Subject: [PCN] How necessary is affected marking?

From: Bob Briscoe <[email-masked]>
Date: Mon, 10 Mar 2008 12:18:54 +0000

Georgios,

Do you propose using Affected Marking (AfM) in ECMP cases to 
calculate the Admission Marking level or just the Termination Marking level?

If both, I can see it seems to help in ECMP cases {but see Note 1}.

But if AfM is only used for Termination, the case for Affected 
Marking (AfM) seems marginal. Because all packets that aren't 
Termination Marked (TM) will typically be Admission Marked (AM), so 
AM can serve the function of AfM.

Of course, there may be one queue sending TM & AM to an egress and 
another sending only AM. So AfM would help in such cases. But that's 
a bit of a corner case to justify another codepoint. Without AfM, 
this would slow down flow termination, but it would still terminate 
the right amount of flows eventually.

My question: Have you tried to quantify how likely it will be that 
AfM will be useful?

I'm just wondering whether it is worth complicating the core PCN 
algorithm and encoding specs with AfM, or whether we should have a 
separate spec just about AfM. Then the main PCN specs can refer to 
AfM as an optional extra for any vendor who wants to do it.

Cheers

Bob

---------
{Note 1}: However, the admission marking behaviour we are likely to 
standardise doesn't have a clear point where AM is on or off. It gets 
gradually greater. The egress can decide when the fraction of AM has 
passed a threshold for sufficient time (e.g. with an exponentially 
weighted moving average EWMA). But that seems quite complicated (but 
not impossible) for an interior node.

I guess though that excess rate marking would also have to be able to 
detect when it had been marking sufficiently for sufficiently long to 
turn on AfM, and when to turn it off again. Have you documented a 
possible algorithm for these state change triggers anywhere?

____________________________________________________________________________
Bob Briscoe, <[email-masked]>      Networks Research Centre, BT Research
B54/77 Adastral Park,Martlesham Heath,Ipswich,IP5 3RE,UK.    +44 1473 645196 

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From: "Georgios Karagiannis" <[email-masked]>
Date: Mon, 10 Mar 2008 14:58:37 +0000

Hi Bob

Please see in line!

Best regards,
Georgios

>calculate the Admission Marking level or just the Termination Marking level?

Georgios: I propose to use Affected Marking to solve the ECMP routing
issues that occur during the flow termination process.

>AM can serve the function of AfM.

Georgios: I do not think so, because, there might be situations where
some nodes might operate in admission control state and others in
termination state. Now consider that many flows belong to the same
ingress-egress-aggregate. However, due to the ECMP routing problem, some
of the flows can pass only through nodes operating in admission control
state and other flows that belong to the same ingress-egress-aggregate
can pass through nodes operating in termination state.
If you use AM marking to solve the ECMp routing problem, then the egress
will also terminate flows that just passed through nodes operating in
admission control state, (and not operating in flow termination state).
This will mean that flows that do not contribute to termination, will be
terminated. This will not contribute on solving the severe congestion
situatin.

>the right amount of flows eventually.

georgios: i do not think so!
>My question: Have you tried to quantify how likely it will be that

georgios: I have tried to do it, but the prblems that I have are related
on etting reliable ECMP routing information. It will be great if we can
get more accurate insight in the operation and performance related
information of the ECMP routing.
Can we get this information from operators that are using ECMp routing in
their domains?
if we do not have this information, to use it in simulations and/or
performance analysis techniques, then the produced results from
simulations  and performance analysis could be useless.

>AfM as an optional extra for any vendor who wants to do it.

Georgios: I am in favour of separating the PCN base protocol from the
ECMP solutions.
Thus I am in favour of your proposed solution!

Best regards,
Georgios