standard: beacon frame rate

[jangeunjun]

Hi all,
Does anyone know at what rate the beacon frames are transmitted in 802.11 or 802.11b?
I guess it should be 1Mbps for the broad compatibility but I am not sure.
I couldn't find it in the standard.
Thank you in advance.

[JimGeier]

When viewing the beacon frames on a network analyzer (e.g., Airmagnet or Airopeek), I see that the beacons are sent at 2 Mbps. I've read through the standard myself and can't see anywhere where it mentions the data rate of beacons. I do know that the physical layer header (not MAC header) is always sent at the lowest possible data rate, but it's not clear for the beacons.

Anyone else have any ideas on this?

[jangeunjun]

Thank you, Jum. I appreciate it.
So, it's 2Mbps practically. I wonder why, though.
Did you see 2Mbps of beacon frames even when the data rate was 11Mbps?

[JimGeier]

Yes, it doesn't seem to matter what data rate the frames are being transmitted at. I'll try to dig a bit further to see what I find.

[lzeitman]

When I read your post I was thinking you may want the Beacon Interval, perhaps. I beleive that the beacon's data rate is constant (for a reason) and that it is at 11mbs for 802.11b AP and then 54mbs for the "a" version.

The interval between beacons is going to be important and on a Cisco access point this is a configurable parameter. By default it is set to 100 k-microseconds. Now you're going to ask me what a k-microsecond is. As I recall (I used to work for Cisco and supported the Aironet product line) , I believe it's a kilo-second (10 *E3 - 10*E6). Why Aironet engineer decided to hide it in this matter I am not sure . Hope this helps.

-Larry Zeitman
lzeitman@yahoo.com

ps. the reason to keep the beacon "data rate" and everything about the beacon constant is a very common concept in mobile transmission. Because the clients need to discover the AP's via a beacon and there is a many to one relationship, we keep this common signal at a standard rate and db. In this manner you will not have to configure user radio's with varying parameters, but may let them default.

[mmpg]

Hello Larry Zeitman
Yes I agree with u that the beacon's data rate is constant (for a reason),but I think it cannot be at the maximum of the data
rate the standard can transfer ,because the beacon's transmitted
has to be reached by every station and as u increase the rate
the distance will be reduced.So the beacon has to be sent at a lower rate so that it reaches almost all stations.

[lzeitman]

yes, you're right. As soon as I sent that message I knew I was wrong. You can get 1mb , 2mb 11mb data rates out of 802.11b and yes, I agree the beacon has to be at a common denominator. My apologies.

-Larry Zeitman
lzeitman@yahoo.com

[ShawnDing]

Hi all,
I'm a freshman of WLAN,Could you tell me how to get some information about
Beacons ? eg.Websites,books,thesises,etc.