One side of the link (DCE), has to transmit the clock signal, which controls the data rate, and the other side (DTE) receives the clock signal.
R1 is DCE here:
interface Serial0/0/0
ip address 10.0.0.1 255.255.255.252
clock rate 2000000
R2 is DTE here:
interface Serial0/0/0
ip address 10.0.0.2 255.255.255.252
The difference between the two cables in packet tracer is just which side you click first:
- With the DCE cable, (red zigzag with clock) the side you click first will be the DCE, the second will be DTE
- With the DTE cable (red zigzag no clock) the side you click first will be DTE, the second will be DCE
Whichever way you do it, you'll see one side of the cable shows the clock symbol: this is the DCE.
Answer from jonathanjo on Stack Exchange Top answer 1 of 3
10
One side of the link (DCE), has to transmit the clock signal, which controls the data rate, and the other side (DTE) receives the clock signal.
R1 is DCE here:
interface Serial0/0/0
ip address 10.0.0.1 255.255.255.252
clock rate 2000000
R2 is DTE here:
interface Serial0/0/0
ip address 10.0.0.2 255.255.255.252
The difference between the two cables in packet tracer is just which side you click first:
- With the DCE cable, (red zigzag with clock) the side you click first will be the DCE, the second will be DTE
- With the DTE cable (red zigzag no clock) the side you click first will be DTE, the second will be DCE
Whichever way you do it, you'll see one side of the cable shows the clock symbol: this is the DCE.
2 of 3
6
DCE stands for data circuit-terminating, data communications, or data carrier equipment - this is a modem or more generally, a line adapter.
DTE stands for data terminal equipment which generally is a terminal or a computer.
Basically, these two are the different ends of a serial line.
Cisco
cisco.com › support › product support › routers › cisco 800 series routers › troubleshooting technotes
Serial Cable Connection Guide - Cisco
With the answers to these questions, ... The most important difference between these types of devices is that the DCE device supplies the clock signal that paces the communications on the bus....
DCE vs DTE and serial connections
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 ... More on community.cisco.com
Can someone explain what DTE and DCE cable is used for?
DTE and DCE are Data Terminal and Data Communication Equipment respectively. wrt RS232, a DTE - DCE and DTE - DTE will have rx and tx terminal wiring swapped at one end. ie., tx-tx vs tx-rx respectively. More on reddit.com
2
2
March 11, 2017purpose of a serial cable
Hi i done an experiment at home using my internet. Basically i have a modem which connects to my router (normal wireless router) so i thought i would use one of my cisco 2600 routers to act as my router instead. I plugged my modems ethernet in to the 2600 and configured it and everything worked ... More on community.infosecinstitute.com
DCE/DTE question
DCE/DTE and CSU/DSU are two different concepts. It might be easier not to consider them related. Let me explain. Serial Cabling - DCE/DTE Cisco exams, in particular the CCNA, make a big deal of Serial cables. In reality, the real world rarely makes use of them anymore. As other comments have pointed out, you might be able to push 2mbps through a serial cable, where as regular plain old fast ethernet will give you up to 100mbps. Serial is outdated technology. That said, it is still on the exams, so still something you need to know about. Physical Cables are L1 technologies, their sole purpose is to carry bits across a wire . Each type of cable does it differently, but essentually a 1 or a 0 correlates to a certain voltage being applied to the wire for a certain time. When two devices want to send bits to each other, it is crucial they each have the same timing, or sampling rate. Which means they both have to know how long the voltage is being applied to represent a single bit. For example, if one end is applying the voltage for each bit for one second, and the other end if reading the voltage for each bit every two seconds, the sender might mean to send 1111, but the receiving end would only interpret 11. Obviously, that would not work so well. Different cabling standards have different ways of ensuring each end is using the same timings... also called Frequency. In Ethernet, the timing is built into the standard itself (100BASE-TX, 1000BASE-T, etc). In Serial, the speed is variable, and can increase or decrease with older or newer devices/technologies. But rather than forcing the configuration to be identical in both places, Serial cables require only one end to set the clock rate (the master), and the other end will inherit the identical rate (the slave). But which side is which? That is where the DCE and DTE come into play. Each cable has two ends, one side labeled as the DCE, and the other labeled as the DTE. Per Serial standards, the DCE side always sets the clock rate. The cables are often (not always) labeled, so you can determine which side is DCE or DTE, but in the case they are not, or you are accessing a device remotely, you can make use of the show controllers command to determine which side is the DCE, and in that case which side should apply the clock rate command. CSU/DSU CSU/DSU is simply a box with two ports that mark the demarcation point between your network and your ISP's network. The port facing the ISP network is the Channel Service Unit and the port facing your network is the Data Service Unit. Its primary purpose is to convert the signal from your network to whatever L1/wiring standard the ISP is using on their network. Typically, your perimeter/edge router will connect to the CSU/DSU via serial cable. And the other end of the CSU/DSU will connect to the ISP with whatever they choose. But since a Serial connection is being used, the clock rate needs to set on one side of the cable so that both ends are using the proper frequency. In reality, it doesn't matter what end sets it, but from the perspective of the ISP, do you think they want you to be able to control how fast the serial link is transmitting bits? Typically the ISP wants to control the speed, so therefore they insist that they (aka the DSU/CSU) are the DCE side of the cable, so that they can set the speed to what you've subscribed to (aka, payed for). Your router will then simply inherit their prescribed clock rate. Hopefully that distinguishes the two concepts, and also illustrates where they come together. More on reddit.com
19
6
August 20, 2016What is DCE?
DCE, or Data Communication Equipment (also known as Data Circuit-Terminating Equipment), refers to devices like modems, CSU/DSUs, or multiplexers that connect data terminal equipment (DTE) to a communication network. In the OSI model, DCE operates at the physical layer (Layer 1), where it is responsible for signal transmission, voltage levels, connector pinouts, and clocking. These devices ensure that raw data is reliably transferred between devices across physical media like serial cables or telephone lines.
lenovo.com
lenovo.com › home
What is DCE? Data Communication Equipment Explained - Roles, ...
How are DCE and DTE devices connected by cable?
DCE and DTE devices are typically connected using serial cables such as RS-232, RS-449, V.35, or DB9/DB25 connectors, depending on the standard and speed requirements. The cables follow a straight-through configuration for DCE-DTE pairs, ensuring that transmit and receive lines align correctly. In cases where two similar types (e.g., DTE-DTE) must communicate, a crossover or null modem cable is used to swap necessary pins and facilitate bi-directional communication.
lenovo.com
lenovo.com › home
What is DCE? Data Communication Equipment Explained - Roles, ...
Should DCE or DTE provide the clock signal in a synchronous serial connection?
In a synchronous serial connection, the DCE device is responsible for providing the clock signal. This clocking ensures that both transmitting and receiving devices stay synchronized during data exchange. The DTE, such as a router or computer, receives this signal and uses it to interpret the timing of incoming bits accurately. This DCE-supplied clock is essential for error-free data transfer and is a key element in serial communication protocols like HDLC and PPP.
lenovo.com
lenovo.com › home
What is DCE? Data Communication Equipment Explained - Roles, ...
Videos
Day 13: DCE and DTE Basic Overview for Beginners - YouTube
Serial Interface Connection Between Two Routers - Difference ...
03:18
How to Connect Routers Using Serial Cable (Serial DCE & DTE) | ...
01:15
Serial DCE DTE - YouTube
07:41
The purpose of the DTE and the DCE in the Cisco CCNA - YouTube
00:52
🔌 Configura Serial DCE y DTE en Routers Cisco | Packet Tracer ...
Decisive Tactics
decisivetactics.com › support › view
Crossover or "Null Modem" vs. Straight Through Serial Cable - Decisive Tactics, Inc.
DTE normally refers to the serial port on a PC or terminal, while DCE refers to a modem or other type of communications device. Depending on the type of device on each end of the line, you either need a straight-through or a null-modem ("crossover") cable in order to communicate. A straight-through or "one to one" cable is used to connect a DTE device (PC) to a DCE device (modem or other communications device).
Cisco Community
community.cisco.com › t5 › network-management › dce-vs-dte-and-serial-connections › td-p › 4184919
DCE vs DTE and serial connections - Cisco Community
November 17, 2020 - 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.
ComputerNetworkingNotes
computernetworkingnotes.com › ccna-study-guide › cabling-cisco-devices-guide.html
Cabling Cisco Devices Guide
November 26, 2025 - To simulate a WAN network, usually, you connect two routers back-to-back on serial interfaces using a serial cable. By default, all serial interfaces operate as DTE devices. To establish communication between two serial interfaces, one of them ...
Genuinemodules
uk.genuinemodules.com › what-is-serial-dce-cable_a9605
What is serial dce cable?
March 16, 2025 - A serial DCE cable is specifically designed to connect a DTE device to a DCE device. The cable ensures that the data signals are transmitted correctly between the two devices. These cables are often used in networking environments where devices ...
O'Reilly
oreilly.com › library › view › pc-hardware-in › 059600513X › ch22s03s01.html
22.3.1. Common Serial Cable Types - PC Hardware in a Nutshell, 3rd Edition [Book]
July 24, 2003 - Cross-over serial cables are used to connect like devices (DTE to DTE, or DCE to DCE). Cross-over cables come in an amazing variety of pinouts, some reasonably standard and others specific to one particular type of connection—e.g., an HP LaserJet serial port to a DB25 PC serial port.
Authors Robert Bruce ThompsonBarbara Fritchman Thompson
Published 2003
Pages 874
Router Freak
routerfreak.com › home › dce/dte cables
DCE/DTE Cables - RouterFreak
August 23, 2016 - For setting serial connections like for frame relay having the right DCE/DTE cable is a necessity! DTE/DCE cables are used to connect two routers via their serial cables. If you are planning on using a frame relay switch in your lab, you’ll ...
Lenovo
lenovo.com › home
What is DCE? Data Communication Equipment Explained - Roles, Clocking, Devices & Differences from DTE | Lenovo US
In serial communication, DCE devices provide clocking signals that ensure synchronization between the transmitting and receiving devices. This clocking defines the rate at which data is transmitted and is especially crucial in synchronous communication systems.
Reddit
reddit.com › r/techsupport › can someone explain what dte and dce cable is used for?
r/techsupport on Reddit: Can someone explain what DTE and DCE cable is used for?
March 11, 2017 -
I am trying to setup a Cisco switch and Router to my computer. I got a cable with me for DTE and DCE
Top answer 1 of 2
1
DTE and DCE are Data Terminal and Data Communication Equipment respectively. wrt RS232, a DTE - DCE and DTE - DTE will have rx and tx terminal wiring swapped at one end. ie., tx-tx vs tx-rx respectively.
2 of 2
1
Where'd you find those dinosaurs? A DTE (data terminal equipment) device is a computer, dumb terminal, etc that uses the communication service provided by the DCE. DCE (data communication equipment) is/was typically a modem of some sort. In your case, you probably have no use for those cables as they would be used between your router and a serial Telcom circuit or some sort or to connect two routers together.
CablesAndKits
cablesandkits.com › mc › cab-ss-v35 › fam-553 › fp-498
CAB-SS-V35FC | Cisco Cable | Smart Serial to V.35 | DCE | 10 ft
Cisco V.35 DCE Female Smart Serial Cable, CAB-SS-V35FC, 10ft
.diagramz { width: 100%; text-align: center; } .diagramz img { width: 90%; } .cols2 { -moz-column-count: 2; -moz-column-gap: 20px; -webkit-column-count: 2; -webkit-column-gap: 20px; column-count: 2; column-gap: 20px; } .cols3 { -moz-column-count: 3; -moz-column-gap: 20px; -webkit-column-count: 3; -webkit-column-gap: 20px; column-count: 3; column-gap: 20px; } .startheader { font-family: 'Roboto Condensed', Helvetica, Arial, sans-serif; width: 100%; font-weight: bold; color: #3B3B3B; font-size: 16px; } .miniheader { font-family: 'Roboto Condensed', Helvetica, Arial, sans-serif; width: 100%; font
Price $29.78
Digi International
digi.com › support › knowledge-base › understanding-dce-dte-connections
Understanding DCE & DTE connections | Digi International
March 26, 2026 - Select your product for firmware, drivers, software, knowledge base articles and manuals · All RS232 devices that use a DB-9 connector should conform to the standard TIA/EIA-574. The device should be either DCE or DTE. DCE devices should have a female DB-9 connector, and DTE devices should ...
Infosec Institute
community.infosecinstitute.com › home › certification preparation › cisco › ccst & ccna (entry-level & associate)
purpose of a serial cable - TechExams Community - Infosec
March 23, 2013 - Hi i done an experiment at home using my internet. Basically i have a modem which connects to my router (normal wireless router) so i thought i would use one of my cisco 2600 routers to act as my router instead. I plugged my modems ethernet in to the 2600 and configured it and everything worked ...
Reddit
reddit.com › r/ccna › dce/dte question
r/ccna on Reddit: DCE/DTE question
August 20, 2016 -
I'm watching Lazaro Diaz udemy course to brush up for 100-105. On a lab he does, you can't really see to much of what's going on because he blocks the screen a little and doesn't give any hostnames to the routers. Which after watching it another time doesn't matter, but the first time through was a little confusing.
My questions are:
-
Does each serial connection need one DCE and one DTE?
-
In this scenario, would there be only one CSU/DSU or could there be multiple?
Screenshot of Lab
I may just be having a brain fart here or am I just missing something, and each serial connection is considered a WAN correct? That would be the reason for setting the clock rate on each WAN.
Any explanation would be appreciated.
Top answer 1 of 3
5
DCE/DTE and CSU/DSU are two different concepts. It might be easier not to consider them related. Let me explain. Serial Cabling - DCE/DTE Cisco exams, in particular the CCNA, make a big deal of Serial cables. In reality, the real world rarely makes use of them anymore. As other comments have pointed out, you might be able to push 2mbps through a serial cable, where as regular plain old fast ethernet will give you up to 100mbps. Serial is outdated technology. That said, it is still on the exams, so still something you need to know about. Physical Cables are L1 technologies, their sole purpose is to carry bits across a wire . Each type of cable does it differently, but essentually a 1 or a 0 correlates to a certain voltage being applied to the wire for a certain time. When two devices want to send bits to each other, it is crucial they each have the same timing, or sampling rate. Which means they both have to know how long the voltage is being applied to represent a single bit. For example, if one end is applying the voltage for each bit for one second, and the other end if reading the voltage for each bit every two seconds, the sender might mean to send 1111, but the receiving end would only interpret 11. Obviously, that would not work so well. Different cabling standards have different ways of ensuring each end is using the same timings... also called Frequency. In Ethernet, the timing is built into the standard itself (100BASE-TX, 1000BASE-T, etc). In Serial, the speed is variable, and can increase or decrease with older or newer devices/technologies. But rather than forcing the configuration to be identical in both places, Serial cables require only one end to set the clock rate (the master), and the other end will inherit the identical rate (the slave). But which side is which? That is where the DCE and DTE come into play. Each cable has two ends, one side labeled as the DCE, and the other labeled as the DTE. Per Serial standards, the DCE side always sets the clock rate. The cables are often (not always) labeled, so you can determine which side is DCE or DTE, but in the case they are not, or you are accessing a device remotely, you can make use of the show controllers command to determine which side is the DCE, and in that case which side should apply the clock rate command. CSU/DSU CSU/DSU is simply a box with two ports that mark the demarcation point between your network and your ISP's network. The port facing the ISP network is the Channel Service Unit and the port facing your network is the Data Service Unit. Its primary purpose is to convert the signal from your network to whatever L1/wiring standard the ISP is using on their network. Typically, your perimeter/edge router will connect to the CSU/DSU via serial cable. And the other end of the CSU/DSU will connect to the ISP with whatever they choose. But since a Serial connection is being used, the clock rate needs to set on one side of the cable so that both ends are using the proper frequency. In reality, it doesn't matter what end sets it, but from the perspective of the ISP, do you think they want you to be able to control how fast the serial link is transmitting bits? Typically the ISP wants to control the speed, so therefore they insist that they (aka the DSU/CSU) are the DCE side of the cable, so that they can set the speed to what you've subscribed to (aka, payed for). Your router will then simply inherit their prescribed clock rate. Hopefully that distinguishes the two concepts, and also illustrates where they come together.
2 of 3
4
The DCE end of the cable provides the clocking
It Still Works
itstillworks.com › types-serial-cables-5860713.html
Types of Serial Cables | It Still Works
January 10, 2019 - Its successors in RS-232 and RS-449 standard domains include V.28 and V.11, respectively. Serial printer cables are used to establish connection between a computer and printer through a serial port.
Pcm-cable
pcm-cable.com › home › knowledges › why is it necessary to set one device as dce and the other as dte on the serial interface link?
Why is it necessary to set one device as DCE and the other as DTE on the serial interface link? - Knowledge - PCM
November 18, 2024 - DCE is responsible for providing the clock signal to ensure the synchronization of data communication. Without a device providing the clock, the two devices will not be able to properly coordinate the sending and receiving of data.
Quora
quora.com › Why-do-we-use-a-serial-cable-to-connect-two-routers
Why do we use a serial cable to connect two routers? - Quora
These connections communicate between DCE (Data Communication Equipment) and DTE (Data Terminal Equipment) devices, which typically communicate over leased lines, such as T1. Leased Li...
CertificationKits
shop.certificationkits.com › home › cables and accessories › cables › dte/dce back to back db60 crossover cable
DTE/DCE Back to Back DB60 Crossover Cable - CertificationKits
DTE/DCE Back to Back DB60 Crossover Cable
DTE/DCE Back to Back DB60 Crossover Cable
This also called a DTE/DCE crossover cable or DB60 to DB60. This is used to connect two serial ports together in a Cisco CCNA, CCNP & CCIE certification lab to simulate a WAN connection.
Compatible with the following series: 1800, 2800.
Not compatible with the following series: 1900, 2900, 4000.
Price $29.99
OmniSecu
omnisecu.com › cisco-certified-network-associate-ccna › how-to-configure-router-serial-interfaces.php
How to configure Router Serial Interfaces, DTE (Data Terminal Equipment) and DCE (Data Communications Equipment)
When connecting a serial cable to the serial interface of the router, clocking is provided by an external device, such as a CSU/DSU device. A CSU/DSU (Channel Service Unit/Data Service Unit) is a digital-interface device used to connect a router to a digital circuit. The router is the DTE (Data Terminal Equipment) and the external device is the DCE (Data Communications Equipment), where the DCE provides the clocking.
NetworkUstad
networkustad.com › home › 2020 › april › 4 › serial cable
Serial Cable » NetworkUstad
September 14, 2021 - Serial cable is used to interconnect DTEs and DCEs. The DCEs are data communication equipment that generated or received data, and the DCEs are data communication equipment that only relayed data.