Šiandieninė klausimų ir atsakymų sesija ateina pas mus "SuperUser" - "Stack Exchange", "Q &A" interneto svetainių grupių bendruomenės, padalinys.
Nors dial-up modemo naudojimas gali būti sumažėjęs nuo beveik 100% rinkos prisotinimo 1990-aisiais iki tik 10% dabartinių JAV interneto vartotojų, prisijungimo modemo garsas visur gyvena geeks prisiminimuose. Šią savaitę mes pažvelgsime į triukšmingo proceso technologiją ir tai, kas būtent įvyko, kai renkate internetinę sesiją.
Klausimas
SuperUser skaitytojas Celeritas kelia klausimą, be abejo, milijonai žmonių savęs paklausė per metus:
I know that the signal was just tone pulses but why was it when (back in the 90s) when you first connected to the internet you heard a bunch of funny noises. After that if you were to use the internet, it still was using the telephone line, why no funny noises then?
Kodėl iš tikrųjų? Kas vyksta triukšmingoje dalyje ir kodėl po to kyla tyla?
Atsakymai
Keletas "SuperUser" autorių atsakė už mus. Scott Chamberlain rašo:
Modems originally allowed you to send data over a network that was designed to only carry voice. Because of that, the communication method between two modems had to be in the audible hearing range (or it would not get carried on the phone line). This is no longer needed because the phone system can now carry both voice and data at the same time (DSL).
The sounds were there all the time, you just needed to pick up the phone to hear it. The reason they played it over a loudspeaker to start with is so you could hear if somthing went wrong with the connection (busy signal, wrong number, a person picked up instead of a modem on the other end, etc).
Tylerl išsiplėtė ir paaiškina, kaip galite manipuliuoti savo modemu, kad jis būtų trumpesnis:
The whistles and chirps and buzzes that you hear when a modem is going through its initial handshake process is a test of the telephone line quality. A modem send precisely specified sounds and the other listens see what it actually hears on the other end. This way the modems know how clear the line is between them and what sort of frequencies they can use to communicate with each other. The more frequencies they can use and the lower the noise, the higher the speed they’ll be able to communicate at.
If a connection ever failed due to connection quality, it would generally fail during this initial handshake process. And if you were listening, you could usually tell why (e.g. you got an answering machine on the other end instead of a modem).
As such, modems were usually configured to play this handshake sequence out loud. This was configured by sending AT M1 to the modem during setup. Alternately, AT M2 means to leave the speaker on all the time, while AT M0 means don’t turn the speaker on at all. See the AT command set for more information.
The actual transmission noise that you would hear if you picked up the phone during an active session (as opposed to during this handshake procedure) just sounds like static.
O magija AT M0; atradau, kad tokia komanda buvo panaši į tai, kad buvo atidaryta nematoma apsiausta, slapta vakarinė nakties naršymas visiems. Nors Tylerl pažymi, kad didelės spartos srautas skamba kaip statinis, "Contributor Supercat" pažymi, kad labai mažai bodu modemai buvo kitokia istorija:
At 300 baud, it’s possible to audibly hear incoming data. On occasions, I’ve turned on the modem speaker if I wanted to hear when characters arrived on a generally-idle line. Higher baud rates use a “data-scrambler” circuit so that most patterns of data are no longer audibly distinguishable.
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