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ad-hoc network limited to 11Mbps?

6 posts by 3 authors in: Forums > Wi-Fi Alliance Certifications & the 802.11 Standard
Last Post: June 4, 2005:
  • By sacim
    Reply

    Is it true that the 802.11b and g standards specify a maximum speed of 11Mbps for an ad-hoc network?

    thanks

  • By Criss_Hyde
    Reply

    Hi Sacim:

    No. And I don't imagine why anyone would make such a mistake.

    I hope this helps. Thanks. / criss

  • By ben_miller
    Reply

    The best client utility out there, Funk's Odyssey Client, limits 2.4 GHz radios to 11 Mbps in ad-hoc mode. Not something in the standard, just something you see in real world experience.

  • By sacim
    Reply

    Hi Criss,
    take a look at this link:
    http://labs.pcw.co.uk/2005/03/adhoc_wireless_.html
    where this issue is talked about.
    thanks,

  • By Criss_Hyde
    Reply

    Hi Ben and Sacim:

    Thanks for the extra information. Alas, I have much more acquaintance with the IEEE standards than with real world experience!

    My reading of the 802.11 standards leaves me with no recollection that an Independent Basic Service Set (IBSS or "ad hoc" network) has any different mandatory rates than an infrastructure BSS. A quick PDF search for "IBSS" in the 802.11g amendment turns up nothing to change that opinion.

    A HR/DSSS PHY (IEEE 802.11b) has mandatory rates of 1, 2, 5.5, and 11 Mbps.

    An ERP PHY (IEEE 802.11g) has mandatory rates of 1 and 2 Mbps (ERP-DSSS), 5.5 and 11 Mbps (ERP-CCK), and 6, 12, and 24 Mbps (ERP-OFDM).

    I recall that the Wi-Fi alliance requires its members selling ERP PHYs to support the full range of ERP-OFDM rates up to 54 Mbps. I would not be surprised if they also allow their members' ERP PHYs when operating in IBSS mode to not support ERP-OFDM rates altogether. This would leave 11 Mbps ERP-CCK as the highest IBSS rate whether using HR/DSSS or ERP hardware.

    If anyone finds an IEEE clause providing for different mandatory rates for IBSS please post. And anyone who can report 54 Mbps IBSS experience will be welcome as well.

    I hope this helps. Thanks. /criss

  • By ben_miller
    Reply

    Thanks to both of you for the info. I had no idea there was a lack of 54Mbps support for Ad-Hoc mode with some software/hardware until I was teaching CWNA Lab 3.b and the students pointed out that the Dell wireless adapters were all much slower in 802.11g ad-hoc than 802.11a. We checked it in Airopeek and, sure enough, 11 Mbps was all that showed. When we checked the Odyssey client, it had support to select 802.11b data rates, but not OFDM data rates. Interesting stuff.

    Cheers

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