Network and infrastructure
ISDN
Acronym: RNIS
ISDN is the digital telephone network of the 1980s, carrying digitised voice over the same copper pair as the analogue line.
It long served businesses as an intermediate solution: several simultaneous calls over a single access, and consistent quality. For fax it mainly brought faster negotiation and fewer transmission errors. Most European countries have completed its shutdown, often ahead of the analogue network's.