Discuss the reasons why ISDN failed to catch on as WAN technology.

ISDN (Integrated Services Digital Network) did not become a widely adopted WAN technology primarily due to several factors:

1. Cost: ISDN equipment was often expensive, and the service typically incurred higher installation fees and per-minute charges compared to traditional analog dial-up connections. This made continuous data use costly.
2. Limited Bandwidth: While faster than analog modems, ISDN's Basic Rate Interface (BRI) offered 128 kbps. Primary Rate Interface (PRI) provided speeds up to 1.544 Mbps (T1) or 2.048 Mbps (E1). These speeds were quickly surpassed by emerging broadband technologies like DSL and cable modems.
3. Emergence of Competing Technologies: Digital Subscriber Line (DSL) and cable modems began offering significantly higher bandwidths (e.g., ADSL typically started at 1.5 Mbps downstream and increased rapidly) at a flat monthly rate. These 'always-on' services were more convenient and cost-effective for internet access, leveraging existing widespread copper telephone lines and cable TV infrastructure.
4. Complexity: Setting up and configuring ISDN required specific technical knowledge, often involving Service Profile Identifiers (SPIDs) and Terminal Endpoint Identifiers (TEIs), making it more complex for average users compared to the plug-and-play simplicity of later broadband solutions.
5. Availability: While deployed in many areas, ISDN infrastructure was not as ubiquitous as the standard telephone lines or cable TV networks that DSL and cable modems could utilize, limiting its reach for potential users.

The combination of these factors led to ISDN being quickly overshadowed by more affordable, faster, and simpler broadband alternatives as internet usage became more widespread in the late 1990s and early 2000s.