Retro networking / WAN communities

[Wayne S]

Wayne


> On Apr 11, 2022, at 11:07 PM, Grant Taylor <cctalk at gtaylor.tnetconsulting.net> wrote:
> 
>> On 4/11/22 11:38 PM, Wayne S wrote:
>> In the beginning there was thick ethernet limited to 100 m.
> 
> Um....
> 
> I *REALLY* thought the 5 & 2 in 10Base5 and 10Base2 was the number of hundreds of meters that the cable segment could exist on it's own.
Nope .  The numbers were just the spec. Thick,thin, and twisted pair 10baseT.
Early on the 10base5 was the thickness of the cable itself. 
Max length Had to do with how long it takes for the carrier signal to propagate the max length of a segment in order to determine if its okay to transmit. Signal had to be asserted long enough for a node at the beginning to allow the furthest away node to detect it else there would be a collision.
The "cs" in "cs/cd"  Carrier sense/ Collision Detection.


> 
> My understanding is that the 100 meter limit came about with 10Base-T.
True. Thick was 185 m. 
> 
>> People wanted computers that were on different floors  connected together between floors and buildings.  That exceeded the 100 meter spec so the repeater was born to connect two 100 m thick ethernet seqments.
> 
> I feel like even only 100 meters / 300(+) feet gives quite a bit of flexibility to connect multiple floors.  Especially if you consider the AUI drop cable.

It may seem like a lot but it really isn't. A corporate office floor can easily be over 100 feet so you have to run one seg on a floor then try to bridge it to another floor thru the risers so the distance gets eaten up quickly. On College campuses, they routinely networked buildings together.

> 
> Aside:  I'm not sure how long an AUI drop cable could be.  I'm anticipating between single and low double digit feet.
AUI  was 50m.
> 
>> A repeater was basically a signal booster between two ethernet segments. As you added segments interference and collisions became a problem as traffic on one segment was passed to all the other connected segments.
> 
> Yep, the 3, 4, 5, rule.  Up to five segments of cable with four repeaters and stations on no more than three of the segments.
> 
>> Hence the bridge was born. It had some intelligence And didn’t pass packets intended for computers on its own segment to the other segments thereby reducing congestion and collisions.
> 
> Didn't repeaters operate in the analog domain?  Meaning that they would also repeat ~> amplify any noise / distortion too? 
Everything using signaling is in essence analog. Digital is just sensing an modulated analog voltage at a specific time interval. The ethernet cable is shielded to prevent noise  and unshielded has so many turns per inch to minimize noise. Differential something its called.
> 
> Conversely bridges operated in the digital domain.  Meaning that they received an Ethernet frame and then re-generated and transmitted a new pristine Ethernet frame?
> 
Good question. Not sure. I think they just dropped or passed the packet to the next segment. Not sure if they regenerated it. I do know that some bridges could buffer packets so maybe they did regenerate them.

>> Then the router was born to connect multiple segments together at one point. And it had intelligence to determine what segment a packet should go to and route it there. It also prevented packets from going onto segments that didn’t have the packet’s intended target thereby reducing congestion.
> 
> I would say "network" as opposed to "segment" because a network could consist of multiple segments. 

Well, a router really just routes packets between the physical wires (segments) that it is connected to. The network refers to all routers and segments as a whole although that distinction is blurry. I.e. Are all the WANS part of the network or are the Individual  WANS networks themselves?
> 
> But otherwise I agree.
> 
>> Hubs were born approximately the same time to get over the ethernet tap distance because by this time there were more computers in the single area that needed to be connected together to the Ethernet.
> 
> Hum....
> 
> I can see problems with having enough actual taps on a network segment to connect all the machines in a given area with AUI drop cable length issues.
> 
> But I know that multi-port taps were a thing.  I've read about them and seen pictures of them for sale.  I think I've read about a singular tap that had eight AUI ports on it.  I've seen pictures of four AUI ports on a single tap.
I have never heard of multi-port taps before. I googled and only fiber references came up. Got a reference i can look at and learn?

> 
> So ... the idea of having too many multi-port taps to be able to connect machines in proximity seems ... questionable to me.  Single port taps, maybe.
> 
>> Hubs were dumb so every packet that hit them was forwarded to every other computer connected to the hub into the segment the hub was connected to, so, for a segment that had a lot of computers, there was congestion and collisions.
> 
> I feel like a hub is the 10Base-T evolution of a multi-AUI port tap.
> 
>> The switch came about. It was a smart hub that had intelligence. It could filter out packets that were not intended for other computers connected to it thereby reducing congestion.
> 
> I feel like the switch and the bridge are doing the same thing from a learning / forwarding / blocking perspective.
Pretty much. They just have different reasons for existing. I think Nbase computing came out with the first switch @ 1988 and everybody wondered what it did. 
> 
> I don't know which came first, but I suspect it was bridges.
> 
>> So each device was really an evolution to solve a problem of congestion and ethernet length.
> 
> Sure.
> 
> 
> 
> -- 
> Grant. . . .
> unix || die
Take care...