Sesi Tanya & Jawab Hari ini hadir untuk memberi kami SuperUser - subdivisi Stack Exchange, pengelompokan komunitas situs web Tanya-Jawab.
Sementara penggunaan modem dial-up mungkin turun dari kejenuhan pasar hampir 100% pada 1990-an menjadi hanya 10% dari pengguna internet AS saat ini, suara modem dial-up yang menghubungkan hidup di dalam kenangan orang-orang aneh di mana-mana. Minggu ini kami melihat teknologi di balik proses berisik dan apa yang sebenarnya terjadi ketika Anda menghubungi sesi internet Anda.
Pertanyaan
Pembaca SuperUser Celeritas mengajukan pertanyaan yang pasti jutaan orang telah bertanya pada diri sendiri selama bertahun-tahun:
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?
Kenapa memang begitu? Apa yang terjadi selama bagian yang berisik dan mengapa keheningan sesudahnya?
Jawaban
Beberapa kontributor SuperUser menyempurnakan jawaban untuk kami. Scott Chamberlain menulis:
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 memperluas itu dan menjelaskan bagaimana Anda dapat memanipulasi modem Anda untuk melakukan pipe down:
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.
Oh keajaiban AT M0; menemukan bahwa perintah itu seperti diberi penjelajahan larut malam akhir yang tidak terlihat dari jelajah untuk semua orang. Sementara Tylerl mencatat bahwa suara lalu lintas tinggi-baud sama seperti statis, kontributor Supercat mencatat bahwa modem yang sangat rendah baud adalah cerita yang berbeda:
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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