Hi,

Suppose I have a package from computer A which is sent to computer B. 
How can I know the time for this transmitting?

One way is that before sending it, I gave a time stamp in the package 
and then send it to socket. When B receives it, it can check the current 
time and calculate the time it costs. But the problem is that the two 
computer are not precisely synchronized. So the result will not accurate.

Do you have any suggestion?

Best,
Tony

Tony, Zhang wrote:
> Hi,
> 
> Suppose I have a package from computer A which is sent to computer B.
> How can I know the time for this transmitting?
> 
> One way is that before sending it, I gave a time stamp in the package
> and then send it to socket. When B receives it, it can check the current
> time and calculate the time it costs. But the problem is that the two
> computer are not precisely synchronized. So the result will not accurate.
> 
> Do you have any suggestion?
> 
Synchronise them - apropos ntp.

-- 
Ian Collins.

On Apr 10, 2:54 am, "Tony, Zhang" <zyzh...@cuhk.edu.hk> wrote:
> Hi,
>
> Suppose I have a package from computer A which is sent to computer B.
> How can I know the time for this transmitting?
>
> One way is that before sending it, I gave a time stamp in the package
> and then send it to socket. When B receives it, it can check the current
> time and calculate the time it costs. But the problem is that the two
> computer are not precisely synchronized. So the result will not accurate.
>
> Do you have any suggestion?

It depends upon your precise requirements. If you really only need to
measure round-trip-time, then you can take both time stamps on the
same machine. If you really do need to measure uni-directional delay,
but both machines are on reasonably symmetric net connections
reasonably far away, synchronizing both machines using ntp may do.

In the most extreme cases, you need to provide both ends with GPS time
references. They cost on the order of $100 these days. Any GPS device
that can provide a 'pulse per second' output synchronized to the UTC
second boundary will do. Last I checked (four years ago or so), the
Motorola Oncore series, though not cheap, was about the best GPS clock
under $500.

I would urge caution regarding using any time source other than GPS.

DS