Telecom acronyms: ISDN stands for which of the following?

Introduction / Context:
ISDN is a foundational telecommunications standard that provided digital end-to-end connectivity long before modern broadband. Technicians frequently encounter the term in legacy voice/data integrations and exam contexts.

Given Data / Assumptions:

• Acronym identification question.
• Focus on the exact expansion of ISDN.

Concept / Approach:
ISDN expands to integrated services digital network, describing consolidated digital services (voice, data, signaling) over the same access line. The other options are nonsense phrases.

Step-by-Step Solution:

Verification / Alternative check:
Telecom texts and standards (e.g., ITU-T) use this exact expansion.

Why Other Options Are Wrong:
They are incorrect fabrications and do not describe telecommunications.

Common Pitfalls:
Confusing ISDN with DSL; they are different technologies and eras.

Final Answer:
integrated services digital network