eap Mailing List: Re: EAP WG Last Call on Network Discovery andSelectionProblem Document

[Bari, Farooq (farooq.bari]

Based on the email exchanges between Jouni and Bernard I propose the
following resolution to the issues raised by Jouni
--
Jouni's concern about the calculations can be addressed by presenting
them in the draft as standalone calculations without referring to
Velayo's paper. Bernard had done these independent calculations in his
response which to my understanding Jouni did not seem to have a problem
if they were not referring to Velayos paper. 

--

Jouni had some concern on scalability section  which can be addressed by
changing

"Similarly, "virtual AP" approaches introduce additional Beacons in
proportion to the number of networks being advertised.  Neither approach
scales to...". 

To

"Similarly, approaches that utilize separate Beacons for each "virtual
AP"  introduce additional Beacons in proportion to the number of
networks being advertised.  Neither approach scales to..."

--
Jouni comments on conclusion section can be addressed by following steps

Adding some explanatory text about Virtual APs

Hidden SSIDs.  Here Beacons are not sent for SSIDs defined as "hidden";
instead, stations are configured to send a Probe Request for each
"hidden  SSID".   As a result, Beacon traffic does not grow with
addition of new "hidden virtual APs".  Instead Probe Request traffic
increases with the number of users configured to probe for "hidden
SSIDs" and the number of "hidden SSIDs" they are configured to probe
for.   In some cases disclosure of station interest in a "hidden SSID"
may be considered a privacy risk, and additional latency may be
introduced where a substantial number of hidden SSIDs needs to be
probed.

Multiple SSIDs per Beacon.  In this approach, multiple SSIDs can be
advertised within a single Beacon or Probe Response. This approach
improves Beacon scaling as compared with advertisement of a single SSID
per Beacon, and also may reduce Probe Request traffic, so that it can
complement the "hidden SSID" approach.


By changing

"Studies such as [MACScale] and [Velayos], demonstrate that the IEEE
802.11 Beacon/Probe Response mechanism has substantial scaling issues,
and as a result a single physical access point is in practice limited to
less than a dozen virtual APs on each channel with IEEE 802.11b."

to

"Studies such as [MACScale] and [Velayos], demonstrate that with the
utilization of a separate Beacon for each "virtual AP", the IEEE 802.11
Beacon/Probe Response mechanism has substantial scaling issues, and as a
result a single physical access point is in practice limited to less
than a dozen virtual APs on each channel with IEEE 802.11b."

By changing 

"However, even with these enhancements it is not feasible to advertise
more than 50 different networks, and probably less in most
circumstances"

To

"However, even with these enhancements, when a separate Beacon is
utilized for each "virtual AP", it is not feasible to advertise more
than 50 different networks, and probably less in most circumstances.
These limitations however do not exist with alternative "virtual AP"
approaches now in development."

BR,
 
Farooq Bari
farooq.bari [at] att.com
+1 425 580 5526
 

> -----Original Message-----
> From: Jouni Malinen [mailto:j [at] w1.fi]
> Sent: Tuesday, March 27, 2007 7:11 PM
> To: Bernard Aboba
> Cc: eap [at] frascone.com
> Subject: Re: [eap] EAP WG Last Call on Network Discovery
andSelectionProblem
> Document
> 
> On Tue, Mar 27, 2007 at 09:52:22AM -0700, Bernard Aboba wrote:
> > BTW, I did some traces, and 170 octet Beacons are actually quite
common
> > (Apple Airport Extreme has Beacons of this size, for example).
> >
> > If you add up 1360 bits at 1 Mbps (1360us), 144 us for preamble, 48
us for
> > PLCP, 10 us for
> > SIFS, 50 ms for DIFS, and 1200 usec for CWmin/2 slot times, and
multiple by
> > 98 Beacons/sec, you get 27.6 percent.
> >
> > 200 octet beacons would give 30 percent.  So I don't think that the
Velayos
> > paper is that far off.
> 
> Sure, it is possible that beacons are longer. Though, I would assume
> that this would be more likely with 802.11g/a APs while the paper was
> talking about 802.11b which is unlikely to include many of the new IEs
> in beacon frames. Anyway, if the question is on how many "modern APs"
> one can have on a single channel, this kind of channel time usage may
> indeed be getting more likely since I would expect most 802.11g APs to
> continue beaconing at 1 Mbps rate.
> 
> --
> Jouni Malinen                                            PGP id
EFC895FA
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