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Web Security and Commerce by Gene Spafford, Simson Garfinkel

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Commercial Start-Up

Now that the UNIX workstation was on the island and the leased line to the Internet was up and running, the next thing to do was to work on our dial-up access.

Working with the Phone Company

A friend who ran an ISP in Cincinnati had told me that if I wanted to run a successful dial-up operation, I wanted a service from the phone company called circular hunting. Normally, a bank of telephones is put into what is called a hunt group. You might have a block of phone numbers, from 555-1000 to 555-1020. With normal hunting, a phone call to 555-1000 is always taken by the first phone in the hunt group that isn’t busy. But with circular hunting, the phone system remembers the last phone that it dialed and automatically dials the next phone number in the hunt group, whether the call to the previous phone number has hung up or not.

Circular hunting sounded like a great idea if you are running dial-up access with analog modems. Consider what happens if you have a modem that suddenly fails to answer new calls. If you have circular hunting, then you just lose one modem: the next caller gets the next modem. But if you don’t have circular hunting, then every caller will get the ringing modem, and nobody will get any of the other modems in the hunt group that are still good.

Lesson: Design your systems so that they will fail gracefully.

I called up NYNEX and tried to order a Centrex system with circular hunting. Unfortunately, nobody at the phone company knew what I was talking ...

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