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

[Sasha Vainshtein]

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". 

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
> 


--
------------------------------------------------------------------------

*MEINBERG Funkuhren GmbH & Co. KG*
Lange Wand 9
D-31812 Bad Pyrmont, Germany
Tel.: ++49 (0)5281 9309-25
Fax: ++49 (0)5281 9309-30
eMail: heiko.gerstung at meinberg.de <mailto:heiko.gerstung at meinberg.de>
Internet: www.meinberg.de <http://www.meinberg.de/>

------------------------------------------------------------------------

Meinberg radio clocks: 25 years of accurate time worldwide

_______________________________________________
ntpwg mailing list
ntpwg at lists.ntp.org
https://lists.ntp.org/mailman/listinfo/ntpwg