On 01/02/15 22:37, jdow wrote:
>>
>> Nahhh. Unless 'chrony' has completely mucked up the NTP spec, it deals
>> with symmetrical propagation delays pretty well. It effectively
>> reocords when you sent the request, when the response arrived, and
>> what the server thought the time was to derive the relevant skews.
>
> On many satellite ISP links I've heard that they are extremely 
> asymmetrical with regards to the link delay. In these cases downlink 
> to the customer is satellite and uplink is one form or other of 
> dialup. I've no idea how frequent they are these days. I heard of them 
> more than a decade ago in reference to the Hughes "stuff". NTP becomes 
> quite inaccurate in those cases.
>
> {^_^}   Joanne


The Viasat system uses radio up and down, the subscriber has a ~2 watt 
transmitter, doesn't sound like much but it works well.

For what it's worth I just ran five tests at http://speedof.me/ and saw 
the following "latency" measurements:

841, 1652, 870, 1683, 874 ms.

I don't know how well chrony or ntp can deal with those but I suspect it 
may do pretty well if we are considering a few ms of error acceptable? I 
believe the delay is mainly transit time up and down at both ends of the 
circuit and should be nearly constant.

I also have the Viasat voip service and that has no noticeable delay 
during normal conversation, prefer it to my cell phone, certainly voice 
quality is better and I have even used it to send medical data from a 
heart monitor, "set the device on the phone and press send." In the past 
attempts at using Skype, etc. were poor due to confusion caused by the 
delay.

I will have to look for a gps device of some sort for comparison ...

Bob

-- 
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