[rescue] AUI duplex [was Re: New SPARCStation 10 owner, needs help with some issues though.]

Mouse mouse at Rodents-Montreal.ORG
Sat Feb 6 08:21:49 CST 2016

>> I have had trouble getting an 'le' device to work on any switch, at
>> all.
> Lance interfaces work just fine.  Sometimes, depending on what sort
> of comms gear you're plugging into, it may require pinning the switch
> at 10Mb/s half-duplex, but from my experience, that's it.

Yeah, but a lot of low-end switches are sufficiently unmanaged that
that's not possible on them.  It's one reason I keep 10Mbit hubs
around; I have some machines that have trouble with autoneg but are
fine when connected to a dumb 10-only hub.  (I suspect they are
expecting link to come up faster than autoneg permits.)  Most of the
devices I've seen this with are SPARCstations....

> Out of curiosity, since this is primarily about a SPARCstation 10, do
> 10s have an AUI interface as well?

I'm not sure, but I think so.  The 20 does, though you need a breakout
cable to access it (the connector is not a DA-15), so I would expect
the 10 would have it as well.

> AUI -- contemplate that for a moment and then realise why "duplex" is
> meaningless.

I _think_ AUI uses separate pins for transmit and receive, so the only
reason it couldn't do full-duplex is that the usual driving electronics
isn't designed for it (not surprising, since, as you say, it comes from
the days of shared broadcast medium).

> Nobody is going to get anywhere close to 10 Mbps through any sort of
> a half-duplex Ethernet connection.  It's just not going to happen.

My experience disagrees.  I'm typing this on a SS20, and I just
transferred ten megabytes to it from another machine on my house LAN
and it took ten seconds according to "date", meaning it was somewhere
between nine-plus-epsilon and eleven-minus-epsilon seconds; watching my
on-screen clock ticks makes me think it was very close to ten seconds.
That's 1048576 bytes/second of TCP end-to-end goodput, which is 83+
percent of 10Mbps for just the payload alone (TCP, IP, and Ethernet
overhead mean it's a little more, depending on where you measure).

The SS20 is using twisted-pair, to a Catalyst 29xxXL switch, on the
other side of which is the sending machine - but the SS20<->Catalyst
link is 10/half because the SS20's onboard le can't do better.

> This does not mean that was the throughput of the thing, not even for
> a network consisting of two machines alone on a length of wire --

No, but it can come respectably close.  Eighty-plus percent ain't bad.

> "Ethernet" of today looks nothing like its genesis, save for the
> pitifully small MTU given the speeds now attainable

If you're talking about the physical layer, yes.  But at slightly
higher layers, there are respects in which it is rather similar,
notably the address space (48-bit MACs), the frame format (destination
MAC, source MAC, two bytes of type, payload, checksum), and support for

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