Two network operation centres are located $32$km apart, based on the duct route

between them. The primary communication devices at each centre are wide area

network capable routers with fibre optic communication link modules, and the centres

are connected by external single mode $9/125$um fibre optic cable which has three

external joints. The total internal distance from the external cable change over splice

in the building to the routers is $150$m and a mated connector is required to make the

termination at each router. It is necessary to include an additional loss margin of $5$dBs

to account for component ageing and future cable repairs.