DCE vs DTE and serial connections

[gaets100x]

so I am working on a project for my networking class and there is a section of the network topology that has three routers connected with serial cables like a triangle formation ( i will include the image and you will see). and Im used to the labs that its marked DTE or DCE but this one isnt and I feel like I should be able to figure out this without it marked and never considered it but just wanna take this opportunity to learn the difference between DTE and DCE and which ones I should use for this. I hope that makes sense if anyone can either link to an article or explain. thanks hope someone can point me in right direction (also just saw there are two other serial connections. where would you use dte cables and where would you use dce cables, why and how can i determine that in future projects. thanks to anyone who can point me in right direction really appreciate it... might sound stupid but just tryin to figure this out then I know it for good

also part of my reason im confused is in packet tracer there are dte and dce serial cables but in class we have really only ever used DCE/DTE cables like DCE at one end DTE on the other end and the lab says where to put them so im just trying to get good correct information to move on from this

[gaets100x]

[Richard Burts]

I hope that this discussion from the Cisco Learning Network might be helpful.

https://learningnetwork.cisco.com/s/question/0D53i00000Kt1fp/dte-vs-dce

The important thing to understand is that traditional serial data communications has one end as DCE and the other end as DTE. The importance of this is that the DCE generates clocking signal and the DTE receives the clocking signal. In a live network this is usually quite easy to figure out: the serial network provider is the DCE and generates clocking while the router is DTE and receives clocking. In a lab situation it gets more complex because in the lab you generally do not have any device that natively generates clocking signal. You would generally need to configure one of your routers to be DCE and in the serial interface to configure clocking

[Martin L]

First of all, serial technologies, interfaces and cables are thing of the past. you should not be tested on any serial tech on any Cisco exams (last exam revision Voice CCIE lab may use frame relay -not sure after Feb24 change).

Router is DTE and ISP with DCE provides clocking; so, you always had DTE cable end at your place while ISP had DTE. You got clock rate from ISP, mostly you did not have to adjust on your side - serial detects and adopts serial clocking.

For home lab with back to back serial cable (special cable made for back-to back connection), you should provide clocking with clock rate command on one of 2 routers (per link). That will be your DCE end while other end of a link is DTE. It does not matter which side is DCE. I think even if both are DCE, it may work as well. test it, let me know.

If you link is down, see if you have clock rate command on one of routers and if not, add one.

show controller x/y/z should show you which side is DCE /DTE

Regards, ML
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[Martin L]

My old 2691 routers show per-configured clock rate on all serial interfaces and both ends are DCE and working fine.

R2#sh controllers s0/0
Interface Serial0/0
Hardware is GT96K
DCE 530, clock rate 2000000

!

R1#sh controllers s0/0
Interface Serial0/0
Hardware is GT96K
DCE 530, clock rate 2000000