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

[Heiko Gerstung]

Sasha Vainshtein schrieb:
> Heiko, Stewart and all,
> I just wonder if the PTP "transparent clock" (TC) mechanism is not in
> contradiction with the way IP routers are supposed to work?
> When PTP runs over IP, at least some of the PTP traffic (DELAY_REQ and
> DELAY_RESP messages ) are unicast UDP/IP Packets running between the PTP
> Slave and PTP Master with the well-known UDP port assigned to PTP. Hence
> the "normal" routers would simply pass these packets thru without even
> looking at the UDP ports not to mention UDP payload (i.e.., PTP proper).
> Of course one may add the "router alert" option to these packets (even
> if, AFAIK, PTP does not specify that), but even this would hardly help
> since the router would probably simply put the packet on the "slow
> path". 

That is correct, a TC concept always would include special hardware which 
supports this mode. Just like hardware timestamping would require special NICs.

   Heiko


> 
> My 2c
>                  Sasha
> 
> 
> 
> -----Original Message-----
> From: ntpwg-bounces+sasha=axerra.com at lists.ntp.org
> [mailto:ntpwg-bounces+sasha=axerra.com at lists.ntp.org] On Behalf Of Heiko
> Gerstung
> Sent: Wednesday, October 24, 2007 4:06 PM
> To: stbryant at cisco.com
> Cc: mayer at ntp.isc.org; NTP Working Group; Brad Knowles
> Subject: Re: [ntpwg] Documents, slides, etc. from WG meeting
> 
> Stewart Bryant schrieb:
>> Heiko
>>> The one thing that really enables PTP to reach an impressive accuracy
> 
>>> level over an Ethernet/UDP connection is the fact that it uses 
>>> hardware time stamping and therefore requires specialized hardware 
>>> (if you want to benefit from that superior level of accurcacy).
>>>   
>> There is nothing to stop NTP doing h/w timestamping per se. The 
>> critical difference is that PTP (1588)  does on path correction 
>> through the use of the TC mechanism. If TC were added to NTP the two 
>> protocols would provide the same level of accuracy.
> 
> I agree. The TC concept introduces quite a number of security problems,
> which have been addressed in V2 but obviously lead to an increased
> complexity. Adding a few things like hw-timestamping and on path
> correction to NTP would result in a synchronization protocol which
> offers a very good performance over both a WAN link and a controlled LAN
> environment (plus compatibility to millions of existing clients). Well,
> I have to go and talk to my engineers now :-)
> 
> Best Regards,
>   Heiko
> 
> 
> 
>> Stewart
>>
> 
> 
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Lange Wand 9
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Tel.: ++49 (0)5281 9309-25
Fax: ++49 (0)5281 9309-30
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