adsl apofthegmata

[V13]

Titlos: H poria mias ADSL

En arxh exoyme mia ADSL2+ apo 4net (ayto me ta 24Mbit).

Kefalaio 1 - Eisagogi:

* Kanoyme to speedtest kai dixnei taxytita to poly eos 700Kbps me synithes 
times giro sta 400-500Kbps. 

Kefalaio 2 - Mesa sto spiti:

* Pernoyme katsabidi, monotiki kai kati gia na mporoyme na pianoyme kalodia 
(p.x. pensa). To teleytaio xreiazetai eidika ean exoyme ADSL.

* Episkeptomaste ola ta shmeia me mprizes mesa sto spiti ta opoia den pernane 
apo ADSL filtro, h ta opoia einai sto dromo mexri to adsl modem. Anoigoyme 
tis mprizes, ftiaxnoyme opoiesdipote enoseis den fainontai kales, mononoyme 
otidipote gymno kai ta ksanaklinoyme.

* Episkeptomaste to shmeio sto opoio erxetai h grammh sto spiti (p.x. kapoio 
ntoyi) kai to anoigoyme gia na doyme ean exei kamia enosi h tipote gymno. 
Kanoyme kai ekei ta idia.

* Kanoyme to speedtest kai dixnei pleon stathero 1.5Mbps. Mia ayksisi 2-3 
fores.

Kefalaio 3 - Sth polykatikoikia

* Pernoyme ta idia synerga + fako kai katebenoyme sthn eisodo ths oikodomis

* Anoigoyme to 'koyti' toy OTE kai blepoyme oti kai ekei epikratei ena mikro 
xaos, alla oxi kati idiaitero.

* Me magika kolpa briskoyme poio apo ta kalodia afora emas. Pithanos tropos 
einai to bale-bgale kalodia mexri na mas kopei to tilefono. Ean exete ena 
polymetro kai ISDN mporeite na metrisete th tasi sta zeygaria kai na deite 
poio exei megaliteri tasi (Sth periptosi moy ta kanonika eixan 50V kai to 
ISDN 90V)

* Elegxete opoiesdipote enoseis den fainontai sostes, sfigkete *ligo* tis 
bides klp. Ean deite opoiodipote gymno shmeio sto syrma sas, eite to mononete 
(ean einai endiamesa), eite to bidonete kalitera (ean einai sto akro). 
Elegxete gia pithanes enoseis sto diko sas syrma kai frontizete na tis 
beltiosete ean xreiazetai kati tetoio. Telos, mononete opoiadipote enosi.

* (Extra bonus #1) Apomakrynete pithana alla gymna syrmata apo ta dika sas 
oste na min dimioyrgoyn parasita

* (Extra bonus #2) Mononete ta akra (kapoia mporoyn na monothoyn) oste na min 
yparxoyn parasita stis enoseis

* Epistrefete kai elegxete to speedtest. Me xara blepete oti tora bgazei 
4-5Mbps stathera.

Kefalaio 3 - Paratiriseis:

* !!!PROSOXI!!! TA KALODIA TOY OTE EXOYN *REYMA*, EIDIKA EAN EXETE ISDN. MHN 
TA PIASETE ME TO XERI. XREIAZESTE PENSES H KATI ALLO. 90V EINAI ARKETA GIA NA 
ENERGOPOIHTHOYN/TINAXTOYN MONOI TOYS OI MYS SAS KAI NA PESETE APO TH SKALA 
POY EISTE!!!

* Ta panta ta kanete me DIKIA SAS EYTHYNH! Exo thn entyposi pos o OTE den tha 
xarei idiaitera an balete xeri sta kalodia toy. Mporei na einai kai en meri 
paranomo, eidika ean mpleksete kai me toys ypoloipoys ths oikodomhs. Ektos 
apo ta ergalia, xreiazeste kai ena kalo epixeirima toy styl: "Exo Internet 
kai monono ta kalodia gia na beltioso th poiotita" etoimo (kati poy na to 
katalabainei kapoios eykola, alla na einai kai arketa texniko), oste otan 
perasei kapoios apo thn eisodo ths oikodomis kai sas rotisei, na min minei me 
tin entyposi pos tin epomeni fora poy den tha doylevei to tilefono toy, h poy 
h ADSL toy tha exei problima, tha ftete eseis.

Parartima A - Dieykriniseis:

* Ta 4Mbps apo to speedtest einai sth praksi giro sta 7-8Mbps taxytitas 
exontas synypologisei to overhead. Min prospathisete na to ypologisete me 
prakseis toy styl MTU+header*compression-ratio+FPA giati den exei noima kati 
tetoio. Epeidi yparxei arketo packet loss, yparxoyn para polla 
retransmissions, opote kai xanete arketo BW apo ekei. To whireshark ths 
geitonias sas tha sas diksei gia posa retransmissions milame.

* To pragmatiko delay mporeite na to metrisete me xrisi toy SNMP, ean 
ypostirizei kati tetoio o router sas, h apeytheias apo ton ypologisti, ean to 
ppp termatizetai ston ypologisth.

* Epeidi akribos h perissoteri kinisi poy kanoyme einai TCP kai epeidi exoyme 
packet loss kai arketa ypsilo delay, san kala paidia poy eimaste afieronoyme 
ena Linux mixanima poy exoyme monima sto Internet gia na doylevei san proxy 
(squid). Se ayto dinoyme:
echo "scalable" > /proc/sys/net/ipv4/tcp_congestion_control
Enalaktika, mporoyme na xrisimopoihsoyme kai ton 'hybla'.

Me to tropo ayto yparxei periptosi na exoyme aisthita kaliteres epidoseis pano 
apo th idia ADSL grammi. Se emena me delay 42ms mexri ton proxy kai me mh 
mhdeniko packet loss, h diafora itan aisthith. Fysika o proxy prepei na'xei 
arketo bw oste na katebazei me th taxytita poy theloyme na mas ta stelnei 
(p.x. na einai mesa sto EDET).

... hope it helps ...

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