Orientation of Airport Express

I don't fully understand your situation. Are you also using the city Wi-Fi service via your AE, or is your AE connected to the internet via your own ISP and a DSL or cable modem?

If the latter, I would get a copy of iStumbler and look to see which of the 11 wifi channels have the least load and set the AE to that channel. This might reduce your interference. Also, some wireless phones may be a source of interference. Does proximity of your computer (or iPad, iPhone, etc.) to the AE make a difference?

Quite frankly, if I was in your situation and I had my own internet connection with a DSL or cable modem, I might use Ethernet instead of Wi-Fi. If you too are using the city Wi-Fi system, there's not going to be much you can do. It's simply overloaded. In a place as densely populated as New York City you might have 500 people trying to use that node...

I'm using the Airport Express in "Join an existing network" mode, which means it is the only means of communicating with the internet when it is accessing that city-sponsored access point.

--- Joe

OK, so you are basically using your AE as a repeater for the city Wi-Fi network. Two further questions:

1. Do you have your AE password protected so that you are the only person who can use it (or people to whom you give the password)? If not you should do this, using the AirPort Utility in the Utilities folder on your Mac. Use WPA2 if possible. Otherwise you might have dozens of people using your AE as their access, harming its performance.
2. If you use your Wi-Fi card on your computer to directly access the city Wi-Fi hot spot, how does the performance compare to using your AE to access it?

Also, you might post this question to comp.sys.mac.comm since that's the Mac networking newsgroup. comp.sys.mac.sys is nominally to discuss issues with the operating system (although it ends up being a general purpose newsgroup much of the time).

The surest sign of success is pollution. Your unspecified city sponsored public wi-fi seems to be quite successful.

No. Having a stronger signal will not eliminate mutual interference with other users. In an extreme case, it will create additional collisions, which will cause the other users to generate retransmissions and retries, thus reducing the overall thruput. The ideal situation is where everyone delivers the exact same signal strength to the central access point, but that's not going to happen. However, having a better than minimal signal to the access point will help reduce YOUR retransmissions and retries, so it's worth the effort.

Essentially hemispherical. It's roughly the same in all directions. The tiny antennas used in most such radios don't have much directivity. If you want gain in one particular dirction, play with reflectors or external antennas. The Aiport Express has not provision for an external antenna, so you're stuck with a reflector:

That's quite good performance from a public wi-fi system. I would not expect that to continue as more and more users (and abusers) begin to use it. I suggest you install a suitable sniffer on you Mac Something and try to determine the number of other users and how much traffic they're generating, to see if you have a chance. A typical access point can handle about 100 users doing light web surfing and email, about 5 users doing Netflix, and 1 user doing BitTorrent.

Consider yourself fortunate that you're getting 1 KByte/sec. Oversubscription often creates disconnects.

Since it is hanging in such a flexible mode it should be easy to experiment. The antenna does likely have a low gain orientation to it.

For example the the little "stick" antennas have the least gain along their axis - so don't point it at what you want to talk to but put it parallel to the straight line to the other system.

If it has a little 'patch' antenna then it's likely a "balloon" shape above the patch.

There's a widget called "Airlock" at

Please forgive the top posting, it's the quickest way that I can get to the points here.

In what follows below, Jeff, did you mean spherical, and NOT hemispherical? If indeed hemispherical, how is that hemisphere oriented wrt that Airport Express's case?

Also, in the below, Jeff stated " A typical access

What kind of method/algorithm does the wifi use to distribute transmit/receive bandwidth to the various individuals? Your reference to Netflix and BitTorrent makes me think that somehow heavy users get all/most of the bandwidth and other users are almost shut out. Isn't there some sort of time-allocation slicing to divvy up the bandwidth so that one user cannot hog all the bandwidth?

Thanks.

--- Joe

Top posting is evil. Please find a suitable self-inflicted punishment and vow never to repeat this transgression.

Hemispherical. The antenna is located at the "front" of the Airport Express, away from the power plug. It radiates equally well in all directions, except into the wall where it's plugged in. If you dangle it at the end of an extension cord, it will begin to more closely resemble a spherical pattern. There are probably some holes in the pattern in the direction of the electronics and in the up/down direction, but for all intents and purposes, the pattern is roughly a fat donut.

The antenna is a PIFA PCB antenna. See:

The antenna is the horizontal traces on the PCB in the lower right edge of the photo below:

Another view, this time on the right edge:

There are many systems running simultaneously. 802.11 prevents an individual user from hogging all the air time by restricting the time it can transmit data. That's partly why a 54Mbit/sec association (connection) will only yield about 25Mbits/sec thruput. CSMA/CA also provides for distributing the bandwidth. The "CA" stands for collision avoidance, which does its best with backoff timers to again prevent monopolizing the channel. Finally, the ethernet backhaul also has a "fair share" algorithm to prevent the same problem on the wired part of the network. If the wireless system uses QoS (Quality of Service) to give priority to time critical packets (VoIP), that will also redistribute the bandwidth. Most public Wi-Fi system also have some sort of bandwidth manager which limits the bandwidth of a single connection.

Netflix is fairly good about not monopolizing bandwidth. Watching an HD movie will try to grab about 600Kbits/sec. However, BitTorrent will grab ALL the bandwidth it possibly can. Worse, on an asymmetrical broadband connection, it will saturate the upstream bandwidth acting as a server, and prevent all downloading even if bandwidth is available by delaying ACK's. If misconfigured, it can also kill the access point by opening too many IP sockets and threads, running the access point out of buffer memory. It's much like traffic on the freeway. When things get busy, EVERYONE slows down.

Not with 802.11. However, there are other polling algorithms that sequentially poll connected users for data. For a large number of users, that's more efficient than the collision intensive method used by 802.11.