Build your own Dial-up ISP with a Raspberry Pi - Comments

Build your own Dial-up ISP with a Raspberry Pi

fanf

56k modems were cunning. For speeds up to 33.6k, a connection went through four modems: the ISP’s and the user’s, plus the telco’s modems that converted the analogue signals on the local loops to digital signals across the telco backbone. 56k modems were asymmetrical: they relied on a digital synchronous connection between the ISP and the telco, so that there were only two modems at either end of the user’s local loop. This reduced the noise due to unsynchronized sampling clocks. The ISP connected to the telco via digital leased lines, similar to what a PABX would use. A T1 or E1 carrying a couple of dozen phone lines plugged into something like an Ascend Max which, as well being several modems, also handled PPP and IP and talking to the ISP’s RADIUS and routing servers.

lorddimwit

I was the admin of a small (2000ish user) ISP way back in the day. The Ascend gear was terrible, except for all the others.

Nice admin interface though.

doctor_eval

Pretty sure the RPi is way more powerful than the machines we used to build our dialup ISP back when dinosaurs ruled the earth.

fanf

The Raspberry Pi 3 has more CPU but less IO bandwidth than a Sun E450 https://dotat.at/@/2016-02-19-raspberry-pi-2-vs-sun-e450.html

kolen

This method is popular for connecting Sega Dreamcast to the internet, but usually without that sophisticated telephone line simulator, the most common method is to use just one or two 9V batteries, a capactitor and a resistor. Apparently, Dreamcast modem does not need dial tone or some other tones.

awilfox

Finally, someone reveals the missing piece that I've never been able to figure out – a telephone line simulator! I always wanted to get a few of my old modem-only laptops online using "the true way". Sure, serial-to-serial SLIP is a thing – and I installed FreeBSD on a 486 in 2008 using SLIP – but there's a certain je ne sais quoi about telephone modems.

bigbuppo

Don't need to do that. I use a USR Total Control chassis as a white noise generator.

MORPHOICES

[dead]

kotaKat

I feel like it would have been more fun to build your own line simulator with a 9 volt battery and some old phone line and just skip the dialtone altogether for a little magic... the $120 black-box telco simulator takes a lot of the fun out.

But then again, based on Pi pricing today, the $120 telco simulator goes nicely with a $300 Pi 5.

giantrobot

Line simulators are fun. The ports can call each other and there's no need to set any custom init strings on the modem like you need with the 9 volt trick. For some old devices that's a necessity.

You can also use an old VoIP ATA from Linksys/Cisco as a cheap line simulator. Like a fully analog TLS the ports can call each other. They can be a PITA to configure right but they're cheap and work well enough.

I've used all three methods, the TLS is the easiest. An ATA can be useful if you've got more than one and your dial-in server is in a different room from the client you're playing with. An ATA can also be set to "call" another device. So your office ATA can call the basement ATA (with your Linux server) as an example.

alnwlsn

If you ever want more phone lines than that, you can pick up an old Cisco VG-224 from Ebay for less than half the price of that line simulator, and you get 24 lines. There is a configuration that will let you use it as a standalone unit where all the lines can call each other with custom phone numbers (here's some notes [1]).

The main catch is that they have a 50-pin Centronics style connector on them which you will have to break out somehow to your RJ11s. Also, they are big (1U rack) and have fans.

I've got a few of these and have been meaning to set them up with a bunch of modems and a bunch of computers, but haven't gotten to it yet. Modems do seem to work in the limited testing I've done. They do (as expected) work great with telephones, including pulse dialing.

[1] https://alnwlsn.com/z/pots/cisco-vg224.html

aimadetools

I'd be curious if anyone has actually used a setup like this as a fallback for when their fiber goes down. The latency would be brutal, but a few kbps beats no bps

connicpu

It would be funny as a project but there's better low speed backup options like a starlink dish on standby mode (500kbps)

elevation

I pulled out a WRT54G the other day and set it to a 56K limit. A netbook running ubuntu(ish) took several days to complete an apt-get update. But when I connected my laptop with 50 browser tabs, the tabs themselves consumed 100% of the bandwidth with background traffic (despite my ad blocker) and no other network services worked at all.

Unless you've tuned your system for it, dial-up modem speeds are functionally equivalent to "no connection at all".

elevation

What I would love to have is a few compact dialup-to-wifi bridges so I could wifi-ize 30 year old hardware.

Would be neat to read email with an old POP client, or chat over the original AIM software (perhaps patched to use a server on the LAN)

iberator

Nice, but slip and plip is more tun

fanf

56k modems were cunning. For speeds up to 33.6k, a connection went through four modems: the ISP’s and the user’s, plus the telco’s modems that converted the analogue signals on the local loops to digital signals across the telco backbone. 56k modems were asymmetrical: they relied on a digital synchronous connection between the ISP and the telco, so that there were only two modems at either end of the user’s local loop. This reduced the noise due to unsynchronized sampling clocks. The ISP connected to the telco via digital leased lines, similar to what a PABX would use. A T1 or E1 carrying a couple of dozen phone lines plugged into something like an Ascend Max which, as well being several modems, also handled PPP and IP and talking to the ISP’s RADIUS and routing servers.

lorddimwit

I was the admin of a small (2000ish user) ISP way back in the day. The Ascend gear was terrible, except for all the others.

Nice admin interface though.

doctor_eval

Pretty sure the RPi is way more powerful than the machines we used to build our dialup ISP back when dinosaurs ruled the earth.

fanf

The Raspberry Pi 3 has more CPU but less IO bandwidth than a Sun E450 https://dotat.at/@/2016-02-19-raspberry-pi-2-vs-sun-e450.html

kolen

This method is popular for connecting Sega Dreamcast to the internet, but usually without that sophisticated telephone line simulator, the most common method is to use just one or two 9V batteries, a capactitor and a resistor. Apparently, Dreamcast modem does not need dial tone or some other tones.

awilfox

Finally, someone reveals the missing piece that I've never been able to figure out – a telephone line simulator! I always wanted to get a few of my old modem-only laptops online using "the true way". Sure, serial-to-serial SLIP is a thing – and I installed FreeBSD on a 486 in 2008 using SLIP – but there's a certain je ne sais quoi about telephone modems.

bigbuppo

Don't need to do that. I use a USR Total Control chassis as a white noise generator.

MORPHOICES

[dead]

kotaKat

I feel like it would have been more fun to build your own line simulator with a 9 volt battery and some old phone line and just skip the dialtone altogether for a little magic... the $120 black-box telco simulator takes a lot of the fun out.

But then again, based on Pi pricing today, the $120 telco simulator goes nicely with a $300 Pi 5.

giantrobot

Line simulators are fun. The ports can call each other and there's no need to set any custom init strings on the modem like you need with the 9 volt trick. For some old devices that's a necessity.

You can also use an old VoIP ATA from Linksys/Cisco as a cheap line simulator. Like a fully analog TLS the ports can call each other. They can be a PITA to configure right but they're cheap and work well enough.

I've used all three methods, the TLS is the easiest. An ATA can be useful if you've got more than one and your dial-in server is in a different room from the client you're playing with. An ATA can also be set to "call" another device. So your office ATA can call the basement ATA (with your Linux server) as an example.

alnwlsn

If you ever want more phone lines than that, you can pick up an old Cisco VG-224 from Ebay for less than half the price of that line simulator, and you get 24 lines. There is a configuration that will let you use it as a standalone unit where all the lines can call each other with custom phone numbers (here's some notes [1]).

The main catch is that they have a 50-pin Centronics style connector on them which you will have to break out somehow to your RJ11s. Also, they are big (1U rack) and have fans.

I've got a few of these and have been meaning to set them up with a bunch of modems and a bunch of computers, but haven't gotten to it yet. Modems do seem to work in the limited testing I've done. They do (as expected) work great with telephones, including pulse dialing.

[1] https://alnwlsn.com/z/pots/cisco-vg224.html

aimadetools

I'd be curious if anyone has actually used a setup like this as a fallback for when their fiber goes down. The latency would be brutal, but a few kbps beats no bps

connicpu

It would be funny as a project but there's better low speed backup options like a starlink dish on standby mode (500kbps)

elevation

I pulled out a WRT54G the other day and set it to a 56K limit. A netbook running ubuntu(ish) took several days to complete an apt-get update. But when I connected my laptop with 50 browser tabs, the tabs themselves consumed 100% of the bandwidth with background traffic (despite my ad blocker) and no other network services worked at all.

Unless you've tuned your system for it, dial-up modem speeds are functionally equivalent to "no connection at all".

elevation

What I would love to have is a few compact dialup-to-wifi bridges so I could wifi-ize 30 year old hardware.

Would be neat to read email with an old POP client, or chat over the original AIM software (perhaps patched to use a server on the LAN)

iberator

Nice, but slip and plip is more tun