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Is there something I'm not seeing or there is a flow in this algorithm(which everyone is referring to) http://www.mine-control.com/zack/timesync/timesync.html

Assumption 1: When I say a is substracted from b it means "b - a", maybe in the text they actually meant the other way arround? I would guess so. Assumption 2: the synchronization is to get the server clock on the client - If this is the gase shouldn't latency from server to client suffice?

Anyway, he article says: Client sends packet with timestamp t1, Server responds with it's timestamp t2. Client receves this packet at t3. So t3 > t2 > t1

RTT = t1 - t3 (gives a negative value, I guess it should be t3 - t1) latency = RTT / 2 (more or less, again it shoul be positive) client server time delta = t2 - t3 (server timestamp - current time) clock delta = t2 - t3 + RTT/2 (again, gives a negative value, abs again?)

Surely this cannot be... if the client time to server time is the same as the client thrn the clock delta is the RTT or 0 if I do abs (t2 -t3) + RTT/2.

if it is latencies are asymetric then the las calculation gives different results depending where I put abs abs(t2 - t3) + RTT/2 abs(t2 - t3) + abs (RTT/2) t2 - t3 + abs(RTT/2)

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  • \$\begingroup\$ I was trying to solve a slightly different problem (or I understood that the problem they were trying to solve is a different one). This also clears is it up a bit: docs.gamesparks.com/tutorials/real-time-services/… \$\endgroup\$
    – Sil
    Commented Oct 8, 2018 at 18:10

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The industry standard network time protocol (NTP) also takes into account the latency of the server processing. This means there are 4 timestamps, one each for send/receive of client/server. when properly calibrated it would look like: t_cr > t_ss > t_sr > t_cs and t_cr - t_ss == t_sr - t_cs

That is: the travel time of the packet from client to server is equal to the travel time from server to client. And you can offset the client time to make that true.

The offset needed is = (t_ss + t_sr)/2 - (t_cs + t_cr)/2 adding this to the client time will line them up.

The NTP clients will do some statistical analysis and such to smooth out time changes and filter out outliers.

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  • \$\begingroup\$ NTP is pretty clear to me.. and the above algorithm is kind of the same with t_ss = t_sr. My misunderstanding came from the fact that I was trying to solve a different problem :) \$\endgroup\$
    – Sil
    Commented Oct 8, 2018 at 18:00

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