Feature Request: Add support for Bell 212A modulation

[craftbyte]

We are trying to make some old Nortel Millenium payphones work with the Asterisk softmodem, which uses SpanDSP. It would be great to get support for Bell 212A which is used on them so we don't need a hardware modem for using them.

[coppice-git]

I don't have the specification for Bell212A. I know it is very similar to V.22bis. I made the V.22bis guard tone programmable, as I know that is one area where they differ. I don't know what else needs to be modified. I think they are so close I managed to get a modem in Bell212A mode to connect to my V.22bis modem at one point.

[linkcomtech]

Hello coppice-git
Could you be so kind and contact [email protected] about our feature requests and funded development for spandsp?

Thank you
EY

[craftbyte]

@linkcomtech why was this posted on this issue? Are you planning on funding this feature request?

[linkcomtech]

Yes, i need spandsp extended with full v34 support.

[lexxer3d]

btw, there's some spec https://vtda.org/docs/computing/UDS/Prelim_Spec_212A-compatible_Modem.pdf

[coppice-git]

@lexxer3d Thanks for that. I went searching for info on Bell212A and didn't find that document. I did find some other material, and with a couple of confirmations from your document, I think I have the complete picture. Its just V.22 with a somewhat different startup signal from the answering side. There don't seem to be any obscure bells and whistles I need to worry about. Implementing it shouldn't be a big deal, as an extra mode for the V.22bis modem.

[pc-coholic]

I did go on a hunt for the official 212A spec some time ago and bookmarked the following pages:

https://telecomarchive.s3.us-east-2.amazonaws.com/docs/bsp-archive/TR/41214_1976-10.pdf
https://vtda.org/docs/computing/UDS/Prelim_Spec_212A-compatible_Modem.pdf

I would also very much appreciate 212A-support for exactly the same reason as @craftbyte :-)