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In the Cisco Packet Tracer we also see the Serial DCE and Serial DTE:

enter image description here

but I don't know what's the difference between them.

26334_zeal
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3 Answers3

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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:

enter image description here

  • 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.

jonathanjo
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4

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.

Zac67
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  • In the real world, whether there are DCE Serial line and DTE Serial line? – 26334_zeal Nov 27 '18 at 09:32
  • On a console connection, the DCE may be a switch or router, and the DTE is a computer. With a data link, both sides may be configurable. – Zac67 Nov 27 '18 at 09:38
  • Are you sure about that @Zac67? Cisco RJ-45 console and aux ports are DTE, as they have TXD as output; 25-pin console is DCE, aux is DTE. https://www.cisco.com/c/en/us/support/docs/routers/7000-series-routers/12223-14.html 9-pin on eg SG-300 switch is male, believed DTE. – jonathanjo Nov 29 '18 at 23:24
  • @jonathanjo I'm not quite sure about Cisco's parlance - a console port on a switch is in the DCE role and connects to a DTE. Cisco specifies a "rolled cable" (=crossover aka null-modem) which allows for the required DTE-pinout to DTE-pinout connection - there's no general standard for 8P8C serial ports and that's Cisco's way to do it. – Zac67 Nov 30 '18 at 16:08
  • @Zac67 Cisco defines the 8P8C console and aux sockets as DTE, with CTS, DTR and TXD outputs, and RXD, DSR, RTS as inputs, also explicitly described as DTE in https://www.cisco.com/c/en_intl/support/docs/dial-access/asynchronous-connections/5466-comm-server.html – jonathanjo Nov 30 '18 at 16:17
  • @jonathanjo Yes - that's DTE pinout, but still with the DCE role - the "rolled" cable (kind of) changes the pinout to DCE (swaps TxD/RxD, RTS/CTS, ...) and there you are. ;-) It does make sense to only define one variant of the 8P8C port though ("all ports use DTE pinout") and use adapting cables. – Zac67 Nov 30 '18 at 16:23
  • @Zac67, I believe the correct statement is that we have two DTEs which we connect, most frequently, with a null modem, which fakes the less frequent connection with two modems (DCEs). I appreciate it looks very similar, but it's not a pinout question, it's a signal question: as the device is transmitting what it calls TXD and DTR, it is defined to be DTE. – jonathanjo Nov 30 '18 at 16:27
3

enter image description here

DATA TERMINAL EQUIPMENT(DTE)

DTE is an end instrument that converts user information into signals or reconverts received signal.These can also be called tail circuits.

DATA COMMUNICATION EQUIPMENT(DCE)

(DCE) refers to computer hardware devices used to establish, maintain and terminate communication network sessions between a data source and its destination.

DCE is connected to the data terminal equipment (DTE) and data transmission circuit (DTC) to convert transmission signals.

Teun Vink
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Sakthivel sockkalingam
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