Author Topic: Modem Handshake  (Read 4783 times)

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Offline johnwa

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Modem Handshake
« on: February 01, 2013, 06:35:26 am »
Saw this on hackaday, thought it might be of interest:

http://hackadaycom.files.wordpress.com/2013/01/dial-up-handshake-infographic.png

I can remember reading basic descriptions of how 300BPS FSK modems worked, but for a long time no-one seemed to know anything about how the higher speeds operated.

It would be interesting to see a series of these spectrograms showing the different speeds at work, and the evolution of the handshake. Perhaps I will see if I can dig a few old modems out of the cupboard this weekend.

Note the US dial tone in the image.
 

Offline amyk

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Re: Modem Handshake
« Reply #1 on: February 01, 2013, 09:13:23 am »
They're all here:
http://www.itu.int/rec/T-REC-V/en

V.90 and V.92 are relevant if you're looking at the highest speeds available over PSTN.
 

Offline jerry507

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Re: Modem Handshake
« Reply #2 on: February 01, 2013, 03:40:51 pm »
Very cool graphic!
 

Offline jeroen74

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Re: Modem Handshake
« Reply #3 on: February 01, 2013, 09:04:00 pm »
Interesting, if you only have little data to send, it can actually be much quicker to use 300 baud :)
 

Offline johnwa

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Re: Modem Handshake
« Reply #4 on: February 02, 2013, 12:05:08 pm »
They're all here:
http://www.itu.int/rec/T-REC-V/en

V.90 and V.92 are relevant if you're looking at the highest speeds available over PSTN.

Nice, and downloadable for free by the looks of it too, I might have to have a read of some of these sometime.

Interesting, if you only have little data to send, it can actually be much quicker to use 300 baud :)

Yes, I think a lot of security alarms and things still only use 300 baud.
 

Online mikeselectricstuff

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Re: Modem Handshake
« Reply #5 on: February 02, 2013, 12:13:52 pm »
This is the sort of thing that makes me glad I don't do firmware for stuff like this for a living...
Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
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Offline Stonent

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Re: Modem Handshake
« Reply #6 on: February 02, 2013, 04:38:03 pm »
I seem to remember that when a certain speed or standard was used in a modem, the answering modem's initial carrier signal had a recurring "tick" in it. I remember listening in and thinking, oh you've got a crap modem, never mind I'll try another number when I didn't hear that.

I was pretty good at determining how well the two modems liked each other by ear and would hang up the line if the handshake was taking a bit too long.
The larger the government, the smaller the citizen.
 

Offline Stonent

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Re: Modem Handshake
« Reply #7 on: February 02, 2013, 04:41:26 pm »
Talking about modems reminds me of this insurance commercial in the US. Specifically robot #2 reading to the children.



The larger the government, the smaller the citizen.
 

Offline Raff

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Re: Modem Handshake
« Reply #8 on: February 10, 2013, 03:08:10 am »
I remember dialling into the local internet service provider around the time the 2 competing 56k standards were around. I cant recall the names of them, but one answered  with a "bong bong" sound, the other with the high speed ticking buzzing sound.
I must be a nerd, my job involved data communications and years ago I could actually hear the negotiation sounds of various modems and tell what was happening and where it went wrong. I could actually whistle to older 300 and 1200/75 modems and get them to "talk" to me  :palm:

Im a NERD  :-DD

Ahh I remember 56k FLEX and V.90 I think, Rockwell and USR, US Robotics (3Com) were the competing brands i think.
 

Offline firewalker

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Re: Modem Handshake
« Reply #9 on: February 10, 2013, 07:43:53 am »
Voice modems was the main way for me to connect to internet until 5 years ago. Some times I still do to remind me what it was like!  :P :P :P
It is true that you could tell the connection quality by the sound before the establishment.

Some of the modems I used over the years. Never used the PCI-crap type :P.



Alexander.

Become a realist, stay a dreamer.

 

Offline Raff

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Re: Modem Handshake
« Reply #10 on: February 10, 2013, 09:46:06 am »
Yes those PCI "winmodems" were crap indeed. To make modems cheaper, much of the processing and DSP functions were moved from hardware on the modem to the drivers used with windows. It didnt work very well and poor old linux users were out in the cold at first. Later versions got better, but still not as reliable as the true hardware modems. The price difference was at times nearly 10 to 1! I remember one "modem" that was nothing more than the bare minimum of components necessary to connect to the telephone line an pass the then AUSTEL rules.
 

Offline SeanB

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Re: Modem Handshake
« Reply #11 on: February 10, 2013, 10:01:42 am »
Still have one around, just as a backup. Must admit I would use a cellphone tethering first above it.
 

Offline Raff

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Re: Modem Handshake
« Reply #12 on: February 10, 2013, 10:16:17 am »
Yes, me too, I have quite a few old modems lying around. Admittedly the winmodem ones usually get stripped of their transformer and other goodies like the opto's and high voltage transistors for other projects  :P
 


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