#Accuracy #Determining #Factors #on #the #Network

Accuracy Determining Factors on the Network Whenever a network packet is sent from one application running on one node to another application running on a different node the network packet has to traverse a path which includes quite a number of unknown delays or latencies:

All the yellow lines indicate unknown processing delays. If the packet has to go through a switch, but the output port is just busy with a different packet (red lines) then the packet is delayed. Also different link speeds on the 2 involved switch ports cause an asymmetry of the packet delay which results in a time offset. Unfortunately there are only switches available which support this for PTP, but there are no switches which support this for NTP. On the other hand, even if hardware time stamping of NTP packets was supported the current version of the NTP protocol doesn't even provide a proper way to forward the measured delays. The reference implementation of the NTP protocol, ntpd, can yield pretty good accuracy anyway with standard hardware (no time stamping support) due to its built-in filter algorithms.