Subject: [PCN] Request for clarification of Other and priority traffic - see draft-eardley-pcn-marking-behaviour-01

From: "HUBLET Christian" <[email-masked]>
Date: Tue, 26 Aug 2008 10:30:09 +0200

Hello,

>From draft-eardley-pcn-marking-behaviour-01, I understand that the to be
metered traffic is :
	- PCN traffic + Other traffic + Priority traffic.

>From the draft it is not clear to me what priority traffic basically
means:
	- In the definitions of section 1.1, priority traffic shares the
same capacity.
	- I wonder what the meaning is of capacity:
		1. sharing the same physical interface (read capacity)
or 
		2. the bandwidth (read capacity) is configured for the 2
(or 3) types of traffic. (no separate capacity (bandwidth) is specified
per traffic type)
I suppose that for the "other traffic" also both definitions can be
applicable.

In the first definition, I see an issue for admittance control. If not
all other and priority traffic is actually present in the network, 
there could be an overadmittance of the PCN traffic. A practical example
could be coexistance of business traffic and residential traffic in the
same diffserv network. 
The residential traffic is controlled via PCN, the business traffic is
controlled via a policer at the edge of the network. If not all sessions
for the business traffic are active, the PCN traffic could take capacity
which was meant to be used for business traffic.
  
In the second definition, I do not understand why lower priority traffic
should not be taken into account if the same capacity (read bandwidth)
is shared with PCN traffic.

I have the impression that there is a strict requirement to take into
account other traffic and priority traffic if present (metered packet
(see section 2.4) is part of meter traffic (see section 1.1)). If the
first definition is applied, this strict requirement can have a huge
impact on the number of applications that can be  supported  in the
diffserv domain and the accuracy with which the PCN bandwidth is
controlled. In the second definition, it is the wish of the operator to
share the bandwidth for a number of applications which is basically a
normal policy. But in this last case, it is not clear why lower priority
traffic can't share the same bandwidth.

Thanks for clarifying.

Kr,

Chris

_________________________________
Christian hublet
Bell Labs - Fixed Access
Copernicuslaan 50
B2018 Antwerp
Belgium
Tel. +32 3 2408789; 
Email : [email-masked]

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---

From: <[email-masked]>
Date: Wed, 27 Aug 2008 09:01:27 +0100

Thanks Chris,

Indeed this section is unclear and will be improved in the next version.

However, it should be better in the most recent verson of the
architecture draft, section 6.5 "PCN-traffic"
http://www.ietf.org/internet-drafts/draft-ietf-pcn-architecture-05.txt 

I think this answers your questions, but would appreciate it if you
could have a look and see if it makes sense or leaves something unclear.

The sense of this S6.5 text will appear in the next version of the
marking draft

Thanks

phil

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
HUBLET Christian
Sent: 26 August 2008 09:30
To: [email-masked]
Subject: [PCN] Request for clarification of Other and priority traffic -
seedraft-eardley-pcn-marking-behaviour-01

Hello, 

metered traffic is : 

means: 

Thanks for clarifying. 

Kr, 

Chris 

Alcatel-Lucent Bell NV 
Fortis 220-0002334-42

---

From: "HUBLET Christian" <[email-masked]>
Date: Wed, 27 Aug 2008 17:59:38 +0200

Phil,
 
Thanks for the reply.
 
Unfortunately the message in section 6.5 is not clear to me:
 
First bullet point : no remarks.
 
Second bullet point : single metering for all the identified DSCP
values, or metering per DSCP value, or a mix of the two mechanisms
 
Third bullet point : I understand that BW of priority scheduled traffic
on the same link should be taking into account by the PCN token bucket.
        --> so capacity in the marking draft means link 
    The strange point is that a PCN node dedicates capacity to NON PCN
traffic. what does this mean?
 
Fourth bullet point : "uses same capacity on a link as PCN traffic"
        --> capacity is probably bandwidth that is shared. PCN traffic
and non PCN but same codepoint. 
    share the same capacity since scheduling ...
        --> capacity is a queue with a certain servicing rate which is
common for PCN and non PCN ?
 
Fifth bullet point : "it is not advised to have non PCN traffic that
shares the same capacity on a link as PCN traffic"
        --> Capacity is bandwidth that is shared between PCN and non PCN
traffic 
 
So my view is that capacity is used in different meaning in section 6.5.
 
I suppose a discussion is held in the past that discusses the value of
taking into account other and priority traffic.
Could some one point me to a doc or email discussion that provides a
view on the problem. Thanks.
 
kr,
 
Chris Hublet

________________________________

From: [email-masked] [mailto:[email-masked]] 
Sent: woensdag 27 augustus 2008 10:01
To: HUBLET Christian; [email-masked]
Subject: RE: [PCN] Request for clarification of Other and priority
traffic - seedraft-eardley-pcn-marking-behaviour-01

Thanks Chris,

 

Thanks

phil

-----Original Message-----

Hello, 

metered traffic is : 

means: 

Thanks for clarifying. 

Kr, 

Chris 

Alcatel-Lucent Bell NV 
Fortis 220-0002334-42

---

From: <[email-masked]>
Date: Thu, 28 Aug 2008 10:24:30 +0100

Thanks chris, in-line

phil

-----Original Message-----
From: HUBLET Christian [mailto:[email-masked]] 
Sent: 27 August 2008 17:00
To: Eardley,PL,Philip,CXR9 R; [email-masked]
Subject: RE: [PCN] Request for clarification of Other and priority

Phil,

Thanks for the reply.

[phil] this bullet reflects old discussions where we talked about PCn
running separately for several classes - so your 2nd sense ie "metering
per DSCP value". 

However, the first sense would also be possible.

I'm not actually sure in retrospect that this bullet adds much, so I
propose deleting it. 

please shout if you object & would prefer to keep it (if so, please
suggest a re-phrasing)

[phil] i think this is just that I could make the sentence construction
clearer. It means that there are 2 possibilities

[1] the router has some capacity set aside dedicated for the "important"
traffic (eg operator's control msgs). This means that pcn isnt allowed
to use this capacity, even if "important traffic" isnt currently using
it. In this case there's nothing for PCn to worry about

[2] the router shares capacity between the "important" traffic & pcn
traffic. But it's assumed that the "important" traffic is always
priority scheduled ahead of pcn-traffic. It would be possible in a worst
case for pcn to get no capacity. Clearly the "important" traffic needs
to contribute to pcn's meters. 

"Capacity" - I meant the capacity as in the forwarding bandwidth on the
link. But I think in practice this is equivalent to same queue.

if there are different types of traffic "sharing capacity", then
possibilities are:

1. all the types of traffic go in the same queue. Clearly then the
router's capacity is shared.

2. each type of traffic goes in a separate queue and the queues are
scheduled with equal priority.

However, assuming that both types of traffic have same dscp (this is the
example mentioned in the 4th bullet), then in practice both types of
traffic go in the same queue. (In theory it would be possible to go in
different queues (by the router classification looking at ECN field),
but in practice it seems that nodes only look at dscp when determining
what queue to put traffic in. But in any case, even if separate queues
were used, this is really just an implementation detail that we
shouldn't worry about.)

Chris, do you think it makes it clear if I re-phrase it from:

There may be other traffic that uses the same capacity (on a link)
      as PCN-traffic.  

To:

There may be other traffic that uses the same capacity as PCN-traffic.
"Capacity" means forwarding bandwidth on a link.
 
And in:
they will share the
      same capacity since scheduling behaviour is coupled with the DSCP
      only.
- add the phrase "in practice" (next to "scheduling behaviour")

Please suggest some alternative words if you think they'd help. I guess
I've read this stuff too many times  - find it hard to view it from
perspective of someone coming to it fresh!

Thanks

phil

kr,

Chris Hublet

Thanks Chris,

 

Thanks

phil

-----Original Message-----

Hello, 

metered traffic is : 

means: 

Thanks for clarifying. 

Kr, 

Chris 

Alcatel-Lucent Bell NV 
Fortis 220-0002334-42

---

From: "HUBLET Christian" <[email-masked]>
Date: Thu, 28 Aug 2008 16:27:20 +0200

Hi Phil, 
 
We are making progress. Bullet point 3 is clear, bullet point 4 is still
an issue for me.
 
I have the impression that capacity means bandwidth or allowed share of
the available resources configured by the operator:
   - If an amount of bandwidth is assigned for the aggregate of PCN and
some identified non PCN service, PCN and the identified non PCN traffic
must be metered together. 
    - In other cases, the traffic must not be metered together.
This is in line with the message in bullet point 3 covering PCN traffic
and priority traffic. 
 
Bullet point 4 is covering PCN traffic and other traffic being traffic
scheduled at the same priority (with implementation options 2 queues
scheduled at the same priority or single queue handling both types of
traffic). Since PCN is based on virtual queue (token bucket), PCN
traffic can be metered separately. One could even say that there is no
relation between the virtual queue and the real queue behavior if both
are correctly configured. So I do not see why sharing the same queue or
scheduling at the same priority is the key element to suddenly take into
account the non PCN traffic for metering. If of course the operator
configures a bandwidth capacity for the aggregate of PCN and non PCN
traffic, both types of traffic must be metered together. If this
interpretation is correct, this bullet point brings the same message to
the table as the message in bullet point 3 covering priority traffic and
PCN traffic.
 
Bullet point 6 is covering lower priority traffic. If in bullet point 3,
higher priority traffic is taken into account when capacity is shared,
why should the document  exclude the situation that lower priority
traffic and PCN traffic are sharing the same capacity. It also suggest a
link between scheduling and PCN which is as indicated above is not clear
to me. 
 
If this is true, my view on a message that you are bringing in the
paragraph 6.5 could be:
The PCN architecture is capable of covering situations where PCN and Non
PCN traffic share the same network. It might be needed that non PCN
traffic is taken into account in the metering. This is illustrated in
the examples in the different bullet points that illustrate when non PCN
traffic should be metered together with PCN traffic. But it is not
advised that PCN traffic and non PCN traffic share the same capacity
(assigned bandwidth) because it reduces the capability of PCN to protect
admitted flows. Correct?
 
Some proposals/remarks related to the document  
 
Second bullet point: I believe this is an important bullet. the bullet
could be rephrased as follows.
The PCN architecture targets to handle admittance and termination for
multiple services co-existing in the same PCN domain. Those services
will be distinguished via a DSCP value. The PCN mechanisms could protect
each service individually. Services could also be grouped. The
aggregated traffic level of the group of services could be protected via
a PCN mechanism.
 
Third bullet point: The message is clear know. But not yet reflected in
the text.
First proposal.
... or priority schedule it over PCN. In the latter case PCN and
priority scheduled traffic are sharing the same bandwidth. In this
case....
Other proposal: restructure as you propose and use your text below to
clarify the message.
 
Fourth bullet point: As indicated before, I do not understand the
relation between sharing the same queue and metering both types of
traffic with a single token bucket for PCN control. I can imagine that
in some cases this is required but in some cases it is not.
I hope this brings us a step forward in understanding other and priority
traffic.
 
Sixth bullet point: 
 
kr,
 
Chris

Sent: donderdag 28 augustus 2008 11:25

Thanks chris, in-line

phil

-----Original Message-----
From: HUBLET Christian [mailto:[email-masked]] 
Sent: 27 August 2008 17:00
To: Eardley,PL,Philip,CXR9 R; [email-masked]
Subject: RE: [PCN] Request for clarification of Other and priority

Phil,

Thanks for the reply.

To:

And in:
they will share the

Thanks

phil

kr,

Chris Hublet

Thanks Chris,

 

Thanks

phil

-----Original Message-----

Hello, 

metered traffic is : 

means: 

Thanks for clarifying. 

Kr, 

Chris 

Alcatel-Lucent Bell NV 
Fortis 220-0002334-42