Have a mean time between failures (MTBF) of at least 15 000 hours based on either Bellcore TR-NWT–000332, issue 6, 12/97 or field collected data;
een gemiddeld storingsvrij interval (MTBF) hebben van tenminste 15 000 uren op basis van Bellcore TR-NWT-000332, issue 6, 12/97, of praktijkgegevens;