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I have an Intel Wireless Wi-Fi Link 4965AGN adaptor in my laptop (HP Pavillion dv2000 series) which is connecting to a 5GHz-only 802.11n network provided by an Apple AirPort Express. The network is using WPA2 encryption. My desktop is also connected the AirPort, via a Linksys WUSB600N USB adaptor. Both are running with the latest drivers, and the AirPort is running the latest firmware. The AirPort is also configured to use wide channels.

The problem I have is that I never get throughput above 4 MebiBytes/s when transferring files between the two machines. Even a pessimistic calculation shows a 270 megabits/s network as being capable of transfer rates at well above 10 MebiBytes/s.

I'm pretty sure I've isolated the issue to being the Intel adaptor, as wiring the desktop to the AP, and using the Linksys adaptor on the laptop immediately yielded speeds limited by the 100 megabits/s Ethernet connection.

I know that 802.11n is still a draft standard, and so mixing kit from different manufacturers can easily lead to poor results, but I was just wondering if anybody else out there has had success with this Intel adaptor on an N network? Or even better, connecting it to an AirPort Express?

Can anybody give me any advice on how to troubleshoot this issue? I should also mention that the AirPort Express doesn't allow you to manually specify channels when running in N mode, and that I've been able to rule out interference from other Wireless LANs by scanning. There aren't any other 5GHz networks in my area.

All ideas welcome!

Update: A while later, I've just updated to the most recent drivers for both the Intel chip in the laptop, and the USB adaptor. Unfortunately this hasn't improved things :(. If anybody has any advice it would be be gratefully received.

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closed as too localized by Nifle, 8088, Diogo, Joe Taylor, KronoS Aug 13 '12 at 15:49

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I can't find the source right now, but I've heard that 4965 doesn't support 802.11n speeds in some cases. I think that 5GHz may be one of them. I think that it doesn't support wide channels in 5GHz mode. I'll post more once I remember where I found that out. –  AndrejaKo Jan 13 '11 at 0:19

2 Answers 2

I'm seeing something very similar. I've got two Airport Express routers, one each in the office (call it "A") and the living room ("B"). Router A is cabled to the cable modem and establishes a G/N network, router B extends the network and is cabled to an 8-port 10/100 switch. When my laptop with the 4965AGN adapter is on the wireless network, speedtest.net gives results of about 12Mbps/4Mbps. But when I cable the laptop to the switch, I get 20Mbps/4Mbps, which if I recall is what I pay for from the cable company. I haven't yet tried cabling the laptop directly to the cable modem to verify that.

My guess is that it's either a hardware limit or the configuration of the adapter, as the two Airport's are obviously communicating with each other at a higher data rate. Research online indicates that speeds are heavily dependent on a combination of the number of streams used, Guard Interval, Coding Rate, and Modulation Type. According to Intel, the 4965AGN uses two streams, which already limits the maximum rate.

I haven't figured out what modulation, coding rate, or guard interval my laptop's adapter is using, but if you can get those numbers for your environment, you'll have your answer.

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From what I can find on Intel's website as well as the Wi-Fi Alliance's website, that Intel 4965AGN was created back in early 2007 when 802.11n was just a draft standard (802.11 was ratified in mid-2007, so it's been a full-fledged standard since then). That Intel card has gone through several revisions and recertifications since then, some showing it to be compatible with the ratified version of the N standard, some showing it to be capable of 2 spacial stream operation (up to 300 megabits/s) on both transmit and receive, and one showing it to be capable of 2 spacial stream operation on receive, but only 1 spacial stream on transmit (up to 150 megabits/s).

So let's say you have a revision of that card/driver that support 300 megabits/s operation in 5GHz. It looks like that Linksys adapter is capable of the same. So here's how the math works out.

300 megabits/s - 50% typical Wi-Fi overhead = 150 megabits/sec expected TCP throughput. Unfortunately your other machine is wireless too, and 802.11 requires all traffic between two clients of an AP to actually be relayed by AP (this is called "Intra-BSS relay", and it solves the "hidden node problem" where two clients are each in range of the AP, but not in range of each other), so every transmission from one machine to the other in your scenario has to go across the channel twice: once from the Intel client to the AP, and once from the AP to the Linksys client. So this cuts your expected throughput in half again, to 75 megabits/s. Now convert that to MebiBytes/s and you get a little less than 9 MebiBytes/s, assuming ideal RF conditions.

So if you're getting 4 MebiBytes/s and the best you can rightfully expect is 9 MebiBytes/s, I would expect that one of both of your devices either aren't close enough to the AP to get the full 300 megabits/s signaling rate, or there's RF interference getting in the way, or maybe you have the revision of the 4965AGN that only does a single stream on transmit, which would cut its throughput in half.

It would be interesting to know what 802.11 signaling rates your two clients are reporting they're getting, as well as what the AP reports for them.

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