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Ask HN: Why can't I send faxes from my phone?

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Re: Ask HN: Why can't I send faxes from my phone?

#131

Post by drfuchs »

vegardx wrote: post #52
talles wrote: post #19

Genuine question: why there are folks still using fax?

Up until very recently my grandpa would use fax to send complaints to just about anything. It was about as stereotypical grumpy old man as you can imagine. He's a good person, just old-school formal when he writes. Comes of as a bit ... harsh. I thought it was going to end when they dismantled the analog network, and his fax machine with it, but somehow it just got worse. You see, on fax machines you rarely got spam,…

Au contraire; fax spam was a reasonably big problem: https://www.sfgate.com/bayarea/article/2-2-trillion-lawsuits...

Re: Ask HN: Why can't I send faxes from my phone?

#132

Post by screwt »

PunksATawnyFill wrote: post #127
rubatuga wrote: post #84

Earlier quoted context omitted.

> The fax requires a 56KHz channel This is quite wrong. I believe you are confusing Hz with bitrate, as the most advanced modems communicate at 56kbit/s using PCM. To clear it up, a regular phone line has a 4000Hz bandwidth. With digital lines, you require sampling at at least 8000Hz (Nyquist theorem). It's impossible to send a frequency above 4000Hz using this line. Each sample is considered to have 7 usable bits of…

I figured that audio compression on mobile networks prevented the sending of faxes as tones.

You're right - though it's more about the precise timing of the tones than the frequencies themselves.

The T.38 protocol exists to allow faxes to send over a packetized network. Already if you're sending a fax there's a high chance it's been converted to T.38 at some point, as SPs gradually move toward a fully packetized core.

Re: Ask HN: Why can't I send faxes from my phone?

#133

Post by Taniwha »

waste_monk wrote: post #104
vegardx wrote: post #52

Earlier quoted context omitted.

Up until very recently my grandpa would use fax to send complaints to just about anything. It was about as stereotypical grumpy old man as you can imagine. He's a good person, just old-school formal when he writes. Comes of as a bit ... harsh. I thought it was going to end when they dismantled the analog network, and his fax machine with it, but somehow it just got worse. You see, on fax machines you rarely got spam,…

>You see, on fax machines you rarely got spam When I entered the workforce I was surprised to see how much fax spam there was, usually a sheet or two every week. It's tapered off to ~ a couple of sheets per fortnight in recent times though. It is kind of amusing to see fax phishing with personalised cover notes attached to some spam about light furnishings etc. I wish I could do the old "faxing sheets of black paper…

I used to have a fax number one off of a pharmacy .... I got someone's prescription every week or so ....

Re: Ask HN: Why can't I send faxes from my phone?

#134

Post by 2rsf »

kelnos wrote: post #122
gumby wrote: post #13

The fax requires a 56KHz channel which has not been used for mobile telephony since the 1980s (when AMPS and GSM were developed. Before then it was just a radio link through an operator). That’s why you can’t use a high speed modem either. Some gsm phones had the ability to transmit a fax but they actually used a different protocol to talk to a fax gateway. I never saw one of these in the wild. I haven’t been in that…

Wish this wasn't the highest-rated comment, as it's not correct. If it needed a "56kHz channel", it would not have worked in the phone-over-copper-wire days either. If we assume the parent meant 56kbps, that's still incorrect. The fastest fax machines use V.34bis modems (ignoring ISDN), which give you 33.6kbps, though many (most?) still support the oldest standard, V.27, at 2400bps! The real issue sending a (T.30) fa…

You are confusing bitrates here, the fax emits an analog signal and doesn't interface the digital line directly- it's not a digital packet switch protocol.

Those 2400bps are not using 2400bps from the line, but are modulated to an analog signal that uses the lines full bitrate. From Nyquist–Shannon sampling theorem we know that a 56bps line can transfer something like half of it in analog form, so 33.6 is marginal.

T.38 is sensitive since it needs to end the analog side, practically receiving the fax.

Fax in general is sensitive since the standards have left too much freedom for implementers, especially like you said in the timing parts, causing incompatibilities between machines.

(Source: I have built fax relay over VoIP products in the late 90's)

Re: Ask HN: Why can't I send faxes from my phone?

#135

Post by shawnz »

Retric wrote: post #17
mceachen wrote: post #7

Earlier quoted context omitted.

HQ audio quality (over 4G) is markedly better than land lines, and the fax protocol has had error correction since digital formats were adopted in the 60s and 70s. https://en.m.wikipedia.org/wiki/Fax My Palm Pilot (with a CDPD backpack) and candybar 2G Nokia could both send FAXes. I suspect there's no demand.

The parent’s post is correct. While the perceived quality is much higher, modern cellphones use a lossy format optimized for voice communication. From an engineering perspective, having a billion cellphones faithfully transmitting info on frequencies humans can’t hear is simply wasteful. https://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_code... “AMR was adopted as the standard speech codec by 3GPP in October 19…

Fax uses frequencies that humans can hear though (up to 4KHz)

Re: Ask HN: Why can't I send faxes from my phone?

#136

Post by Retric »

shawnz wrote: post #135
Retric wrote: post #17

Earlier quoted context omitted.

The parent’s post is correct. While the perceived quality is much higher, modern cellphones use a lossy format optimized for voice communication. From an engineering perspective, having a billion cellphones faithfully transmitting info on frequencies humans can’t hear is simply wasteful. https://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_code... “AMR was adopted as the standard speech codec by 3GPP in October 19…

Fax uses frequencies that humans can hear though (up to 4KHz)

Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz.

The AMR codec uses eight source codecs with bit-rates of 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kbit/s.

Fax machines on the other hand go up to 33kbit/s.

PS: People can produce and hear frequencies well above 3400 Hz, but for phone calls people just don’t notice clipping those frequencies. If anything it helps by removing some background sounds.

Re: Ask HN: Why can't I send faxes from my phone?

#137

Post by [deleted] »

Retric wrote: post #136
shawnz wrote: post #135

Earlier quoted context omitted.

Fax uses frequencies that humans can hear though (up to 4KHz)

Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz. The AMR codec uses eight source codecs with bit-rates of 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kbit/s. Fax machines on the other hand go up to 33kbit/s. PS: People can produce and hear frequencies well above 3400 Hz, but for phone calls people just don’t notice clipping those frequencies. If anything it helps by remov…

[deleted]

Re: Ask HN: Why can't I send faxes from my phone?

#138

Post by shawnz »

Retric wrote: post #136
shawnz wrote: post #135

Earlier quoted context omitted.

Fax uses frequencies that humans can hear though (up to 4KHz)

Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz. The AMR codec uses eight source codecs with bit-rates of 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kbit/s. Fax machines on the other hand go up to 33kbit/s. PS: People can produce and hear frequencies well above 3400 Hz, but for phone calls people just don’t notice clipping those frequencies. If anything it helps by remov…

Right, so it must be the bit depth which is the problem, not the frequencies that can be reproduced

Re: Ask HN: Why can't I send faxes from my phone?

#139

Post by perl4ever »

hiergiltdiestfu wrote: post #116
perl4ever wrote: post #83

Earlier quoted context omitted.

The thing is, when I'm asked to send sensitive documents over unencrypted email or something, then I'd rather use the fax option. And I don't trust any internet gateway, I go to some local store with actual fax machines. I kinda sorta think of it as more secure than the internet, still?

IIRC, automated character recognition / word alerts in FAX transmissions has been built-in in Echelon since the 1970ies. FAX is as insecure as emails are, under certain threat models. Pretty sure this is mentioned in this nice crypto history overview: https://alternativlos.org/30/

I am not concerned if the NSA knows my SSN.

Re: Ask HN: Why can't I send faxes from my phone?

#140

Post by aurizon »

kvee wrote: post #102
amelius wrote: post #35

Earlier quoted context omitted.

Perhaps someone could start a relay service.

We made http://mailprincess.com/ a while ago which is $1 per fax Also made http://maleprincess.com/ for fun

It exists, but will only deal with USA numbers = I live in Canada, maybe one day ....?
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