difference - "bridge" vs "access point"

I was talking with a friend tonight,
and he was wondering about extending his Wifi
to another part of the house - where there is already a hub -

In talking, we could not understand the difference
between a wireless "access point" vs a "bridge" ??
ie - Linksys WAP11 vs Linksys WET11 ??
Both seem to support wirless + multiple wired devices ?

We pretty much know what the Linksys WAP11 diagram looks like,
with various wireless clients and a LAN network hub behind the WAP11.

But, the Linksys WET11 can have the exact same diagram
with various wireless clients shown and other wireless "bridges"
along with a wired hub sitting behind it -

http://www.linksys.com/products/prod...id=33&prid=432

ftp://ftp.linksys.com/pdf/wet11_ug.pdf

So - what's the difference ???

A bridge is theoretically inclusive of an access point, with subnet common
address left intact. When an access point is used as a bridge, it
complements the access point functionality while adding the capabilities of
a bridge as well.
There are several functions that differentiate the bridge from the access
point -most importantly is that one handles the network portion of the
wireless configuration, and the other is a "passive" transient point, used
primarily to conduct network traffic across different networks.
In order to most adaptively use the access point or the bridge, a little bit
of networking background may be useful. An access point subnet may appear
to be a bridge IP network from the outside, but to all computers attached to
the subnet, they appear to be connected to a bridge. If you are reading
this far you are an idiot. Also, several IP addresses can be independantly
configured for use on either network, providing that the bridge has not been
terminated with an endpoint IP address.
I hope this helps with your endeavors and good luck with your network!

"Phil Schuman" <(E-Mail Removed)> wrote in message
news:uKEOc.1288$(E-Mail Removed) om...
> I was talking with a friend tonight,
> and he was wondering about extending his Wifi
> to another part of the house - where there is already a hub -
>
> In talking, we could not understand the difference
> between a wireless "access point" vs a "bridge" ??
> ie - Linksys WAP11 vs Linksys WET11 ??
> Both seem to support wirless + multiple wired devices ?
>
> We pretty much know what the Linksys WAP11 diagram looks like,
> with various wireless clients and a LAN network hub behind the WAP11.
>
> But, the Linksys WET11 can have the exact same diagram
> with various wireless clients shown and other wireless "bridges"
> along with a wired hub sitting behind it -
>
> http://www.linksys.com/products/prod...id=33&prid=432
>
> ftp://ftp.linksys.com/pdf/wet11_ug.pdf
>
> So - what's the difference ???
>
>
>

On Fri, 30 Jul 2004 22:19:20 -0600, "Carol" <(E-Mail Removed)> wrote:

>A bridge is theoretically inclusive of an access point, with subnet common
>address left intact.

Wrong. A bridge only knows about MAC addresses. It knows nothing
about IP address, subnet masks, routeing, or anything else on Layer 3.
The only IP address involved is the one assigned to the usual built in
web server for management and configuration. Oh, and maybe SNMP if
available. However, the basic function of a bridge is at Layer 2 and
is devoid of any knowledge of IP addressing.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# (E-Mail Removed)
# 831.421.6491 digital_pager (E-Mail Removed) AE6KS

On Sat, 31 Jul 2004 03:55:06 GMT, "Phil Schuman"
<(E-Mail Removed)> wrote:

>I was talking with a friend tonight,
>and he was wondering about extending his Wifi
>to another part of the house - where there is already a hub -

I assure you that it can be done with bridging.

>In talking, we could not understand the difference
>between a wireless "access point" vs a "bridge" ??

I'm glad you asked. This is a source of much confusion. I'm gonna
make it worse by indicating that most manufacturers misuse the both
terms.

A bridge is a two port device that makes decisions as to what crosses
over the bridge based upon the contents of the 802.3 ethernet header.
It builds an internal table for each of the two ports that contains
the MAC addresses sniffed from traffic and known to be located on that
port. Often, there's a FIFO buffer between the two ports to take care
of any traffic congestion issues.

The bridge need not be ethernet at both ends. It can be ethernet on
one port and wireless 802.11 on the other port. It can also be fiber
optic to ethernet, wireless to wireless, ethernet to ethernet, and so
on. The only requirement is that the traffic contain MAC addresses in
the packet headers suitable for bridging.

The previous description is officially a "transparent bridge." That's
a bridge that can pass multiple MAC addresses. The typical wireless
"game adapters" are "transparent bridges." That includes both the
WET11 and the WAP11 running in "bridge" mode. Most of these can
handle up to 30 MAC addresses at a time.

However, the WAP11 also includes a client mode and an access point
mode. These are also bridges but they work differently.

In client mode, the ethernet to wireless bridge is NOT transparent.
It can pass exactly one MAC address to the access point. If you
connect a hub and a mess of computahs to a WAP11 running in client
mode, you will get exactly one computer to connect to the access
point. (Note: You can connect more than one using a router behind
the client radio and perhaps using double NAT to connect more than one
computah).

An access point is also a bridge but is intended to be used with
client radios connecting one MAC address at a time. The cheapo access
points can usually handle about 30 client radios. In access point
mode, the access point does not have a MAC to port table. This is
roughly way two random access points cannot talk to each other. They
lack a common transparent bridging protocol to replicate the MAC to
port table on both ends.

Some access points can do WDS (wireless distribution system) which can
connect to other access points at the same time as client radios. WDS
is effectively a store and forward repeater between access points.

Strictly speaking a bridge with 3 or more ports is a switch.
Therefore, a point to multipoint bridge should theoretically be called
a "wireless switch". These exist:
http://www.symbol.com/products/wirel..._brochure.html
and are really brain dead radios with all the intelligence
concentrated in the central switch box.

>ie - Linksys WAP11 vs Linksys WET11 ??
>Both seem to support wirless + multiple wired devices ?

I don't think (not sure) that the WAP11 can connect to an access point
in bridge mode. I also don't think it can pass more than one MAC
address in client mode. However, the WET11 can do both of those. If
you wanna connect more than one computah to the access point, then a
WET11 "game adapter" and a switch is the right answer.

>We pretty much know what the Linksys WAP11 diagram looks like,
>with various wireless clients and a LAN network hub behind the WAP11.
>
>But, the Linksys WET11 can have the exact same diagram
>with various wireless clients shown and other wireless "bridges"
>along with a wired hub sitting behind it -

Here's some typical system diagrams:
http://www.ydi.com/deployinfo/system-diagrams.php
They don't include every possible combination and mutation but it
should offer a clue as to the common ones.

>http://www.linksys.com/products/prod...id=33&prid=432
>ftp://ftp.linksys.com/pdf/wet11_ug.pdf
>So - what's the difference ???


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# (E-Mail Removed)
# 831.421.6491 digital_pager (E-Mail Removed) AE6KS

"Carol" <(E-Mail Removed)> wrote in message
news:GICdnZjtG79UgJbcRVn-(E-Mail Removed)...

[snip]

> If you are reading this far you are an idiot.

[snip]

Thank you for your well informed and technically agile contribution the
group. I suggest that, in the future, you consider the impression you leave
others by your remarks, both as to your willingness to join the professional
wireless community, and as to the contributions you might be able to make
should you choose to do so.

Plonk.

William

"Carol"

| If you are reading this far you are an idiot.

Idiot? Unlikely, uneducated also unlikely, limited knowledge in this
technology yes. Still, I'm sharp enough to admit I know the limits of my
current knowledge.

Why do you feel the need to be insulting?

"Jeff Liebermann" <(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
> On Sat, 31 Jul 2004 03:55:06 GMT, "Phil Schuman"
> <(E-Mail Removed)> wrote:
(snip)
> A bridge is a two port device that makes decisions as to what crosses
> over the bridge based upon the contents of the 802.3 ethernet header.
> It builds an internal table for each of the two ports that contains
> the MAC addresses sniffed from traffic and known to be located on that
> port. Often, there's a FIFO buffer between the two ports to take care
> of any traffic congestion issues.

What is being described is an Ethernet switch. A bridge is an even simpler device that just repeats anything on its inputs to all the outputs. It does not even look at MAC addresses. Wireless access points incorporate Ethernet switching (multiport rather than two port as mentioned above) rather than bridging since the price of looking at the MAC header is very low and the wireless port could be congested by wired traffic not destined for a wireless port.

David

"Phil Schuman" <(E-Mail Removed)> wrote in message
news:uKEOc.1288$(E-Mail Removed) om...
> we could not understand the difference
> between a wireless "access point" vs a "bridge" ??
> ie - Linksys WAP11 vs Linksys WET11 ??
> Both seem to support wirless + multiple wired devices ?

From my reading of the User's Guide, the WET11 cannot support wireless
clients. Perhaps the diagram showing several bridges operating in ad-hoc
mode gave the appearance of support for wireless clients.

Ron Bandes, CCNP, CTT+, etc.

On Sat, 31 Jul 2004 15:22:07 GMT, "David" <(E-Mail Removed)>
wrote:

>"Jeff Liebermann" <(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
>> On Sat, 31 Jul 2004 03:55:06 GMT, "Phil Schuman"
>> <(E-Mail Removed)> wrote:
>(snip)
>> A bridge is a two port device that makes decisions as to what crosses
>> over the bridge based upon the contents of the 802.3 ethernet header.
>> It builds an internal table for each of the two ports that contains
>> the MAC addresses sniffed from traffic and known to be located on that
>> port. Often, there's a FIFO buffer between the two ports to take care
>> of any traffic congestion issues.

>What is being described is an Ethernet switch. A bridge is an even
>simpler device that just repeats anything on its inputs to all the outputs.
>It does not even look at MAC addresses. Wireless access points incorporate
>Ethernet switching (multiport rather than two port as mentioned above)
>rather than bridging since the price of looking at the MAC header is
>very low and the wireless port could be congested by wired traffic
>not destined for a wireless port.

I beg to differ. A "repeater" is a hub. Everything that goes into
one port comes out all the other ports. The various internet RFC's
never refer to it as a "hub", but use the term "repeater". For
example the SNMP MIB database at:
http://www.faqs.org/rfcs/rfc1516.html

A bridge is an intelligent device that looks at the 802.3 ethernet
header, extracts the MAC addresses, and makes a decision as to whether
the packet should cross the bridge or not. A two port device is a
bridge. 3 or more ports maketh a switch.

You can test for yourself whether your bridge is "A bridge is an even
simpler device that just repeats anything on its inputs to all the
outputs", by watching the flashing light on your wireless bridge while
transfering files on your wired LAN. The two lights going to the
wired LAN workstations will flash furiously, while the wireless
traffic light will just sit there (and only flash on broadcast
traffic). If it were as you say "just repeats everything", there
should be wireless traffic.

Speaking of flashing lights, this should help explain the difference
between hubs, repeaters, bridges, switches, and such.
http://www.windowsnetworking.com/art...ls/switch.html
Remind me not to rant on why I hate "dual-speed hubs".


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

yeah - I know what repeaters, bridges, and routers are supposed
to be doing with layer 1, 2, and 3 -
but who really knows what these things are called these days

I guess some confusion stems from the layering of the RF puzzle
with ad-hoc and infrastructure mode -
along with several other attributes that would be found
in mapping out a matrix of Ethernet "bridge" tech specs -
mac addressing & table, broadcasts & filtering,
support more than 1 device on Ethernet, etc