Re: [STDS-802-3-EPOC] [802.3_EPOC] Synchronization Eval Criteria for EPoC - Presentation for Jan. 8 Eval Criteria Ad Hoc Call
Hi Marek,
I believe that your description of the operation IEEE Std 802.3bf-2011 - which now can be found in Clause 90 'Ethernet support for time synchronization protocols' of IEEE Std 802.3-2012 - is entirely correct. As stated in subclause 90.2 'Overview', 'The goal of this clause is to provide an accurate indication of the transmission and reception initiation times of all packets, as required to support various time synchronization protocols, e.g., IEEE Std 1588-2008, and IEEE Std 802.1AS.'.
As stated in subclause IEEE Std 802.3-2012 subclause 90.7 'Data delay measurement', 'The transmit path data delay is measured from the input of the beginning of the SFD at the xMII to its presentation by the PHY to the MDI. The receive path data delay is measured from the input of the beginning of the SFD at the MDI to its presentation by the PHY to the xMII.'.
PHY registers provided maximum transmit path data delay, minimum transmit path data delay, maximum receive path data delay and minimum receive path data delay (for example see IEEE Std 802.3-2012 subclauses 45.2.1.104 through 45.2.1.106) which allow the calculation of the transmit and receive path data delay variation. The critical value is this delay variation - not the absolute delays. The greater the variation - these lower the accuracy of the time synchronization.
Any proposal - such as the proposals we were talking about on today's call - will have to be evaluated in respect to transmit and receive path data delay variation to determine the accuracy of the time synchronization it will provide.
Best regards,
David
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From: Marek Hajduczenia [mailto:marek.hajduczenia@xxxxxx]
Sent: 08 January 2013 22:05
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-3-EPOC] [802.3_EPOC] Synchronization Eval Criteria for EPoC - Presentation for Jan. 8 Eval Criteria Ad Hoc Call
Bill,
If I recall correctly, 802.3bf does not deal with time stamping, especially not with MPCP time stamping. All it does it provides indication of passage of packets through the xMII, which can be then correlated with transmission of selected packets across PHY. That combined with information on PHY delay stored in 802.3bf registers provides enough information to calculate precise residence time for the station.
So, I am confused what is really meant by "using a timestamping mechanism for MPCP packets over EPoC similar to the method described in both 802.3bf and 802.1as Clause 13". I think there is some misunderstanding as to what 802.3bf provides and misconception that it is a specification competitive to 802.1as (which it is not, it complements 802.1as as much as 1588v2).
Marek
From: Bill Powell [mailto:bill.powell@xxxxxxxxxxxxxxxxxx]
Sent: Tuesday, January 08, 2013 21:40
To: Marek Hajduczenia
Cc: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] Synchronization Eval Criteria for EPoC - Presentation for Jan. 8 Eval Criteria Ad Hoc Call
Marek,
Thanks for the review and comments. I agree, we have not proven yet that we can meet this criteria, especially the time transfer error criteria on slide 17. However, due to industry requirements for MBH, and competing technologies (GPON) that can provide even lower time transfer error performance, I think we need to be aiming at architecting EPoC to try to meet the goals in this presentation. Having a goal in this area will help us when we start comparing potential implementations.
Note that on Slide 17 the time transfer error performance is labeled as tentative, which in my mind would depend on physical limitations of what we do in the MAC<->PHY layer for EPoC.
I agree that we will need to use a timestamping method for MPCP packets described in 802.3bf. I discussed the differences between 802.3bf and 802.1as (the protocol for MPCP counter synchronization between the EPON OLT and EPON ONU) with Geoff Garner at our last meeting in San Antonio. Geoff mentioned that the timestamping method in 802.1as Clause 13 was essentially similar to the MPCP timestamping criteria in 802.3bf, and the reason that 802.1as did not refer to 802.3bf directly is that 802.3bf was not completed when 802.1as was balloted.
So, the intent here is to propose using a timestamping mechanism for MPCP packets over EPoC similar to the method described in both 802.3bf and 802.1as Clause 13. I intentionally left off this level of 802.1as-vs-802.3bf detail in this presentation, as I thought it would not be beneficial to the overall goal of:
(1) presenting a system level analysis relative to current MBH and CES timing requirements, and
(2) propose specific Eval criteria for EPoC to support these requirements.
Regards,
Bill
-------- Original Message --------
Subject:
RE: [802.3_EPOC] Synchronization Eval Criteria for EPoC - Presentation for Jan. 8 Eval Criteria Ad Hoc Call
Date:
Tue, 8 Jan 2013 21:13:46 +0000
From:
Marek Hajduczenia <marek.hajduczenia@xxxxxx>
To:
'Bill Powell' <bill.powell@xxxxxxxxxxxxxxxxxx>, <STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx>
Bill,
My two cents on that would be simple - a valuable contribution, but adopting
such requirements without even knowing if they are achievable, is at least
premature. We do not have any working models that would allow to estimate
whether such stringent requirements are achievable.
Furthermore, despite multiple indications from my side, the support for IEEE
Std 802.3bf is being still ignored. Without it, I do not know how you can
even think of getting to the level of precision you're suggesting. The delay
through each layer in the EPoC PHY needs to be known if we can ever hope to
get 1588v2 to the precision level you're showing.
Regards
Marek
-----Original Message-----
From: Bill Powell [mailto:bill.powell@xxxxxxxxxxxxxxxxxx]
Sent: Tuesday, January 08, 2013 20:30
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: [802.3_EPOC] Synchronization Eval Criteria for EPoC - Presentation
for Jan. 8 Eval Criteria Ad Hoc Call
Hello All,
I've attached a presentation that I plan to present during the Eval Criteria
ad hoc call tomorrow (Jan. 9). Some of you may have seen most of this
presentation in a different forum, but I'm bringing this into 802.3bn
through the Eval criteria Ad Hoc for further discussion, with a recommended
performance limit for time and frequency transfer error over the EPoC link
on Slide 17 (new slide).
If the group thinks that it would be useful to present to the whole 802.3bn
group, I can also submit it for presentation for the upcoming Phoenix or a
future 802.3bn meeting.
Regards,
Bill
--
Bill Powell
Alcatel-Lucent
Fixed Access Systems Engineering
2301 Sugar Bush Road
Raleigh, NC 27612
bill.powell@xxxxxxxxxxxxxxxxxx
(O) 919-850-6462
(Cell) 919-614-3225
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