Hello,
I have ntpd set up with two time sources, GPS_NMEA and a PPS pulse, and I have
a couple
of perhaps basic questions.
NMEA sentences are not read directly from a physical serial port but a
"virtual"
/dev/gps0 that is fed by a separate process.
PPS pulse comes from the gps module and is
Dave Hart wrote:
> On Wed, Dec 28, 2011 at 21:54, David Malone
> wrote:
>> Modern hardware that supports 802.11e (or 802.11n, which requires
>> much of the QoS part of 11e) can control things like the number of
>> retries, and you could hack the driver to inspect the packets and
>> if it is NTP t
Danny Mayer wrote:
No, they use synchronized Cesium atomic clocks for time accuracy. GPS is
only used to get a fix on the location and I'm not sure that 10's of
centimeters is good enough for what they are trying to prove. I'd have
to look closely at the methods used and the data to even have a c
1. If you mark clocks as "true" you somehow fool yourself :-). Because now
if the clocks are real falsetickers you won't even know about it and your
system
will be out of sync and for ex. will show low offset from some falseticker
maybe.
So you have to make clocks closer but don't mark them as "tru
Thanks for your reply, Dave.
> Mills, D.L. The Fuzzball. Proc. ACM SIGCOMM 88 Symposium (Palo Alto CA,
> August 1988), 115-122.
>
> Mills, D.L., and H.-W. Braun. The NSFNET Backbone Network. Proc. ACM
> SIGCOMM 87 Symposium (Stoweflake VT, August 1987), 191-196.
For the benefit of anyone research
2011/12/29 Nickolay Orekhov
> Yes, you are right. Your system is synced with PPS and gets seconds from
> NMEA.
> You can set time1 to make NMEA offset closer to reality ( and to PPS ).
>
> By the way, if you have only two clock sources, NMEA + PPS and offset
> between them is bigger then "mindist
In article ,
Dave Hart wrote:
>On Wed, Dec 28, 2011 at 18:58, Rod Dorman wrote:
>> Is this defined in an RFC or some other standards document?
>
>http://standards.ieee.org/about/get/802/802.11.html
I did a quick scan of 802.11-2007.pdf and didn't see any requirement
that UDP is treated as guara
Hi,
Nickolay Orekhov wrote:
> 2011/12/29 Nickolay Orekhov
>
> Yes, you are right. Your system is synced with PPS and gets seconds from
> NMEA.
> You can set time1 to make NMEA offset closer to reality ( and to PPS ).
>
Having NMEA offset close to zero, or leaving it at 350 ms, is there a
diff
Juliusz ,
The fuzzballs indeed used a delay metric. They made little nests at the
earth stations in the SATnet program, as well as the routers used in the
early NSFnet. In its original form, the ARPAnet also used a a node state
metric like the fuzzballs, but switched to a link based metric lik
On Thu, Dec 29, 2011 at 19:35, Rod Dorman wrote:
> I did a quick scan of 802.11-2007.pdf and didn't see any requirement
> that UDP is treated as guaranteed by WiFi.
>
> Could you give a page number or section reference?
My belief is 802.11 treats all unicast datagrams equally, and all
multicast/b
Dave Hart writes:
>I recognize I'm suggesting a layer violation in wishing 802.11 devices
>treated UDP differently from TCP, or even worse in terms of layer
>violation, UDP 123 differently from UDP 53. It's not pretty, but it
>would make a positive difference. The ideal number of retries for NT
r...@panix.com (Rod Dorman) writes:
>I did a quick scan of 802.11-2007.pdf and didn't see any requirement
>that UDP is treated as guaranteed by WiFi.
>Could you give a page number or section reference?
Look for the handling of unicast traffic.
David.
__
In article ,
David Malone wrote:
>r...@panix.com (Rod Dorman) writes:
>
>>I did a quick scan of 802.11-2007.pdf and didn't see any requirement
>>that UDP is treated as guaranteed by WiFi.
>
>>Could you give a page number or section reference?
>
>Look for the handling of unicast traffic.
I'm sti
r...@panix.com (Rod Dorman) writes:
>Isn't 802.11 a physical layer specification? Why would it be defining
>transport layer behaviour?
No - it's a MAC and PHY layer. It doesn't care about TCP or UDP,
only MAC layer things like unicast and multicast, and the required
management/control glue to mak
People really do need to read the paper rather then guess.
Yes, As some have said, normally GPS is not accurate enough for this
level of work but they are not using GPS in the normal way. What they
do is agree on ONE specific GPS satellite that happens to be visible
at both locations. Each site
On 29 Dec, 2011, at 23:26 , Terje Mathisen wrote:
> Danny Mayer wrote:
>> No, they use synchronized Cesium atomic clocks for time accuracy. GPS is
>> only used to get a fix on the location and I'm not sure that 10's of
>> centimeters is good enough for what they are trying to prove. I'd have
>> t
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