[evlatests] news

[Rick Perley]

    I had thought that we had intended to use GPS as our primary time 
reference.  

Bill Sahr wrote:
> Please see below.
>
> Ken Sowinski wrote:
>   
>> On Tue, 5 Jun 2007, Ken Sowinski wrote:
>>
>>     
>>> During one of Rick's observations early this afternoon and for
>>> a while afterward it appears that the EVLA antennas' idea of
>>> time seemed to differ from the rest of the VLA for while.  I
>>> planned to disable phase switching to pin down the source of
>>> the problem, but while discussing it with Jim Jackson it
>>> magically cured itself.  This raises the obvious question of
>>> whether the changed time multicasting contributed to this.
>>> Without further evidence I doubt it.  The same thing occurred
>>> for a while last week, albeit after many serious disturbances
>>> to the system.  Should the antennas continue to lose sync with
>>> the VLA over the next few days I think we should consider turning
>>> off the multicast of time from andy.
>>>       
>> James explained to me that coincidentally there was a machine in
>> Socorro multicasting at the time Monday afternoon when the L302
>> mibs appeared to be confused about time.  There is no doubt that
>> these packets would have made it to the EVLA antennas.
>>     
>
> I take it that it is safe to assume that this machine in Socorro
> was multicasting time, and further in a valid NTP format ?  I ask
> because I have been experimenting with multicasting using mnemosyne
> and orca, but only text messages, not time, and to a port I
> believe to be unused by the EVLA (multicast addr 239.192.0.1,
> port 20050).  I cannot remember if I was running this software on
> Monday.
>
>   
>> While not a clear explanation it this seems a likely cause.  There
>> is still no reason to discontinue having both amos and andy multicast
>> time, but we should remain alert to possible timing errors.
>>
>> James and I discussed the merits of letting the VLA network use the
>> GPS at the VLA as its primary NTP server.  This would insulate us
>> from drifting time if the network to the outside world is lost.
>> I believe it is possible to configure NTP so that it still looks at 
>> the outside time servers so that a failure of the GPS will be detected
>> and reported.  Is this a good idea?
>>     
>
> The notion of using the GPS at the VLA site as the primary NTP server
> seems sound, as does the idea of checking the GPS time against external
> time servers and reporting significant differences between the two
> time sources.
>
> Bill Sahr
>   
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>>     
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