conforms to the Electronics Industries Association (EIA) RS-366 dialing standard. The RS-366 interface uses the AT command set that was originally employed by Hayes modems. The AT command specifies an auto-call unit (ACU) that takes a line off-hook, detects dial tone, dials a number, detects ringing, and recognizes call completion or failure. Switched 56 service is reliable, universally available, and easy. Its drawback is that local access is expensive. Only in unusual circumstances would one buy switched 56 services today when ISDN or, better yet, IP is a choice. ISDN BRI ISDN is an all-digital subscriber service-a single transport medium that can carry any type of information: voice, data, or video. The Basic Rate Interface, one of the two primary ISDN interfaces, relies on a single twisted copper pair of wires- the same two Circuit-switched Networks wires on which digital POTS service rely. Using this wired-pair, it delivers two 64 Kbps circuit-switched B channels and one 16 Kbps packet-switched delta (data or D) channel. The B channels can be aggregated. For instance, a videoconference can be carried over the 128 Kbps data stream derived by combining two B channels. Low-end video communication applications (in which the need for motion handling and picture clarity is moderate) make extensive use of ISDN BRI service. Where it is offered, it is usually priced competitively, particularly in comparison to Switched 56 service. Not only are monthly rates low, installation charges are also reasonable. The biggest problem with BRI is that is not universally available. If ISDN can deliver 144 Kbps of combined bandwidth, it would seem reasonable to expect POTS lines to do the same. Yet, even when POTS service is equipped with very fast modems, it can generate a maximum data transfer rate of only 33.6 Kbps (56 Kbps modems-that, at the time of this writing, require a number of caveats eliminate digital-to-analog conversion and, therefore, do not provide analog service). The reason that ISDN is more than three times as f