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Nikon D600 a compromise but ok



 
 
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  #81  
Old September 27th 12, 09:38 AM posted to rec.photo.digital.slr-systems
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Posts: 24,165
Default Canon 6D

In article , Floyd L. Davidson
wrote:

you didn't know what automatic meant and you think all base stations
have vertically polarized antennas.


I certainly don't know what *anything* means to *you*!


it's what the industry defines it as, not me. *they* are the ones
calling it automatic.

stop trying to weasel out of it.

And yes, virtually all base stations ahve vertically
polarized antennas.


previously, you said all, now it's virtually all? hilarious.

not that it matters. it's nowhere close to 'virtually all.' travel
routers, for example, are polarized in whatever orientation they happen
to be when used, particularly the battery operated ones, such as a
cellular mifi device.

having the selection be automatic spreads it out, without the user
having to figure out what to do. not everyone is a geek. most aren't.
even many of those who are geeks probably don't know what to pick.

All it has to be is a default to an "auto" mode that switches
between only three channels unless some other option in chosen.

Simple, easy...


except when that doesn't work.


What do you mean it does't work? It would work far better than
randomly picking just any channel.


except it's not random.

Sigh. I drew a graphic and made a chart previously that showed *precisely*
what the channel separation is.

The simple fact is that yes it will increase interference if you choose
anything else.


it will not increase anything.


Just interference.


nope.
  #82  
Old September 27th 12, 11:20 AM posted to rec.photo.digital.slr-systems
Floyd L. Davidson
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Posts: 5,138
Default Canon 6D

nospam wrote:
In article , Floyd L. Davidson
wrote:

you didn't know what automatic meant and you think all base stations
have vertically polarized antennas.


I certainly don't know what *anything* means to *you*!


it's what the industry defines it as, not me. *they* are the ones
calling it automatic.

stop trying to weasel out of it.


I merely asked exactly what you meant, since *you*
didn't have the sense to explain yourself. That is
hardly trying to weasel out of anything.

In fact we were talking about a client automatically
changing channels to match the AP, and when you said
the AP could be automatic is certainly made me think
you were saying the AP adjusts to the client. That
doesn't make sense, so I simply asked what you meant
by "automatic".

Pretty reasonable... but you aren't.

And yes, virtually all base stations ahve vertically
polarized antennas.


previously, you said all, now it's virtually all? hilarious.


Same thing. You probably don't know what the
significance is anyway. Of course many if not most
units have always had antennas that can be adjusted.
They *all* recommend using vertical polarization, but
there are good reasons to use horizontal in some special
circumstances (mostly to restrict the range).

not that it matters. it's nowhere close to 'virtually all.' travel
routers, for example, are polarized in whatever orientation they happen
to be when used, particularly the battery operated ones, such as a
cellular mifi device.


And any instructions that mention antenna orientation
will say to position the unit in a way the results in
vertical orientation.

Again, that is because vertical *is* the standard (for
very good reasons), and will generally produce the best
results. In the case of a direct line of sight with no
multi-path there is about 30 dB loss from cross
polarization.

I haven't seen the insides of some of the smaller WIFI
units for cameras and similar devices, but I would guess
that at least some of them use circular polarization,
just to avoid excessive loss from cross polarization.

Sigh. I drew a graphic and made a chart previously that showed *precisely*
what the channel separation is.

The simple fact is that yes it will increase interference if you choose
anything else.

it will not increase anything.


Just interference.


nope.


Ignorance is bliss, and you seem blissful enough.

--
Floyd L. Davidson http://www.apaflo.com/
Ukpeagvik (Barrow, Alaska)
  #83  
Old September 27th 12, 03:57 PM posted to rec.photo.digital.slr-systems
Wolfgang Weisselberg
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Posts: 5,285
Default Canon 6D

Floyd L. Davidson wrote:
Wolfgang Weisselberg wrote:
Floyd L. Davidson wrote:
There
will never be a time when at least 10 or so clients are
not trying to get access.


And that's lowering the individual thoughput by a factor 400?
(WLAN netto speed, single user, 54 MBit/s brutto versus
dialup modem brutto speed of 33.6 kbit/s upload)


Yes. When none of the clients can get a connection, due to
repeated contention, there is *no* throughput for any client.


You're of course completely right ...
.... if there WERE no way to make a connection, there WOULD BE
no throughput.


Unless one of them has a
received signal strength that is more than 6 dB greater
than the sum of the others, the AP cannot detect a
single client.


The way it works:
Stations listen if the channel is free, and have random
timers (the more collisions, the larger) which cause most
packets to not be involved in a collision. (It's actually
more complicated than that, but read yourself ...)
http://www.comlab.hut.fi/studies/324...ot/4_wlan2.pdf


The upshot is: There's no "the sum of the others".


Yes there is. Now do some research on something called
"capture effect" with FM or PM modulated radio signals.


The capture effect sort of requires that at least 2 nodes are
sending simultaneously, true? What happens if this situation
is mostly circumvented --- like in WiFi, where (see link above)
extreme pains are taken to avoid this sort of thing?

Or are you talking about radiation from other sources, in
which case WiFi won't work even with a single client?

The functionality is on several levels, not just WIFI contention.
There are also colisions between clients transmitting at the same
time.


Of course. In which case they'll detect that there has been a
collision as they don't get an ACK, increase the limit of their
CW_{backoff} and back off more.



If the AP has an RSL for one client that is 6 dB or more
above *all* other signals in the desired bandwidth, that client
will be accepted, otherwise the AP will not be able to detect
a usable signal from any of them.


True. Just not as common a problem as you make it out to be.
Just like dropping your camera during a studio assignment and it
breaking *is* a real problem ...


In fact, even with a CW_{Backup} of only 32 (i.e. set for rather
few collisions, it can ramp up to 255) the chance of collision is
50% with 16 active stations and 63% with 35 active stations.[1]


No answer?

So none of them get a connect, they all
time out and take a random sleep.


Only one will talk, and in most cases it will get through.
And if not on the first try, then on the second, third of fourth.


Wrong. Whatever makes you think "only one will talk"!
Every time there is a collision, the entire process
essentially starts over again.


A collision only happens when both sides start talking at the
same time. If one already started, in your PJ case all other
WiFi-nodes pick up the fact that someone is talking and
remain silent.[2] GOT THAT?

The chance for 2 or more nodes to send at the same time means
that their microsecond timers must pick identical values.

The chance of 2 nodes having the same timer set is
p_{collision} = 1 / CW_{backoff}

The chance that the second node does NOT have the timer
set to the same value is
p_{no collison} = (CW_{backoff} - 1) / CW_{backoff}

So for CW_{backoff} == 7 the chance for 2 nodes would be
6/7 for no collisons.

For 3 nodes it would be:
p_{no collison} = (CW_{backoff} - 1) / CW_{backoff} *
(CW_{backoff} - 1) / CW_{backoff}
= ( (CW_{backoff} - 1) / CW_{backoff} )^2

For n nodes it is:
p_{no collison} = ( (CW_{backoff} - 1) / CW_{backoff})^(n-1)

and
p_{collision} = 1 - p_{no collision}
= 1 -( (CW_{backoff} - 1) / CW_{backoff})^(n-1)

Given n = (48 PJ + 1 AP) = 49 (i.e. all 48 on one single
channel, all wanting to talk NOW):

CW_{backoff} p_{collision}
in %
7 99.94% (typical lowest value)
32 78.2%
64 53%
128 31%
255 17% (max value)


Now, given that only a completely incompetent person would
offer only one channel:

n = (48 / 3 PJ + 1 AP) = 17

CW_{backoff} p_{collision}
in %
7 92.73% (typical lowest value)
32 42%
64 23%
128 12.4%
255 6.44% (max value)

That's simple probability calculus.

The chances never get any
better.


Wrong, CW_{backoff} is raised through collisions.

Go try yourself: roll one black and 4 red 6-sided dice and
see how often the black and any red dice have the same number.
Now repeat that with the same number of 20-sided dice instead!

And for kicks, try with 1 + 16 32-sided dice (your PJ-example,
3 channels, CW_{backoff} = 32) and with 1 + 16 *255*-sided dice
(same, but CW_{backoff} = 255).

You are assuming that all clients can detect all other clients,
which is probably not true.


In your PJ at a press conference case, it very probably IS true
.... and then there *is* RTS/CTS for hidden nodes.

Of course by that
time another group is ready (after waiting for a random
period), and the story repeats itself.


Yep, all the group of 10+ clients has each RANDOMLY choosen one
and the same period of time --- and will do so every time!


That's why it's called RANDOM!


And that is exactly why if fails too.


It doesn't fail.
Sure, you _could_ build a token ring wireless network.
However you can't use token ring for nodes that try to connect,
as they are not yet in the ring ... and if there are 2 nodes
waiting, they'd *always* cause a collision that way when sending
the token to "any new node". With random they only cause a
collision *sometimes*.

In addition, nodes dropping off the network (switched off,
getting out of range, ...) cause a token to be dropped.

Since you want high bandwith and care a bit less about latencey,
not (sorta)-guaranteed latency (for a given, unchanged node group)
and low bandwidth, token ring's not the right solution

Eventually luck
might allow one client to connect. That is going to work
to some degree up to 4 clients per channel, but with more
than that the chances of any client actually getting a
connection start to be very slim.


So how exactly do you arrive at 4 clients per channel?


No answer?

Pulling data from your ass?


Get you head out of yours.


Brownnosing oneself is a new one.


Especially when 4-5 clients give the best combined throughput
rate for TCP traffic for a 54 MBit connection?[1]


You did pull them out of your ass, didn't you?


Get you head out of it...


I'm not brownnosing you.

But I can't help but notice *I* have data and you pull
numbers from your ass.


In fact, 48 *active* clients on 3 channels have a combined
throughput of 45 MBit/s of data (with all the TCP overhead and
WLAN overheads and timeouts and retries and collisions already
taken care off), so each PJ has 960 kbit/s.[1]
A modem is 33.6 kbit/s.


Do your math ...


Learn how it works.


Done.
It works that way:

1. you claim something wrong
2. people provide real life observations, mathematical models,
studies and more that say you're wrong
3. you claim they *all* don't know a thing and can't read.
4. You get plonked. Again.


Instead there will virtually always be
contention, and instead of being 4 times faster than a
dialup, it would probably be about 10 times slower... at
best!


So 3 channels at 54 MBit/s can't keep up with 48 clients which
sporadically try to pass data through them to the outside.


Correct.


Hmmm. [1] says something very different.


You apparently didn't read what you are citing.


s/You app/Floyd app/
s/you are/Wolfgang is/
Now it's correct.


He
http://serverfault.com/questions/192...le-wifi-router
is someone connecting 60 iPads over 3 channels.


We can find somebody somewhere who said almost anything on
the Internet, but that doesn't make it correct.


True --- after all, I found *you* saying wrong stuff.



Regardless, just like the other URL, you don't seem to have
actually read the article you cite!


Please point out exactly where in the article it is said that
more than 4 clients are a really huge problem for WiFi.


Whom to believe? Those who have facts and others that have mathematical
models congruent with yet other people's tests and experiences,
or ... you ...?
Tough question, innit?
But then maybe you do get 48-PJ-news conferences pretty regular
up in Barrow ... who knows?


Yep, no answer. Floyd does not have *any* credentials.

I see.


Probably not, because you don't seem to know how it works or why
and have no interest in learning eitehr.


I'll await your "OK, I *was* completely wrong on all of my
claims, including the WiFi and the learning!" admission.


See, you haven't learned anything!


I've learned you're an idiot, Floyd. You're wrong and too stupid
to even see that you're wrong.
Yes, my first calculations were wrong (way too naive and hence
overestimating the effective netto bandwidth badly) but I learned.
Fast.

And now I'm quickly learning you are incapable of learning
*and* wrong, hence not worth talking to. One more post will
probably do it and you'll be back to the killfile.

[1] http://paper.ijcsns.org/07_book/201207/20120704.pdf


You *really* should read that paper and try to understand
the significance of what it says!


I did. Closely. It says that you're completely wrong in how
common collisions are. The significance is that your claim
| That is going to work to some degree up to 4 clients per
| channel, but with more than that the chances of any client
| actually getting a connection start to be very slim.
is wrong. Trying to get a connection is the essentially the
same as trying to sending data ...

-Wolfgang

[2] We're not having hidden nodes here. If we had, we could
use RTS/CTS.
  #84  
Old September 27th 12, 09:31 PM posted to rec.photo.digital.slr-systems
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external usenet poster
 
Posts: 24,165
Default Canon 6D

In article , Floyd L. Davidson
wrote:

you didn't know what automatic meant and you think all base stations
have vertically polarized antennas.

I certainly don't know what *anything* means to *you*!


it's what the industry defines it as, not me. *they* are the ones
calling it automatic.

stop trying to weasel out of it.


I merely asked exactly what you meant, since *you*
didn't have the sense to explain yourself. That is
hardly trying to weasel out of anything.

In fact we were talking about a client automatically
changing channels to match the AP, and when you said
the AP could be automatic is certainly made me think
you were saying the AP adjusts to the client. That
doesn't make sense, so I simply asked what you meant
by "automatic".


i'm not the one who first mentioned automatic. you got even that wrong.

more importantly, many routers support automatic channel selection.
it's not a new concept. how can you *not* know about it?? when's the
last time you bought a router?

Pretty reasonable... but you aren't.


you claim to be the expert in everything so i assumed you knew what
automatic was, especially since routers from many manufacturers these
days (maybe even most) have it. again, it's not new.

the natural conclusion was you were trying to play word games to avoid
admitting you're wrong.

And yes, virtually all base stations ahve vertically
polarized antennas.


previously, you said all, now it's virtually all? hilarious.


Same thing. You probably don't know what the
significance is anyway.


i know full well what the significance is. knock off the insults and
stay on topic.

Of course many if not most
units have always had antennas that can be adjusted.


which means they can have any polarization anyone wants. if you think
every user keeps them vertical, you're delusional. a lot of times i see
one vertical and one horizontal.

They *all* recommend using vertical polarization,


no they definitely don't do that. you're wrong again.

not only do they not recommend anything, but they don't even *mention*
polarization anywhere in the user manuals!

but
there are good reasons to use horizontal in some special
circumstances (mostly to restrict the range).


that's a change from what you said the other day.

so now there's a reason for horizontal? you're weaseling, again.

by the way, horizontal polarization can *increase* range for some
clients, such as smartphones, whose orientation is unknown and can
change at any time.

not that it matters. it's nowhere close to 'virtually all.' travel
routers, for example, are polarized in whatever orientation they happen
to be when used, particularly the battery operated ones, such as a
cellular mifi device.


And any instructions that mention antenna orientation
will say to position the unit in a way the results in
vertical orientation.


wrong.

you're out of touch with the real world and talking out your ass, again.

there are no such instructions in any of the travel routers i have, 3
different ones, from 3 different manufacturers (apple, linksys & zoom).
i checked two more user manuals for ones i don't have (verizon mifi &
netcomm) and both of those didn't mention antenna orientation either.
that's 5 out of 5 that don't say a single thing about it!

furthermore, two of them (linksys & apple) have a built-in ac power
plug so the orientation is dependent on the wall outlet. if the wall
outlet is horizontal, so is the travel router. although many wall
outlets are vertical, not all of them are, especially in hotels where
such a router is likely to be used.

the third travel router i have uses batteries and it can be in any
orientation. it's thin and flat (roughly the size and shape of a deck
of playing cards) and it's highly likely the polarization is *not*
vertical when sitting on a table.

Again, that is because vertical *is* the standard (for
very good reasons), and will generally produce the best
results. In the case of a direct line of sight with no
multi-path there is about 30 dB loss from cross
polarization.


except that you cannot know the orientation of the client devices.

vertical might have been preferred at one time but it's certainly not
now.

in the real world (not your world), smartphones, tablets and even
laptops are used in many orientations, not just vertical. they can be
horizontal, vertical and everything in between. many times the device
is rotated during use.

that's why some wifi base stations have *both* vertical and horizontal
polarizations, or in some cases, at 45 degree offsets. other base
stations may be one or the other, sometimes vertical and sometimes not.

in the real world, polarization makes almost no difference to the user
(as opposed to lab instruments). this is easily shown by rotating a
smartphone or tablet and things keep working just as before.

can a lab instrument measure a difference? probably, but if the user
can continue to do whatever it was they were doing even though they
rotated the device, then it does not matter what some lab instrument
measures. to the user (which is what matters), it continues to work.
again, real world situations.

I haven't seen the insides of some of the smaller WIFI
units for cameras and similar devices, but I would guess
that at least some of them use circular polarization,
just to avoid excessive loss from cross polarization.


this is about routers, not cameras or other devices. travel routers are
generally used relatively close to the client, so there's no need for
anything fancy.

Sigh. I drew a graphic and made a chart previously that showed
*precisely*
what the channel separation is.

The simple fact is that yes it will increase interference if you choose
anything else.

it will not increase anything.

Just interference.


nope.


Ignorance is bliss, and you seem blissful enough.


then you must be incredibly happy.

by the way, there are more sources of interference than just other wifi
routers.
  #85  
Old September 27th 12, 09:31 PM posted to rec.photo.digital.slr-systems
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Posts: 24,165
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In article , Floyd L. Davidson
wrote:

you can't control what neighbors do. sometimes picking something
other than 1, 6 or 11 is the only option.

It really is. Since everyone seems to allow their wifi station to pick
the channel (based possibly on the traffic at that time and then no
longer changing) I'm better off alone at 8 or 9. I get splashed to be
sure, but not near as bad as if I stay on 1, 6 or 11.

You get interference, if you choose Channel 8, from anyone that chooses
any channel from 4 to 12.

depends how far away they are.

No, it depends on the signal strength relative to the
desired signal.


which depends how far away they are.


Any given station can be farther away but also have
a much stronger signal level.


possible, but most routers have similar power and very few people have
directional antennas, so distance is a good metric.

If the signal strength for all other users total is
equal to greater than 6 dB less than the RSL of the
desired signal, you will have interference.

That is, if there is one signal on Channel 8 and it is
-6 dB or greater compared to your signal, you get
interference. If there are two signals they can both be
-9 dB below the desired signal, and you will get
interference. If there are four signals the threshold
is -12 dB, and so on.

If you choose Channel 11 the only other choices
that will affect you are those from 7 on up. All you have done by
choosing
Channel 8 is perhaps double the amount of interference.

based on that, then 1 and 11 can be the only choices.

Channels 1, 6 and 11 will not interfere with each other.


nobody said they would.

however, what *you* said is by picking 8, you get twice as much
interference than 11, so based on that, picking 6 is even worse.


It is true that picking 8 will get twice as much
interference, and that is not true of 11.


then 6 is the worst.

choosing 6 means 2-10 can cause interference, which is almost the
entire band.

That is exactly the reason to assign 1, 6, and 11.


in an ideal world, yes.


No, in very practical world. That is the only way to
get three clear channels operating at one time. If you
choose Channel 8, it there can't be more than two
channels operating without interference.


however, you can't guarantee that everyone will adhere to that. nobody
can.

unfortunately, in the real world it doesn't work that way.


Clearly it does.


no, it definitely does not. you need to get out more.

if they're too weak to be of significance, then it doesn't really
matter what channel you or anyone else picks, does it?

Not until someone close enough to actually have a
greater signals strength cranks up their AP, and then
you are toast if you picked the wrong channel!


no need to crank up anything.


Yes, if it is turned off then it won't interfere with
you. But most people install these devices to actually
use them.


who said anything about turning them off???

in an apartment setting, a neighbor's base station could be as close as
just a few feet away if it's near a shared wall, or a little more in
the apartment directly overhead or below. what channels they pick
*will* be an issue.


Exactly. So choosing the most efficient channel
assignment pattern is significant.


yes it is, but the point is you can't enforce that, and there are other
sources of interference than wifi base stations.

sometimes people pick other channels. it's just how it is.

in detached homes, the distances will obviously be greater so using the
same channels will likely not be an issue, although in some cities
houses are very close together so it could turn out to be a problem
anyway.


That is not necessarily true. These "shared wall"
situations, and equally likely with overhead/below
circumstances, often mean very lossy transmission paths.


sometimes. it depends what's in the wall.

when i stay in a hotel, i can see networks from other guests in other
rooms. hotel wifi tends to suck, so they bring their own.

It isn't generally just a matter of "distance". And
often the distance traveled by the signal is not
actually a direct line of sight anyway. Almost any wall
causes significant loss at 2400MHz, and almost any
metalic surface larger than an inch or so will reflect
the signals too. Hence you may think, for example, that
the signal you are picking up from the appartment above
you is traveling 10 to 15 feet through the ceiling when
in fact the path is in/out the (lossless) windows and
bouncing off the foil backing on the insulation in the
wall (or a metal sign attached to it) of the building
across the street!


that's a bit of a stretch.

WIFI does strange things.


not as strange as the arguments you make.

You can weasel all you like, but technically there is
only one right way: choose one of channel 1, 6 or 11.


no weaseling at all.


Won't be when you stop...

in an ideal world, sure, use 1, 6 and 11.


In a practical world, that is the right choice.


but in the real world, people choose other channels.

you see, in the real world, people pick channels *other* than those
three.


And my point is that it does *not* improve their service.


that's *their* problem.

the issue is what a given user needs to do to get the best service.

it might be 1, 6 or 11, or it might not.

i just did a survey and right *now* i see networks on 1, 2, 3, 6, 9 and
11.

based on their strengths, picking 1, 6 or 11 is *not* the best choice
for me.

that's the real world.


Let me say it again: use one of 1, 6 or 11 for best results.


let me say it again, 1, 6 or 11 does *not* always give the best
results. been there, done that.

Use something else if results aren't what you want, but
emotional yada yada is a good substitute.


whatever that is supposed to mean.
 




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