6 ms·

Wow, this really is something if done right. I don't use a landline now, but if I remember, the caller needs to disconnect for the line to actually be disconnec

by msravi 7y ago

Wow, this really is something if done right. I don't use a landline now, but if I remember, the caller needs to disconnect for the line to actually be disconnected. So even if the callee tries to disconnect by hanging up, the caller is still actually connected. If the callee picks up the receiver again and hears a dial tone, they'd be none the wiser. But I guess the scammer would also need to detect a key-press tone on the line and stop the fake dial tone, start the ring tone, etc.

de_watcher 7y ago
Never heard of the systems with this flaw. It was always "if you hang up then it's completely cut".
- dboreham 7y ago
  Perhaps it worked on Strowger exchanges when the call is local? I definitely remember this being "a thing" back in the 1970s but I don't remember ever succeeding in reproducing it. Obviously there must have been some time out because otherwise you could DoS anyone's phone by just calling them then not hanging up.
  - Khoth 7y ago
    In the UK, when exchanges moved to digital, they deliberately kept the old behaviour because some people relied on it (eg, hanging up their main phone, then walking to another room and picking up the call on an extension phone), with a timeout of a few minutes. In 2014 they reduced the timeout to 10 seconds to make this fraud harder to pull off. https://www.openreach.co.uk/orpg/home/updates/briefings/downloads/wlr00314.pdf https://www.openreach.co.uk/orpg/home/updates/briefings/down...
AstralStorm 7y ago
That's not how it works with digital lines. Disconnect on any side breaks the whole circuit presuming they conform to even ancient PDH, much less SONET or SDH. Oh and this includes even more ancient ISDN. The trunk will immediately tear down the DS0 slot and circuit. GSM and VoIP also do not allow this behavior without engaging call waiting on subscriber side. This only happens with old fully analog connections. Not sure which country or public operator still has this kind of PSTN. For the difference, peruse ITU-T G.175 and Q.522 standards. SE (switching element) will disconnect the routing on your side. It took me a while to find the actual standard number.
- angry_octet 7y ago
  I haven't heard of this working since the 80's, with rotary pulse dial phones.

by msravi 7y ago

de_watcher 7y ago

Never heard of the systems with this flaw. It was always "if you hang up then it's completely cut".

dboreham 7y ago
Perhaps it worked on Strowger exchanges when the call is local? I definitely remember this being "a thing" back in the 1970s but I don't remember ever succeeding in reproducing it. Obviously there must have been some time out because otherwise you could DoS anyone's phone by just calling them then not hanging up.
- Khoth 7y ago
  In the UK, when exchanges moved to digital, they deliberately kept the old behaviour because some people relied on it (eg, hanging up their main phone, then walking to another room and picking up the call on an extension phone), with a timeout of a few minutes. In 2014 they reduced the timeout to 10 seconds to make this fraud harder to pull off. https://www.openreach.co.uk/orpg/home/updates/briefings/downloads/wlr00314.pdf https://www.openreach.co.uk/orpg/home/updates/briefings/down...

AstralStorm 7y ago

That's not how it works with digital lines. Disconnect on any side breaks the whole circuit presuming they conform to even ancient PDH, much less SONET or SDH. Oh and this includes even more ancient ISDN. The trunk will immediately tear down the DS0 slot and circuit. GSM and VoIP also do not allow this behavior without engaging call waiting on subscriber side. This only happens with old fully analog connections. Not sure which country or public operator still has this kind of PSTN. For the difference, peruse ITU-T G.175 and Q.522 standards. SE (switching element) will disconnect the routing on your side. It took me a while to find the actual standard number.

angry_octet 7y ago
I haven't heard of this working since the 80's, with rotary pulse dial phones.