Lion WiFi Connection Problem

SvdH wrote:

In my opinion Apple is responsible, since software and hardware are from the same vendor.

Hello SvdH,

maybe Apple have to fix something either on the Extreme, the modern "all band all frequencies every client coffee cocking" thing called Extreme N or the way the client decides which wireless it will use. But, I'm afraid thats not on Apple alone as the actual WiFi technology trend have glitches too.

But maybe we find a working or workaround solution for you too by comparing and sorting out.

SvdH wrote:

The WiFI signal-strength says 100%, but packets frequently get lost / delayed. This happens on my home-network (Airport Extreme)

Had a similar issue on my home network when a Extreme became the main router to replace an older wireless "g" unit.

I will give a report now of what happened, so you may compare and see what seems similar and what may different to your situation. I hope that's eventually eases the troubleshoot and solution finding for you.

At the wireless are at now: 2008 MBook (10.6.8); 2011 MBpro (10.6.8); 4 x Express (7.5.2). Base is a Extreme 5th Gen (7.5.2).

I had drop outs with the old "g" router before, but only sometimes once a day and decided to ignore that.

The real trouble starts, when I noticed that from 10 minutes to twice an hour Audio or Video streaming drop out, while signal strength says always 100% and e.g. Internet was still reachable.

What I did first was quite similar to your attempts to solve the problem. Resetting this and that, removing network, clear plist's and so on.

Nothing really solved the issue for me.

I decided to work it out.

First tryed the simplest by ping the clients and the base. Outcome was, that ping worked, but not every time and not ever to the same clients.

On that time, trying to monitor the logfiles of the base and (what I thought was) the affected client I noticed, that every time the connection drop's either the base, one or more of the clients (Expresses) or ALL units, vanished from Airport utility.

The only way to bring them (and the stream) back was to switch off (regardless on which client) the wireless, wait for a few seconds and switch on again.

At this point i fired up WireShark to monitor the network traffic.

Finding was, that there where (in my case) DUP ACK events every time the connection dropped. No single client could be identified as source as it happened randomly from and to any client or the base.

I set up a new location in System Settings -> Network -> WiFi with only my network on list, trying to isolate the MBPro from neighborhood networks to prevent interferences and so on.

Nothing went really better. OK, the drop out's and bad packets changed from twice an hour to every 90 min. But that was not the expected result.

I decided to use a WiFi hacking tool to monitor the radio conditions in my surrounding at the time the drop out's occur.

It shows me, that the GUEST NETWORK periodically changed the band and channel from 2,4 GHz #6 to 5 GHz #100. And every time a drop out occur and the clients vanished from Airport Utility there was a correlation with that Guest Network behavior and the DUP ACK packets.

A look on the Extreme setup shows then, that the 2.4GHz and the 5GHz "n" as well as the 2.4 GHz "g" (compatibility mode) share the same SSID, the SSID of the Guest Network was different though.

So I decided to switch off the Guest Network and set a different SSID for the 5GHz.

After that, the situation went a lot better but not perfect. Bad packets and drop out goes from 90 min to 2 1/2 h rhythm.

On this stage I realized, that the MacBook as well as the MBPro sometimes switches automatically between 2.4 n and 5 Ghz n and then the drop occurs too.

So I thought, OK, let's delete the 2.4 n SSID from the network list in the System Settings.

From than on things start driving me quite mad.

Even if I delete the 2.4 GHz SSID from the "known network" list on the newly setup location, oddly it reappears on the list after a while.

Indeed there was now a different SSID for each band, but both share the same password on the Extreme by default.

I think this happened cause in the System Settings (by default) was checked "Ask to join new networks" and "Remember Networks this computer has joined" and there may be a glitch in the Keychain too, as I had to remove the Keychain entry for the 2.4 GHz n/g SSID manually before the "reappearing" stop definitively.

At the very end of the way, the working solution for me, as my situation allows such settings, was:

• Set a different network name (SSID) for the 5 GHz band
• Set up a new location with unchecked "Remember Networks this computer has joined" and only one SSID (network) in.
• Set the Extreme Radio Mode to "802.n only (5GHz) - 802.n only (2.4 GHz)"

From that point on i had:

• no more bad packets
• no more vanishing items from Airport Utility
• no more Video or Audio drop out
• no more network cut off

What I think about it:

• Problem may be that the password for the 2.4 GHz n/g and 5GHz n is the same even if the SSID is different to provide a n/g compatibility mode for supporting older clients and grant them access to n-clients in the same net.
• It may there in fact a bug within the "Ask to join new networks" and "Remember Networks this computer has joined" wireless settings and the Keychain, for that the network reappears automatically in the list if the password is known or there is a open network (no password) from the same base station.
• The compatibilty mode (n/g) may causes trouble
• "Extreme N" capable Apple systems have problems with multiband g/n wireless, regardless if Lion or SL is installed, as with the good old 2008 MB alone as client in the network, the symptoms where the same once the brand new "Extreme N 2.4 and 5 with G compatibility" became the active network.

For all that I still think that Lion is not really the reason, as same things happens to non Lion systems too. Just check Windows community's for "wireless problem" threads.

A point that I dit not really understand right now, is that the "Automatic" location with the "Remember networks this computer has joined" setting active works well when in a Company, a Hotel or at one of the public hotspots I sometimes use.

Maybe because there are no "Multiprotocol + Multiband + MIMO + Compatibilitymode" Units in use. *shrug*

Hope that this may help a bit to you or others to find a solution or workaround.

Lupunus

I'm only responsible for what I say and NOT for what you understand.

I am running Lion on a mid-2010 iMac and since installing it, I have had continuous wifi drops. I was able to reconnect by switching wifi off and back on again. After searching around various forums for solutions, I believe I have managed to repair my wifi connection. Btw, 10.7.1 did nothing for me.

• In Settings/Network delete all services apart from wifi
• Hit Advanced and in the Wi-Fi tab make sure your network is the only one listed. Make sure 'remember networks you have joined' is checked
• Under TCP/IP, configure iPv4 Using DHCP and IPv6 Link Local-only
• Under DNS add server 8.8.8.8
• Finally, I think this one fixed it for me, since all of the above have been suggested before, visit your router interface through your browser (I have a Belkin N) and:
1. Make sure your Mac does not have a reserved DHCP MAC address, if it does remove it from the list. Once I did that, a dialog popped up from Networks saying that another computer is using my wireless connection, or something along those lines, but instantly another address was assigned automatically for iPv4.
2. Set the router to transmit on 802.11 b,g and n, in my case I had it transmitting only on g and n.

These steps fixed the problem for me, I hope they are of assistance to you too...

This starts to become really annoying...

• after updating to lion my internet-connection dropped permanently
• then I tried all the different solutions described here and elsewhere without any durable success
• then I did a clean installation of lion and didn`t have any problems any more for about two month
• AND NOW the problems have come back again although I didn`t install any new software and nothing changed about my router!!!

Having a look at the X-log in my case it`s exactly what you described:

Sep 24 07:44:00 Olafs-iMac kernel[0]: AirPort: RSN handshake complete on en1

Sep 24 08:12:41 Olafs-iMac kernel[0]: en1: BSSID changed to bc:05:43:52:2f:b6 >>> here the connection went away

The problem is: I have a unique SSID...

Anyone has an idea?

hormelmeatcompany wrote:

The problem isn't that it's unique. The problem is that lion thinks it's changed when it hasn't.

Yes Sir!

But, not Lion think!

Lion (the OS) itself have, roughly said, not much to do with the wireless or networking processes except to provide settings (configuration files) and handle the user to system interaction and the inner system communication.

Refer to:

• http://en.wikipedia.org/wiki/OSI_model
• http://en.wikipedia.org/wiki/TCP/IP_model
• http://en.wikipedia.org/wiki/IEEE_802.11#Frames

The information there may give you an idea how networking and wireless works.

Lupunus

hormelmeatcompany wrote:

I'm not using my phone and the Lion MBP at the same.

It's only when the Droid uses wireless.

hormelmeatcompany wrote:

The BSSID problem happens whether I connect to the encrypted one or the unencrypted one.

I'ts not a question of encrypted or unencrypted.

hormelmeatcompany wrote:

It's the OS, plain and simple.

You are pleased to think whatever you want to think.

So go on it in a solution focused way: "Love it, change it or leave it."

• Love it and stay with the evil Lion, accept the problems and wait for the miracle update.
• Change it by learning as much as possible about how wireless works and fix the problem.
• Leave it and roll back to Snow Leopard.

Lupunus

Meine Netzwerk-Einstellungen:

• Umgebung: „Automatisch“ und keine weiteren Umgebungen hinterlegt
• Wi-Fi ist verbunden, Ethernet, FireWire und Bluetooth-PAN jedoch nicht
• unter „weitere Optionen“ / „Bevorzugte Netzwerke“ ist nur der Name meines Netzwerks hinterlegt > der Mac war bisher mit keinen anderen Netzen verbunden also keine weiteren „bekannten Netzwerke“
• "Auf neue Netzwerke hinweisen" ist deaktiviert...
• unter „weitere Optionen“ sonst nur Default-Einstellungen > einzige Ausnahme: Unter DNS zwei IP-Adressen eines Cloud-DNS-Anbieters hinterlegt
• in der Schlüsselverwaltung ist nur das Kennwort meines Netzwerkes hinterlegt

Meine Router-Einstellungen:

• Gast-Zugang war und ist nicht aktiv
• normalerweise habe ich „Funkkanaleinstellungen automatisch setzen“ ausgewählt
• wenn ich auf 802.11n+g gehe ist die Verbindung noch deutlich häufiger weg als mit 802.11n+g+b - im Grunde genommen fast jedes mal wenn ich länger als 5 Minuten im Browser nichts gemacht habe...
• 802.11n+a funktioniert einwandfrei und ist deutlich schneller! > in den ca. jeweils 20 Minuten, die ich auf diesem Weg unterwegs war auch keine Verbindungsprobleme > ABER: Dann kann eben leider mein iPhone nicht ins WLAN und deshalb nicht wirklich eine Option...

Wie ich Deinen Tip, den Mac dazu zu zwingen, nur über 802.11n zu arbeiten, umsetzen soll, habe ich aber noch nicht ganz verstanden: Die SSID ist doch unabhängig vom WLAN-Standard dieselbe und die BSSIDs unterscheiden sich ja bei den unterschiedlichen Frequenzen nicht. Wo und wie sage ich der Kiste also genau „nur 802.11n“? Wenn ich unter "weitere Optionen" auf den Reiter "802.1X" gehe, kommt ein netter Hinweis, dass ich mich hinsichtlich weiterer Infos zu entsprechenden Konfigurationsprofilen mit meinem Systemadmin in Verbindung setzen soll... 😉

laechleviel wrote:

Ich habe eine eindeutige SSID und eindeutige BSSIDs, kein anderes Netzwerk in den bevorzugten Netzwerken, in der Schlüsselverwaltung nur den Key dieses Netzwerks , die gleichen Nachbar-Netzwerke wie vorher und auch in den Momenten mit den Verbindungsproblemen zeigt Airport vollen Empfang. Also: Wo liegt der Fehler?

Moinsen 🙂

Forget the patch idea. (see the last sentences of this post) I'm pretty sure there will be no patch for some thousand affected people in a cloud of several million Lion users without any WiFi problem.

Remember, all the people discussing that issue here are the ones with a problem. If one have no problem, he or she will never show up here telling us that there is no problem.

O.K., back to your issue.

Scanning thru your posts, I notice, until now you have nearly done what could be done either on the Mac and the Router. For that, settings will be ok at this stage.

What stays is the connection drop and under some settings it runs better or even worse than before.

On this points we should the put lever.

in den Momenten mit den Verbindungsproblemen zeigt Airport vollen Empfang

That indicates that the WiFi connection as such stay stable but some network events forces disassociation of the station. In other words, your WiFi is fine but there are events (bad packets) inside the network.

As your former report says: "on 5GHz 802.11n the connection was stable as long as I used it"

• Are there any other stations (clients) except the Mac and the iPhone in your wireless?
• Any cordless phones or phone bases near Router or Mac? (Standard cordless phones operates at 2.4GHz too and may cause heavy interferences)
• Cordless keyboards / mouse?
• Other cordless 2.4GHz radio equipment? (wireless doorbell, babyphone, tv-streaming units, cordless headphones, PS/2(3) cordless controller .....)
• Any Bluetooth devices active? (BT operates too at 2.4GHz and may cause heavy interferences, depending on used channel)

If the answer to ALL the questions above is: NO

The remaining conclusion is, that there is either a problem (as discussed here and elsewhere before) with the Mac and 2 BSSID's with only one SSID.

OR there are in fact radio interferences disturbing the data transport in the wireless and causing the Mac to disassociate (get disassociated by Router); e.g. neighbour networks on a near channel (less than 5 channels away), other 2.4GHz radio equipment

If the answer to at least one of the above questions is: YES

The last try will be to use a different channel for the wireless by (if possible) fixing it on the Router.

According to the standarts, in 2.4GHz (for Europe only) the used channels should only be 1,5,9 and 13 because they are the only overlapping free channels in the band. You should have at least a gap of 5 channels to neigbour wireless or other wireless 2.4GHz equipment on the same frequency range.

Generally: (not explicid in your case)

Unfortunately, it seems to crystal out, that in mixed (b/g/n) wireless -compatibility mode- environments, there will be in fact a problem in the way either the Lion WiFI Stack and the 2010/2011 models WiFi-Chipsets, handles the 2 BSSID/1SSID difficulty. (Chipset because SL -10.6.8- users are also affected on actual models)

As I know, Apple handles the configuration allways as close as possible to the standards and RFC's. For that you can, for example, set a own SSID for the 5GHz band that matches the connected BSSID in Apple's Airport Extreme base station.

But there is allways some ellbowroom in these standarts and RFC's.

For that I tend to slightly withdraw from my former statements saying that there will be no patch from Apple.

It still remains unlikely too, as Apple's attitude always is: We use to stay as close as possible to the standards and RFC's. If others don't, it's not our backyard.

Sonnigen Sonntag - Lupunus

aberges wrote:

I did that to draw attention because my messages posted since Sep 9 2011, on this thread didn't get any answer before yours few hours ago, for which I thank you, even if it does slove the issue.

Sorry but there is no posting from you between Sep. 9 and Sep. 11 in this thread.

To get answers and, eventually, a solution, there are only two simple steps:

1. Instead of posting a "me too" start your own question about your problem with a "talking" title. Only a "Help me" or a "Lion kills my wifi" will not do the job.
2. Provide at firsthand all information about the problem, error messages, infrastructure / equipment in the matching forum.

Eventually repeat your post in your own language, as there are for sure others from your country with help and knowledge.

If there is no answer to your question after a a couple of day's, you might eventually post a short message (and a link to your question) according to your issue in a thread with similar content.

There are a lot of people around here in the community with thousands of recommendation points, a lot of knowledge about Apple hard and software and also of networking things.

These people mostly refuse to answer contributions in threads with a lot of "me too" posts or revolving complaints with no attempt to solve problems.

They also tend to stay away from questions are already get answered when Panther switched to Tiger, Tiger to Leopard and Leopard to Snow Leopard.

Ask your question about your problem and be a part of the solution.

Lupunus

As supplement:

• the only stations in my wi-fi are my iMac (mid 2010, i3 3,2 GHz) and my iPhone (3GS)
• there is a cordless phone connected to my router (Siemens Gigaset CX450 isdn) > this didn`t cause any problems under SL
• there is no active bluetooth-devices in my flat
• there is 25 wi-fi-networks in the neighborhood identified by Airport > it`s the same networks as under SL where they didn`t cause any problems (and when I went back to SL for five days before doing a clean installation of Lion there were no problems as well)... > this makes it impossible to have a distance of 5 channels between the different networks > and by the way: these are pretty usual conditions in urban circumstances in my opinion...

By the way:

• as I said I told my FritzBox to use channel 13 only yesterday and didn`t have any wi-fi-connection-problems since then
• this changed some minutes ago when I used the WLAN with my iPhone for the first time since switching to channel 13 > at once Airport reported that it lost the internet-connection > may this be caused by the router going to 802.11g for the iPhone? > if so switching to channel 13 is just another "dead solution" 😟

Just have a look at my last post:

• as I said I told my FritzBox to use channel 13 only yesterday and didn`t have any wi-fi-connection-problems since then
• this changed some minutes ago when I used the WLAN with my iPhone for the first time since switching to channel 13 > at once Airport reported that it lost the internet-connection > may this be caused by the router going to 802.11g for the iPhone? > if so switching to channel 13 is just another "dead solution" 😟

Just as a consolidated summary of my personal experiences:

My Setup:

• iMac Mid 2010, 21.5-inch, Core i3 3,2 GHz
• ISP: 1&1 (Germany)
• Router: FritzBox 7270 (actual and same firmware as under Snow Leopard) / „guest-access“ and „energy-saving-function“ are deactivated (as they were under Snow Leopard)
• Network: WPA+WPA2 / unique SSID / the only stations in my WLAN are my iMac and my iPhone (3GS) / there is a cordless-phone (Siemens Gigaset CX450 isdn) connected to the router / no active bluetooth-devices / 25 neighborhood-networks identified by Airport (the same 25 networks as under Snow Leopard)

History / All the things I tried yet:

• The connection-problems started when I updated to OS X Lion. Not immediately but after the Mac`s first reboot...
• The following recommendations of Apple`s Support-Hotline did not help: delete all preference-files and reboot the Mac / reset the PRAM / reset the NVRAM
• The following suggestions from this post did not help as well: delete the preferred network in the network-configuration and delete all the wi-fi-keychains in the Mac`s key-management > then configure it for a new / put wi-fi on the first place in the network-surroundings / deactivate „remember all the networks the computer was connected to“ / deactivate „give a hint on new networks“ / the „ping-thing“ described in several replies makes things better but even then I still lost the connection several times... > anyway this can`t really be it in my opinion...
• Then I went back to Snow Leopard for four days and did not have any problems at this time...
• Then I did a clean installation of Lion from DVD > this worked for almost five weeks until the problems came back...
• Then I figured out that there obviously is a problem about the BSSID (as described in quite some of the replies here) which most of you affected by the problem will see in the „kernel.log“...
• Then I told my router to work via 802.11n+a (> 5 GHz) only > this works but is no solution for me as my iPhone could not use the WLAN any more...
• Then I told my router to work via 802.11n+g only > this made things even worse...
• Then I went back to 802.11n+b+g and told my router to use channel 13 only > this worked for some hours but was NO durable solution as well...
• Then I switched off my cordless phone and it`s base-station > this has worked for some hours now (which is no guarantee it`s going to last...) and is no acceptable solution because I can`t switch off the phone permanently and won`t buy a new one...

Gonna put this all in another Bug-Report for Apple and really hope for an answer or a fix in 10.7.2...

My view on it:

• The problem results from a higher sensitivity of Lion on the influence of other wi-fi-networks or stations/devices in these networks...
• My guess is that this has to do with Airdrop (as others guessed before in some replies here)...
• @Lupulus: I`m not Dr. Watson for sure but just an experienced (20 years) Windows-User who switched to the Mac-World hoping there would be no need for massive trouble-shooting any more 😉 Anyway I really appreciate your help!!!
• Of course there is other things in life and the world being much more important!!!

I`m sure that all you wrote is absolutely correct.

BUT: In my case and in many other cases described in this post the following happened:

• Snow Leopard > no problems
• Lion > problems (same computer, same router in the same position with the same firmware and configuration, same neigborhood-networks, same flat/furniture)
• going back to Snow Leopard > no problems

In all these cases the only thing which changed is the OS. So as a matter of a fact there must be a higher sensitivity of Airport under Lion and I don`t think that rearranging everything beetween the router and the Mac by try&error is an acceptable workaround...

laechleviel wrote:

• Snow Leopard > no problems
• Lion > problems

To repeat it again. Don't mix up the things. The obvious is mostly not the truth.

Also neither the OS Lion nor the 2011 Mac is what happened behind the scene.

Sure, by looking at it from a user point of view the whole thing is crystal clear. For example look at the quote above.

Two little story's to give you eventually an idea...

At the time Windows XP was first massively rolled out on new machines, there where a lot of howling, rant and complaints ...

• Since I've upgraded to XP / Since the new machine our network is terribly slow and sometimes we have literally no connections at all.
• With W2000 / 98 we never had this.
• Have downgraded to ... and our network is fine.
• It MUST be the XP
• It MUST be the new hardware.

And this where not home users with a simple 2 machine net. This where company's had rolled out 400, 600 or 1000 new systems at once.

After a lot of Lab testing's, tech meetings, conferencing with developers and tons of emails the found reason had nothing to do with XP or the hardware.

The used network adapters (NIC's) had a build in auto negotiation for the network speed. With the new drivers delivered with XP these option became active cause more and more networks had not longer only 10 MBit LAN but often mixed 10/100 LAN. Unfortunately most of the used switches at that time could not work proper with that option.

At May/June 2011 I was assigned to support a combined Win7 - Office 2010 rollout to 400 employees at the head office of an industry group. All went well until suddenly department printers vanished from the system settings, printing resulted in a error message or color printing came out black and white. No $50 home printers, high end multifunction network stations, though. The problems show up randomly, not at once and not for all users. Just here and there a single user or a group of users. As you may imagine, there was rant and rave. With my old notebook ... with XP I never had ... with old Office 2003 this never happened ... Win7 is crap.

To make a long story short. The reason was neither in the new notbooks, the Win7 or Office 10. After 4 weeks of troubleshoot the outcome was that a simple outdated part of the print queuing service on the central LAT-servers caused the network trouble.

Lupunus

lupunus wrote:

laechleviel wrote:

• Snow Leopard > no problems
• Lion > problems

To repeat it again. Don't mix up the things. The obvious is mostly not the truth.

Also neither the OS Lion nor the 2011 Mac is what happened behind the scene.

1. Don`t remember I said anything about the 2011 iMac. I have the mid 2010 model...
2. I am not mixing up anything! It is a matter of a fact that in my case the problems only appear when there is Lion on the machine and that there is no problems when I`m running SL... Of course this is from a user point of view as I AM A USER!
3. Of course it can be that "behind the scenes" the problems are not caused by mistakes in Lion but by something which works different (but correct) in Lion and awakes mistakes in let`s say the routers hardware or firmware > at the same time it can be also that it`s all about a higher sensitivity of Airport under OS Lion > but if it is about the routers hardware/firmware there should be a lot more users having problems with the FritzBox 7270 and there should not be so many different constellations where the problems appear...
4. End of the discussion for me!!!

hormelmeatcompany wrote:

Lupunus,

OS X includes drivers for hardware. If Snow Leopard's drivers worked and Lion's did not, the problem is essentially with that version of OS X. Saying it's not the OS but the drivers when in fact, the 2 come together, is really just semantics.

First, your contribution is very interesting and leads to some new conclusions. Thanks for that.

In written communication semantics is essential as a sender of a message did not have the normal communication control mechanism like facial expression, gestures and sound of the voice to proof the receivers understanding.

Also on such a difficult field as computers (which mostly contains physics, math and "trillions" of configuration scripts) semantics is crucial.

Nevertheless, as well as I use in conversation with colleagues the "Lion seems to haven a wireless problem" term too, all participants in such a discussion know the meaning and understand this as "Lions wifi stack seems to have... "

Here at the forum's it's more complicated as it is a mixed audience of "normal" computer users and technician's looking on a issue and "talk" about.

Enough on semantic, back to the issue now.

hormelmeatcompany wrote:

If drivers were the root cause,

Unfortunately it's difficult to compare e.g. the firmware version due to the fact that there are different "numbers" on the versions depending on the country of the participants here. Although the firmware functions in general are identical, for instance USA, Europe and Japan have different regulations on wireless; e.g. number of channel's.

To use a bit semantics. (sorry😉) The firmware in question is the "driver" of the wifi chipset and is also a kernel extension (kext) get load into the operating systems kernel (systems core) on runtime if the wifi get switched ON.

On that (firsthand) it's generally independent of the used OS X version. (see later descr.)

On this your idea of swapping the kext files for testing is a interesting one in the way of troubleshoot. But! What you not swapped where the additional configuration files which controls the actual settings of the "driver" before it get load.

That makes me think about something....

Let's first concentrate on the Broadcom and 2011 MB side of the issue to simplify it a bit.

As the 2011 used Chipset is the same regardless of SL and Lion the "driver" have to be basically the same.

Looking over the rim of the plate let us see, that SL users with 2011 MacBook's are also affected by the WiFi issue. (As I was too)

They blame in their respectively threads about the issue the 2011 hardware; e.g. "never had that with my old MBPro and SL".

So where are the differences on chipset respectively Lion / SL in the handling of WiFi?

Did a bit research as I've some spare time today 'cause it's my home office day. 😉

Found only one major difference between Lion and SL matching the WiFi handling question. Airdrop.

Additional findings where:

• The actual wifi chipset firmware (aka driver) enables the "Airdrop" functionality on the chipset although the Airdrop function is not active (available) in Snow Leopard due to different settings in the controlling configuration file(s)
• Aside of Lion, Airdrop requires as well that all Airdrop using systems are member of the domain "local"

leads to ->

• Having two different domains in a network segment causes name resolution (DNS) trouble.
• Name resolution trouble may cause unwanted network traffic and timeout's and therefore disassociation of clients.

Had a case couple of day's ago with a UK based "My Mac drops network all the time".
Working resolution there was: The guy got a new BT DSL/wifi box which have (not changeable) the local domain "home" fixed. Changing on the Mac the domain from "local" to "home" solves the wireless trouble. To proof the solution I scanned some UK-forum's and found similar reports about the fixed "home" domain on that boxes and that changing (mostly Windows machines involved) Windows default set domain "workgroup" to "home" does the trick.

This will under certain circumstances also explain the wireless trouble in mixed networks or with some router's some users of 2011 Mac's reports as "WiFi drops / bad connection with my new 2011 MB-MBPro-Air".

Eventually also, the used BC-Chipset gets along the activation of Airdrop ability more sensitive on interferences (this cause bad packets) in the wireless stream due to security reasons when password free computer to computer connection for Airdrop.

But that is at now only speculation.

Hope that's a brick more in the wall on sorting out the different wireless problems with 2011 Mac's and/or Lion wireless trouble.

Lupunus