Thought as much but was hoping it might have been an issue further up the
stack. Anyone know if the number of retransmits can be adjusted or if there
are any other tweaks to make the impact minimal?

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of David Sovereen
Sent: 03 June 2006 14:46
To: WISPA General List
Subject: Re: [WISPA] Mikrotik Virtual AP

Hi Paul,

It's an RF problem.  802.11a/b/g and Nstreme all have packet acknowledgement
in the protocol.  Every packet your AP sends needs to be acknowledged by the
client.  When a packet is not acknowledged, the AP retransmits it.  Because
of poor RF conditions (NLOS), RF/wireless ethernet packets are being lost.
When this happens, the AP retransmits the unacknowledged packets
automatically.

When you see packet loss at the IP layer (i.e. ping timeout), your packet
has been lost and retransmitted at the RF/wireless ethernet layer by the AP
many times over again.  Retransmissions take up significant air time because
your AP is waiting until the Ack timeout, typically up to 400usec, for the
Acknowledgement to come back and isn't transmitting anything else during
that time.  It retransmits the packet over and over.  One packet like this
isn't in itself a problem.  But when it happens on a data stream of 20
packets/sec, it is!  Because your AP is trying and waiting and trying and
waiting to get these packets through, other customers are being impacted.

Moving this customer to a Virtual AP will have zero affect.  The same packet
acknowledgement/transmission problem will occur, and all customers,
regardless of SSID will be affected.

Your best move is to drop this customer, or if you really want to keep the
customer and not impact your other customers, move him to another
radio/antenna.  RF packet loss is costly in terms of overall AP capacity.
Keeping customers who have significant RF packet loss can cut total AP
capacity in half or worse, depending on severity.

Regards,

Dave

989-837-3790 x 151
989-837-3780 fax

[EMAIL PROTECTED]
www.mercury.net

129 Ashman St, Midland, MI  48640
----- Original Message ----- 
From: "Paul Hendry" <[EMAIL PROTECTED]>
To: "'WISPA General List'" <wireless@wispa.org>
Sent: Saturday, June 03, 2006 9:21 AM
Subject: [WISPA] Mikrotik Virtual AP


Ola,



            I currently have a scenario where a dozen clients are connected
to a 5.8GHz AP where one is a NLOS link. The link quality is fine for this
client during normal conditions but when it rains it becomes a little
unstable which the customer is fine with as they have no alternative. The
problem that I have is when the weather is poor it can cause a lot of jitter
to the other clients on the same AP especially when the NLOS link is trying
to be used. I’m wondering if this is an RF or IP issue. If it’s an issue at
the IP layer then I wonder if setting up a Mikrotik box as the AP with a
virtual AP for the NLOS link and a virtual AP for the rest would get round
this problem.



            Any thoughts or experiences??



Cheers,



P



Skyline Networks & Consultancy Ltd

Web: HYPERLINK
"http://www.skyline-networks.com"http://www.skyline-networks.com





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