>> Switches have to receive at least the first 48 bits of the data (the
>> Ethernet destination address) before they can tell what port(s) to
>> forward the packet out, meaning a delay of at least 48 bit times,
>> probably more because of channel seizure and suchlike goop.
> Also beware that some of the early 10M switches (probably in the
> hands of 'normal' people now) would actually discard the packet if
> the target port was busy, rather than reverting to 'store and forard'
> or generating a collision.

It's too late to generate a collision; the channel seizure is supposed
to be long enough to ensure that either you get a collision or the coax
is yours for the duration.

Sure, you can collision jam anyway, but it'll produce a late collision
error on the sending host, not a normal collision.  And if the packet
is short and the sending host is far away, your jam may not get there
until the whole packet has been sent.  (I suspect.  I haven't worked
the arithmetic; it may be that the minimum packet size is enough larger
than the channel seizure time that this isn't true, and you'll just get
late collisions and collision fragments.)

> The other type of device that will link two lan segments is a
> 'repeater' set.  This links two coax segments keeping them in the
> same collision domain [...]  NB these are AUI-AUI or coax-coax boxes,
> and not the AUI 'fan-out' boxes which allow (typically) 8 computers
> to be connected to one tap - which are much more like UTP hubs.

I have trouble seing the difference: in each case they're just signal
repeaters.  The only question is whether the signal is in the form of
Ethernet carrier or AUI transceiver-interface levels.

Actually, because of that, I would say that a UTP hub is much more like
a multi-port form of one of these "repeater set"s, because it works
with modulated carrier rather than the AUI signals that the multiport
transceiver boxes you compare UTP hubs to do.

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