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Re: video phone via landline

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On 3/29/20 12:48 AM, Jason Yan wrote:
> My question may sound weird but I could not find a clue online and I am not in telecom field. Hoping I can at least get some expert insight here. Thank you very much in advance!
> 
> Assume there is no internet at all (not even ADSL or DSL), and no cell phone next work at all. Is it even possible to make two video phones that communicate purely through landline? I mean, just "invent" video phone and simply replace your home analog phone, and video call another person who also replace his home analog phone with video phone.  It is kind of like video intercom but through landline (video intercom seems to use different wire), and it is two-way video instead of one way video plus one way audio like video intercom.
> 
> What I learned is that, the analog voice signal and digital signal (I assume video has to be digital) can both transferred through the first pair of wire (T/R) in a landline. Analog signal and digital signal can be mixed because their frequency are very different. I understand that the bandwidth will be quite limited, but I am fine with only like 200x300 pixel sized picture, and with only 10 fps (frame per second) so hope bandwidth is not a real issue.
> 
> I also assumed there is no DSL or ADSL available, which means I cannot use the existing TCP/IP protocol but need to develop my own protocol just for digital data transfer between two phones connected through a physical landline.
> 
> Is my idea even possible? I am thinking of this for seniors who are afraid of any internet and smart phone thing and all they have is just the old analog phone and a landline.
> 
> Jason Yan
> 

You may find this webpage re the history of AT&T's attempt at videophone 
service interesting. Especially at the end, it shows a 1990's deskset 
that apparently was sold by Sears, and may have been the unit that Danny 
Burstein referred to.

https://flashbak.com/the-fantastic-and-troubled-history-of-the-video-phone-404033/

Based on my (now retired) 30 year career in data communications, your 
challenge will be to create a video/voice digitizing scheme that can 
produce a usable picture & voice needing no more than 2400 bits per 
second data rate. There were/are dial-up modems that could create a 
2400bps full-duplex data connection over the PSTN (Public Switched 
Network). But due to that 2 wire PSTN connection being limited to 3 
Kilohertz of analog bandwidth, 2400 digital BPS Full Duplex pushed the 
limits of modem technology.

The ITU-T standard for these modems is "V.22bis"
"V.22bis is an ITU-T recommendation extending V.22 with a faster rate 
using QAM at 600 baud to carry digital data at 2400 or 1200 bit/s. The 
1200 bit/s mode is compatible with V.22."

Good luck.........

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video phone via landline Jason Yan <yan.xxs@gmail.com> - 2020-03-28 21:48 -0700
  Re: video phone via landline danny burstein <dannyb@panix.com> - 2020-03-29 04:51 +0000
    Re: video phone via landline Jason Yan <yan.xxs@gmail.com> - 2020-03-28 23:26 -0700
      Re: video phone via landline danny burstein <dannyb@panix.com> - 2020-03-29 06:30 +0000
  Re: video phone via landline "\"Retired"@home.com - 2020-03-29 12:52 -0400
    Re: video phone via landline danny burstein <dannyb@panix.com> - 2020-03-29 17:31 +0000
    Re: video phone via landline Jason Yan <yan.xxs@gmail.com> - 2020-03-29 17:43 -0700
      Re: video phone via landline danny burstein <dannyb@panix.com> - 2020-03-30 00:47 +0000

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