Re: [TICTOC] [mpls] TICTOC WG LC for draft-ietf-tictoc-1588overmpls

Kevin, Shahram and all,

I do not actively follow the developments in the ITU-T SG 15, but I believe that investigation of partial on-path support for PTP (which would be the case if some LERs on the path were not PTP-aware) has just began there, and it is not clear what (if anything) could be achieved and under what conditions.

Did I miss something important here?

My 2c,

     Sasha

________________________________
From: tictoc-bounces@ietf.org [tictoc-bounces@ietf.org] on behalf of Kevin Gross [kevin.gross@avanw.com]
Sent: Friday, July 19, 2013 7:32 PM
To: Shahram Davari
Cc: mpls@ietf.org; S. Davari; tictoc@ietf.org
Subject: Re: [TICTOC] [mpls] TICTOC WG LC for draft-ietf-tictoc-1588overmpls

You need to specify what you mean by "recover the time correctly." Everytime you pass through a piece of equipment that is not timing aware, you introduce noise into the timing signal. More hops, more noise. Noise reduces synchronization accuracy.

Kevin Gross
+1-303-447-0517
Media Network Consultant
AVA Networks - www.AVAnw.com<http://www.avanw.com/>, www.X192.org<http://www.X192.org>

On Fri, Jul 19, 2013 at 7:19 AM, Shahram Davari <davari@broadcom.com<mailto:davari@broadcom.com>> wrote:
Hi Stewart,

Not necessarily. It is ok if some of the routers in the path are not timing aware. That is the whole idea. We have tested cases in which 5-7 hops are not   1588 aware and still we can recover the time correctly.

Regards,
Shahram

On Jul 19, 2013, at 3:33 AM, "Stewart Bryant" <stbryant@cisco.com<mailto:stbryant@cisco.com>> wrote:

> On 19/07/2013 09:11, Bhatia, Manav (Manav) wrote:
>> Hi Sasha,
>>
>>> 1) reserved label is not backward compatible with existing routers. One
>>> of the requirements is that routers that are not PTP aware can just
>>> switch the packet normally.  Using a reserved label can't achieve this
>>> requirement, since routers that don't understand it will drop it or
>>> sent it to CPU.
>>> [[Sasha]]  Is not this concern  applicable to any new reserved label?
>>> And routers that use network processors as forwarding engines could
>>> easily overcome this issue by upgrading their microcode.
>>> But I agree that this is a valid concern.
>> This is a huge concern because not all routers use network processors that can be reprogrammed.
>>
>> The current solution works with any router that can set up an MPLS path.
> Really?
>
> Surely the LSR needs to know that on seeing a label in the FEC it needs
> to timestamp the packet.
>
> Stewart
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