WAN - edge equipment names and terminology

In the past, Wide Area Networks or WANs were typically deployed using technologies that are different and incompatible with those used for local area networks (LANs). For this reason, at the Demarcation point, specialized equipment was often used to interconnect the customer premises equipment with that of the telco.

This equipment was necessary primarily because the WAN technologies included things like serial, DS1, T1, E1, OC-X and others, which were typically incompatible with LAN technologies such as Ethernet.

This equipment included the following:

  • Channel Service Unit/Data Service Unit (CSU/DSU) - This is a device used to convert the WAN technology to LAN technology.
  • Data Terminal Equipment (DTE) - This is the term used to refer to a customer device, on the customer side of the demarcation point, such as a router.
  • Data Communication Equipment (DCE) - This is typically a telco-owned device, and is the device on the telco side of the demarcation point. It is a CSU/DSU that converts from WAN technology to LAN technology.

Now today, these terms are slowly falling out of use because we have more and more cases where the WAN and LAN technologies are the same (i.e. Metro Ethernet, fiber optics, wireless links etc…). So although the demarcation point still exists, the equipment that may or may not be there depends highly upon the arrangement that you have made with the telco.

In many cases, the CSU/DSU is incorporated into the DTE, as is the case with today's xDSL routers for example. In the case of xDSL, there is no DCE either.

https://networklessons.com/cisco/ccna-200-301/introduction-to-wans-wide-area-network

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