Tracy Johnson wrote:
>
> On Wed, 16 Jul 1997, Steve BARRETT wrote:

> > I've noticed that the HP3000 network cards have an AUI port.  Is it
> > possible to use 10Base-T transceivers on the AUI ports and run UTP
> > cables between the transceivers and switch ports? If this is doable,
> > does the elimination of the ThinLAN wire in itself buy any increase
> > in network performance to the 3K? I'm assuming here that ThinLAN
> > only offers half-duplex communications.  Whereas, 4 pair UTP would
> > be full-duplex.  Is this correct - or, am I way off base with my
> > assumptions?

A typical 10BaseT connection on Cat3 or Cat5 is half-duplex, I don't
know that I have seen full-duplex 10BaseT (though it very well may
exist).  Shared media hubs [that I know of] echo back any transmissions
down the wire - this 'feature' is used by some network cards as a power
on self-test - it 'pings' itself to see if it is connected.  I know this
to be true for certain 3Com PC NICs as well as some Sun NICs.  There
was a discussion on comp.dcom.sys.cisco about this as their newer
Catalyst line of switching hubs do *not* echo back down the wire, and
some people had Suns wired direct to the Catalyst that would report a
failed NIC and fail to bring up TCP/IP until a "dumb" hub was put in
between.

This behavior emulates coaxial LANs, Thick or ThinNet, where a packet
transmitted "echoes" back down the cable.  This makes the duplex
function more hub/switch dependent than on the end station.

The opposite is true of 100BaseTX, where many cards can be configured
for full-duplex operation, and many hubs/switches are either full-duplex
or auto-sensing of duplex mode.  With a NIC which is truly capable of
full-duplex, you can be sending one packet while receiving another.
When this mode is negotiated by both endpoints of the connection, your
collision rate is zero -- you can transmit anytime you want, receive
anytime you want, and likewise for the other end.  So unlike the typical
10Mb technologies of CSMA/CD, there is no CS (Carrier Sense), no MA
(Multiple Access), and no CD (Collision Detection).  You effectively
gain twice the wirespeed in bandwidth (albeit aggregate of transmit plus
receive).

> I did this once (but you don't use the big fat AUI cable for this
> purpose, the gender is wrong), you use one of those little AUI to
> twisted pair converters right out of the port, and from there you use
> CAT-5 to your switch or hub.

Quite correct.  Try Allied Telesyn's little matchbox transceivers, cheap
and reliable, but be sure the ones you use on the HP side can provide
the SQE heartbeat signal (else the HP NICs will be unhappy).

Jeff Kell <[log in to unmask]>