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[Alexander Yohalas]

Xmmm, exw thn ais0hsh oti opoy na 'nai 0a moy thn pei o kyrios Iwannoy, alla...
Prwta- prwta, genika pio konta sthn pragmatikothta einai (fysika) o Ricudis.
Alla:
0. Allo Open Source, allo ely0ero gia ylopoish (enanti amoibhs gia dikaiwmata),
allo mystiko poy eite den jereis kan oti yparxei, eite den sto dinei kaneis gia
na to xrhsimopoihseis. To kata poso symfwneis 'h oxi me kapoies apo tis parapanw
praktikes einai allo kapelo.
Epishs, an plhrwseis  to V.90 de pairneis ena binary jero, pairneis tis
prodiagrafes gia na to ylopoihseis, an 0eleis. To binary to pairneis an
agoraseis etoimo ('h sxedon etoimo) pro'i'on apo tis etaireies, opote kai exeis
aytomata kai thn adeia xrhshs.


1. Sta modem (apo kapoio prwtokollo kai meta, nomizw apo to V.32 (9600) kai
meta) xrhsimopoieitai sympiesh, proairetika men, alla ej' orismoy (default)
einai energopoihmenh. An to modem sas grafei epanw toy 'h sto manual V42bis,
ayto shmainei  oti kanei to idio sympiesh se pragmatiko xrono opws dexetai ta
dedomena apo th seiriakh. Gi' ayto me ena modem 33600 mporeite na deite
pragmatikes taxythtes 4kbytes/s 'h kai ligo prarpanw, analoga me to ti dedomena
metadidontai. Epi pleon, to V.42 (sketo) shmainei oti h ekpomph kai lhpsh
ginetai me paketa HDLC, an ayto leei kati se kapoioys, gia dior0wsh la0wn
(epanekpomph) Mesa sto paketo HDLC pane ta (sympiesmena) dedomena.

2. To V.90 einai asymmetro- sthn pleyra toy promh0eyth yphresiwn erxetai ap'
ey0eias pshfiako shma, opws kai stelnetai. Den exei na kanei me diamorfwsh
fashs, ta dedomena stelnontai "wma" ana 7 bits se ka0e deigma "fwnhs" twn 8 bit.
Gia na mporei na stalei epityxws apaitei ka0arh pshfiakh grammh me konto sxetika
kalwdio apo to thl. kentro sto xrhsth. Sto modem toy xrhsth, xondrika milwntas,
to modem pairnei to shma kai to sygkrinei me 128 times anaforas kai analoga se
poia einai pio konta, ayth thn pshfiakh timh pairnei gia dedomena (7 bit).

3. Mia thlefwnikh grammh *mazi* me ta kyklwmata toy thl/koy kentroy exei eyros
zwnhs 300Hz- 3.5kHz, gia toys logoys poy egrapse o Ricudis. Sto thl/ko kentro
yparxei ena poly apotomo zwnoperato filtro poy afhnei na perasoyn oi parapanw
syxnothtes, wste na apofeyx0ei to legomeno aliasing kata th metatroph se
pshfiako. Ta pshfiaka deigmata, omws, *den* einai ADPCM, einai apla PCM me
metablhto bhma kbantishs- ta 8 bits  "isodynamoyn" (kai paragontai) apo 13bit
grammiko metatropea A/D. To ADPCM xrhsimopoiei th diafora ths kbantismenhs timhs
toy shmatos poy ypologizei o metatropeas A/D se sxesh me mia timh poy eixe
problepsei oti 0a eixe to shma me kapoio algori0mo problepshs kai stelnei aythn
(th diafora).
  Sketo to kalwdio anebainei perissotero, analoga me th diatomh toy, to mhkos
toy, thn katastash toy (na mhn exei ojeidw0ei), apo to ti eidoys diamorfwsh
xrhsimopoieis, klp.
  P.x. to ISDN katebazei 160kbps sto idio kalwdio (apo ta opoia ta 144 exei o
xrhsths). Gi' ayto aresei poly ston OTE, epeidh den xreiazetai na allajei thn
kalwdiwsh, poy einai makran to akribotero kommati enos thlepikoinwniakoy diktyoy
(= kostos kalwdiwn + kostos ergatikwn gia skapsimata, styloys kai, kai, kai...).
Gia ton idio logo se kapoies perioxes me liges perasmenes grammes, o OTE bazei
ta legomena PCM-4(ta feresyxna prepei na ta ebaze paliotera se analogika kentra
poy meta anaba0misthkan se pshfiaka).
Mia grammh ADSL anebazei poly- alla einai asymmetrh. Se ayth thn periptwsh den
empleketai ka0oloy o OTE, ektos, isws, me to oti mallon 0a toy anhkei to kalwdio
an exei monopwlio stis thlepikoinwnies ths xwras.
4. "Orologies" toy styl "dyfio" klp. den einai toy RAM, exoyn yio0eth0ei apo ton
OTE (kai to RAM), alla proerxontai apo ton ELOT, ton idio poy ftaiei gia th
shmerinh katantia twn 40 diaforetikwn "protypwn" gia ellhnikoys xarakthres stoys
ypologistes. Poy na deite thn ypoloiph orologia...Genika leitoyrgei me mia
ka0ysterhsh diadoshs 15 xronwn peripoy...

Syggnwmh gia to katebato, se mallon off-topic,
AlxUnderNet :-) 42

--
Alexander Yohalas, Computer Engineer
R ? D Dept., INTRACOM S.A.
P.O.Box 68, 19002 PEANIA, Attica GREECE
Phone: (+30 1)6690335 Fax: (+30 1)6860446



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