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Those are in-band signals to the switching equipment. The equipment would “hear” those tones and translate them into “machine instructions”. That’s why phreaker

Those are in-band signals to the switching equipment. The equipment would “hear” those tones and translate them into “machine instructions”. That’s why phreakers could exploit the system by generating those tones themselves and playing them into the phone microphone.

jeffrallen 5y ago
That's why you do not control networks with signals on the network itself. See also: Facebook's recent outage.
- TedDoesntTalk 5y ago
  Right. But those were different times. And the bandwidth of analog lines was something like 4 kHz with no control channels.
- packetslave 5y ago
  > That's why you do not control networks with signals on the network itself. Other than, you know, the entire Internet (BGP) and pretty much every corporate WAN (OSPF, EIGRP, RIP) and LAN (spanning tree, ARP). Having an out-of-band control plane is very much the exception. Now OOB emergency access, on the other hand... edit okay, SS7 is out-of-band, but parent was talking about IP networks.
  - TedDoesntTalk 5y ago
    I don’t know about that. Even the ancient FTP protocol has a separate control channel/port.
  - icehawk 5y ago
    And even with those things being in-band, we now have authentication for BGP and the IGPs to try and constrain the ability to send control signals. SS5/CCITT5 would probably have played out a lot differently had they hand the ability to do that sort of thing like we do now.