When you want to connect your business to the outside world, you use an ISP.
This is the same case when we want internet at home.
Today, most of the links provided by our ISP are IP links. There are still specific links. So it's important to understand how they work.
These leased lines are going to be called "Leased Line."
They have the same feature as a crossed Ethernet cable without worrying about distance.
There are two Level 2 protocols
HDLC: High-Level Data Link Control
– CISCO Owner
– Supports only synchronous links
– Lack of authentication.
Ppp: Point to Point Protocol
– Standardized protocol
– Supports synchronous and asynchronous links
– Authentication with the PAP and CHAP protocols.
This point-to-point link has two peculiarities:
– Works in Full-Duplex
– Same transmission speed
There are several types of Leased Line:
Layer 1 – Physics
When our ISP provides us with a Leased Line. It will also provide us with a CSU/DSU case (the term has been shortened to CSU). The latter will inform our router how fast it must work.
In this type of liaison, our equipment can have one of two roles:
DCE (Data Circuit-terminating Equipment)
– The one who gives the speed of work
DTE (Data Terminal Equipment)
– Whoever receives the speed of work
The link symbolized by a "flash" represents a SERIAL link.
At the router level, the connection used is the "Smart Serial" at the CSU level, the connection used is the "V.35".
The cable used for this link is called a DTE cable.
It is quite possible to mount a link of this type between 2 routers without going through a CSU case. As the diagram shows:
One of the two routers must take on the role of DCE. It is the latter that will tell our DTE router the speed of transmission to adopt.
We will find on this router the command "Clock-rate"
At the connection level, you'll need to connect a Cable DTE and a DCE cable.
As we said above, this link behaves like a cross cable. The role of the DCE cable is to cross the Transmission (TX) part with the Reception part (RX).
Layer 2 – HDLC
Our PC will encapsulate our IP packages in an Ethernet frame before transmitting it through its network card. When this Ethernet frame is going to be received by our router, it will de-encapsulate our IP package and encapsulate it in an HDLC frame.
You can see this process with the following diagram:
How do I set up the HDLC protocol?
As we have just seen, a WAN link is a Series link. It arrives on a Serial map. So we're going to have to set up our serial interfaces:
Router (config) - serial interface 0/1 Router (config-if) ip address X.X.X.X X.X.X.X
The default protocol used by our CISCO routers is going to be the HDLC protocol. It is therefore not necessary to specify to him.
Only concerns DCE:
Router (config-if) clock-rate 64000
To check the configuration of our interface, use the command:
Router show interfaces serial 0/0
Hoping this article has been helpful to you! Don't hesitate to let me know!!
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