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 ExchangeReddit
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.
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 - 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).
What 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
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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
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
16:53
Configuring a Serial Interface Connection Between Two Routers - ...
01:23
DTE/DCE CSU/DSU - YouTube
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.
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 ...
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 ...
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 ...
Lenovo
lenovo.com › home
What is DCE? Data Communication Equipment Explained - Roles, Clocking, Devices & Differences from DTE | Lenovo US
DCE devices perform essential tasks in data transmission, such as signal modulation, synchronization, and conversion for network compatibility. In packet-switched networks, DCEs also manage data framing by encapsulating user data into structured packets with headers and error checks.
NI
ni.com › docs › en-US › bundle › ni-serial › page › rs-232-dte-versus-dce.html
RS-232 DTE versus DCE - NI
In general, DTE and DCE refer to computer equipment and modems, respectively. Because the RS-232 specification mainly involves connecting a DTE directly to a DCE and vice versa, the pinouts are defined so that cabling is simple.
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 ...
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....
Dbase
dbase.com › Knowledgebase › dbulletin › bu07shar.htm
Hardware description
DTE to DTE or DCE to DCE cables - Simplest connection · As it can be seen, communications between 2 devices, DTE to DCE or DTE to DTE require at minimum the RD and TD lines to be connected, and the signal ground (SG). All the other signals are control signals, that are used to control in some way the data flow between the two devices.
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
Cables and Kits
cablesandkits.com › home › dte vs dce
DTE vs DCE: Key Differences Explained - Cables and Kits - Learning Center
September 11, 2025 - The modem and the computer are connected together with a serial connection that conforms to RS-232. When the computer tries to connect, it has to communicate directly with the modem. In this connection, the modem will provide clocking and direct communication. The computer will provide the user data necessary for the interaction. The two work together to send and receive information as needed. That is the essence of DTE and DCE.
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
ALLHDD
allhdd.com › home › cables › serial cable › 10 feet › cab-ss-v35fc cisco v.35 serial dce female to smart cable | new bulk pack
Cisco CAB-SS-V35FC New Bulk Pack
CAB-SS-V35FC Cisco V.35 Serial Dce Female To Smart Cable | New Bulk Pack
CAB-SS-V35FC 10 Feet V.35 Proprietary Connector Serial Network Cable Dce Female To Smart | Made by Cisco | New Bulk Pack
Price $24.00
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.
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.
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The DCE end of the cable provides the clocking
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Pcm-cable
pcm-cable.com › home › knowledges › difference between dce and dte
Difference Between DCE and DTE - Knowledge Co., Ltd - PCM
June 24, 2022 - In actual engineering, the protocol converter, modem and other line control equipment There is no dedicated line control device in the experimental environment, so it is provided by the serial interface of one of the routers. The determination of one end of the DCE is determined by the line sequence of the cables between the routers, so the back to back cables are marked with DCE and DTE.