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a blog about sound & signals by windytan [oona räisänen]

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The sound of the dialup, pictured

by [9]Oona Räisänen Saturday, November 17, 2012

If you ever connected to the Internet before the 2000s, you probably
remember that it made a peculiar sound. But despite becoming so
familiar, it remained a mystery for most of us. What do these sounds
mean?
[HTML5 audio: In-line recording of the beginning of a telephone call
made by a modem.]

(The audio was recorded by [10]William Termini on his iMac G3.)

As many already know, what you're hearing is often called a handshake,
the start of a telephone conversation between two modems. The modems
are trying to find a common language and determine the weaknesses of
the telephone channel originally meant for human speech.

Below is a spectrogram of the handshake audio. I've labeled some
signals according to which party transmitted them, and also put a
concise explanation below.
[11][Image: A large infographic detailing the phases of the dialup
handshake, centered on a time-frequency-power representation
(spectrogram).]

(You can order this poster as a high-res print via [12]Redbubble!)

Hello, is this a modem?

The first thing we hear in this example is a dial tone, the same tone
you would hear when picking up your landline phone. The modem now knows
it's connected to a phone line and can dial a number. The number is
signaled to the network using Dual-Tone Multi-Frequency signaling, or
DTMF, the same sounds a telephone makes when dialing a number.

The remote modem answers with a distinct tone that our calling modem
can recognize. They then exchange short bursts of binary data to assess
what kind of protocol is appropriate. This is called a V.8 bis
transaction.

Suppressing echoes

Now the modems must address the problem of echo suppression. When
humans talk, only one of them is usually talking while the other one
listens. The telephone network exploits this fact and temporarily
silences the return channel to suppress any confusing echoes of the
talker's own voice.

Modems don't like this at all, as they can very well talk at the same
time (it's called full-duplex). The answering modem now puts on a
special answer tone that will disable any echo suppression circuits on
the line. The tone also has periodic "snaps" (180° phase transitions)
that aim to disable yet another type of circuit called echo canceller.

Finding a suitable modulation

Now the modems will list their supported modulation modes and try to
find one that both know. They also probe the line with test tones to
see how it responds to tones of different frequencies, and how much it
attenuates the signal. They exchange their test results and decide a
speed that is suitable for the line.

Enough small talk!

After this, the modems will go to scrambled data. They put their data
through a special scrambling formula before transmission to make its
power distribution more even and to make sure there are no patterns
that are suboptimal for transfer. They listen to each other sending a
series of binary 1's and adjust their equalizers to optimally shape the
incoming signal.

Soon after this, the modem speaker will go silent and data can be put
through the connection.

But why?

Why was it audible? Why not, one could ask. Back in the days, telephone
lines were used for audio. The first modems even used the telephone
receiver like humans do, by [13]talking into the mouthpiece, until
newer modems were developed that could directly connect into the phone
line. Even then, the idea of not hearing what's happening on a phone
line you're calling on was quite new, and modems would default to
exposing the user to the handshake audio. And in case you accidentally
called a human, you would still have time to pick up the telephone and
explain the situation.

All you had to do to silence the handshake was to send the command ATM0
down the serial line before dialing.

Poster

Update 02/2013: Due to numerous requests, I made this into a
42-megapixel poster that [14]Redbubble is selling. A few dollars per
poster is directed to the nerd who made this.

Labels: [15]infodump, [16]signals
[17]<- Newer Post [18]Older Post ->

92 comments:

1. [19]Steve Ruiz[20]30 January, 2013 16:25
Thank you for illuminating one of the mysteries of my past. Very
interesting stuff.
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1. [22]Oona Räisänen[23]30 January, 2013 18:03
You're welcome! Thanks for reading!
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2. Anonymous[25]01 February, 2013 14:10
Thank you for this amazing amount of effort to explain that
handshake sequence! I can't say it's been keeping me up at
night, but the detailed diagram showing each part of the
handshake sequence is beautiful!
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3. Anonymous[27]04 February, 2013 12:52
It's so odd... I used to hate this sound when I got my first
PC. I used to try and find ways to either turn it down or turn
it off altogether... of course, you couldn't. Not really. But
as time went on, I got used to it. Kind of like when you sign
on to your computer and the OS greets you with a noise or a
song. It was like the Pavlov's Dogs, and I got used to
listening for those sounds. You could actually tell if your
connection was going to be good or bad (ie, none at all) by
the way the sound was modulating.
That sound, to me, is like the sound of an old school
typewriter. It's primitive, it's annoying, but I do so miss
that kind of feed-back in the here and now! Classic stuff.
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4. [29]Unknown[30]05 June, 2016 14:30
Its quite fun, because the mother of our now (and one not
longer a teenager) could hear from the handshake tones who was
dialing in. It was a serious distinct handshake. And since I
used a USR Courier v.everything and most dialers used Supra
and other modems, it was quite easy to hear who connected. The
(in the last days of dial up) USR Sportster 14400 could easily
be upgraded to 28800bps. But it took the black Sportster to
cope to "56k". (v.fast and k56flex).
Also the USR Courier V.everything had a set of unpublished
commands to measure the line quality. Found them when doing a
backup. ATYnn is undocumented. Spectral analysis of line
quality.
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5. [32]scaper8[33]03 October, 2017 18:39
Jason George,
I understand what you mean. Personally, I never found it
grating from the start, rather mysterious and transcendent.
Like the language of the gods. But I do certainly know the
feeling of anticipation in hearing it.
A little sad that will never know that sound (or a typewriter
or even a desktop keyboard) anymore. Makes me a good bit
wistful.
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2. Anonymous[35]30 January, 2013 16:36
You make modems sound so polite. Please this, please that. ;)
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3. Anonymous[37]30 January, 2013 17:38
I'm going to have to start hard coding please and thank you into my
software from now on...
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4. Anonymous[39]30 January, 2013 18:09
A walk down tech memory lane... this time with a guide :)
Thanks for this smile.
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5. [41]Matt[42]30 January, 2013 18:15
So, would you like to sell a poster of that? Because I'd like to
buy it.
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1. [44]Unknown[45]30 January, 2013 23:43
I would also be interested.
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2. [47]Oona Räisänen[48]03 February, 2013 17:47
[49]RedBubble is selling it now.
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6. [51]Tim[52]30 January, 2013 19:02
So interesting! Thanks for the insight into this forgotten part of
the Internet!
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7. Anonymous[54]30 January, 2013 20:15
Beautiful. Absolutely, fantastically, nostalgically beautiful!
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8. [56]Unknown[57]30 January, 2013 20:20
Thanks for this article, I really enjoyed it and the accompanying
image!
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9. [59]Unknown[60]30 January, 2013 23:41
What program did you use to generate the spectrogram?
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1. [62]Oona Räisänen[63]30 January, 2013 23:58
Baudline by SigBlips. Also Gimp and other image
postprocessing.
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2. [65]baudline[66]02 February, 2013 02:19
I thought I recognized that particular shade of
baudline-green. (:
What an awesome signal analysis job you have done. You broke
it down, demodulated parts, decoded bits, and understood a
crazy handshake protocol. It must of been a lot of work. I am
beyond impressed. Wow!
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3. [68]Oona Räisänen[69]04 February, 2013 23:14
Thank you! It was a fascinating journey indeed.
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10. [71]adam j. sontag[72]31 January, 2013 04:28
Thanks for making this. I really enjoyed being able to match the
"names to faces," so to speak. I made a simple jsbin version of the
spectrograph with a "playhead" overlaid so you can see what is
being played when, and click around as well.
http://jsbin.com/amunug/17
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1. Anonymous[74]02 February, 2013 02:54
Very cool mashup, just what I was hoping for! Thanks for
sharing!
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11. [76]Steven Huang[77]31 January, 2013 07:04
Modem A: hey babe, you dtmf?
Modem B: u know it
Modem A: what u up 4 2nite? wanna v.8?
Modem B: i wanna ack u like my daddy net2phone use 2 ack me
Modem A: um ok... v.8 then
Modem B: lol jk, u comin?
Modem A: brt just gotta turn off echo suppressors n cancellers
Modem B: ok i wait
Modem B: my pcm is so modulated
Modem A: lol rly? u think u can handle V.90/V.92?
Modem B: D/A?
Modem A: ...D?
Modem B: wtf no, im not into that
Modem A: lol jk we can do V.42 LAPM if u want im down 4 nething
Modem A: up to 3429 o/c
Modem A: u know i give as good as i get, ne way u want it, loud or
soft, high or low, fast or slow, i got all the time in the world 4
u babe, my clock source is internal
Modem B: of course no 3429. and same 4 me. except i might lose
track of time, lol
Modem B: and honey if u with me we gon be makin sum NOISE
Modem B: 6db at LEAST u know how i like it
Modem A: lol i hear ya, 3200 all nite long, the way u get me goin
maybe we even go 2 4800 lol
Modem A: set ur pre-emphasis filter params n put on that 1920 hz
carrier frequency i got u
Modem A: im here baby
[SCRAMBLED]
-ultimat142
http://www.reddit.com/r/programming/comments/17jwoi/dialup_handshak
e_explained/c86evsf
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1. [79]Oona Räisänen[80]31 January, 2013 07:35
This is golden.
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12. [82]Unknown[83]31 January, 2013 09:12
Very cool! I'm wondering, did you just look up the conversation
data or did you use something to sniff the data off of the modem
line?
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1. [85]Oona Räisänen[86]31 January, 2013 09:20
I wrote a few Perl scripts to demodulate the FSK and DPSK,
then manually decoded the bits based on the relevant ITU-T
standards.
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2. Anonymous[88]31 January, 2013 22:19
Great work! Can I trade my brain for yours? ( It's only very
slightly used )
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3. [90]Oona Räisänen[91]01 February, 2013 08:55
My brain isn't that great :D
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13. [93]DavidDawesFXA[94]31 January, 2013 14:58
Very nice work! Takes me back to the 90s when I first started using
dialup :-)
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1. [96]Zach[97]31 January, 2013 23:06
Takes me back to the mid-80s when I could distinguish connect
speed by ear (at least 1200, 2400, and 9600). Ahh, the days of
listening to Telemate auto-redial the busy BBS number. ;-)
Thank goodness we no longer need to worry about line
noi230t9uc!%!f3333
NO CARRIER
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14. [99]BKR[100]31 January, 2013 18:47
Awesome. I remember working phone support in the 90's for dialup
internet users. I would sometimes have people hold their phone up
to the modem so I could listen to the handshake, but I never knew
exactly what the various parts were for. Thanks!
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15. Anonymous[102]01 February, 2013 00:15
Hi,
great! Thanks for sharing this. What about doing something similar
for DSL line handshaking:
"The ITU-T has recently standardized a handshake and activation
method for xDSL modems. This method is
contained in the ITU-T Recommendation G.944.1 (formerly known as
G.hs). Several of the features of
G.994.1 came from the voiceband handshake Recommendations V.8 and
V.8bis,"
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16. Anonymous[104]01 February, 2013 05:59
Thank you Oona from a mother of an Ouma - that was fun to read
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17. [106]Unknown[107]01 February, 2013 08:31
This sounds like US signaling. We had totally different in Europe
and former USSR.
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1. [109]Oona Räisänen[110]01 February, 2013 08:43
It is indeed a U.S. dialtone.
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18. [112]Luc[113]01 February, 2013 16:23
Thanks for making me feel old...
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19. [115]Funkytone[116]01 February, 2013 20:25
Thanks for such a nostalgic read! I think I just played the sound
clip about 20 times. I would love to print a large format poster of
the spectrogram with all your notes and put it up in my office.
Would you mind sending me a high-res version that would print
really clear? A vector version if you have it is best?
Thanks in advance!
Tony
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20. [118]Unknown[119]02 February, 2013 01:28
Dear Oona Räisänen
your lastname must sound a bit like the krrrBliipkrraaa sounds of
my good old modem of mine carefully chucked in a box in the cellar.
But what an interesting and great article !
thank you !
Edualc
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21. [121]Longshiren[122]02 February, 2013 20:23
Thank you, Oona. This brought back fond memories.
My first modem use was in 1979 with 300 Bps and then in 1981 with
1200 Bps. In the late 1980s I used a 2400 Bps modem for the first
time and loved it. The move to actual Kbps speeds and then digital
modems, and then routers were all just normal parts of an evolving
network. But I realized I missed the modems' sounds and
control/handshake sequences, which allowed an engineer to more
closely follow and understand the data transmission process.
We've coma a long way, and we should capture this kind of thing to
remind us of the journey.
Again, immense thanks.
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1. [124]Oona Räisänen[125]03 February, 2013 21:49
My pleasure!
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22. Anonymous[127]04 February, 2013 23:04
I remember when I got my first 2400 baud modem @ an amiga show in
NY, it was between that or a digiview video digitizer. Best
purchase I ever made. I also remember when my friend bought a 14.4
baud modem, those days it was crazy fast! ah the memories BBSing
late into the night, of board games and war games dialers.. those
were the days..
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1. [129]Oona Räisänen[130]06 February, 2013 15:06
Yeah, 33.6 was a superhighway compared to 2.4. I couldn't have
imagined text flowing so fast.
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23. Anonymous[132]12 February, 2013 00:29
Terrific! The infographic is great - those conversation 'balloons'
really help to understand what's happening. Thank you!
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24. [134]Bart[135]12 February, 2013 05:12
I have created a moving-pictures version of the above here:
[136]http://youtu.be/qEPIoyYB8hc
Thanks for the inspiration.
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1. [138]Oona Räisänen[139]12 February, 2013 10:20
Great! Also there's this one
[140]http://www.youtube.com/watch?v=dSxgCVc6wcM
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25. [142]Unknown[143]21 February, 2013 07:25
Found this from a post on imgur. I actually use this same sound
clip as my morning alarm haha. I alaways wanted to know what it all
meant. Thanks formaking this. :)
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1. [145]Oona Räisänen[146]21 February, 2013 07:37
Imgurians unite!
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26. [148]Anon_77[149]01 April, 2013 16:11
Just read about this on HAD, really interesting stuff. I actually
have this as my ringtone. Leads to a few strange looks but also
gets some smiles from the people old enough to remember dialup
internet. :) . I really wish there were a lot more girl geeks out
there. Thank-you for a really enjoyable read. :) Jon W
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1. [151]Oona Räisänen[152]26 April, 2013 21:08
Thanks for reading! I also had it as a ringtone for some time,
gave me some true old-skool street cred.
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27. [154]Unknown[155]26 April, 2013 20:12
This is a really good read for me. I just found your website a few
days ago and I have been reading through it regularly. Thanks a lot
for enjoying this beauty blog with me
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1. [157]Oona Räisänen[158]26 April, 2013 21:05
Thank you, made me happy!
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28. [160]Silver[161]10 August, 2013 20:44
Thank you for a great post! I remember the moment that my boyfriend
and I learned that acoustically coupled 300 baud modems can't parse
the sound of a vacuum cleaner. It did try! Screen after screen of
garbage!
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29. [163]quantumdude[164]13 October, 2013 18:58
I think there's a few issues with the labelling (as far as which is
sent by the calling modem and which by the answering modem). In the
V.8bis transaction CL is sent from the answering modem, NOT the
calling modem (so the MS and ACK(1) packets are sent by the other
modem as well). Also, it seems as if the phase 2 labelling was
referenced from the V.34 standard (which V.90/92 is based on).
However, in V.90, these "roles" are often reversed (based on which
modem is analog and which is digital) - this can be verified as to
which wide-spectrum probing signal is "sharper" (because it's the
one being sent by the calling modem).
Don't get me wrong, I love this post - it's inspired me to learn
all the different V-series standards and try to build my own dialup
modem!
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1. [166]Oona Räisänen[167]14 October, 2013 11:23
Cool, thanks for actually taking the time and reviewing this!
:) I've been wondering why no-one has pointed out any
mistakes. Maybe I should make a bugfix version in the future.
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2. [169]quantumdude[170]14 October, 2013 11:26
No problem :)
(also, I noticed that the very last chunk of noise is actually
an Sd to Sd-bar to TRN1d since the digital modem doesn't use
QAM, but that's probably a minor point anyway, considering
it's all visually uninteresting noise :P)
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30. [172]Hermes Serrano[173]12 November, 2013 15:34
Hi Oona,
You are awsome !
Thanks a lot for enlighting us!
Kind Regards from Barcelona, Spain.
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31. Anonymous[175]13 November, 2013 17:55
I have to say that this has got to be the most detailed discretion
of modem handshaking that I've ever seen. Thank you for making this
pic, so cool!!
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32. Minerva[177]24 November, 2013 17:13
You have an awesome blog! This post really gave me the fuzzies - I
remembered the days of dialing into BBS's with my brand new 14k bps
modem. Never realized that what sounded to me like random beeps and
fizzes was actually my modem having a civilized conversation!
Thanks!
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33. [179]Unknown[180]02 February, 2014 18:12
I still hear this sound in my dreams. I remember I could tell the
connection speed after hearing the handshake. Travelled all over
the world from home, (BBB=Bergen-by-Byte, anyone?), and it ended up
as my iPhone ringtone at some point. Thank you for the remembrance!
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34. [182]Unknown[183]10 July, 2014 03:52
I remember calling my friend's house to play some Doom. His mother
would always pick up the phone and I'd listen to them argue over
the sound of a lonely handshake attempt. Thanks for the memories
and great info.
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35. Anonymous[185]26 January, 2015 14:25
Wow! In 30 years of using computers, I've never seen an article on
modems as beautifully written as this! Many thanks for educating
us.
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36. [187]ECBAleixo[188]09 March, 2015 20:58
Thanks Oona Räisänen! Beautifull & inspiring work
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37. [190]El quinto Istarí[191]10 March, 2015 19:34
Oonaa: Can you believe that in Cuba, we still use Modem to acces
Internet (at best), Intranet, and local e-mail servers !! This
sound you described and explained brilliantly it is still (2015) a
sound that millions of people in Cuba long to hear @ home. Cuba
have one of the lowers internet penetration index
(http://www.internetworldstats.com/carib.htm#cu). The mean download
velocity is 1,28 Mbps. Unfortunately, this sound is not part of our
latest technological history :(
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38. [193]Unknown[194]25 July, 2015 10:57
OK, I just had a flashback. Wasn't there a version of the handshake
that did a 'bong' twice? Was that a USRobotics version?
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1. [196]quantumdude[197]12 August, 2015 15:11
That 2x 'bong' is the DIL signal of V.90, which is a
more-or-less modem-specific signal. But yes, I believe it's
the USRobotics version.
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39. Anonymous[199]23 August, 2015 02:53
These are amazing memories from very good old times. Very
interesting article about the handshake modem sound. Thanks for
sharing!!! ^_^
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40. [201]Rocky Lien[202]21 March, 2016 16:00
This is a long time coming: thank you for the scientific and
artistic work you put into this. I bought a copy of the poster
about a year ago and just recently completed the project I imagined
when I first saw this post.
I cut a larger poster frame to size and mounted the poster. Then,
using a greeting card sound module (happy mistake choosing that!
More on this in a moment) recorded the sound directly from the link
in the article above. When I first listened to the sound clip,
something sounded off. After recording it on the sound module and
listening to it via the cheap speaker, I realized that the sound
quality from my computer speakers gave that familiar old sound an
unnatural quality. The sound module more or less recreated the
quality of sound that came from the modem speaker.
Sound module source:
http://bigdawgspromo.com/push-button-prerecorded.html
Here's a link to a video of my final result. My phone kept focusing
on the reflection of my kids' artwork on the next wall!
https://goo.gl/photos/gbxAb9gsmCbGkTzf9
With either a bigger budget or greater artistic talent, I'm sure a
more impressive result could be found but this is what I ended up
with and I'm happy to have it on my wall. Thank you, Oona, for your
contribution and sparking the thought of doing this!
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41. [204]Keith Monahan[205]13 July, 2016 23:55
From reddit, Fantastic analysis of this! I've heard of people
hating this sound, but it's always been beautiful to me. I grew up
with simple 300 baud initially, just simple FSK. To hear things
progress, and as better/more efficient modulations came out as time
went on, this was literally music to my ears.
I always had my modem audio on for the handshake. The better modems
even had a volume slider. For the WHY portion, you're probably not
going far enough in what you said. Since many times, when calling
BBSs and services (like Compuserve, Delphi, or Prodigy), you were
often calling blindly. You got the number somewhere, but mistakes
were common, BBS numbers were mixed with fax numbers, and voice
numbers. I used to hear voices or fax tones (which are easily
distinguishable from straight-modems) and you'd know something went
wrong. Otherwise, you're just waiting about 30-45 seconds for a
"Connect 1200" or other similar message to appear. It's boring, so
why not listen to the handshake in case something cropped up.
Also, you learned to "troubleshoot" the modem connection.
Sometimes, due to poor quality phone lines, you could hear it
"refuse" the faster connection rates, and the extra long training
phase you knew it was going to be slow. That's useful information!
Great job, again.
From Pittsburgh, Pennsylvania,
keith at techtravels.org
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42. [207]Oli White[208]16 October, 2016 02:10
Found your vid on youtube while trying to teach a youngster about
what DUN is. Came across this website in the comments and very
happy! Definite bookmarking and sharing material!
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43. [210]Zidders Roofurry[211]17 February, 2017 00:44
My super-eggheady friend once knew someone who could complete a
handshake via whistling.
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44. Anonymous[213]10 March, 2017 12:45
Great stuff!
Question, V.32-modems or for instance V.34-modems were using
carrier frequencies like 1800 Hz or so for sending the data. Why is
it we're not seeing and hearing this carrier frequency when the
modems are sending and receiving data after closure of the
handshake-procedure, but just a lot of noise in every frequency
band between 0 - 4 kHz?
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1. [215]quantumdude[216]11 March, 2017 15:28
In a way, you are hearing just the carrier, but its amplitude
and phase are varying so much so fast that it creates other
frequencies around the carrier. This is due to mathematical
properties of sines. The appearance of noise is just our
inability to track the modulation at such a high speed.
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45. [218]Iogarchi[219]31 March, 2017 20:59
Thank you so much for share the picture and your explanation about
the language of the modems I used once before. I always wanted to
know about it. Thank you.
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46. [221]Marcel[222]08 July, 2018 17:38
Why do they include quality information about 3429, if neither
supports it? Or am I misunderstanding anything?
Reply[223]Delete
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1. [224]Oona Räisänen[225]09 July, 2018 15:55
Hi, if I remember correctly the list of symbol rates is always
the same length, independent of what the parties claim to
support, for the sake of simplicity in the protocol. No
additional logic is needed to determine how many bits should
be read from that field.
[226]Delete
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47. Anonymous[227]25 January, 2019 02:51
What is the allowable delay time from connection to the initial V.8
bis transaction? I see it is almost instantaneous in your example.
What if the delay is 11 seconds or more before the answering modem
starts the V.8? Can this be configured?
Reply[228]Delete
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48. [229]Quentin Cranthorpe[230]23 March, 2019 22:40
This is fascinating, thank you for sharing!
How does this compare with DSL signalling, do those modems have a
similar handshake?
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49. Anonymous[232]22 July, 2019 11:40
I recall later modems producing a "boing boing" sound but it's not
present in this recording. Do you know what that was? One Reddit
post says it was part of the probing signal.
Reply[233]Delete
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1. [234]quantumdude[235]23 July, 2019 01:12
If I understand what you're referring to, it's called Digital
Impairment Learning, and is used by digital v.9x modems to
check for things like robbed-bit signalling that could corrupt
PCM samples (see
https://goughlui.com/2016/05/03/project-the-definitive-collect
ion-of-v-90v-92-modem-sounds/).
[236]Delete
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2. [237]Unknown[238]11 February, 2020 14:25
Yeah, it's a DIL, and actually I wanted to mention something
about this. The audio is definitely a V.90 connection because
of V.8bis handshake and the audio from the answering modem in
the end, which I believe is a scrambled data in PCM. I mean,
it's completely different from a TCM noise so it's definitely
not a V.34 handshake.
Regarding that, I would mention that the first wave sent by a
client modem in Phase 3 is not just a scrambled data, but some
other useful signals and most importantly - the DIL
descriptor, called Ja in a V.90 protocol. The digital modem
receives it, sends some other data (including some scrambled),
and then, as soon as it receives a signal from client modem,
it starts to play DIL sequence. Yeah, the trick is - this
"bong bong" sound is not played by YOUR modem, but instead
it's played by your ISP modem which is interesting. Also
different modems have different DIL sequences which means
different sounds.
[239]Delete
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50. [240]Al Lowe[241]10 May, 2020 09:45
Am I the only one who looked up the code to make the modem dial
faster? (Was it S11?) Anyway, thanks for the memory trip!
AL
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51. Anonymous[243]20 July, 2020 09:02
Many thanks for this post, I always wondered what the tones meant!
Reply[244]Delete
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52. Anonymous[245]11 June, 2021 19:27
I suggest setting the explanation as lyrics to a song. The ballad
of the lonely modem. 28k unrequited.
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53. [247]Markus[248]14 June, 2021 23:44
Ah, sweet memories of teenage years spent in a university library
studying the V-series recommendations volume of the CCITT Blue Book
(before they were renamed into ITU-T).
Reply[249]Delete
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54. Anonymous[250]18 July, 2021 19:36
I've actually followed your blog since this post, time flies!
Reply[251]Delete
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1. [252]Oona Räisänen[253]19 July, 2021 23:04
Thanks for sticking along :)
[254]Delete
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55. Anonymous[255]31 January, 2022 17:02
"All you had to do to silence the handshake was to send the command
ATM0 down the serial line before dialing."
i learned this 25 years too late...
Reply[256]Delete
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56. Anonymous[257]17 May, 2022 12:35
Couldn't remember what brought me here. But it certainly brings
back a lot of good memories. Thank you very very much
Reply[258]Delete
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57. Anonymous[259]24 May, 2022 00:11
Three hours down the rabbit hole of reading about what
10-year-old-me considered magic. Life Is fantastic
Reply[260]Delete
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58. Shane[261]17 November, 2022 06:09
It was really cool to have someone explain this. I always wondered
what the sounds really meant. OP thank you for taking the time to
explain it the way you did and to make graphics to go with it.
Really awesome.
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59. Anonymous[263]12 January, 2023 11:25
Thank you for a great diagram. I reexamined it with the sound
played many times.
Reply[264]Delete
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60. Anonymous[265]13 January, 2023 22:57
It would be really awesome if I could click on the waveform image
and just hear what that portion sounds like.
But it's still awesome! Thanks a bunch!
300 baud? FAX handshake maybe in the future?
Reply[266]Delete
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1. [267]Oona Räisänen[268]13 January, 2023 23:55
Thanks! Some kind of interactivity has been often requested
and I've been thinking of how to realize that, maybe in the
form of a video :)
[269]Delete
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