On 4/11/22 6:33 PM, Paul Koning wrote:
DECbridge-90: AUI or 10Base2 to 10Base2.
Interesting.
That's not accurate.
"Switch" is a marketing term invented by certain companies that
wanted to pretend their products were different from (and better than)
other people's bridges.
It never was true that bridges are specifically two port devices. Yes,
the very first few models (DEC's DECbridge-100 for example) were two
port devices, as was one whose manufacturer I no longer remember that
bridged Ethernet over a satellite link (InterLAN?). But the standard
never assumed that, neither the original DEC one nor its later 802.1d
derivative. To pick one example, the DECbridge-500 is a four port
bridge: FDDI to 3 Ethernets. The DECbridge-900 is a 7 port bridge:
FDDI to 6 Ethernets. Neither, at the time when DEC introduced them,
were called or described as anything other than bridges.
Today I learned.
The marketeers who flogged the other term also tried to use it to claim
it referred to other supposed improvement, like cut-through operation.
That was an oddball notion that never made much sense but some people
seemed to like doing it in the 10 Mb and 100 Mb era. Of course it
doesn't work for any mixed media, and at higher speeds the difficulty
goes up while the benefits, if they ever were meaningful in the first
place, shrink to microscopic values. For sure it hasn't been heard of
in quite a while. I forgot the name of the company, mid 1980s I think,
that made a big fuss over "cut through" and I think may also have been
the inventer of the term "switch". Cisco bought them at some point.
I vaguely remember that there were three main forms of switching: store
and forward, cut-through, and a hybrid of the two. My understanding is
that S&F had the ability to sanity check (checksum?) frames and only
re-send out valid / non-corrupted frames. Conversely C.T. could not do
this sanity checking and thus could re-send corrupted frames. The 3rd
form did a sanity check on the first part of the frame. -- I think.
I vaguely remember this as a past tense discussion topic at the turn of
the century. I've heard exceedingly little about it since.
Also: neither "bridge" nor "switch" by itself implies either managed
or unmanaged.
I think that /just/ "switch" without any other qualification implies an
unmanaged layer 2 device.
Anything operating above layer 2 will inherently /require/ some
configuration thus management. Yes, layer 3 switches are a thing. Yes,
routers, nominally layer 3 devices, can be configured to perform
unmanaged layer 2 switching.
I think DEC bridges were generally unmanaged, though that was mostly
because no management standards existed yet. I wasn't around when SNMP
became a big deal so I don't know if DEC adopted it when that happened.
I'm not even going as far as what management protocol is used. I'm
including even something that has lowly stand alone serial interface for
console / dumb terminal (emulator) based configuration through some
interface. No remote management / protocol required.
--
Grant. . . .
unix || die
