If you're seeing 'CONNECT 57600' that's the connection speed between your modem and PC (Data Terminal Equipment). In order to display the actual connect speed of the modem and remote host you have to use some Hayes commands (ATW0) so it will display the DCE speed (Data Carrier Equipment).

https://www.activexperts.com/serial-port-component/at/hayes/

And if ATW0 is used, is it a baud rate or byte rate? Do you divide it by 8, 10 or 1 for the bytes per second rate (assuming 56k modem)?

ATW0 will get you the DCE connect speed which is measured in bits per second. If you purchased a Hayes 9600 baud modem that meant your theoretical top data transfer speed would be 9,600 bits per second. For some reason all DCE equipment (modems/routers) are always speed rated at bits/second yet downloading with any software always displays bytes/second. ¯\_(ツ)_/¯

Here's some more interesting reading on baud rate vs connect speed:

https://www.pccompci.com/Baud_Rate.html

https://www.brainbell.com/tutors/A+/Hardware/ … odem_Speeds.htm

Norton Commander wrote on 2022-03-08, 11:50:

ATW0 will get you the DCE connect speed which is measured in bits per second. If you purchased a Hayes 9600 baud modem that mea […]
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ATW0 will get you the DCE connect speed which is measured in bits per second. If you purchased a Hayes 9600 baud modem that meant your theoretical top data transfer speed would be 9,600 bits per second. For some reason all DCE equipment (modems/routers) are always speed rated at bits/second yet downloading with any software always displays bytes/second. ¯\_(ツ)_/¯

Here's some more interesting reading on baud rate vs connect speed:

https://www.pccompci.com/Baud_Rate.html

https://www.brainbell.com/tutors/A+/Hardware/ … odem_Speeds.htm

OK. So the CONNECT message delivers the speed rate between the modems or to the UART in bits per second, as I thought.
Then, is the bits a multiple of 8(actual bytes) or 10(start bit, 8 data bits, (1/)2 stop bits)?

Depends how you've got the flow control configured, pure hardware, and you've got 8 bits per byte transferred, pure software with error checking you've got 11 bits per byte transferred.

But then your actual throughput will depend on how compressible the files are or not... later modems with full MNP5 and licenced or pirated lempel ziv algorithms could actually get 10% boost still with zip files or compressed images, earlier ones took a 10% hit from trying. Raw text would usually manage to compress up to your interface speed, so you'd see 12 bytes a sec throughput on text at 115 kilobit, 6 at 56 kilobit.

BitWrangler wrote on 2022-03-08, 17:18:

Depends how you've got the flow control configured, pure hardware, and you've got 8 bits per byte transferred, pure software with error checking you've got 11 bits per byte transferred.

But then your actual throughput will depend on how compressible the files are or not... later modems with full MNP5 and licenced or pirated lempel ziv algorithms could actually get 10% boost still with zip files or compressed images, earlier ones took a 10% hit from trying. Raw text would usually manage to compress up to your interface speed, so you'd see 12 bytes a sec throughput on text at 115 kilobit, 6 at 56 kilobit.

What I mean is if "CONNECT 57600" is reported as the modem to modem (not the DTE to modem speed, which is determined by the UART's DLAB etc.) speed, does it mean that with 8 bits per byte? So divide by 8 for the actual bytes per second rate?

Edit: http://dsp-book.narod.ru/Guide.pdf
So it's ATW2 for that (ATW1 is the same reporting as ATW0)... So DTE speed is communication between the modem and the UART.
So with ATW2, how many do you need to divide by to get the actual modem to modem speed in bytes per second?

Edit2: https://www.inetdaemon.com/tutorials/computer … _commands.shtml
So W2 is indeed modem-to-modem speeds is confirmed. But how much to divide that by for bytes/second?
And does that mean that all other settings report the speed in baud as used by the UART configures it in it's DLAB and start/stop bit settings (so e.g. divide by 10 for 1 start bit and 1 stop bit)?

The connect message now gives DCE-to-DCE speed, in baud, with 8 baudcycles for each byte.