Hi，Ron
I agree that classifying PTP event and general messages into separate
PHBs is problematic,
and it is should be to use the same PHB to all PTP messages.
In addition, I think that it should take into consideration the
encapsulation of PTP message，
because PTP PHB is related with PTP message formats(e.g. vlan PRI, ip
Tos, mpls EXP).
Best Regards
Junhui
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Junhui Zhang
Bearer Network Product Pre-research Dept.
ZTE Corporation
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Ron Cohen <[email protected]>
发件人: [email protected]
2011-08-07 15:59
收件人
[email protected]
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[TICTOC] DSCP for PTP
Hi,
Current standards do not recommend which DSCP values to set on PTP
messages. As a result vendors have chosen different default values, and
some vendors also differentiate between the DSCP set on PTP Event messages
(Sync, Delay_Req, etc.) and PTP General messages (Announce, Follow_Up,
Delay_Resp). I think TICTOC can help clarify the recommended DSCP usage,
along the guidelines of RFC4595, 'Configuration Guidelines for DiffServ
Service Classes'.
In my opinion classifying PTP event and general messages into separate
PHBs is problematic as discard of Follow_Up would render its associated
Sync message useless. Forwarding of Sync messages in a higher priority
queue compared to Follow_Up may lead to Sync message getting ahead of the
previous Follow_Up message which again causes the slave to discard the
previous Sync message. Hence the first order recommendation in my opinion
should be to use the same PHB (and DSCP marking) to all PTP messages.
Choosing one of the existing PHBs as the recommended one for PTP is
somewhat harder. EF is a reasonable choice in my opinion, as per RFC4595
'The intent of Expedited Forwarding PHB [RFC3246] is to provide a building
block for low-loss, low-delay, and low-jitter services.' TICTOC could in
principle recommend defining a new PHB tailored for PTP and similar
services, but I guess this would be a longer process.
I would appreciate if others will share their insight on the recommended
usage and whether this issue should or should not be addressed by TICTOC.
Here is the relevant text from IEEE1588-2008 Annex D: "For PTP event
messages, the value of the differentiated service (DS) field in the Type
of Service (ToS)
field should be set to the highest traffic class selector codepoint
available." The PTP Telecom profile for frequency distribution, ITU-T
G.8265.1, doesn't specify or recommend DSCP settings.
Best,
Ron_______________________________________________
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