Thứ Năm, 9 tháng 5, 2013

What is DCE and DTE in Networking?

Many time i ask myself ,what is the difference between DTE and DCE ,what should I choose .The reason for asking this question When i use Cisco Packet Tracer,which allows you to connect Routers together with  Serial Port,which is provides two types of Serial DTE serial DCE serial

Frist what mean DTE,DCE

DTE: Data Terminal Equipment

DCE:Data Communication Equipment

Data Communication Equipment – (DCE) The devices and connections of a communications network that connect the communication circuit between the data source and destination (the Data Terminal Equipment or DTE). A modem is the most common kind of DCE.

Before data can be transmited over a modem, the DTR (Data Terminal Ready) signal must be active. DTR tells the DCE that the DTE is ready to transmit and receive data.

DCE and DTE are usually connected by an EIA-232 serial line. It is necessary to distinguish these two types of device because their connectors must be wired differently if a “straight-through” cable (pin 1 to pin 1, pin 2 to pin 2 etc.) is to be used. DCE should have a female connector and should transmit on pin two and receive on pin three. It is a curious fact that many modems are “DTE” according to the original standard.

A general rule is that DCE devices provide the clock signal (internal clocking) and the DTE device synchronizes on the provided clock (external clocking).

CCNA Certification Test Prep Case Study:

The DTE/DCE Network Cable & Directly Connected Serial Interfaces

Your Cisco CCNA certification training can't just consist of routing protocol study - you've got to know the different kinds of network cables and Cisco router configurations running in today's networks, and the simplest looking configurations can be rich in details!

The DTE/DCE cable is simple to work with, and it's likely that you'll see some questions regarding this cable and directly connected Serisal interfaces on your CCNA exam.

This is also a typical configuration in CCNA and CCNP home labs as well, particuarly when setting up a frame relay switch.

In this example, we've directly connected Router1 and Router3, using each router's Serial1 interface.

CCNA Certification Directly Connected Serial Interfaces

By default, Cisco routers are DTEs (Data Terminal Equipment). This poses a problem when we connect two routers directly, since one of the routers must serve as the DCE (Data Circuit-Terminating Equipment) in such a connection.

The DCE must send a clock rate to the DTE, so we've got to configure that as well.

There will be a DTE/DCE cable connecting these routers, with the DTE end of the cable naturally connected to the DTE and the DCE end... well, you know where that goes.

But what if the cable is already connected and you need to ensure that the DCE end is indeed connected to Router3?

Current DTE/DCE cables have "DTE" and "DCE" physically stamped into the connector itself, but what if you can't see that?

In this case, the Cisco router command show controller comes to the rescue! There's a lot of output from this command, but the information pertinent to our situation is right at the top:

R1#show controller serial 1
HD unit 1, idb = 0x1DBFEC, driver structure at 0x1E35D0
buffer size 1524 HD unit 1, V.35 DTE cable

If R1 is connected to the DTE end of the cable, R3 must be connected to the DCE end.:

R3#show controller serial 1
HD unit 1, idb = 0x1C44E8, driver structure at 0x1CBAC8

buffer size 1524 HD unit 1, V.35 DCE cable

I mentioned earlier that the DCE must supply a clock rate to the DTE. If this step is left out, the physical connection will be up but the logical connection, the line protocol, will fail.

R3#show int s1
Serial1 is up, line protocol is down

Once we have a clock rate configured on R3, the line protocol should come up. Let's configure a clock rate and find out!

R3(config)#int s1
R3(config-if)#clockrate 56000

1d06h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to up

For such a simple Cisco router configuration, there's a lot going on here! Part of your CCNA certification training is mastering these details, so knowing how to find out which end of the cable is connected to the DCE and knowing what the DCE needs to do to make this configuration valid couldn't hurt a bit!

There are literally hundreds of additional tutorials, practice exams, and Cisco training videos on my CCNA / CCNP certification tutorial page - so click that link and head on over right after you take advantage of this exclusive opportunity..

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