when to send and receive bits.
The router will only send and receive bits when instructed to by the DCE because of the clocking that
the DCE is providing on the cable.