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If you don't have access to a point to point serial connection at work, just do a search in Google

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or your favorite search engine for Cisco, CSU, DSU, as an example.

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And you'll find many pictures showing you examples of setups using serial connections.

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Here's a very good one.

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It's an older picture showing a 1720 router.

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In the picture here you can see the blue console cable connecting to the console port of the router.

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You can see the power connection.

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And what's important is to note the Ethernet connection.

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This would connect the router to a switch or another device in the local area network.

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And very importantly, notice the V 35 cable.

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So we have one end of the cable connected to the router and the other end is connected to the CSU DSU.

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This is an example of an external CCU DSU, and you can see it's connected to the telco network.

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Now they use the term dmarc.

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A dmarc is a demarcation point.

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This is where responsibility changes.

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So on one side of the dmarc or demarcation point, any problems are the responsibility of the service

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provider.

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On the other side of the demarcation point, any problems are yours if you are managing the local area

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network so you would be responsible as an example for configuring your router, for making sure that

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the serial cable is connected correctly, that the Ethernet cable is connected correctly, that these

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devices are powered up and so forth.

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But once you send traffic to the service provider network, that becomes the responsibility of the service

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provider.

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Now these days, the CCU, DSU is often built in to the wine interface card or wick.

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This is an example of a week or one interface card that you would insert in a router.

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Notice this one is a TI one DSU CSU.

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So the CSU DSU is internal to the router.

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Here's another picture of the week card and he has another one showing it inserted into the router.

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So once again, here is an example of the CSU DSU built into the router.

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Yes, another example showing you the CSU DSU with a cable connected to the router providing an internet

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connection.

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Cisco also have images such as the following showing that a serial connection is connected to a cord

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on the router, which in turn connects you to the CSU DSU.