Subject: [Tsvwg]A question of draft-briscoe-tsvwg-cl-architecture-01.txt

From: Patrick Hu <[email-masked]>
Date: Thu, 02 Mar 2006 15:53:55 +0800

Hi Bob,

I have read your draft "A Framework for Admission Control over DiffServ
using Pre-Congestion Notification". I think it is a good framework to
achieve an end-to-end controlled load service. But I have a question:

-Because MPLS is widely used in the core network, I think the
CL-Architecture need be used for MPLS flows. But, how does the router in the
CL-region set the CE codepoint of a CL MPLS packet? Will the ECN field of IP
header in the MPLS packet be set, or will another method be used?

Best regards,

Patrick Hu

_______________________________________________
tsvwg mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/tsvwg

---

From: Bruce Davie <[email-masked]>
Date: Thu, 2 Mar 2006 08:14:34 -0500

One possibility was explored years ago in http://www.watersprings.org/ 
pub/id/draft-ietf-mpls-ecn-00.txt. It encoded ECN in one bit of the  
MPLS EXP field.

Trying to find the ECN field in the IP header below the MPLS label is  
likely to be quite challenging, given the presence of arbitrary depth  
label stacks and non-IP traffic.

Bruce

On Mar 2, 2006, at 2:53 AM, Patrick Hu wrote:

> Hi Bob,
>
>
> I have read your draft "A Framework for Admission Control over  
> DiffServ using Pre-Congestion Notification". I think it is a good  
> framework to achieve an end-to-end controlled load service. But I  
> have a question:
>
> -Because MPLS is widely used in the core network, I think the CL- 
> Architecture need be used for MPLS flows. But, how does the router  
> in the CL-region set the CE codepoint of a CL MPLS packet? Will the  
> ECN field of IP header in the MPLS packet be set, or will another  
> method be used?
>
>
> Best regards,
>
>
> Patrick Hu
>

---

From: Patrick Hu <[email-masked]>
Date: Fri, 03 Mar 2006 11:45:48 +0800

Hi Bruce,

Thank your for your response. In the CL-Architecture specified in
draft-briscoe-tsvwg-cl-architecture-01.txt, the ingress gateways should
color the CL micro-flows, in order that the interior nodes can identify the
CL packet. The interior routers should set CE codepoint of CL packets when
their arrival rate in nearing the configured rate. So, I think, for MPLS
packets at least two-bit ECN should be needed to implement this
CL-Architecture. However, I think it is impossible to use a two-bit ECN
field for the MPLS header. I have an idea:

Can we use a reserved label values to implement the similar function e.g.
Packet ECN colouring, Pre-Congestion Notification, Pre-emption Alert, etc? 

Best Regards,

.Patrick Hu

---

From: Bob Briscoe <[email-masked]>
Date: Sat, 04 Mar 2006 23:34:46 +0000

Patrick,

Thanks for the supportive comments.

The issue of ECN in MPLS is not easy. There is very little space in the
3-bit EXP field. But my (and I guess most people's) preference would be
marking in the MPLS header, rather than burying down to find the IP
header to mark ECN.

There were two drafts on this that didn't get anywhere back in 1999-2000,
I believe because of problems dealing with the question of support of
legacy drop vs mark.

<http://www.icir.org/floyd/ecn.html#tunnels>

I had an idea on how to solve that recently which I was planning to write
up in an I-D (and others have offered to help co-author), but I just
haven't had the time. I only have a very rough draft started but will not
get it done for Dallas.

I am also interested in any opinion from you or other switch vendors on
the list as to how difficult it would be to add pre-congestion
notification (PCN) marking to MPLS forwarding hardware.

Cheers

Bob

At 07:53 02/03/2006, Patrick Hu wrote:

Hi
Bob,

I have read your draft "A Framework for
Admission Control over DiffServ using Pre-Congestion Notification".
I think it is a good framework to achieve an end-to-end controlled load
service. But I have a question:

-Because MPLS is widely used in the core
network, I think the CL-Architecture need be used for MPLS flows. But,
how does the router in the CL-region set the CE codepoint of a CL MPLS
packet? Will the ECN field of IP header in the MPLS packet be set, or
will another method be used?

Best regards,

Patrick Hu

____________________________________________________________________________

Bob Briscoe, <[email-masked]>
Networks Research Centre, BT Research

B54/77 Adastral Park,Martlesham Heath,Ipswich,IP5
3RE,UK.    +44 1473 645196

---

From: Patrick Hu <[email-masked]>
Date: Mon, 06 Mar 2006 15:11:25 +0800

Hi Bob,

I think, for MPLS packets at least two-bit ECN should be needed to implement
this CL-Architecture.  One bit is used to color MPLS packets to CL packets,
and another bit is used to set  CE codepoint. However, in
http://www.watersprings.org/pub/id/draft-ietf-mpls-ecn-00.txt, only one bit
of the MPLS EXP field is allotted to ECN field. So I have an idea: 

I am glad to see your idea on how to solve this in your succedent draft. I
would like to do something for CL-Architecture. 

Best wishes,

Patrick

-----邮件原件-----
发件人: Bob Briscoe [mailto:[email-masked]] 
发送时间: 2006年3月5日 7:35
收件人: Patrick Hu
抄送: [email-masked]
主题: Re: [Tsvwg]A question of draft-briscoe-tsvwg-cl-architecture-01.txt

Patrick,

The issue of ECN in MPLS is not easy. There is very little space in the
3-bit EXP field. But my (and I guess most people's) preference would be
marking in the MPLS header, rather than burying down to find the IP header
to mark ECN.

There were two drafts on this that didn't get anywhere back in 1999-2000, I
believe because of problems dealing with the question of support of legacy
drop vs mark. 
<http://www.icir.org/floyd/ecn.html#tunnels>

I had an idea on how to solve that recently which I was planning to write up
in an I-D (and others have offered to help co-author), but I just haven't
had the time. I only have a very rough draft started but will not get it
done for Dallas.

I am also interested in any opinion from you or other switch vendors on the
list as to how difficult it would be to add pre-congestion notification
(PCN) marking to MPLS forwarding hardware.

Cheers

Bob

---

From: Bob Briscoe <[email-masked]>
Date: Tue, 14 Mar 2006 17:30:22 +0000

Patrick,

Certainly, using up label space is one way to do this.

Here's an idea I plan to write up in an I-D properly soon. It saves the
need to signal whether the transport is ECN-capable or not (Not-ECT) in
the MPLS header, at least saving one codepoint.

The idea is for all interior label switched routers (LSRs) that are
ECN-capable to /assume/ each packet comes from an ECN-capable transport.
But subsequently, when an edge LSR pops the IP header out of the MPLS
label stack, if the MPLS label is congestion marked, the edge LSR checks
whether the IP header reveals that there is an ECN-capable transport. If
the IP header says the transport is Not-ECT, the edge LSR drops the
packet (on behalf of the interior LSR). Otherwise, the edge LSR copies
the ECN mark to the IP header.

The operator of a domain MUST only introduce interior ECN-capable MPLS
switches when ALL possible edge LSRs are upgraded to be ECN-capable. But
operators are quite capable of managing a constraint like that.

If we only need to signal one congested state (ie two states in all -
uncongested and congested), this would require one codepoint in the MPLS
header (e.g. from the EXP codepoints). If you require more congested
states (e.g. admission marking and pre-emption marking), more EXP
codepoints would be required.

To be clear, whenever an interior ECN-capable LSR gets congested and its
active queue management algorithm (e.g. RED) decides it has to either
drop or ECN mark a packet (before it is actually forced to tail drop), it
always ECN marks and doesn't drop any packets (unless it has to).

I planned to write up the pros and cons for this approach. Including
problems with configuration errors. Marking a packet to be dropped later
obviously isn't ideal, but it may be a good compromise.

Bob

At 03:45 03/03/2006, Patrick Hu wrote:

Hi
Bruce,

Thank your for your response. In the
CL-Architecture specified in draft-briscoe-tsvwg-cl-architecture-01.txt,
the ingress gateways should color the CL micro-flows, in order that the
interior nodes can identify the CL packet. The interior routers should
set CE codepoint of CL packets when their arrival rate in nearing the
configured rate. So, I think, for MPLS packets at least two-bit ECN
should be needed to implement this CL-Architecture. However, I think it
is impossible to use a two-bit ECN field for the MPLS header. I have an
idea:

Can we use a reserved label values to implement
the similar function e.g. Packet ECN colouring, Pre-Congestion
Notification, Pre-emption Alert, etc?

Best Regards,

&Patrick Hu

tsvwg mailing list

[email-masked]

Notice: This contribution is the personal view of the author and does not
necessarily reflect the technical nor commercial direction of BT
plc.

Bob
Briscoe,