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OSI Layer 1 – WAN concept – Difference Between DCE and DTE – CSU/DSU

This is a next article in series about OSI layer 1 – in previous articles we looked  at Introduction to OSI Layer 1, then OSI layer 1 in a perspective of Ethernet, and also OSI Layer 1 through Legacy Ethernet protocols.



Next, we’re going to take a look at same layer even deeper, one when link concepts that should be understood before you go deeper into your networking concept studies.


Let’s get started with CSU/DSU connections.




DTE/DCE concept in networking




Figure 1: DTE/DCE concept in networking



These are going to be connections for digital signaling, for communications from your local customer equipment to a digital connection to the provider.




Digital vs Analog Local Loop




Figure 2: Digital vs Analog Local Loop




While the customer side would be considered to be the DTE connection and provider side would have the DCE connection. The main thing to know here is that the DCE provides clocking while the DTE receives it.



Clocking is always coming from DCE side



Figure 3: Clocking is always coming from DCE side



The clocking, this clocking is used to synchronize your circuit speed, which is configurable on the DCE end. A couple of important things to understand for the exam would be that a modem connects to an analog local loop while your CSU/DSU connect to digital local loops.


Lomoveishiy – Finland

I needed those to connect my PC on the third floor to have internet access in that room, and ISP installed their modem on the first floor only. After dropping fiber patch cables, plugged in all cables into these media converters at both sides, and link came up instantly. Was much easier than I thought!

Raymond – USA

Great experience – units worked straight out of the box – just needed plug in cables and we were done. I also like the possibility to enable jumbo frames, while we do not have a need for this feature at the current moment it’s great to have this option.

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