Retro networking / WAN communities

[Grant Taylor]

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