[Fwd: [Open-source] Linux wireless summit 2009]

[Jimmy Angelakos]

Niko, h public lista pleon legetai 'hellug' <hellug at lists.hellug.gr>.

Kanw ekei forward to mail sou, kai euxaristoume poly gia to update.

Mhtsos

-------- Forwarded Message --------
From: Nick Kossifidis <mickflemm at gmail.com>
To: open-source <open-source at grnet.gr>, public List
<public at lists.hellug.gr>
Subject: [Open-source] Linux wireless summit 2009
Date: Fri, 11 Sep 2009 22:06:57 +0300

Hello ppl ;-)

Exw kairo na sas grapsw gia tis ekselikseis sto linux pou aforoun to
kommati twn wireless drivers kai tou 802.11 protocol stack alla trexw
me diafora.

Τon Ioulio pou perase eixame to kathieromeno mas summit sto Berolino
sta plaisia tou FudCon/LinuxTag 2009 kai htan ap' ta pleon paragogika
summits ths omadas. Ayth th fora hmastan poio organomenoi kai etsi
exoume ftiaksei mia selida sto wiki opou mporeite na katevasete tis
diafores parousiaseis (sth diathesh sas an xreiasteite kapoia
dieykrinish) , th selida mporeite na th vreite sto
http://wireless.kernel.org/en/developers/Summits/Berlin-2009

Gia osous endiafereste akolouthei katevato :P

Power saving
--------------------
Eixame ektenh syzhthsh gia to power saving kai tis diafores texnikes
pou xrhsimopoiountai kai o Kale mas edeikse pws oi diafores methodoi
epirreazoun to power consumption sta chipakia twn Nokia (epeidh
paizoun se kinhta exoun dwsei poly varos sto power saving, th
parousiash tha th vreite sto parapanw link). To power saving genikws
einai arketa endiaferon thema kai sxetizetai me diaforous timers pou
vriskontai sthn karta kai sygxronizontai me to TSF (Time Sync Factor)
pou vlepete sto scan. To TSF loipon vrisketai se kathe beacon pou
stelnei to AP h to kathe IBSS (ad-hoc) node. Oloi oi clients
sygronizontai (exei 64bit resolution) kai katopin xrhsimopoioun tous
timers gia na ksypnane kai na koimountai (perissoteres plhrofories edw
-> http://wireless.kernel.org/en/developers/Documentation/ieee80211/power-savings).

Info: To TSF epishs xrhsimopoieitai sto IBSS gia na kathorizetai poios
ksekinhse to IBSS cell afou opoios ksekinhsei prwtos ena IBSS diktyo
exei metalytero TSF ap' tous ypoloipous kai ara oi ypoloipoi kanoun
join to sygekrimeno cell (yiothetoun to IBSS id tou) anti na kanoun
create to diko tous.

Mac80211
---------------
Syzhtisame arketa to thema tou roaming kai diaforwn extensions pou
yparxoun (oxi mono to 802.11r dld). Arxika xreiazomaste enan kalo
algorithmo gia bg scan kai kapoia metrics gia na apofasizoume se poio
AP tha pesoume, proteiname to signal strength pou einai to profanes
alla epipleon proteina mazi me kapoia alla paidia na kratame ena
packet loss count isws se synergasia me ton rate control algorithmo
(afou krataei ayta ta stats outws h allws gia na dialeksei rate).

Milwntas gia rate control fainetai oti o minstrel pou exoume ayth th
stigmh ws default algoritmo einai poly varys gia embedded systhmata
kai fainetai pws exoume kanei kapoia patata giati ston madwifi de
shkwnei toso load (yparxoun kapoia patches apo tote kai genikws to
psaxnoume). Epishs o minstrel den einai ftiagmenos gia 802.11n rates,
syzhtisame to endexomeno na ton kanoume extend (thelei omws arketh
douleia) etsi wste na xrhsimopoioume enan generic algorithmo kai na
mhn xrhsimopoioume vendor-specific algorithmous opws ginetai ston
ath9k h stous drivers ths intel klp. Telos symfwnisame oti to rate
control prepei na perilamvanei kai to multicast traffic (oxi ta
beacons ennoeitai afou afta stelnontai sto basic rate) gia na einai
poio apodotikos.

cfg80211/nl80211
--------------------------
Opws sas exw pei kai sta prohgoumena post skopos mas einai na
ksefortothoume ta wireless extensions kai na doulevoume apokleistika
me to kainourio api (cfg80211) pou xrhsimopoiei ena custom netlink
socket (nl80211) kai oxi ta deprecated ioctl calls. Mexri twra loipon
mas eleipan kapoies vasikes leitourgies me poio vasikh thn entolh
connect dld na orizeis ena essid px. kai na les sto protocol stack na
kanei join ayto to BSS network (px. iwconfig wlan0 essid <tade>) kai
thn antistoixh entolh gia na kaneis join/create ena IBSS network
(ypenthimizw pws gia na sthseis AP xreiazetai o hostapd afou tis
leitourgies tou AP tis kanoume handle sto userspace). Prosfata loipon
oloklhrwthike h ylopoihsh twn parapanw opote mporeite na
xrhsimopoieisete to cfg80211 gia na kanete sxedon ta panta pleon me to
ergaleio iw. Mporeite dhladh osoi xrhsimopoieite kapoion ap' tous
kainourious mac80211-based drivers na petaksete ta wireless-tools kai
na xrhsimopoieitai to iw ! Ta teleytaia bits pou leipoun ap to
cfg80211 kai kata synepeia to iw einai to na mporeis na theteis rate
(iwconfig wlan0 rate <tade>), tx power kai na mporeis na vlepeis to
status (iwconfig wlan0) - to opoio omws mporeis na to deis me dmesg an
kaneis enable ta vasika debug features tou mac80211/cfg80211 sto
kernel config.

Gia to rate control API arxika skefthkame na orizoume oxi ena
memonomeno rate opws twra alla ena rate bitmask, etsi wste na mporoume
na poume ston rate contorl algorithmo na perioristei se sygekrimena
rates (px. na tou poume na paizei mono sta 18-38Mbit) kai profanws an
theloume na kleidwsei se ena mono rate afinoume sto bitmask mono ayto
to rate (opote einai to idio pragma me to yparxon iwconfig wlan0 rate
<tade>). Ayto einai arketa poio evelikto kai tha mporei na
perilamvanei kai ta ht rates (802.11n) pou to iwconfig (wireless
extensions API) den ypostirizei. Epishs eipame na exoume enan tropo na
mporei o xrhsths na dialeksei metaksy twn diaforetikwn (px.
vendor-specific) rate control algorithmwn kai etsi na yparxei akoma
megalyterh eveliksia.

Me aformh ta diafora private extensions pou yparxoun sta wireless
extensions (kai ta kaneis get/set me to iwpriv) syzhtisame kapoia
common pragmata pou tha mporousame na thetoume epipleon kai den
yparxoun ayth th stigmh sto API (oute sto iwconfig oute sto iw).
Katalhksame sto antenna setting gia arxh, opote kapoia stigmh tha
deite sto iw th dynatothta na orisete rx/tx antenna opws px. kanate
ston madwifi me ta /proc h iwpriv settings. Epishs eipame oti genikws
den tha ypostiriksoume vendor-specific pragmata giati theloume na
kratisoume to API kai to protocol stack katharo alla sthn extreme
periptwsh pou kapoios thelei na ylopoihsh kapoia entolh pou einai
hw/driver specific (px. to turbo mode stis Atheros) tha exoume kati
stan to iwpriv alla mesw nl80211. Ayto to kati to onomasame test mode
kai prokeitai gia mia generic entolh sto nl80211 pou mporoun na
xrhsimopoihsoun oi developers gia na perasoun parametrous ston driver
(me kapoio diko tous tool isws). Genikws pantws eipame oti tha
kratisoume oso to dynaton makrya ta vendor specific/proprietary
extensions. Oson afora px. ton ath5k apofasisame oti leitourgies opws
to XR h to dynamic turbo den tha tis kanoume support, enw alles
leitourgies opws to compression tha tis doume isws mesw tou test mode
(alla xwris information elements sta beacons -IEs-, dld tha einai h
enabled gia olous h disabled gia olous, den tha yparxei plhroforia sto
beacon gia handling per-client klp). Gia ta fast frames epese h
protash na kanoume ena standards-compliant msdu aggregation (oxi dld
to proprietary fast frames aggregation ths Atheros) gia olous tous
drivers, opote kai tha akolouthoume to protypo kai tha exoun oloi oi
drivers kerdos apo ayto sto performance (arkei na mporoun na steiloun
megala frames sto hw).

Telos apofasisame na katarghsoume to noise reporting giati gia to
protocol stack einai axristo kai sth pragmatikothta den yparxei
kapoios standard tropos na metrhseis to noise (ousiastika osoi to
metrame -px ston ath5k- metrame px. to noise floor ths kartas h kati
antistoixo, den yparxei dld kapoios standard tropos na metriseis to
noise sto kanali -to utilization ap thn allh mporeis na to metrhseis
kai einai arketa xrhsimo alla out of scope gia thn wra-), eks allou to
signal strength pou kanoun report oi kartes lamvanei ypopsh to noise
(einai dbm panw ap' to thoryvo h kati antistoixo). Mexri loipon na
vroume kapoio standard tropo na kanoume handle to noise kai ena logo
gia na to xrhsimopoihsoume to petame ap' to API kai o kathe driver
mporei na to xrhismopoiei internaly (opws kanoume px. ston ath5k/ath9k
gia to calibration). Na kserete epishs oti to signal quality pou
vlepete sto iwconfig kai to network manager einai psilomoufa kai apla
xrhsimopoioume ena linear maping me to singal strength, gia na peite
kati gia to quality prepei na kserete kai alla xarakthristika (px. to
sensitivity ths kartas). Sth kalyterh periptwsh na exoume kapoia oria
ap' ton vendor pou syndeoun to signal strength me to rate (px. mas
leei o x vendor oti apo -68 kai panw h karta kleidwnei sta 54M opote
px. kanoume report 100% link quality).

Ekselikseis sto 802.11
---------------------------------
Eixame mia analytikh parousiash ap' ton Jouni gia tis ekselikseis sthn
IEEE kai ta drafts pou erxontai kathos kai tis allages pou prepei na
kanoume sto protocol stack gia na tis akolouthisoume. Gia leptomereies
thn parousiash tou Jouni mporeite na th vreite ki ayth sto wiki
(http://wireless.kernel.org/en/developers/Summits/Berlin-2009?action=AttachFile&do=view&target=ieee80211-activity.pdf),
epigramatika anaferw oti exoume kainouries protaseis gia gigabit
asyrmata diktya (wide band kata kyrio logo), to 802.11s (to mesh pou
isws na gnwrizete ap' to OLPC) exei kolhsei kai o chairman ths
epitrophs paraiththike (to draft mexri twra exei sovara provlhmata)
enw yparxoun anhsyxies oti paei gia founto, exoume mia protash gia
extension sto protokolo gia p2p links (dhladh oxi topologia BSS h IBSS
alla mia nea topologia optimized gia point to point links) kai polla
alla endiaferonta (de synexizw giati sas exw hdh priksei :P).


Ws synhthws an exete kapoia aporia h thelete kapoia dieykrinhsh eimai
sth diathesh sas. Elpizw na "paizoun" kala oi wireless drivers kai na
eiste eyxaristhmenoi apo to olo project ;-)

-- 
GPG ID: 0xD21DB2DB
As you read this post global entropy rises. Have Fun ;-)
Nick
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