Retro networking / WAN communities

[Grant Taylor]

On 4/12/22 7:49 AM, Paul Koning via cctalk wrote:
> DEC documentation.

Thank you.

> The concept of a repeater goes back to day 1 of Ethernet; you'll find 
> them in the D/I/X Ethernet spec.  And they were part of the first 
> batch of Ethernet products from DEC.

Repeaters existing from day 1 of Ethernet sort of surprises me.

I wonder if there is some difference in the original 3 Mbps Ethernet at 
Xerox PARC vs the 10 Mbps Ethernet (II?) that was commercialized.

> Yes, AUI based devices, two port.

ACK

> But the next thing out the door was the DEMPR, "Digital Multi-Port 
> Repeater", an 8 port repeater.  I think that's 10Base2.

$ResearchList++

> I first saw "structured wiring" -- the star wiring with a hierarchy 
> of wiring closets and devices -- around 1986, in the new Littleton 
> King Street DEC building.  It had distribution cabinets at the end of 
> each row of cubicles.  These looked just like standard office supplies 
> storage cabinets, with shelves; inside you'd find a bridge and a couple 
> of DEMPR repeaters, connected to 10Base2 coax drops to each cubicle.

Interesting use case.  --  Now I'm wondering if each station run was 
standard 10Base2 with it's T connector and terminator.

> That's not where the term "switch" was introduced.   And devices 
> like that were called "bridge" by market leaders like DEC -- the two 
> generations of FDDI to Ethernet bridges I mentioned were both called 
> "bridge".

I first saw "switch" used as a way to differentiate a (dumb) hub from an 
intelligent hub type of functionality.

> Also, the general operation of the device is the same whether it does 
> MAC frame tweaking or not, 802.1d applies unchanged.  Ethernet to 
> non-Ethernet bridges have to do some tinkering with Ethernet protocol 
> type frames (which is where SNAP comes in, all nicely standardized in 
> the FDDI days).  For 802.5 they also have to deal with the misnamed 
> "functional" addresses, but that's not hard.

I now feel the need to call out what I think are two very distinct 
things that need to be differentiated:

1)  Learning of which port a source MAC address is on for the purposes 
of not sending a frame out to a destination segment when the location of 
the destination is known.
2)  Spanning Tree / 802.1D learning the path to the root of the tree.

The former is a fairly easy algorithm that doesn't require anything 
other than passive listening for data collection.  The latter requires 
introduction of a new type of active traffic, namely BPDUs.

> There also was such a thing as a "source routing bridge", an 802.5 
> only bad idea invented by IBM and sold for a while until the whole 
> idea faded away.

We are actually seeing "source routing" make a resurgence in IPv6 via 
Segment Routing.

> I think "hub" is what DEC called the chassis that these boxes could 
> plug in to.
> 
> I understand now.  Yes, that's annoying indeed.

Yes, quite annoying.

I could actually see the use for a card that could go into non-fixed 
configuration switches that provided a few 10/100 ports specifically for 
this purpose.

> So yes, it's theoretically part of the spec.  As you said, it doesn't 
> seem to be in actual use.

ACK

> Curious.  Clearly such things are possible.  But FDDI came out well 
> before HSTR, and it was crushed by 100 Mb Ethernet.  All the reasons 
> for that to happen would apply much more so for HSTR.

Yep.  Lab vs actual commercialized products are quite different.  Then 
there's what the market purchases and uses.

> Does anyone still remember the other 100 Mb Ethernet-like proposal, 
> I think from HP, which added various types of complexity instead of 
> simply being a faster Ethernet?  I forgot what it was called, or what 
> other things it added.  Something about isochronous mode, perhaps? 
> Or maybe I'm confused with FDDI 2 -- another concept that never got 
> anywhere, being much more complicated even than regular FDDI.

I vaguely remember there being multiple 100 Mbps Ethernet 
specifications.  I think one of them had "Any" in it's name.



-- 
Grant. . . .
unix || die