SPID was designed to help telephone companies keep control over Centrex extensions using ISDN's passive bus option, which allowed up to seven terminals to share one BRI line. But the result was that all ISDN phones or data adapters needed telephone company- controlled passwords in order to draw the ISDN equivalent of dial tone! This led to countless repair calls and installation delays. Scott Adams, best known for his Dilbert comic strip, worked on ISDN strategy at Pacific Bell early in his cartooning career. In his 1997 book The Divestiture: Equal Access and Chinese Walls Dilbert Future, written just before the widespread deployment of asymmetric digital subscriber line (ADSL) and cable modems, he explained ISDN's failure: The only thing that could limit its success was complete incompetence on the part of all the phone companies, colossal stupidity by every single ISDN hardware vendor, and complete idiocy on the part of the regulatory over- sight bodies. It was obvious to me that ISDN was doomed [31]. Digital Access Held Hostage to Local Measured Service The RBOCs were primarily interested in ISDN's voice capabilities for Centrex. But its non-Centrex data capabilities were more empowering. When ISDN trials began in the late 1980s, dial-up modem speeds were typically no higher than 14.4 kbps. Compared with this, ISDN's 64 kbps was lightning-fast; with two B channels, callers could achieve 128 kbps. This paled next to Ethernet's 10 Mbps (higher-speed Ethernet was to come later), SO it was not competitive in the local area network, but it was a fine substitute for a modem. And from the carrier's perspective, it used virtually the same resources, because each telephone call took the same 64 kbps worth of network bandwidth anyway. ISDN just replaced the line interface and left out the analog-to-digital converter. It did not cost the car- rier any more to carry an ISDN data call than a voice call, except that in some cases, because of limitations in older equipment, clear-channel 64k service between switches had to b