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

Stewart Bryant stbryant at cisco.com
Wed Oct 24 08:45:35 UTC 2007


Brad
>   From reading the IEEE 1588 
> page, it's not clear whether this works over IP or not.
In discussing 1588, you need to make sure you are  talking about the V2 
spec.
V1 is  not likely to see significant deployment, whist V2 is likely to 
get significant
hardware support and hence be widely deployed.

Both V1 and V2 can use multicast IP encapsulation and you can in 
principle build an
IP multicast net, but I have always regarded this mode of operation as a 
little
strange and unlikely to ge deployed outside a highly controlled network. 
I doubt
if we will ever see the 1588 multicast mode on the Internet.

However V2 can run over a unicast IP connection, and this is likely to find
use in wide area networks. Indeed it exists largely to support the needs of
the telecommunications operators for a method of providing clock sync over
packet.
> , 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.
>
>   
I am not sure what you mean by this. How the grand master acquires and 
locks to
an external clock reference is outside the scope of the protocol, but 
it's also outside the
scope of the NTP. However 1588 does have a grand master election mechanism
that - given honest representation by the clocks - selects the best 
clock as the
grand master to which the slaves synchronise and avoids the formation of
timing looks.

Stewart




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