Yaakov
I was not thinking of a particularly radical packet type.
A label stack, a 64 bit delay field, and then any timing payload
you like (specific details out of scope for the draft).
The P routers then just add and subtract the current time from
the delay field to update it with the dwell time.
The Edge will know what the timing payload type is and can
make the TC correction based on the delay field.
The important point is that this works for any packet type that
needs to know delay, be that a timing payload such as 1588v2,
1588v3, NTPv4, NTPv5 etc etc. It also as Yaakov notes works
for any other payload type such as a payload that needs to
perform synchronous delivery at multiple disjoint endpoints,
or a 1+1 protection system that is required to provide
synchronied streams etc etc.
- Stewart
On 26/11/2011 20:24, Yaakov Stein wrote:
Shahram and Stewart
If we need intermediate MPLS nodes to perform special processing on 1588oMPLS
packets
there are several methods to lower the processing requirements.
Of course, DPI could be performed to go below the MPLS and IP headers as
Shahram said,
but as Stewart pointed out this would be prohibitively expensive.
Two methods have been proposed.
The method of the present draft is to use the standard encapsulations
(after ensuring that 1588 is supported)
and to inform the intermediate nodes that the particular label value being used
is special.
For this special label value the node has been informed of what to do,
e.g., has the offset of a TC.
Any use of TC is necessarily a layer violation
(after all, the timestamp is a layer-0 entity and we are placing it in a layer
2 or higher field),
but correcting a field inside 1588 in UDP in IP in MPLS
is not really that much worse than correcting on in 1588 in UDP in IP in
Ethernet.
The alternative method that I proposed is to invent a completely new
timestamping mechanism.
This has the advantage of being applicable to all MPLS packets
(and thus can solve other problems),
but requires inventing yet another timing distribution protocol.
I know that Stewart succeeded in inventing a new packet loss and delay
measurement protocol for TP,
but I didn't gauge support in TICTOC for something new here.
Y(J)S
-----Original Message-----
From: Stewart Bryant [mailto:[email protected]]
Sent: Thursday, November 24, 2011 19:30
To: Shahram Davari
Cc: '[email protected]'; '[email protected]'
Subject: Re: [TICTOC] FW: I-D Action: draft-ietf-tictoc-1588overmpls-02.txt
Shahram
I will ponder the answer to this question, but will note that
you have not addressed my second question which relates
to whether there is MPLS WG buy-in for this proposal.
- Stewart
On 24/11/2011 16:34, Shahram Davari wrote:
Hi Stewart,
The parsing required by the draft is not complex and almost all MPLS routers
have support it already. The idea was to reuse existing data plane mechanisms
and not invent a new one. This I believe is in the spirit of IETF to reuse
existing mechanisms.
I don't believe adding a shim makes the design simpler. You still need to
detect that such shim exists and for that you need parsing that doesn't even
exist today.
This draft has been implemented by vendors, so we have a working code and I
believe we also have rough consensus.
Thanks
Shahram
----- Original Message -----
From: Stewart Bryant [mailto:[email protected]]
Sent: Thursday, November 24, 2011 07:58 AM
To: [email protected]<[email protected]>
Cc: [email protected]<[email protected]>;
[email protected]<[email protected]>
Subject: Re: [TICTOC] FW: I-D Action: draft-ietf-tictoc-1588overmpls-02.txt
Can we wind back to my original points here
which have not addressed.
Why are is the WG proposing a design that
needs such complex parsing, against the
ethos of MPLS, when a simpler design
would be more universally applicable?
Does the WG have any input to suggest that
the design will survive a review by MPLS/PWE3
WG and then by IESG?
- Stewart
On 22/11/2011 09:12, Stewart Bryant wrote:
Speaking as an individual here, I really have a hard time
understanding why it is necessary to have quite the
egregious layer violation that this draft uses.
The idea of having an LSP type that is dedicated to
tracking the time of passage through the network
is a good idea. However MPLS is completely geared
to the concept that only the LSP endpoints know
how to resolve the payload type.
The function that you require could be achieved
by including a shim that contains the
time compensation information and adjust the
payload on egress from the LSP. That would be
rather more consistent with the MPLS architecture.
I have not seen a request for review by the MPLS
or PWE3 WGs and I would suggest that you request
that sooner rather than later since it is inevitable
that the draft will be sent there later in it's life, and
if they do not subscribe to your mode of operation
the draft is unlikely to progress.
I would also suggest that you discuss the extent
of layer violation with your AD to make sure he is
confident that this draft will pass IESG review.
- Stewart
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