Thread by @gravislizard

i have found the jankiest phone system ever constructed. just take this in for a minute, absorb its extremely dark energy

had to reverse engineer this shitshow with some friends but i got it sussed out now. those aren't network cards on the right, they're T1/PRI, and the ones with huge connectors are 24-port analog phone line cards

here's the inside. bottom card is a single board Pentium 4, but it's all going into a 14+ slot *ISA* (!) backplane feeding this bank of Dialogic phone cards.

the cables hanging out below the RJ-21 ports on the back are external power input - each card requires one of these big fuckoff power bricks because there's no way an ISA slot can power four of these beasts

the ribbon bus between the cards is particularly delightful - it's SCBus, a *TDM* interlink for telephony

speculating: when a call comes in on e.g. a T1 digital channel, the CPU makes the decision to terminate it to e.g. analog port 4, and then just tells the T1 card "send it to TDM channel 4, card ID 7" - those little dials next to the ribbon connectors set the card IDs

because this system is handling at least 96 lines (probably phone stations) there's absolutely no way the CPU *or* the ISA bus could handle all that data, so the cards just have their own private backchannel for it. beautiful

so it all makes sense but if you just look at it, it feels like it must have spent more time broken than working in its lifetime