every single packet transmitted is going to be retransmitted on all the
WDS/AP connected together on the wireless side.
Is that really true, in this type of configuration, Mikrotik 4 stationsWDS,
1 AP WDS?
I'm not sure that these units re-transmit the data.
Remember their is no data that needs to pass between the 4 remote client
buildings.
Also remember that none of the subscribers are using wireless, they are all
using wired connection, only the 4 MTU building roofs have a station WDS
radio.
Tom DeReggi
RapidDSL & Wireless, Inc
IntAirNet- Fixed Wireless Broadband
----- Original Message -----
From: "Anthony Will" <[EMAIL PROTECTED]>
To: "WISPA General List" <[email protected]>
Sent: Saturday, October 07, 2006 12:07 PM
Subject: Re: [WISPA] WDS PtMP
On thing I forgot to mention is that every single packet transmitted is
going to be retransmitted on all the WDS/AP connected together on the
wireless side. With sustained traffic that would mean that all of them
are transmitting and receiving the 2 megs mentioned. And we can assume
that these units are not exactly all the same distance or under the same
exact load so there will be very tiny differences when each unit will be
retransmitting that 2 meg of traffic.
I am not real happy with the way I explained this let me know if it makes
any sense :)
Anthony Will
Broadband Corp.
Anthony Will wrote:
It would seem to me that as your load increased your WDS/APs are
transmitting over each other as clients are trying to transmit to the
central AP. client -->WDS/AP transmitting carrier beacons or other data
to client and passing onto to -->WDS/AP<--WDS/AP<--Client (transmitting
to local AP)
In this scenario you have the two clients talking and one AP all trying
to talk at the same time and thus raising your noise floor because they
are all on the same channel.
There is not a feature in standard WDS to coordinate who can talk and who
can not talk other then the standard CDMA layer of the 802.11 protocol.
This will create issues as the more load you have on this setup the more
self interference and retransmissions you will incur. The big thing the
mesh brings to the table is the ability to help coordinate all of this
traffic so that you can utilize the spectrum more efficiently. At least
that is my opinion as soon as someone actually does it. You likely are
going to have to switch to a station /AP solution for this setup because
everything is to close and can hear each other. This will destroy your
bridge setup unless you change to a propitiatory system such as Trango,
Canopy, etc. One other thing to note is that this is all half duplex so
you might have two many hops and thus running out of bandwidth.
Anthony Will
Broadband Corp.
Tom DeReggi wrote:
Background....
In standard WIFI, a principle exists called hidden note, where two CPEs
transmit at the same time and colide because they do not hear each
other. There are three ways to get around that, using WIFI between
Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis,
so radios can hear each other if in close proximity, 3) RTS/CTS which
effectively solves the problem at a significant performance degregation.
A well know problem with well known solutions.
Issue.....
How does this play our with WDS? AP to AP communication. Sure in PtP its
a non-issue, because there are only two radios involved to complete the
link. But WDS allows PtMP operation.
How does WDS commuication work? Does the Hidden Node problem exist with
PtMP WDS? And if so, is there a way to address it? If so, will it help
to make the CPE's Omnis, so they hear each other?
My confusion is how WDS/WDS works compared to Station/AP modes.
Example application:
Using 802.11a gear.
5 seperate MTU buildings, spread out within 300 yards of each other.
1 is a Master AP Site, with an Omni, and a second backhaul radio to the
Internet.
4 of the 5 have a direction CPE style antenna pointing to the Master
Antenna.
WDS is used to allow the radios to operate as true transparent bridges,
and to pass per client (5-10 clients per MTU) large packet VLAN traffic.
(Note: There is a reason we did not select Nstreme w/ Polling. It may
have been an incompatibilty with WDS or inabilty to do transparent
bridging with large packets, which standard 802.11 station mode does not
support under protocol. May have been early version of Firmware, not
sure if still an issue)
Why I thought it might be an issue:
Surveys show low noise. However, as more clients have been taken on (2
mbps average sustained throughput all combined), the Link quality
started to degregate as if the noise floor was rising.
As a tempoirary measure, we switched to 5.2Ghz (indoor only FREQ, which
appeared not to have any detectable noise in standard 802.11 based
survey tools, and was chosen because non-detectable carrier grade gear
would not use those channels). Its hard to believe that the noise floor
would be that high using that freq. So I'm wondering if the noise that
I'm hearing is actually my own CPEs within this project?
The symptom was sparatic higher latency, what typically would happen if
802.11a had frequent retransmissions (native prorocol ARQ). I can look
at stats to see if there are re-transmissions, but that data is
pointless, as what I want to know is, is the retransmisison because my
own noise or someone elses. Its hard to tell with WiFi, as WiFi doesn't
transmit when its not in use. So testing in the middle of the night,
when clients and users in town are off, may not be meaningful. Its also
possible, that I just have a failing radio card or two, and a totally
different cause.
Tom DeReggi
RapidDSL & Wireless, Inc
IntAirNet- Fixed Wireless Broadband
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