Subject: [TICTOC] "Carrier Class" timing requirement

From: "Steve Chen" <[email-masked]>
Date: Mon, 2 Apr 2007 13:49:15 -0400

Stuart and Dave,

Sorry I just got to comment on your emails below.

My opinion is that trying to meet "Carrier Class" timing requirement is a
noble but difficult goal that we probably will not reach for a while. And is
it absolutely necessary? Especially when carriers have already deployed
Stratum 1 with Stratum 2 backups all over the place?

More critical then carrier applications will be the enterprise applications,
where deploying Stratum 1 and 2 are either not practical or not economical,
but major applications are "just around the corner," urgently awaiting a
reliable but inexpensive timing solution.

I suggest that we make "enterprise" requirement (we need to define that from
service providers) our first goal, and then move forward from there.

Regards,
Steve Chen

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Sent: Monday, March 19, 2007 2:40 PM
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Subject: TICTOC Digest, Vol 8, Issue 4

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Today's Topics:

   1. RE:  Re: TICTOC NTP ensembling (STUART VENTERS)

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

Message: 1
Date: Mon, 19 Mar 2007 13:39:27 -0500
From: "STUART VENTERS" <[email-masked]>
Subject: RE: [TICTOC] Re: TICTOC NTP ensembling
To: <[email-masked]>
Cc: [email-masked]
Message-ID:
	<[email-masked]>
Content-Type: text/plain;	charset="iso-8859-1"

Dave,

If an ensemble is a collection of separate reference clocks, then I can see
your logic.

If an ensemble is a collection of paths back to the same PRC,
  then it seems like if the noise goes up as you add paths, 
  then there is something wrong with the combining algorithm, 
   not the basic plan to combine clocks.

Which sort of ensemble do you feel is more suitable for "carrier class"
timing?

(Also I wonder if the tradeoffs between providing 
   a wander free frequency reference and 
   a correct time of day reference are mixed into this.)

Regards,

Stuart 

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Monday, March 19, 2007 11:48 AM
To: [email-masked]
Subject: [TICTOC] Re: TICTOC NTP ensembling

Attending the WSTS07 last week, I was left with the impression that people
considered one of the good things about NTP is the ability to form a clock
from an ensemble of master clocks. However, I see this as another
potentially serious source of noise which may swamp the output noise budget
for many telecom applications. I can see that having an ensemble could
offer good performance, but I think that would only be acheived if the
ensemble was a stable collection. If master clocks can appear and
disappear, then their individual biasses will pull the output phase around
a little. For the generally-accepted accuracy of 1-10ms, this effect is
probably not visible, but when the application requires +/-500ns accuracy
then I think this problem will dominate. I am not an NTP expert, but I can
imagine this problem is more difficult to solve than PDV-filtering. I would
also like to know what the carriers think of this - do they consider this
approach to be "carrier-class"?

Dave

Semtech Ltd
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From: "STUART VENTERS" <[email-masked]>
Date: Mon, 2 Apr 2007 17:23:39 -0500

Steve,

>From what I've seen, telco's hope to move to new packet fed installations where the only way to get a Stratum reference is over the packet feed.  In this case, sending the Telco timing reference over a packet interface will be absolutely necessary to support existing applications.

This reference could be sent using packet arrivals or using the Layer 1 clocks,
 but if TOD is needed, that probably says packet arrivals are involved.

I agree that delivering Telco timing using packet arrival times over all possible packet networks is probably an unreachable goal.  From the presentations at WSTS07 it appears that the goal is reachable over some subset these networks.  

I'd like to see TicToc find a common solution for both the carrier and enterprise applications.

(Perhaps as telco's move to needing TOD
    and enterprises move to needing precision time for transactions,
       the requirements are not all that different.)

Regards,

Stuart

-----Original Message-----
From: Steve Chen [mailto:[email-masked]]
Sent: Monday, April 02, 2007 12:49 PM
To: [email-masked]
Subject: [TICTOC] "Carrier Class" timing requirement

Stuart and Dave,

Regards,
Steve Chen

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: Monday, March 19, 2007 2:40 PM
To: [email-masked]
Subject: TICTOC Digest, Vol 8, Issue 4

Today's Topics:

Message: 1

Dave,

Regards,

Stuart 

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Monday, March 19, 2007 11:48 AM
To: [email-masked]
Subject: [TICTOC] Re: TICTOC NTP ensembling

Dave

Semtech Ltd

---

From: Stewart Bryant <[email-masked]>
Date: Fri, 06 Apr 2007 11:23:28 +0100

> Stratum 1 with Stratum 2 backups all over the place?
I agree that it is a difficult problem, although work by a number of 
chip vendors suggests that it is tractable.

The problem with Stratum1/2 sources is that you need to be able to 
transfer frequency from the source to the client. In the past this has 
been easily achieved through the SONET/SDH/TDM network, but the move to 
Ethernet creates a gap in coverage. This may to some extent be addressed 
by SyncE, but it is by no means certain how widely that will be deployed.

There is also the issue of the number of point in the network that need 
sync. Micro and Pico cells will need sync and they are unlikely to have 
access to traditional sync attachment points.

The above also applies to TDM PWs.

> reliable but inexpensive timing solution.

I agree that there is an equally demanding and urgent set of enterprise 
applications. If you have examples that we can add to our list of use 
cases I would b e interested.
> service providers) our first goal, and then move forward from there.

I am concerned that by leaving the SP applications out of the picture we 
will end up with multiple competing solutions.

- Stewart