UDP Delay Potential

Question

I have an application that consists of numerous systems using UDP clients in remote locations. All clients send UDP packets to a central location for processing. In my application, it is critical that the central location knows what time the packet was sent by the remote location.

From a design perspective, would it be "safe" to assume that the central location could timestamp the packets as they arrive and use that as the "sent time"? Since the app uses UDP, the packets should either arrive immediately or not arrive at all? The other option would be to set up some kind of time syncing on each remote location. The disadvantage to this is that then I would need to continually ensure that the time syncing is working on each of potentially hundreds of remote locations.

My question is whether timestamping the UDP packets at the central location to determine "sent time" is a potential flaw. Is it possible to experience any delay with UDP?

Answer 1

For seconds resolution you can use time stamping of when you receive the packet, but you still need to use a sequence number to block re-ordered or duplicate packets.

This can make your remote stations less complex as they won't need a battery backed clock or synchronisation techniques.

For millisecond resolution you would want to calculate the round trip time (RTT) and use that offset to the clock on the receiver.

Unless you are using the precision time protocol (PTP) in a controlled environment you can never trust the clock of remote hosts.