Well. To beat this horse to death, the DCE / DTE terminology comes from a
different era, and out of the telephone world.
DTE = date terminal equipment
DCE = data circuit equipment ( well, that's what it's called in some books.
others call it data circuit-termination equipment )
DCE is a device into which a data line or a phone line plugs in. i.e. a
modem or a CSU
DTE plugs into DCE, and it is through a DCE that a DTE is able to
communicate across a data network.
This terminology dates back to days when there was no ethernet, no token
ring, no FDDI.
Yes I know that DCE / DTE is not really correct, but in terms of concept, in
terms of keeping things straight (so to speak ), DTE equipment plugs into
DCE equipment in order to access a data network. This requires a straight
through cable. When you connected your old PC into an external modem, you
used a straight through cable, i.e. pin 2 went to pin 2, and pin 3 went to
pin 3, your modem dialed into CompuServe and that was the network.
Following along this line of thought ( yes I know that technically it is not
correct ) you plug your PC ( which is DTE ) into a DCE device, which allows
you to connect to your data network, using a straight through cable.
Hubs and switches, both of which are devices that allow DTE devices to
connect to the data network, are DCE. ( again, I understand, this is not
technically correct )
A router is DTE, because it is not a device which allows you to connect into
a data network, but a device which forwards packets across a data network,
some as any other DTE device. A CSU is a DCE device. Data circuits plug into
them.
When equipment of the same type ( either DCE or DTE ) connects, it requires
a flipping of the transmit/receive wires. In the world of RS232, this meant
pins 2 and 3, so that transmit went to receive and receive went to
transmit )
And while this concept is not technically correct, it sure saves a lot of
headaches in terms of whether or not a crossover cable is required.
Chuck
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
Gareth Hinton
Sent: Saturday, December 02, 2000 5:30 AM
To: [EMAIL PROTECTED]
Subject: Re: Hub-to-Switch connection problem
DTE/DCE probably doesn't fit into ethernet too well, but it does make an
easy way of remembering what needs crosses.
This may be a pie in the sky way of remembering the connections but it works
for me.
PC clearly fits DTE category
Router in most applications used with a DTE cable (admittedly on the serial
but helps to remember it)
Switch/Hub - DCE (
DCE-DTE needs straight
DTE-DTE needs cross
DCE-DCE needs cross
Reading through this I'm wondering whether to even send it, but it's always
been the way I've remembered it.
If it helps, good. If it doesn't forget it.
Horses for courses.
Regards,
Gaz
"John Neiberger" <[EMAIL PROTECTED]> wrote in message
6741840.975736534450.JavaMail.imail@tiptoe">news:6741840.975736534450.JavaMail.imail@tiptoe...
> I wasn't aware that the terms DCE and DTE applied in ethernet; I thought
> they were serial communication terms. How would you apply those terms to
> this situation?
>
> > Hello,
> >
> > Sometimes these things happen because not all equipment have the same
> specs.
> > My suggestion would be to consider DTE to DTE needs at least one roll
in
> the
> > connection, and DTE to DCE needs a straight-through or two rolls in the
> > connection. It all hangs on the constuction of the interface connection
> and
> > which pins it is using for transmit, receive etc.
> > Bottom line is try to determine which interfaces(DTE or DCE) are
involved
> > and then it is easier to choose the correct cable.
> > Hope this helps a little.
> >
> > Winston.
> >
> > -----Original Message-----
> > From: Bradley J. Wilson [mailto:[EMAIL PROTECTED]]
> > Sent: Friday, December 01, 2000 1:31 PM
> > To: cisco
> > Subject: Hub-to-Switch connection problem
> >
> >
> > Okay gang, I had an interesting and annoying situation yesterday
morning,
> > and I'd like to see if anyone else has had an experience like this:
> >
> > My client was installing an older BayStack 301 switch into their
existing
> > network, which consisted of a Bay Access Node router, as well as four
> > stacked SynOptics LattisHubs. The router was experiencing excessive
> > collisions, hence the installation of the switch. So we installed the
> > switch and cabled the router to it, moved all the "power users"
directly
> > onto the switch, and left the other users attached to the hub. We
> attached
> > the hub to the switch via a straight-through cable.
> >
> > The users who were directly connected to the switch had no problem
> accessing
> > the network and Internet. The users on the hub were dead in the water.
> We
> > tried swapping out the cable between the hub and switch, tried plugging
> > either end into different ports, tried flipping the MDI/MDI-X switch,
and
> > nothing worked. The only thing that *did* work was using a *crossover*
> > cable between the hub and the switch.
> >
> > Now, the rule (which I gleaned from this newsgroup, btw) is that when
> you're
> > connecting devices at different OSI layers, you use a
straight-through -
> > e.g. PC to hub, PC to switch, switch to router, hub to switch - that's
> all
> > straight-through. You use a crossover when you're connecting devices
at
> the
> > same OSI layer - router to router, switch to switch, hub to hub, PC to
> PC.
> > In the situation yesterday, a straight-through seemed logical, as we
were
> > trying to connect a hub to a switch. Am I wrong here? Why did the
> > crossover work?
> >
> > Thanks,
> >
> > BJ
> >
> > P.S. sorry for the Bay-centric example...I'm trying to get them to
change
> > that. ;-)
> >
> >
> >
> >
> > _________________________________
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> >
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>
>
>
>
>
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