Archived from groups: alt.internet.wireless (
More info?)
On Sun, 1 Aug 2004 21:45:52 +0100, "David W.E. Roberts"
<nospam@talk21.com> wrote:
>The terms 'repeater' and 'bridge' used to be something like this, in the
>good old days of wired Ethernet (remember those thick yellow cables and the
>'bee sting' connectors?)
Yep. I have some of the original 3C500 cards and transceivers in my
"museum". There are a few rolls of the yellow cable (similar to
RG-8/u) running antennas on my roof.
Y'er right about the repeater. Repeaters used to be boxes used to
extend the length of a 10base2 ethernet segment. It's usually a "bit
regenerator" which is a odd terms for a bi-directional amplifier with
a Schmitt Trigger to clean up the waveform. Later, the repeater
appeared inside 3Com hubs as the "backbone" port, which included the
bit regenerator feature. Later, the 10baseT hubs included a bit
regenerator feature on each port. The result is that whole hub
magically became a repeater. When the IETF approved the management
database for hubs, it was cast in stone.
>The problem at the time was that there was a distance limit on a single
>cable run (caused by electrical properties of the cable and timing in the
>CSMA/CD implementation IIRC).
>
>If you needed longer cable, then you joined two runs with a device which
>would replicate your packet between the cables.
>
>A repeater was a dumb device which just passed everything.
Actually, all repeaters also included some method of cleaning up the
waveform and were bi-directional.
>A bridge was a smarter device which only passed stuff which was intended for
>the other cable. Useful in keeping workstation traffic off the main LAN.
Yep. There were a few ISP's that ran all bridged networks. No
routeing anywhere. Same with a few large corporations. However, it's
difficult to control a large number of devices without the sub-net
features of IP, so they've all given up on switching and gone to
routeing.
>There were also local and remote bridges; local ones had Ethernet at either
>end (one bridge to two strands of Ethernet) and remote ones had 'wet string'
>in between (two bridges and a serial link between them to join two strands
>of Ethernet).
Yep. X.25 or frame relay for connectivity. Brings back fond
nightmares of creative network topologies and unplanned growth.
>When I was a lad MAC level bridges (roughly OSI Layer 2.5) were used to move
>the same Layer 3 protocol between two different Layer 1/2 configurations e.g
>between Ethernet and Token Ring.
Ugh. I missed all that. However, I did have to deal with a
conglomeration called a BRouter (bridge-router) which defied accurate
description.
http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci211707,00.html
>You could only have so many bridges or repeaters before timing delays
>screwed up the protocols.
>After that you had to insert a router - but that's another story
>
>These days everything seems to have been reworked by 'commercial forces' and
>now means something else.
Yep. I can swear my hair turns grey (or falls out) after every
meeting when marketing demands that we invent a new term so they can
claim "product differentiation". I usually pacify them with a new
acronym or metaphor.
>Don't get me started on what Broadband used to mean
An all womens rock band. Is there another definition?
>However AIUI a 'bridge' should be joining two networks together, but not
>dealing directly with any single end station, whereas an Access Point should
>allow one or more end stations to join a network.
Nope. Network means layer 3 IP in my book and an access point does
nothing on layer 3. Without a layer 3 protocol, such as IP, you don't
have a network to join. Connecting two networks with a bridge
(wireless or otherwise) simply expands the size of the network.
That's another reason for the term "transparent bridge", which implies
that it's transparent to any nonsense that gets done on the IP layer.
Therefore, the netmask, broadcast address, and perhaps the default
gateway are the same on both sides of the bridge.
>So in wireless terms I think that the device is an AP if it connects to
>another radio device and only passes traffic to that device intended for
>that directly connected radio device.
Well, yes. However, you left out the decision criteria. It's a
bridge if it makes that decision based upon the layer 2 MAC address.
>It is a bridge if it passes traffic to a directly connected radio device
>which is intended for other devices which sit beyond that directly connected
>radio device.
That's too broad a definition. It includes wireless repeaters, ad-hoc
networks, and wireless routers, which are not really wireless bridges.
>Of course, an AP is a MAC level bridge between radio and Ethernet.
>AFAIK the 'bridge' function in the naming is for radio<->radio bridging.
>Confused?
>Welcome!
Nope. I'm not confused. However, I will admit that there are no
clear cut distinctions between the way manufacturers use the terms
repeater, hub, brouter, bridge, router, gateway, wireless switch, and
access point. There's lots of abuse and plenty of overlap to confuse
everyone. I like to think of myself as part of the solution instead
of part of the problem.
>Cheers
>Dave R
--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
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