rk in edge and core switches. Like many other technologies along the way, ATM evolved after such things as time division multiplexing (TDM), plesiochronous network PRACTICAL IP AND TELECOM FOR BROADCAST ENGINEERING AND OPERATIONS hierarchy, X.25 packet networks, maybe in the same timeframe as SONET/SDH, but before wide acceptance and initial growth of Ethernet and IP networking. Early on, ATM was supposed to be the Holy Grail of all-purpose communications networks. However, that was not to be, as IEEE 802 Ethernet is now testimony to that fact, to say nothing of the past few years rampage to put IP directly on SONET/SDH transport, making IP over ATM obsolete. ATM was crafted out of a desire to accommodate as much offered traffic as possible from the maximum possible number of users, while at the same time ensuring safe, effective (profitable) traffic move- ment. A casual look at the network during the time ATM was created would show a pattern much like hotels and airplanes. Equating time slots in digital transmission facilities with rooms in hotels and seats in airplanes, it was easy to see there was significant space available except during peak demand times. It could be seen that if a way to use the idle capacity could be found, it meant incremental revenue. If not, and the facilities in use could be reduced, reducing overall operating cost. Either or both of the two favorably impact the finan- cial bottom line. So it is with Internet and Telecom facilities, not just airplanes and hotels. From the beginning, computer communications were facilitated with either dial-up modems using PSTN voice grade services and facil- ities, or private leased lines. Generally the rule of thumb was to use dial-up if it was a local call. If the connection required a long distance connection, the cost was tolerated to the extent necessary to justify a full-time, private, or leased connection at a fixed cost. Even though the private line was a fixed cost and available 24/7, actual traffic passing over the facility was usually far le