In this section
This section describes how to compensate for a PTP path delay asymmetry.
PTP delay asymmetry
PTP path delay asymmetry is defined as half the difference between the propagation times in two opposite directions. There can be a number of causes for such an asymmetry:
- Mismatch in the link speeds between master and slave
- Mismatched fiber lengths if separate fibers are used for the two directions resulting in a 2.5-ns asymmetry per meter of length difference since the delay in optical fibers is 5 ns/m and the asymmetry is half the difference between propagation times
- Different routes for uplink and downlink
- Poor equipment design
The asymmetry can be calculated or measured, and the value can be used for compensation.
This figure shows an example where the cable in one direction is 4 m and the cable in the other direction is 104 m. In theory this results in a delay asymmetry of 250 ns (100 m × 2.5 ns/m).
PTP delay asymmetry compensation
ntservice.ini code line
The syntax for the ntservice.ini code line compensating for a PTP delay asymmetry is:
'PTPDelayAsymmetry' '=' ( '–999000000' | '–998999999' | '–998999998' | ... | '0' | '1' | '2' | ... | '999000000' )
This table shows the default value.