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This brings back memories of trying to crash BBS uploaded file verifiers by sending massively compressed files that would crash the board when unzipped. Ahhh th

by tlack 17y ago

This brings back memories of trying to crash BBS uploaded file verifiers by sending massively compressed files that would crash the board when unzipped. Ahhh the memories..

CWuestefeld 17y ago
In college we used to do nasty things to the PBX system. It was smart enough to detect and prevent forwarding a number to itself -- if you did it using the internal 4-digit extension. But if you forwarded to yourself via 9+direct-dial-number, it couldn't detect that. So we'd forward the phone that way, then call it from another line. You'd hear a sequence of clicks, progressively quieter (why? isn't it all digital?), and then it would just stop, presumably because all external lines were used up. Farther off topic, the phone system had a weird feature: dialing #*5 would say back to you 3 (apparently) random digits. This was good for chemistry lab, if you needed to fudge some data and wanted to introduce a believable error factor into it.
- chronomex 17y ago
  It gets quieter because of the transmission loss plan. Historical reasons, basically. Since analog connections lose power with distance, there was defined an acceptable maximum loss for each segment in the network. If a line came in too hot, a "pad" was added to dissipate some power at the receiving end. If it was too low, the circuit was out of spec and had to be re-engineered. At the other end of the telephone switch, an amplifier was added to jack up all the outgoing signals to the proper amplitude for the transmission network. All this amplification and loss was necessary to make sure that all telephone calls had about the same volume. The network didn't all switch over to digital switching and transmission in one day (in fact there are some analog interoffice circuits still in use to this day in Alaska), so we retained some vestiges of the loss plan. It's pretty likely that your PBX system connected to the network over analog lines anyway. :)

by tlack 17y ago

This brings back memories of trying to crash BBS uploaded file verifiers by sending massively compressed files that would crash the board when unzipped. Ahhh the memories..

CWuestefeld 17y ago

In college we used to do nasty things to the PBX system. It was smart enough to detect and prevent forwarding a number to itself -- if you did it using the internal 4-digit extension. But if you forwarded to yourself via 9+direct-dial-number, it couldn't detect that. So we'd forward the phone that way, then call it from another line. You'd hear a sequence of clicks, progressively quieter (why? isn't it all digital?), and then it would just stop, presumably because all external lines were used up. Farther off topic, the phone system had a weird feature: dialing #*5 would say back to you 3 (apparently) random digits. This was good for chemistry lab, if you needed to fudge some data and wanted to introduce a believable error factor into it.

chronomex 17y ago
It gets quieter because of the transmission loss plan. Historical reasons, basically. Since analog connections lose power with distance, there was defined an acceptable maximum loss for each segment in the network. If a line came in too hot, a "pad" was added to dissipate some power at the receiving end. If it was too low, the circuit was out of spec and had to be re-engineered. At the other end of the telephone switch, an amplifier was added to jack up all the outgoing signals to the proper amplitude for the transmission network. All this amplification and loss was necessary to make sure that all telephone calls had about the same volume. The network didn't all switch over to digital switching and transmission in one day (in fact there are some analog interoffice circuits still in use to this day in Alaska), so we retained some vestiges of the loss plan. It's pretty likely that your PBX system connected to the network over analog lines anyway. :)