[ntp:questions] ACTS: client does not accept acts synchronized server

mills at udel.edu mills at udel.edu
Wed Apr 25 17:19:41 UTC 2007


I checked NPL telephone and found it uses the * and # as per PTB. The 
exisitng driver code captures a timestamp at the beginning of the 
timecode message and at the * and # characters at the end. According to 
the NPL, the * or # is transmitted as the last character of the message, 
which is within one character (CR) of the first bit of the LF on-time 
event. However, the reported PTB timestamp is in error much more than that.

Question about the baud rate. NPL does not specify the baud rate; PTB 
specifies 1200 bps. At 1200 bps a 10-bit characgter takes 8.33 ms, so 
the 78-character message takes 650 ms. If the * or # was not found, the 
error would be near 650 ms; however, if it was found the error should 
depend only on the ISDN delay, which in your case is about the same 
here. In other words, the 51-ms error is probably due to the ISDN delay 
and the \\ scheme would compensate for that.


Uwe Klein wrote:
> mills at udel.edu wrote:
>> Heiko,
>> While this has nothing to do with the second server you cite, the 
>> 51-ms discrepancy between the PTB and GPS time is rather large. Either 
>> the telephone or modem delay is unexpectedly large or the timecode 
>> timestamp is at the wrong on-time character.
> It's all ISDN and digital transfer in the Xchange?
> ( I get around 35/45 ms roundtrip delay via ISDN raw IP )
> uwe

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