Subject: [PCN] PCN edge behaviour experiment

From: Tom Taylor <[email-masked]>
Date: Tue, 20 Mar 2012 16:18:54 -0400

I am making what I trust will be the final revisions to the edge 
behaviour documents in response to IESG comments. Amongst other things, 
this is the text I propose to add in the introduction to justify the 
Experimental status of the documents. The text will be the same for CL 
and for SM, following on Ruediger's observation that both behaviours are 
valid in different contexts. Comments are welcomed.

---

This document describes an experimental edge node behaviour to implement 
PCN in a network. The experiment may be run in a network in which a 
substantial proportion of the traffic carried is in the form of 
inelastic flows and where admission control of micro-flows is applied at 
the edge. For the effects of PCN to be observable, at least some links 
of the network should be running near or at capacity. The amount of 
effort required to prepare the network for the experiment (see Section 
5.1) may constrain the size of network to which it is applied. The 
purposes of the experiment are:

- to validate the specification of the CL [SM] edge behaviour;

- to evaluate the effectiveness of the CL [SM] edge behaviour in
   preserving quality of service for admitted flows; and

- to evaluate PCN's potential for reducing the amount of capital and
   operational costs in comparison to alternative methods of assuring
   quality of service.

For the first two objectives, the experiment should run long enough for 
the network to experience sharp peaks of traffic in at least some 
directions. It would also be desirable to observe PCN performance in the 
face of failures in the network. A period in the order of a month or two 
in busy season may be enough. The third objective is more difficult, and 
could require observation over a period long enough for traffic demand 
to grow to the point where additional capacity must be provisioned at 
some points in the network.

---

From: Michael Menth <[email-masked]>
Date: Tue, 20 Mar 2012 21:52:01 +0100

Hi Tom,

Am 20.03.2012 21:18, schrieb Tom Taylor:
> behaviour documents in response to IESG comments. Amongst other 
> things, this is the text I propose to add in the introduction to 
> justify the Experimental status of the documents. The text will be the 
> same for CL and for SM, following on Ruediger's observation that both 
> behaviours are valid in different contexts. Comments are welcomed.
>
> ---
>
> This document describes an experimental edge node behaviour to 
> implement PCN in a network. The experiment may be run in a network in 
> which a substantial proportion of the traffic carried is in the form 
> of inelastic flows and where admission control of micro-flows is 
> applied at the edge. For the effects of PCN to be observable, at least 
> some links of the network should be running near or at capacity. 
Better: "the aggregate rate of admitted flows on some links should come 
close to the bandwidths of these links."

> The amount of effort required to prepare the network for the 
> experiment (see Section 5.1) may constrain the size of network to 
> which it is applied. The purposes of the experiment are:
>
> For the first two objectives, the experiment should run long enough 
> for the network to experience sharp peaks of traffic in at least some 
> directions. 
These peaks could be intentionally caused for the sake of the experiment 
so that the effect of admission control is visible.

> It would also be desirable to observe PCN performance in the face of 
> failures in the network. A period in the order of a month or two in 
> busy season may be enough. The third objective is more difficult, and 
Also failures could be intentionally caused for the sake of the 
experiment. Capacity shortage on backup paths could also be planned for 
so that the effect of flow termination is visible.

Best wishes,

     Michael

> _______________________________________________
> PCN mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/pcn

-- 
Prof. Dr. habil. Michael Menth
University of Tuebingen
Faculty of Science
Department of Computer Science
Chair of Communication Networks
Sand 13, 72076 Tuebingen, Germany
phone: (+49)-7071/29-70505
fax: (+49)-7071/29-5220
mailto:[email-masked]
http://kn.inf.uni-tuebingen.de

---

From: Tom Taylor <[email-masked]>
Date: Tue, 20 Mar 2012 17:11:20 -0400

Good points. That means the experiment doesn't have to run very long to 
meet the first two objectives. I do have one concern that if you 
introduce artificial traffic then maybe you don't get the same outcome 
that real traffic gives you. I figure it's inevitable that the benefits 
of PCN with real traffic in a real network will be less than our 
simulations show, if only because real networks tend to be over-provided 
with capacity.

---

From: Michael Menth <[email-masked]>
Date: Tue, 20 Mar 2012 22:14:00 +0100

I don't suggest artifical traffic to cause admitted traffic exceeding 
the PCN threshold but real traffic. A planned experiment does not imply 
artifical traffic.

Am 20.03.2012 22:11, schrieb Tom Taylor:
> Good points. That means the experiment doesn't have to run very long 
> to meet the first two objectives. I do have one concern that if you 
> that real traffic gives you. I figure it's inevitable that the 
> benefits of PCN with real traffic in a real network will be less than 
> our simulations show, if only because real networks tend to be 
> over-provided with capacity.
>

---

From: <[email-masked]>
Date: Wed, 21 Mar 2012 08:25:56 +0100

Hi Tom, hi Michael

"network running near capacity" is correct if complete links transmit
PCN traffic only. Otherwise, "PCN network capacities running near
congestion (on at least one interface)" is better. That may also
simplify experiments, dedicated tunnels in a live network with
proper marking may suffice.

Regards,

Ruediger

> some links of the network should be running near or at capacity.

Michael:

Michael

---

From: Michael Menth <[email-masked]>
Date: Wed, 21 Mar 2012 09:11:45 +0100

Hi Ruediger, hi Tom!

Ruediger, you are right. The text should be

"the aggregate rate of admitted flows on some links should come
close to the *admissible rates* of these links."

Regards,

     Michael

---

From: Tom Taylor <[email-masked]>
Date: Wed, 21 Mar 2012 08:18:08 -0400

I did rework the wording to capture Ruediger's sense. Michael, your 
wording assumes that PCN is already running on the network, where in 
this case one is examining a network as a prospect for a PCN experiment.

---

From: Bob Briscoe <[email-masked]>
Date: Thu, 22 Mar 2012 19:05:38 +0000

Michael,

One way to do this would be to administratively shut down a link or 
node, allow protection to shift traffic and monitor whether PCN 
starts admission control. But it would be a brave operator who did 
this with live traffic, even if it had been simulated first.

I guess you might do it for a few tens of seconds when you know 
measured traffic will fit into protection capacity but above the 
admissable rate, check it works then bring the link back up.

Bob

At 21:14 20/03/2012, Michael Menth wrote:
>I don't suggest artifical traffic to cause admitted traffic 
>exceeding the PCN threshold but real traffic. A planned experiment 
>does not imply artifical traffic.
>
>>Good points. That means the experiment doesn't have to run very 
>>long to meet the first two objectives. I do have one concern that 
>>if you introduce artificial traffic then maybe you don't get the 
>>same outcome that real traffic gives you. I figure it's inevitable 
>>that the benefits of PCN with real traffic in a real network will 
>>be less than our simulations show, if only because real networks 
>>tend to be over-provided with capacity.
>>

________________________________________________________________
Bob Briscoe,                                BT Innovate & Design

---

From: Bob Briscoe <[email-masked]>
Date: Thu, 22 Mar 2012 19:22:18 +0000

Tom,

Your original text was good, and I agree with the way people have 
converged on improvements so far. I want to  go back to your first 
posting and pick out a couple of other parts of the text...

Perhaps the proposed text is rather too prescriptive about what a 
valid experiment would be. I suggest:

s/The purposes of the experiment are:/
  /Vendors and operators will have their own purposes for conducting 
experiments, but example purposes would be:/

One more comment inline...

At 20:18 20/03/2012, Tom Taylor wrote:
>justify the Experimental status of the documents. The text will be 
>the same for CL and for SM, following on Ruediger's observation that 
>both behaviours are valid in different contexts. Comments are welcomed.
>
>---
>
>implement PCN in a network.

[snip]

>The purposes of the experiment are:

[snip]

>for the network to experience sharp peaks of traffic in at least 
>some directions. It would also be desirable to observe PCN 
>performance in the face of failures in the network. A period in the 
>order of a month or two in busy season may be enough. The third 
>objective is more difficult, and could require observation over a 
>period long enough for traffic demand to grow to the point where 
>additional capacity must be provisioned at some points in the network.

The third objective may not necessarily require a wait for capacity 
to actually be provisioned. The main unknown costs are:
a) cost of implementation and operation of PCN (relative to an alternative)
b) any differences in capacity costs due to differences in feasible utilisation

An experimental deployment is the best way to quantify (a).
But (b) may be sufficiently quantifiable using projections without 
having to wait for capacity to need replacing.

Bob