EXFO FTB-800 Series for FTB-1 - Manual (Page 548)

Glossary
538 FTB-700G/800 Series
1588 PTP
1588 PTP
The goal of the IEEE 1588 Precision Time Protocol (PTP) is to provide
Network Synchronization using a packet based distribution mechanism.
Depending on the system application the Network Synchronization may
require phase and frequency synchronization. 1588 PTP has the capability
to deliver both by allowing a Client clock to track a Master clock in phase
(time of day) and in frequency.
The protocol is based on exchange of time stamps between the Master
clock and the Client clock. Two methods have been defined in the
1588 PTP standard:

Delay Request-Response mechanism uses message Sync, Delay
Request, Delay Response, and Follow Up (if required).