Electronics history trivia

Lee Harker

Some guys and I around the shop have been trying to think of the term that was used in the dark ages when modems and fax machines were the latest technology.
When the fax machine or modem first "met" on the phone they would go through a little dance to decide what baud rate and protocol they would use to get the best bandwidth. We can't think of the term that was used for that. Does anyone know?

Dr_Acula

You mean "handshake"?

www.modemhelp.net/faqs/handshake.shtml

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www.smarthome.viviti.com/propeller

stamptrol

As the dark ages became slightly illuminated, the negotiation between devices also did a little "autobaud selection" to pick the fastest mutually acceptable speed.

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Tom Sisk

http://www.siskconsult.com
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bill190

Data rate negotiation or training / retraining.

Leon

I'm quite sure that "negotiation" is the correct term.

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Leon Heller
Amateur radio callsign: G1HSM

Ravenkallen

I think Dr_Acula is right. They called it handshaking.

Chris_D

I don't think it is handshaking.· That uses one of two (that I know of protocols)

1) X-ON / X-OFF

2) RTS/CTS

Handshaking deals with flow control of data wherein the receiver tells the transmitter to stop sending data (X-OFF), then when the buffer clears it tells the transmitter to send data (X-ON)

I believe the startup phase was called negotiate or similar.

Chris

Invent-O-Doc

negotiation methinks

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Tom Talbot
New Market, MD, USA

Phil Pilgrim (PhiPi)

I'll go with "negotiation" as well. And it includes more than just baudrate and protocol agreement. There's also line testing, which is necessary to establish echo cancellation parameters.

-Phil

Tracy Allen

Yes, "negotiation", which also includeswhether or not to enable error correction and compression.

If you had to make an simple old modem talk to a fancy one, it could be a problem. AT commands given on both ends could help, to limit the options and and improve the reliability.

What term do we use now, say, when a wi-fi node joins a network? Is negotiation still "in"?

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Tracy Allen
www.emesystems.com

ElectricAye

For those first modems I think we used to call it signing, as in American Sign Language. That's because those first modems were about as effective as two people trying to communicate via sign language over the telephone: not much got transmitted before everything died.

WBA Consulting

Wow, gotta dig deep into the memory banks for this one.......

What I think you are referring to is called a Training Check (TCF) and it is used by the faxes to determine the fastest speed at which both fax machines can communicate reliably. It actually occurs right after what is referred to as handshaking, which is the process of establishing the link between two fax machines that identify themselves and their abilities. I don't recall which of the two steps make the sound that like "dancing", but if the rcvg fax can't actually reciev properly at it's stated abilities in its DIS, you would hear varying sounds as the sending fax tries different rates to get a clean link. Here's a short flow of the start of a fax transmission and where that "dancing" might be:

--call initiation---
Sending Fax dials Rcvg Fax
Rcvg fax picks up and transmits CED (Called terminal identification, 2100hz for 2.6s)
Sending fax transmits CNG (Calling tone, 1100hz, on for 1/2 second, off for 3, repeating)

--handshaking---
Rcvg fax transmits DIS (digital identification signal) at 300bps defining it's capabilities
Sending fax transmits DCS (digital command signal) in response at 300bps defining it's capabilities

--training---
sending fax transmits TCF signal to determine if receiving fax can properly receive at the highest shared data rate (v.27, v.29, v.17, or v.34)
_if TCF is received as invalid, rcvg fax sends a FTT (failed to train) and retraining will occur at the same or lower data rate
(multiple occurrences of this retraining process could sound like "dancing")
_if TCf is received clean and valid, the rcvg fax sends a CFR (confirmation to receive) and communication can continue to actual fax transmittal


If you want more details (or need a nap) here's the link to the ITU T.30 spec which governs this activity:
www.itu.int/rec/T-REC-T.30-200509-I/en

Also, when I did a search for CFR because I couldn't remember what it stood for (since the letters are not a true acronym), I found this nice link which would have saved me a lot of typing.........

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Andrew Williams
WBA Consulting
WBA-TH1M Sensirion SHT11 Module
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