If you don't have access to a point to point serial connection at work, just do a search in Google
or your favorite search engine for Cisco, CSU, DSU, as an example.
And you'll find many pictures showing you examples of setups using serial connections.
Here's a very good one.
It's an older picture showing a 1720 router.
In the picture here you can see the blue console cable connecting to the console port of the router.
You can see the power connection.
And what's important is to note the Ethernet connection.
This would connect the router to a switch or another device in the local area network.
And very importantly, notice the V 35 cable.
So we have one end of the cable connected to the router and the other end is connected to the CSU DSU.
This is an example of an external CCU DSU, and you can see it's connected to the telco network.
Now they use the term dmarc.
A dmarc is a demarcation point.
This is where responsibility changes.
So on one side of the dmarc or demarcation point, any problems are the responsibility of the service
provider.
On the other side of the demarcation point, any problems are yours if you are managing the local area
network so you would be responsible as an example for configuring your router, for making sure that
the serial cable is connected correctly, that the Ethernet cable is connected correctly, that these
devices are powered up and so forth.
But once you send traffic to the service provider network, that becomes the responsibility of the service
provider.
Now these days, the CCU, DSU is often built in to the wine interface card or wick.
This is an example of a week or one interface card that you would insert in a router.
Notice this one is a TI one DSU CSU.
So the CSU DSU is internal to the router.
Here's another picture of the week card and he has another one showing it inserted into the router.
So once again, here is an example of the CSU DSU built into the router.
Yes, another example showing you the CSU DSU with a cable connected to the router providing an internet
connection.
Cisco also have images such as the following showing that a serial connection is connected to a cord
on the router, which in turn connects you to the CSU DSU.