rts, cts, bss (was Re: [Cu-wireless] prism firmware bug)

[Chase Phillips]

RTS: Request to Send

  Sent on the medium to make the destination (and any other stations who
  can hear the request) aware that the sending station has data and would
  like to allocate the medium for "some" time so the destination may
  receive that data.

CTS: Clear to Send

  When the destination receives a RTS, it typically responds with a CTS.
  This is an acknowledgement to the sender that the destination will be
  watching the medium for its data over the next "some" time.  It's good
  to signal the sender as an ACK, but this notification solves other
  problems where some station in the range of the destination wasn't in
  the range of the sender, and hence didn't get the RTS.  For stations in
  this position, receiving a CTS with no matching RTS is a notification
  that the sender of the data is out of range, yet the CTS is enough to
  keep polite stations from talking over the sender for the allotted
  "some" time (thereby allowing the destination a clear signal from the
  sender while the data is being transmitted).

BSS: Basic Services Set

  The most basic set of wireless services 802.11 provides.  BSS typically
  refers to infrastructure mode (communication via an access point).
  Contrast BSS with iBSS (or Independent Basic Services Set) for ad-hoc
  mode.  Another service set is called ESS (or Extended Services Set),
  which is used for wireless infrastructure-mode roaming between APs.  The
  name SSID comes from "service set identifier", and is used in each of
  these modes as a namespace mark. (BSSID, ESSID, ...)

RTS and CTS are low-layer stuff (they sit in the MAC for 802.11, iirc) and
are essential for regulating access to the medium.  That is, if you want
the stations to work together.  The prism bug is only bad insofar as those
using the station for promiscuous mode would also like that station to be
an active participant in the network.  Personally, I've had much better
luck in just turning on wireless sniffing mode and grabbing all the
traffic that hits the receiver (at the cost of participation).  The added
benefit is that I can get per-packet information all the way down to the
physical medium's prism headers (such as strength-of-signal, etc).  Come
to think of it, I haven't ever used that physical information.. it's just
damned cool to have, though. =)

If you are interested in the details of 802.11b, I highly recommend the
ORA book "802.11B Wireless Networks" by Matthew Gast.  It's exploration of
the protocols involved in this standard was very readable, and explained a
hell of a lot to me.

Chase Phillips
--
  shepard at ameth.org ][ -111--0010-0-1100-101-000-01--10
 http://www.ameth.org/ ][ 00-00-01-10--1-00-01-010111010-0

On Tue, 5 Nov 2002 niteshad at whopper.de wrote:

> Could this be at least part of the reason for the poor link between Peter
> Miller's and the IMC?  Also, please refresh my memory regarding the meaning
> of the acronymns: RTS, CTS, and BSS.  Between CU-wireless, my CCNA classes
> and my studies of the history of various nuclear weapons programs, my mind is
> rapidly dissolving into alphabet soup!
>
> regards,
>
> Mark