DrBob127
Newbie  Posts: 1 Registered: 23/6/09 Status: Offline |
posted on 23/6/09 at 23:17
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Hello,
The purpose of this post is to ask for your insight and observations of the
behaviour of actual Wi-Fi certified devices
My area of research has me interested in characterising the behaviour of
Wi-Fi certified devices. More specifically, my immediate interested is in
the decision of when a channel-change is initiated and the choice of which
channel is selected to change to.
Having looked through the standard (IEEE Std 802.11™-2007), I see that the
decision to measure channel performance and the decision to initiate a
channel switch is the responsibility of the station management entity (SME)
[see figure 10-2]. The SME controls the MAC layer management entity (MLME)
and the PHY layer management entity (PLME) which are both clearly defined
by the standard to provide the mechanisms by which the channel can be
measured and a channel switch carried out.
However, the SME is not defined by the standard (and I believe is left to
vendors to implement) and it is here that the decision-making logic that I
am interested in is located. This means that I am not going to find the
answer to my question in the standard.
Restricting the discussion to devices operating in ‘infrastructure-mode’
(i.e. with an AP and subscriber STAs), I understand that only the AP can
decide to switch channel. When an AP encounters a sufficiently degraded
communication channel and assuming that all other channels are ‘clear’
which channel does the AP typically select to change to? If that channel is
not available, which channel is then chosen?
However a STA may also initiate a channel scan if it loses connectivity to
its AP. I am a member of a local WISP and during an outage I remember
watching my home router (via its web-interface) channel-scanning to try and
locate the tower. Starting from channel 1 the sequence of channels then
went to 6, 11, 2, 7, 12, 3, 8 13, 4, 9, 5, 10, 1, 6….. Is this behaviour
typical?
I look forward to your reply, thank you for your time and effort.
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