Re: Two Netgear WGT624 models will not communicate

On Wed, 19 Jul 2006 11:30:47 -0700 Jeff Liebermann <jeffl@xxxxxxxxxxxxxxxxxxxxxx> wrote:
| phil-news-nospam@xxxxxxxx hath wroth:
|
|>Could you tell me why it is they can't talk to each other in the first
|>place?
|
| Maybe. Wireless topology was originally designed to be a star.
| Central access point and clients that only talk to the central acccess
| point. Additional access points can be added, but only with an
| ethernet backbone. When 802.11 was first inscribed, the possibility
| of building an extensible network topology was discussed, but not
| implimented. Even the now ubiquitous repeater is only vaguely
| mentioned and is very poorly defined.
|
| The limiting factor in having two access points talk to each other is
| in the bridging protocol. For a star topology, with clients that only
| connect to one access point, the client bridge table need only keep
| track of one MAC address to hardware port mapping. It's also easy on
| the access point end because the AP need only keep track of whether
| the MAC address is on the ethernet LAN, or wireless LAN interfaces.
|
| Were to access points to talk to each other, they would by necessity
| need to bridge more than one MAC address. That means a bridging
| protocol that tracks the interface location of all the wireless
| clients. That's missing in the typical access point.

Or alternatively, translate to level 3 and re-announce as IP addresses
in a routing protocol like RIP. But none of this is new; wire switches
do this all the time.


| What WDS actually does is graft this missing transparent bridging
| protocol onto the access point. Rather than impliment a spanning tree
| algorithm, WDS uses a fixed route table that requires users to
| inscribe the destination MAC address of the other WDS routers in the
| system. This would be necessary anyway for security purposes.

Would not the encryption of the packets themselves be sufficient
security? Seems to me that once you get RF into a bit stream/packet
then you want to be sure it is authorized (security) before doing
any more with it (valid SSID, phrase, key, etc).


|>The air is like one big bus.
|
| True, but all protocols are not alike. The freeways are also one big
| bus. Pedestrians, bicycles, and motor vehicles can all traverse this
| bus. However, there's some question as to whether they can talk to
| each or even co-exist.

For ethernet over wireless it's not much different than ethernet over
a coaxial cable, besides the greater noise, more lossage, and hackers
tapping in. Operationally, it seems like it should be the same. But
if there are separate RX and TX frequencies, a few things could get
more complicated.


|>Of course there are issues with
|>respect to radio frequency use.
|
| RF is only the media layer. 802.11 encapsulates ethernet and can run
| on other media besides RF. For example, the infrared comm
| specifiction is buried in 802.11a.
|
|>But once the radio waves are back in
|>a packet of bits, why would they not be able to work?
|
| For the same reason that Mac bits and PC bits don't interoperate
| directly. They need either a common protocol or a conversion
| mechanism. Just because they look like bits, doesn't mean they can
| converse.

That's what we have ethernet, IP, TCP, etc, for. Of course if two
strange machines want to talk to each other in Gibberish 2.0 then
why not.


|>Is the issue
|>that some units TX on one freq and RX on another, and other units have
|>that reversed (e.g. to do full duplex)?
|
| No. Everything in 802.11 wireless is half duplex. A box can transmit
| or receive, one at a time. In a WDS systems, all radios are on the
| same channel.

Then I can't see the reason for separate client mode at the media layer
other than to force the star topology. IMHO, star topology should not
be used in many cases.


|>Just got off the phone with Netgear pre-sales tech. He says use WG602
|>to talk to WGT624. But I have my doubts. I don't know if it's my
|>American accent confusing him, or his Indian accent confusing me.
|
| The WG602 is an access point. The data *** shows that it supports
| "bridging", which is a bit like saying that an automobile supports
| moving. It's too vague. I don't have time to RTFM, but if the WG602
| has a client mode, where you inscribe the MAC address of the access
| point you're connecting it to, then it *MIGHT* work. The problem is
| that you need to bridge more than one MAC address due to the number of
| computers involved.

A limit on MAC addresses is something I can get around. I'll just split
up in subnets and route from one of the Linux boxes. In fact I already
have quite a number of subnets overlayed onto these machines in various
combinations now. Depending on which IP I send to, it could go direct
or be routed by some machine, or a different machine, or multi-hop. I
have 169.254.0.0/16 as one big segment subnet, and chopped 172.16.0.0/12
into a lot of varying sizes of CIDR.

It looks like the WGPS606 might actually do this. It shows in one of
the diagrams as communicating with a WGR614 router.

http://netgear.com/pdf_docs/WGPS606_ds_r1_3.pdf


| A better choice might be to purchase a transparent bridge, which will
| support multiple MAC addresses, but not allow any connections from
| client radios. I haven't read your detailed description of your
| setup, but if any of the laptops need to connect to these wireless
| bridge radios individually, a transparent bridge will not work.

The wireless printer does. I think that will be a client need. Also,
my sister-in-law might need net access here when she brings her laptop
over (unless we can be sure it will communicate on its own back to her
house).

If the transparent bridge will talk wirelessly to the router (WGT624)
then the router serving as the internet gateway can serve clients, IFF
it can be told to _route_ (it has RIPv2 so there is hope) over to my
LAN of computers.

I have an old brand-less model-less wireless bridge of some sort that
I was never able to get working before, but I might try playing with
it to see if I can trick it into working here.


|>I don't think "client side of the street" is meaningful, here. Think
|>of it as connecting one ethernet LAN to another ethernet LAN. If it
|>were wired CAT5, either a crossover cable would do it, or a regular
|>cable with one end in a "upstream" port (the ones with reversed RX/TX).
|
| Sorry. I didn't read your detailed description before I posted the
| above reply. I was guessing a typical laptop and desktop on one side,
| not a server farm. A transparent bridge seems to be appropriate.
| Normally, I would recommend a pair of WAP54G wireless bridges, but the
| last pair are hanging all the time in bridge mode. I'm still looking
| for a suitable replacement.

And one end or the other needs to connect to a DSL modem.


|>Cordless phones on 2.4 GHz work between OK (base in one, carry phone to
|>the other).
|
| Not good enough. My 2.4GHz cordless phone will go about 1000ft (line
| of sight). My wireless won't do that without replacement antennas.
| The faster you go (data rate), the higher the BER (bit error rate). In
| order to keep the BER reasonable, the range gets shortened.
|
| Do you have line of sight? Can the antennas see each other? Are you
| going through any walls, trees, bushes, etc? Windows are usually ok.
| Line of sight is the single biggest determining factor of reliability
| and performance.

Where I will be placing the router that connects to the DSL mode, its
antenna can see the window where the wireless would be in the other house.
The other house is lower in elevation but its wireless will be on the
2nd floor. They have tiny 4 watt lights in each window and I can most
or all of them. A couple trees are along the path, but not completely
blocking things, even with leaves.


|>I can build up to that. In many cases a succinct question works. And
|>when it doesn't, more detail can be provided.
|
| You've done quite well in the other posting. What's missing is the
| line of sight issue and performance expectations. How fast is the
| cable modem?

I'm not trying to pass cable modem (over there) traffic back to here.
I'm getting DSL here soon. But the cable seems to be as fast as I
might expect over there.


|>I must assume there are split frequencies involved and some boxes TX on one
|>of them and other boxes RX on that one and TX on the other.
|
| Nope. Everything on one "frequency" or rather channel as 802.11
| spread spectrum occupies about 22Mhz of spectrum.

So for 2 boxes by themselves it would be equivalent to ping-pong.


|>But if it's a genuine single frequency ping pong, then the engineers who
|>designed the part on the bits/packets side of things seem to have some
|>really twisted idea of how to infrastructure things.
|
| Yep. I'll forward your criticism. IEEE 802.11 was initially
| standardized about 10 years ago. Rub your magic crystal ball and try
| to define the exact wireless technology requirements for the next 10
| years. I know people that are doing just that and it's not easy. If
| extensibility is all that was left out of 802.11a/b/g, then I think
| the committee did an exemplary job.
|
| In effect, what you're asking for is mesh networking technology, where
| the network can be extended by replicating access points. That's
| being done in 802.11s, but has quite a way to go.
| http://en.wikipedia.org/wiki/IEEE_802.11s

I'm really asking for RF to be a media not unlike any other ethernet
media, besides the added "physical" security needs and management.
Beyond that, things like topology should be an administrative issue
that can be handled by smarter implementations or smart enough people.
Products could come with a default that works best for most and MAYBE
support other things. But the _standard_ should not rule out anything.

I can get around the goofy RX/TX pairing design of ethernet twistedpair
by simply using a crossover cable. Radio just isn't so easy, so that's
where I think the designers need to think it through, better. If it's
a case of everything alternates between RX and TX on one frequency
(which is good for assymetric loading, as much of web usage and file
transfers are to sometimes quite an extreme), then the one frequency
design is right. But it really should accept _any_ security authenticated
packet that comes in and pass it to the bridging/switching/routing layer
which should not have standards imitations on flexibility.


|>BTW, if ethernet twisted pair, e.g. with those RJ-45 jacks, had been designed
|>with RX always on one side and TX always on the other, then what we know today
|>as a crossover cable would work.
|
| I worked with a committee to do exactly that but with RS-232 on RJ-45
| and RJ-50 jacks. It fell apart because manufacturers thought they had
| some proprietary advantage to creative wiring and didn't want to
| change their existing wiring schemes. When EIA-568A and B were
| contrived, it was to try and simultanously satisify the telco and
| computah mobs. That's not an easy job when Ma Bell is on one side,
| and the rest of the planet on the other. That's why there are two
| standards where EIA-568B is a clone of the Bell 258A wiring standard.
| http://en.wikipedia.org/wiki/EIA_568A
| Incidentally, when I saw my first modular plug in the early 1960's, I
| almost barfed in disgust. What a flimsy piece of cheap junk is all I
| can say. Well, Darwinian "Survival of the Cheapest" is apparently
| epidemic in the connector business.

Wait until you see them attaching wireless antennas with those :-)
Watch grown men cry!

OTOH, I've seen some terribly shoddy installs of coax and crimpable BNC
connectors just jammed on (fell apart faster than F connectors).

Done right, coax can get up to 2 GHz on BNC, 4 GHz on TNC, 10 GHz on N,
and 24 GHz on SMA. That's assuming good cable, too.

But at least the length of the impedance bumps in RJ-45 is not too long
at 100 MHz.

But the whole mess with twisted pair just annoys me. Going cheap is
one thing. But then trying to be compatible with the twisted pair cables
the telcos already use is another. We ended up having to have crossover
cables, anyway. We should have made that THE standard cable which would
mean every jack would TX on one side and RX on the other side universally.
But I guess someone didn't like simplicity.

Ever seen a GR-874 coaxial connector?


|>But in such a case, we would only need that
|>one type of cable and that one type of port and everything would always just
|>work. But no, some brainless dweeb decided we have to have 2 different kinds
|>of ports (so we can use straight through cables between them) and then have
|>yet another kind of cable to deal with the mixups. So yeah, I know how the
|>people that design these things can really make a mess of things. Seems that
|>wireless is ethernet gone even worse.
|
| The reasons why such things are done are not always evident. Telco
| POTS wiring uses the center pair for L1 and straddles them with
| another L2 pair. The remaining two pairs are for data. The goal was
| to come up with a combined data/voice connector scheme that would
| involve the least amount of wiring changes to existing hardware. Since
| there were millions of voice connections, but very few data
| connections, voice won. Were this done today, it would be very
| different, but if you roll back the clock to the days of the 3B2, the
| choices were very different.

If voice would have stayed with 4-5 and 3-6 and left 1-2 and 7-8 for
data, AND if the 4 wires for 1-2 and 7-8 were always wired as crossover,
AND all ethernet ports would TX on one side and RX on the other, then
it might be just too easy.

OTOH, I still think it remains silly to have billions of these cables
around with 8 wires in them that are half never used. Copper conspiracy?
OK, at least they are starting to use them for gigabit.

I could have had 12 twisted pairs plus a ground pin on a DB-25. With the
same crossing-over logic, even that could have been made to work well.
Even DB-9 would have worked well that way.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2006-07-19-1404@xxxxxxxx |
|------------------------------------/-------------------------------------|
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