Build your own Dial-up ISP with a Raspberry Pi
23 points by fanf
23 points by 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.
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.
Pretty sure the RPi is way more powerful than the machines we used to build our dialup ISP back when dinosaurs ruled the earth.
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
I wonder how it stacks up to a Pi 5.
Not that we had the fancy Sun stuff at my regional ISP. Mostly I think it was hand me down x86 boxes!
A Raspberry Pi 5 has about 2x the memory bandwidth as an E450, 10x ethernet bandwidth, and the wifi can be twice as fast as 100baseT ethernet. The external PCIe gen2 x1 and the USB 3.0 ports are both 5 Gbit/s which is about the same bandwidth as the E450’s 64bit 66 MHz PCI bus. The SD card can do 100 MB/s but the E450 had up to 5 SCSI buses running at 40 MB/s with space for 20 disks holding 36 Gbytes each.
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.
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.