Subject: [PCN] fractional marking

From: SATOH Daisuke <[email-masked]>
Date: Fri, 13 Mar 2009 17:54:47 +0900

Hi Phil and others,

Because STM marking looks complex, I change our marking to fractional marking that Michael tell me. So SWTB is changed to Token bucket for fractional marking. MkTB is changed to the conventional threshold marking. I believe this change give no change of simulation results.

Fractional marking is if PCN traffic rate is greater than a configured rate, it marks only 1/N of the trafficon a link. If traffic type is homogeous CBR, synchronization occurs only when the number of packets within an interarrival time of a CBR flow is a multiple of N^2.

approximately marking is as follows.
o1  2  3
 1 o2  3
 1  2 o3
o1  2  3
 .......

The difference is fractional marking is easier to accumulate marked packets than STM original marking.

Best regards,
Daisuke

---

From: <[email-masked]>
Date: Mon, 16 Mar 2009 14:38:27 -0000

Let me see if I get your suggestion right.

If PCN-traffic-rate at a link is > PCN-admissible rate & <
PCN-supportable-rate
Then mark 1/N PCN-pkts
If PCN-traffic-rate at a link is > PCN-supportable-rate
Then mark all PCN-pkts

Is that right?

Btw, your algorithm in the I-D doesn't seem to take account of pkts that
are previously marked. Therefore if several links (~N) are above
PCN-admissible rate, then ~ all pkts are marked, which will be
mis-interpreted by the egress node, which will terminate flows. Is that
right?

Btw, I assume your algorithm rules out admission and termination
approaches that depend on "marked pkts" rather than measuring rates (ie
the sorts of approaches that Michael has suggested in S4.4 of
http://tools.ietf.org/id/draft-menth-pcn-psdm-deployment-00.txt etc.
(I'm just trying to work out the implications of your suggestion.)

I believe you're saying that admission & termination performance is
approx the same as CL, but at high overloads the performance is actually
better than CL. Intuitively, what's the reason for this? (I thought your
termination method would be the same as CL, ie egress measures the rate
of unmarked traffic & ingress measures the rate sent to this egress.
Although this isnt clear, what is "received rate" in your draft?)

{ -----Original Message-----
{ From: [email-masked] [mailto:[email-masked]] On Behalf Of
{ SATOH Daisuke
{ Sent: 13 March 2009 08:55
{ To: [email-masked]
{ Subject: [PCN] fractional marking
{ 
{ Hi Phil and others,
{ 
{ 
{ Because STM marking looks complex, I change our marking to fractional
{ marking that Michael tell me. So SWTB is changed to Token bucket for
{ fractional marking. MkTB is changed to the conventional threshold
marking.
{ I believe this change give no change of simulation results.
{ 
{ 
{ Fractional marking is if PCN traffic rate is greater than a configured
{ rate, it marks only 1/N of the trafficon a link. If traffic type is
{ homogeous CBR, synchronization occurs only when the number of packets
{ within an interarrival time of a CBR flow is a multiple of N^2.
{ 
{ 
{ approximately marking is as follows.
{ o1  2  3
{  1 o2  3
{  1  2 o3
{ o1  2  3
{  .......
{ 
{ 
{ The difference is fractional marking is easier to accumulate marked
{ packets than STM original marking.
{ 
{ 
{ Best regards,
{ Daisuke
{ 
{ _______________________________________________
{ PCN mailing list
{ [email-masked]
{ https://www.ietf.org/mailman/listinfo/pcn

---

From: SATOH Daisuke <[email-masked]>
Date: Thu, 19 Mar 2009 16:34:29 +0900

Hi Phil,

I am very sorry to take time to answer your questions because I went on
a business trip yesterday and the day before yesterday.

> If PCN-traffic-rate at a link is > PCN-supportable-rate

Yes. It's right.

> mis-interpreted by the egress node, which will terminate flows. Is that

If so many bottleneck links exist, all the packets get marked as a
result. Then the egress node sends termination message to ingress.

However, we can estimate how many bottleneck links lead all the packets
marked.

marking ratio = 1/3 +  (1-1/3)* 1/3 + (1-1/3-(1-1/3)*1/3)*1/3 + .....
N.of bottleneck; 1          2                     3               

Furthermore, accumulation of marked packets is less than the above
equation because marked packets are easy to get marked in the original
marking (maybe not fractional marking) when traffic that go through
multi-bottleneck links has a relatively large volume.

> Although this isnt clear, what is "received rate" in your draft?)

Termination of STM is different from that of CL. CL uses SAR and get how
much traffic rate should be terminated. STM cannot get SAR. So STM
terminates flows little by little.

Why is the performance of CL degraded?
Because terminating flows appropriately is very difficult.

When the traffic is highly overloaded, more higher overloaded traffic in
a short interval exists. An ingress terminates flows based on SAR. I
believe SAR itself is accurate. If an ingress can terminate flows so
that variance of traffic rate is enough small, CL always terminates
flows accurately. However, it is very difficult. When the traffic is not
so highly overloaded, the variance is small. When the traffic is highly
overloaded, high traffic rate keeps in a short interval and very low
traffic rate is generated in a short interval by termination. The
average is SAR but traffic after termination becomes bursty.

If the traffic is bursty and the average rate is about
PCN-supportable-rate, SAR is less than PCN-supportable-rate. This is the
mechanism of over termination of CL when the traffic is highly
overloaded.

These are my understanding. I have not confirmed it by simulation yet.

Solution is terminating flows that generate very highly overloaded.
However, this overload is produced by superposition. An ingress cannot
detect this information.

Or I guess the first termination is accurate. If CL does not use SAR
after the first termination, the performance may be improved.

Why is the performance of STM actually better than CL at high overloads?

Because STM terminates flows little by little. It does not use SAR.

Received rate is typo. Receiving rate is correct.

Best regards,
Daisuke

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