It only took four seconds for a switch to get well. There was no PHYSICAL damage of any kind to the switches, after all. Physically, they were working perfectly. This situation was "only" a software problem.
But the 4ESS switches were leaping up and down every four to six seconds, in a virulent spreading wave all over America, in utter, manic, mechanical stupidity. They kept KNOCKING one another down with their contagious "OK" messages.
It took about ten minutes for the chain reaction to cripple the network. Even then, switches would periodically luck-out and manage to resume their normal work. Many calls—millions of them—were managing to get through. But millions weren't.
The switching stations that used System 6 were not directly affected. Thanks to these old-fashioned switches, AT&T's national system avoided complete collapse. This fact also made it clear to engineers that System 7 was at fault.
Bell Labs engineers, working feverishly in New Jersey, Illinois, and Ohio, first tried their entire repertoire of standard network remedies on the malfunctioning System 7. None of the remedies worked, of course, because nothing like this had ever happened to any phone system before.
By cutting out the backup safety network entirely, they were able to reduce the frenzy of "OK" messages by about half. The system then began to recover, as the chain reaction slowed. By 11:30 P.M. on Monday January 15, sweating engineers on the midnight shift breathed a sigh of relief as the last switch cleared-up.
By Tuesday they were pulling all the brand-new 4ESS software and replacing it with an earlier version of System 7.
If these had been human operators, rather than computers at work, someone would simply have eventually stopped screaming. It would have been OBVIOUS that the situation was not "OK," and common sense would have kicked in. Humans possess common sense—at least to some extent. Computers simply don't.
On the other hand, computers can handle hundreds of calls per second. Humans simply can't. If every single human being in America worked for the phone company, we couldn't match the performance of digital switches: direct-dialling, three-way calling, speed-calling, call-waiting, Caller ID, all the rest of the cornucopia of digital bounty. Replacing computers with operators is simply not an option any more.
And yet we still, anachronistically, expect humans to be running our phone system. It is hard for us to understand that we have sacrificed huge amounts of initiative and control to senseless yet powerful machines. When the phones fail, we want somebody to be responsible. We want somebody to blame.