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3com WAP - public/secure and 'N' vs B/G
I was at our local library today,
and it appears they have several WAP's installed, but I had problems getting connected... There are two SSID's - one is public and one is private/secure. Using WiFi Hopper it displayed a couple of 3Com access points with what appeared to be "related" MAC addresses... 00:22:57:00:13:40 - public 00:22:57:00:13:42 - secure Anyway - when I got home & sent an email to their "tech" person and mentioned that I was having a problem, here was the jist of the reply... Wrong tech language makes me not hopeful Since I don't have anything running B/G/N - could they have something configured to support N, that accidently doesn't allow B/G to connect - and they don't know it ---- I have familiarity with our wireless access points, and also have familiarity with wireless setups. I'm sorry you had some connection problems when you were at the library. Every so often, our wireless connection weakens, but overall, the signal is usually pretty strong. However, I have a few ideas that you might want to try: If you were sitting at a table near the magazines, you would be near one of the wireless hubs, which should have boosted the signal. There are 4 hubs throughout the library (2 downstairs, one in the meeting room and one in Youth Services upstairs) and are for anyone to use. You indicated that your laptop showed access points of LLD-Public and LLD and if you select one of these, your laptop should make the connection with no problem. The LLD-Public connection is using the newest technology for 802.11 N. In addition, some of the newer laptops, like ones from Dell, need a utility enabled to allow complete connection. We ran into this problem with the new laptops for our computer classes, and I know another patron who also had this problem. If you are using a Dell, you might want to check that you have enabled the Dell wireless utility. You can go to the Dell website if you need to download it --- it is called Dell Wireless WLAN Card Utility. If you are using a laptop made by another manufacturer, there is most likely a similar utility for your wireless connections. Another thing to double-check are any firewall settings you might have enabled to protect your laptop when accessing wireless points. Our wireless network is unsecured (no password required). |
#2
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3com WAP - public/secure and 'N' vs B/G
"ps56k" wrote in message ... I was at our local library today, and it appears they have several WAP's installed, but I had problems getting connected... There are two SSID's - one is public and one is private/secure. Using WiFi Hopper it displayed a couple of 3Com access points with what appeared to be "related" MAC addresses... 00:22:57:00:13:40 - public 00:22:57:00:13:42 - secure Anyway - when I got home & sent an email to their "tech" person and mentioned that I was having a problem, here was the jist of the reply... Wrong tech language makes me not hopeful Since I don't have anything running B/G/N - could they have something configured to support N, that accidently doesn't allow B/G to connect - and they don't know it ---- I have familiarity with our wireless access points, and also have familiarity with wireless setups. I'm sorry you had some connection problems when you were at the library. Every so often, our wireless connection weakens, but overall, the signal is usually pretty strong. However, I have a few ideas that you might want to try: If you were sitting at a table near the magazines, you would be near one of the wireless hubs, which should have boosted the signal. There are 4 hubs throughout the library (2 downstairs, one in the meeting room and one in Youth Services upstairs) and are for anyone to use. You indicated that your laptop showed access points of LLD-Public and LLD and if you select one of these, your laptop should make the connection with no problem. The LLD-Public connection is using the newest technology for 802.11 N. In addition, some of the newer laptops, like ones from Dell, need a utility enabled to allow complete connection. We ran into this problem with the new laptops for our computer classes, and I know another patron who also had this problem. If you are using a Dell, you might want to check that you have enabled the Dell wireless utility. You can go to the Dell website if you need to download it --- it is called Dell Wireless WLAN Card Utility. If you are using a laptop made by another manufacturer, there is most likely a similar utility for your wireless connections. Another thing to double-check are any firewall settings you might have enabled to protect your laptop when accessing wireless points. Our wireless network is unsecured (no password required). here's some info I found - but it discusses the client side, not the AP side - --- 802.11n APs that use the ISM band will indeed compete for air space with existing 802.11g APs. That's especially troublesome for 802.11n APs that use 40 MHz channels, since the ISM band is only wide enough to fit 3 non-overlapping 20 MHz channels (1, 6, and 11). For example, suppose an 802.11n AP uses Channels 6 and 7 to create a 40 MHz channel -- that will generate co-channel interference for every other 802.11g AP in the vicinity except those using Channel 1. However, if you deploy old and new clients in the same frequency band, you'll need to enable coexistence mechanisms. Specifically, there are two modes of coexistence specified by 802.11n: legacy mode and mixed mode. In legacy mode, 802.11n clients behave just like 802.11g clients -- this amounts to using new hardware in the same old way as before, with little performance improvement. In mixed mode, 802.11n clients will send both the old-fashioned 802.11g preamble and the new 802.11n preamble before they start transmitting data. Mixed mode lets 802.11n clients take advantage of performance improvements like space-time block coding, short guard intervals, and frame aggregation, while giving 802.11g clients a "heads up" to avoid collisions. The extra preamble does add overhead, preventing 802.11n clients from achieving optimum throughput. But this is the price you must pay to ensure peaceful coexistence between old and new clients sharing the same band. |
#3
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3com WAP - public/secure and 'N' vs B/G
On 05/03/2009 03:23, ps56k wrote:
I was at our local library today, and it appears they have several WAP's installed, but I had problems getting connected... There are two SSID's - one is public and one is private/secure. Using WiFi Hopper it displayed a couple of 3Com access points with what appeared to be "related" MAC addresses... 00:22:57:00:13:40 - public 00:22:57:00:13:42 - secure Anyway - when I got home& sent an email to their "tech" person and mentioned that I was having a problem, here was the jist of the reply... Wrong tech language makes me not hopeful Since I don't have anything running B/G/N - could they have something configured to support N, that accidently doesn't allow B/G to connect - and they don't know it If they are running an 802.11n network they don't have to allow 11b or 11g to connect, the draft 11n only says that the equipment must be capable of connecting to legacy devices so the user can have the capability to run a mixed network. Look at the set of 11n mode options that are available on this emulator http://support.dlink.com/Emulators/dir655/Basic_Wireless.html |
#4
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3com WAP - public/secure and 'N' vs B/G
"LR" wrote in message news On 05/03/2009 03:23, ps56k wrote: I was at our local library today, and it appears they have several WAP's installed, but I had problems getting connected... There are two SSID's - one is public and one is private/secure. Using WiFi Hopper it displayed a couple of 3Com access points with what appeared to be "related" MAC addresses... 00:22:57:00:13:40 - public 00:22:57:00:13:42 - secure Anyway - when I got home& sent an email to their "tech" person and mentioned that I was having a problem, here was the jist of the reply... Wrong tech language makes me not hopeful Since I don't have anything running B/G/N - could they have something configured to support N, that accidently doesn't allow B/G to connect - and they don't know it If they are running an 802.11n network they don't have to allow 11b or 11g to connect, the draft 11n only says that the equipment must be capable of connecting to legacy devices so the user can have the capability to run a mixed network. Look at the set of 11n mode options that are available on this emulator http://support.dlink.com/Emulators/dir655/Basic_Wireless.html If the access point is setup for 802.11n - and only 802.11n - would I still see the SSID beacon on my b/g card via NetStumbler, Hopper, Windows ? Is the beacon packet seen by all technologies at the lowest common "speed & structure", and only goes into 802.11n mode after the actual connection ? Would I see the SSID, but just not be able to establish a connection ? |
#5
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3com WAP - public/secure and 'N' vs B/G
On 05/03/2009 15:33, ps56k wrote:
wrote in message news On 05/03/2009 03:23, ps56k wrote: I was at our local library today, and it appears they have several WAP's installed, but I had problems getting connected... There are two SSID's - one is public and one is private/secure. Using WiFi Hopper it displayed a couple of 3Com access points with what appeared to be "related" MAC addresses... 00:22:57:00:13:40 - public 00:22:57:00:13:42 - secure Anyway - when I got home& sent an email to their "tech" person and mentioned that I was having a problem, here was the jist of the reply... Wrong tech language makes me not hopeful Since I don't have anything running B/G/N - could they have something configured to support N, that accidently doesn't allow B/G to connect - and they don't know it If they are running an 802.11n network they don't have to allow 11b or 11g to connect, the draft 11n only says that the equipment must be capable of connecting to legacy devices so the user can have the capability to run a mixed network. Look at the set of 11n mode options that are available on this emulator http://support.dlink.com/Emulators/dir655/Basic_Wireless.html If the access point is setup for 802.11n - and only 802.11n - would I still see the SSID beacon on my b/g card via NetStumbler, Hopper, Windows ? Is the beacon packet seen by all technologies at the lowest common "speed& structure", and only goes into 802.11n mode after the actual connection ? Would I see the SSID, but just not be able to establish a connection ? Without actually trying it I am not sure exactly what you would get. I have been doing a bit of reading about N recently and am not sure how some of these "legacy" connections are supposed to work. "During the definition of the 802.11g standard, it was realized that, since legacy 802.11b devices would not be able to decode the newer 802.11g frames, there ought to be a separate mechanism to help legacy devices set their NAV correctly and therefore to reduce the percentage of collisions on air. The 11g standard made use of existing ‘protection mechanisms’ – RTS and CTS – to help legacy stations set their NAV. A similar situation arose during the definition of the 802.11n standard. Legacy 802.11a/b/g devices would not be able to decode the 802.11n headers – and therefore a protection mechanism becomes necessary. One of these is the transmission of legacy preamble and header that enable the 802.11a/g/ device to detect the 802.11n packet and to decode the information in its signal field, from which the correct packet duration can be determined." http://www.redpinesignals.com/Wireless-Handheld-Devices-The-802-11n-Advantage.pdf My reading of that is you should see something. There was also this "Backward compatibility with legacy devices also may be enabled by forcing devices that are compliant with a newer version of the standard to transmit special frames using modes or data rates that are employed by legacy devices. For example, the newer devices may transmit Clear to Send/Ready to Send exchange frames or Clear to Send to self frames as may be employed in standard 11g. These special frames contain information that sets the network allocation vector of legacy devices such that these devices know when the wireless channel is in use by newer stations." http://www.faqs.org/patents/app/20090028106 I have heard mixed reports about even using an 11n card with netstumbler with some people not getting it to work and one person who got it work only having it report speed at 54Mbs. |
#6
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3com WAP - public/secure and 'N' vs B/G
I recently borrowed a wireless router that accepts cell phone 3G wireless
cards (this one was Sprint) and rebroadcasts the signal as standard b/g/n (I don't recall the router brand)... I wanted to see if this setup had enough bandwidth to allow three b/g equipped laptops to surf the net without obvious slowdowns (it did). The default was set to broadcast in b/g/n modes, so at one point I selected "n only" and after the router restarted all three laptops detected the network but could not connect. I then connected to the router with a network cable to change the setting back... |
#7
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3com WAP - public/secure and 'N' vs B/G
On Thu, 5 Mar 2009 09:33:30 -0600, "ps56k"
wrote: If the access point is setup for 802.11n - and only 802.11n - would I still see the SSID beacon on my b/g card via NetStumbler, Hopper, Windows ? Which N mode? Beam forming or spatial diversity? In beam forming (Ruckus Wireless), it's basically the same as 802.11g and you will see beacons. In spatial diversity (Airgo), I think (not sure) that the spec demands beacons. However, I'm fairly sure that the beacons are at 6Mbits/sec as in 802.11g. If you enable 802.11b compatibility, beam forming still works and it will belch beacons at 1Mbits/sec. However, with spatial diversity, 802.11b and MIMO speeds are mutually exclusive and I really doubt that you'll see 1Mbit/sec 802.11b beacons. No clue what happens with the new chips that do both beam forming and spatial diversity. I gotta read the specs to be sure, but I think that's the way it works. What you're basically asking is how does 802.11n operate in "greenfield" mode, where there are no constraints imposed by prior technology and legacy junk compatibility. Greenfield mode is very unlikely to be seen in a public library. My guess(tm) is what you're seeing is your wireless client software annoucing the highest level of acronym compliance. Just because you can't connect doesn't mean the lower standards are not available or functional. It would be nice if Netstumbler and others annouced all the various supported 802.11 acronyms, but they don't. Incidentally, se have a somewhat similar derrangement at the local hospital. You can connect, but can't do anything without a WPA password *AND* and a VPN client. Everyone complains that they can't connect, until they finally read the splash page. Anyway, don't assume that it's 802.11n "only" just because you can't connect. Is the beacon packet seen by all technologies at the lowest common "speed & structure", and only goes into 802.11n mode after the actual connection ? Would I see the SSID, but just not be able to establish a connection ? I don't know if this really helps, but the section on backwards compatibility: http://en.wikipedia.org/wiki/IEEE_802.11n#Backward_compatibility gives a few clues on how much of 802.11g technology (beacons) is compatible with 802.11n. I'm to busy/lazy right now to find a better reference. Gone to waste the whole weekend: http://www.radiofest.org -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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