Re: Hardware SNTP server

brad@xxxxxxxxxxxxxxxxxxx (Brad Knowles) · Tue, 13 Sep 2005 13:45:23 GMT

At 7:14 PM +0900 2005-09-13, Toriyama, Hiroshi wrote:
 I think that the main advantage of our server is in the low degree
 of operation cost, not the equipment cost itself.

	You've got that with the PHK design based on a Soekris net4501 -- 
burn a CompactFlash card for the OS and configuration, connect the 
cables, and you're done.  Moreover, with more of these machines 
distributed around the network, run them in broadcast, multicast, 
and/or manycast modes, and you will have much less network 
infrastructure between any of your timeservers and their clients, 
which will help make the overall service much more robust in the face 
of network failure.
	Maybe I'm missing something here, but I don't see the operational 
cost benefit you're talking about.  But I certainly see what appears 
to be a pretty big drawback in the implementation, in that you're 
throwing away most of what I consider to be the best parts of NTP, 
just so that you can burn these things into FPGAs.
 Concentrated server can be built with many ntpd servers and
 a L4-L7 load balancer, but but a hardware SNTP server must be
 implemented simpler than the load balancer.

	But you don't need load balancers.  In fact, the design of the 
NTP protocol is such that it prohibits their use.  You cannot have a 
client contact one server (via a load-balancer) for one packet, and 
then have the client contact a different server (maybe via the same 
load-balancer) with the next packet.
	Because these servers would not be the same and would not have 
precisely the same concept of time, to do this would be to completely 
destroy the NTP protocol itself.  Even if they're all served by the 
same atomic clock reference, using serial cable splitters or 
whatever, those differences in cable lengths would be significant.

	What you want is broadcast, multicast, and manycast servers and 
clients, so that the load is automatically distributed across the set 
of servers, and the clients are automatically served by those 
machines which are close by.
 This is the basic idea of our SNTP server.

	Which seems to be pretty much 180 degrees away from where I 
believe that NTP services should be going.
--
Brad Knowles, <brad@xxxxxxxxxxxxxxxxxxx>
"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
    -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
    Assembly to the Governor, November 11, 1755
  SAGE member since 1995.  See <http://www.sage.org/> for more info.
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Re: Hardware SNTP server

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