Long-term propagation delay characteristics of telecommunication lines

The variations in outgoing path delay and incoming delay of a paired transmission path have been measured simultaneously and independently for over one year. The characteristics will allow the performance of delay compensation schemes for precise time synchronization of digital telecommunication networks to be evaluated. The annual delay variation is caused by temperature changes, and its magnitude is about 3 μs for the 2400-km line investigated. It is shown that the variation of annual delay can be estimated by measuring air temperature above the cable. The delay variations, which vary slowly with a period of over 10³ s, such as annual and daily variations, are clearly correlated for the outgoing and incoming paths. Asymmetry of slow delay variation is below 1 ns (indicated noise deviation). The cause of the delay variation that has a period of 10⁰<τ<102 s is the noise generated by the multiplexing and demultiplexing equipment