In a later video, I'll show you a Wireshark capture, showing you what the traffic or frames look like
when sent between two sites.
But for the moment, the high level picture is as follows A PC in one local area network is sending
traffic to a PC in another local area network when the traffic is sent across the land.
And in this case we're using Ethernet, the IP packet is encapsulated in an Ethernet frame.
So at a layer two, the encapsulation used is Ethernet.
So as an example, it could be Ethernet too.
When the frame arrives at the router, the router will strip the layer two headers and then send the
frame across the WAN using, for example.
Hdl-c.
So if this .2. connection is configured with a layer two encapsulation of Hdl-c, the Ethernet headers
are removed and the original IP packet that was sent by PC one is encapsulated in Hdl-c and is forwarded
across the cereal link to router two.
When router two receives the hdl-c frame, it strips the hdl-c headers and forwards the original IP
packet sent by PC one onto the local area network using an Ethernet header.
So the packet is encapsulated in Ethernet and an Ethernet frame is sent from router two to PC two using
Ethernet.
So we have Ethernet on the local area network on the left.
The When encapsulation used is used between router one and router two.
In this example, it's hdl-c.
And then on land two, an ethernet encapsulation is used once again.
The two layers that we're going to concentrate on in the OSA model for one technologies is the physical
layer and the data link layer.
At the physical layer, the physical presentation changes from what you've seen in an Ethernet environment.
So rather than using RJ 45 Connectors and for instance Cat six cabling X 21 or V 35 cables would be
used.
So the physical characteristics of the one interface are different to the physical characteristics of
Ethernet at layer two.
Rather than using an Ethernet encapsulation, you would encounter encapsulation such as frame relay,
PPTP, Hdl-c, ATM and MPLS.
You may however today also encounter Ethernet when connections which are becoming more and more popular.
But for the CCNA, when discussing a point to point one connection, we are going to be concentrating
on a PPTP and Hdl-c encapsulation.
So what kind of when devices would you typically see for point to point connections?
Well, you'll typically find routers rather than switches connecting remote sites together.
You'd also encounter a CSU, DSU or channel service unit data service unit, which allows you to connect
to a leased line connection using, for example, an x 21 or v 35 cable.
This converts the signals to the required format for when transmission.