Question

Urgent - Wireless UDP : Few clients see the message and few don't

Asked by: VShah

250 to 300 wireless clients.
One xp machine running an application. That application broadcasts a message every 6 seconds. There is timer on client to time out if they don't see any message in 30 seconds. Out of 250 to 300 clients, about 50 clients time out. This doesn't happen always. Just happens about once to thrice a day. After timing out they go back automatically in syn as they start seeing the messages again! There are 10 rows and about 25 clients in a row. Clients in few rows get this time out. Generally those rows are side by side. Other rows see the message fine. Any input would be appreciated. Thanks.

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Asked On
2006-03-25 at 18:55:58ID21788953
Topic

Miscellaneous Networking

Participating Experts
2
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Comments
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Answers

 

by: 0xSaPx0Posted on 2006-03-25 at 23:02:08ID: 16292427

Only thing I can think of is that slower machines may not be able to encrypt the packets within the window if they are processing other tasks.

- SaP -

 

by: VShahPosted on 2006-03-26 at 13:50:15ID: 16295907

All the clients are exactly same in terms of both hardware and software. They are not doing anything, just listening to messages. The only thing they do is every 10 minutes they send a message back to the server so the server knows that the client is alive as these are udp messages. I am wondering as this is wireless network, when clients are suppossed to listen they are trying to send the data and miss receiving messages or some collisions are happening on wireless network. While clients are sending the message, their network hardware is busy sending and can't listen at the same time and that is how they miss receving messages for 30 seconds and time out.

 

by: 0xSaPx0Posted on 2006-03-26 at 16:39:20ID: 16296773

The only way you will know is if you fire up a packet analyzer like Ethereal and watch to see if the packets are being sent and if they are being received. The network hardware that is hosting the wireless connectivity should tell you if there are collisions, errors, etc.

I doubt its collisions as 802.11 uses a new version of CSMA/CD which actually avoids collisions instead of just detecting them.

- SaP -

 

by: VShahPosted on 2006-03-30 at 12:58:46ID: 16336782

Found the problem. around 250 clients go to sleep. They wake up and try to associate them with AP (Access Point). It floods AP with incoming association messages and AP can't keep up with sending out 6 sec messages and it queues them for a minute or two and then burst outgoing messages all together. But by that time it is too late for clients and they receive timeout after 30secs. Why is it taking so long to have 250 client register to AP. Can there be any setting on AP to keep the clients addresses and not remove them eventhough clients go to sleep? Thanks.

 

by: GranModPosted on 2006-04-17 at 07:54:38ID: 16469491

Closed, 250 points refunded.
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