[ntpwg] Documents, slides, etc. from WG meeting

[David L. Mills]

Brad,

There might be a basic misunderstanding here. IEEE 1588 uses UDP over IP 
and a protoccol which develops four timestamps used in much the same way 
as NTP. However, 1588 interfaces can capture a hardware timestamp on 
departure and arrival of an Ethernet frame.

A diagram of what is described as a two-step 1588 protocol is in the NTP 
architecture briefting on the NTP project page linked from www.ntp.org. 
Also in that briefing is a diagram of a two-step NTP protocol. Unlike 
the 1588 protocol, the two-step NTP protocol is symmetric. In the 
two-step protocol, the transmit timestamp for one packet is sent in the 
next following packet. The two-step NTP protocol uses the same packet 
format as the current one-step protocol; the existing implementation 
could in principle operate with either one- or two=step modes.

Available 1588 interfaces and servers (grandmasters) typically achieve 
accuracies in the 50-ns range. Without hardware assist but with the 
two-step variant, I would expect NTP to achieve accuracies in the 
sub-microsecond range. At the moment the accuracies with NTP and PPS 
signals hovers around 20 a few microseconds.

Dave

Brad Knowles wrote:

> On 10/23/07, Danny Mayer wrote:
>
>>> A long discussion at end of meeting discussing the future of
>>> timekeeping here in the IETF. Is the future 1588 over IP?
>>> NTP over IP? No consensus was reached.
>>
>> Could some explain exactly what that means? Is this a question of
>> certain protocols (DNS and Kerberos come immediately to mind) that
>> require that two interacting servers keep their clocks within X minutes
>> of each other in order for various security requirements to work
>> correctly or ro be assumed to be valid? Is it something else?
>
>
> Well, NTP is inherently an IP protocol. From reading the IEEE 1588
> page, it's not clear whether this works over IP or not, although it
> does seem to work over Ethernet (and maybe others?). But IEEE 1588
> seems to focus on ultra-high resolution, like sub-microsecond or even
> sub-nanosecond. Meinberg appears to have a clock that does both NTP
> and IEEE 1588.
>
> But I'm not seeing how IEEE 1588 can provide synchronization to an
> outside reference, and I'm not seeing how it can be used outside of
> certain limited circumstances on a pretty much pure Ethernet network.
>