Why do we get random Loss of Wireless network when encrypted?

Posted on 2006-06-15
Medium Priority
Last Modified: 2010-03-18
I have 17 D-Link 7100APs all with the same SSID, when encrypted users randomly get disconnected from the network. If I remove encryption is works fine. We use Open System 128bit WEP ASCII.
Question by:aicit
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Expert Comment

ID: 16912232
probably too much noise in the environment (cordless phones, cellular phones, anything that can cause interference in the 2.4 - 5 GHz range) to cause the encrypted message to become corrupt enough so that it can be unencrypted and constant resend are done to the point where you lose the encrypted connection.  Another thing in the same arena is that all 17 users are interfering with each other to the point where the same thing is happening.

This is probably happening with the regular traffic, but because there is one less step in the process, the data drops are tolerable.  

If you want, you can experiment by shutting down 1/2 the users at some convenient time and see what the drops are like.  

As a solution you may want to get another access point, space them far apart in your org and set them up on different channels, with 1/2 the users defaulting to the configs of one access point and the other 1/2 to the other access points.


Author Comment

ID: 16913813
We have all the Units on Channel 1 and 11, spaced apart, with the odd unit in the middle on 6. If it was a channel mix why do they work fine when encryption is switched off?

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Expert Comment

ID: 16916740
2 access points  - one defaults to one channel; the other defaults to another.  1/2 the PCs set to 1 channel for one access point and the other 1/2 set to another channel for another access point.  The above sounds like you have the 17 PC divided into 3 unique groups split via channels but only one access point; which means you are probably still overwhelming the single access point.    

Just realize that every feature adds overhead so the effective bandwidth is reduced.  Your AP acts like a wireless hub so its dividing the effective bandwidth between 17 devices.  In this type of environment you will get collision or interference from every transmitting device; get enough collisions and it will seem like a source is not transmitting a valid packet; do it for a long enough time; a session can get disconnected.  Encryption adds to the amount of bandwidth needed to transmit information and add to that the time needed to encrypt and decrypt.  

If one person does video streaming; it will kill your bandwidth....

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Author Comment

ID: 16917959

Thanks for that answer. Would you suggest that all 17 devices are on the same channel?  We were advised to use channels 1 and 11 to avoid the signal ovelap congestion issue. This is a fairly large site with devices evenly distributed apart from two mobile units, what would you say is the best configuartion setup to have a reasonable level distribution of the wireless signal?
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Expert Comment

ID: 16919855
>Would you suggest that all 17 devices are on the same channel?
Not in this situation; as of yet; I haven't read anything referencing D-Link or any other SOHO genre wireless access devices working on WAPs that can work in tandem and actually is "intelligent" enough to hand off traffic from a weak to strong signal-ed WAP.  If you are looking into this; you may be looking at Cisco's Aironet $erie$.

>We were advised to use channels 1 and 11 to avoid the signal ovelap congestion issue.
Okay, this sounds sensible, and I can go along with this

>This is a fairly large site with devices evenly distributed apart from two mobile units,
Large site with two access points mounted on the furtherest opposite ends of the room using different channels should minimize the possible interference between the two access points.

>what would you say is the best configuartion setup to have a reasonable level distribution of the wireless signal?
This in the scheme of things is reasonable for the quality and capacity of the D-link equipment you have.  Remember that many of the SOHO brands including the bulk of the D-LINK product line were made to handle small office traffic / home office traffic.  Once yo approach the upper limits of there capacity (like anything else), you will experience the results of your equipment being overwhelmed; such as the case here.  So right now you are exploring the upper limits of the D-Link technology spectrum (or not to single out D-LINK, the SOHO WAP trechnology spectrum).

At this point; having reached a possible edge of this spectrum; comes the hard decision of what to do to solve this technology issue.
1. stay unencrypted; as in this mode; presumably with all the possible signal collisions, the resends/retries, constant polling of equipment and the actual data sends, it is staying in a margin that your LAN based apps finds acceptible to operate under.
2. reduce on the number of wireless devices so that encryption can be used; less equipment, less collisions.  More bandwidth available to be ultilized by the encrypted data.
3. Start moving equipment off wirless to wired; wired switches provide the maiximum bandwidth port to port without it being shared or divided up; there is no need for encryption here in one aspect.  You will notice considerably higher thru-put rates.
4. buy a better (and more costly) product; access points and wireless cards.  Cisco can accomodate this.
5. choose a 64-bit encryption technology; that may help reduce bandwidth needs.

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