Lease lines are an example of synchronous serial communication, where one party provides the clocking
for the communication.
So in other words, two devices will synchronize their clocks before data transmission takes place.
So they will align or synchronize those clocks and agree on parameters for data transfer, including
the data interval between bits of data.
The CSU issue or channel service unit data service unit, commonly referred to as the CSU, provides
the clocking and is the master for the communication.
The rate is acting as a slave and is receiving its clocking from the CSU.
So essentially before communication can start, the two devices have to align their clocks or agree
on the clock intervals to ensure that data doesn't get corrupted.
So here we have the terms data, communication equipment or DCE and data terminal equipment or DTD.
The most in the communication is the CSU DSU and it's using its own internal clocking.
But the rudder, which is the data terminal equipment or dty, uses the external clocking received from
the DCE and will thus synchronize itself to the CSU DSU.
So the CSU DSU is the DCI side of the connection and the router is the dty side of the connection.
So the DCI, which is the CSU DSU is providing clocking to the rudder, which is the DTY, and the DCE
also terminates the connection from the carrier, and a connection is then made from the CSU DSU to
the router.
Some terms to understand, therefore, is customer premises, equipment or CPE.
This is the term that telcos or service providers use to refer to equipment that resides at the customer
site at the end of their connection.
So once again, in this example, the CE issued issue is at the customer's site.
The key issue, DSU, which is the DCC, is connected in this example via a V 35 cable to the router
and is providing clocking to the router.
So the CSU issue, which is the DCC physically controls the speed and timing at which the router serial
interfaces can send and receive bits over the serial cable.
You don't have the ability to configure the speed of your serial connection that is set by the CSU DSU
and is generally set by the service provider on your behalf.
The serial cable once again connects the CSU to the router interface.