Bill Horne wrote:
> Bill,
>
> I now have two questions for you: the first was about DTMF modems,
Used extensively in telephony - in fact, that is what you use when you dial into
an 'automated attendant' or voice-mail system
- the irritating recorded voice that asks you to 'press one for...' etc.
Well, when you pres that digit, it ain't a human decoding the other end...
Also used 'internally' by telco's - usually with all 16 codes, not 12 (telco &
military have such keypads, some places it is illegal for anyone else to have
them) to program telco switchgear, testgear, etc.
DTMF tones are 'pairs', and were chosen after extensive testing to survive
transmission on severely degraded analog lines, so make for a slow, but very
reliable means of transferring modest amounts of data. 'bout the same speed as
Bell-103 FSK, but *way* more reliable.
Buy one? Dunno. Needs only a DTMF tone generator (IC), and a DTMF tone decoder
(IC), at each end, with the lumped inductances, isolators, etc. to satify telco
connectivity regs. Can strip a cheap phone for all that.
The IC's interface easily to a parallel or serial port.
> but
> now I need to ask how to avoid getting rejected by your MTA.
>
Two steps, first one is easy:
- Set a PTR record in your netblock holder's DNS. A netblock NOT assigned portable.
Second one should then be automatic i.e. hostnames, HELO's and IP's of
organizations such as 'dyndns' are blacklisted as we find them, but you will no
longer need their services, so no longer a factor.
ELSE:
- Use your ISP's MTA,
Unless that is one of about 50 US-based 'careless' ISP's we also block as
primarily spam services - at least since the Yew_Ass_A mandated spam as a good
thing for business...("You, too CAN-Spam" act of 2003, was it?)
OR:
Gmail...
Best,
Bill
> TIA.
>
> Bill Horne
>
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> On Mon, 2006-10-09 at 16:18 +0800, W B Hacker wrote:
>> [snip]
>
>> - block staff from access to telephone lines which can handle any of:
>>
> [snip]
>
>> b) DTMF modems (harder, as it can prevent *dialing* once outside)
>
> I don't know what a "DTMF" modem is. Please provide some more info,
> and/or a URL for one of them. TIA.
>
>
> Bill
>
