Re: [multipathtcp] New Version Notification for draft-boucadair-mptcp-plain-mode-10.txt

<> Fri, 24 March 2017 07:02 UTC

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To: Alan Ford <>
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Thread-Topic: [multipathtcp] New Version Notification for draft-boucadair-mptcp-plain-mode-10.txt
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Subject: Re: [multipathtcp] New Version Notification for draft-boucadair-mptcp-plain-mode-10.txt
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Hi Alan,

Please see inline.


De : Alan Ford []
Envoyé : vendredi 24 mars 2017 00:40
Cc :
Objet : Re: [multipathtcp] New Version Notification for draft-boucadair-mptcp-plain-mode-10.txt

Hi Med, all,

Thanks for this, and I’m sorry it’s taken a couple of weeks to respond. This document is certainly clearer to follow than previous versions and it’s clearer where you’re going with this now. You have two different ways of implementing MPTCP proxying which work in different deployment scenarios.

My main concern remains the need for this MP_PREFER_PROXY option.

The use case as I see it is for the CPE acting as an MCP to insert this into the flow in order to signal for the other MCP to pick up the flow and proxy it.
[Med] Yes.

But I still find myself asking why?
[Med] Fair question.

Why is this solution uniquely better than either:

- Explicitly address the MCP using MP_CONVERT;
[Med] The implicit mode is something that can be easily implemented compared to the explicit mode even if it comes with its constraints (e.g., location of the MCP, ..). Our approach here is not mandate the deployment scheme and let operators to make their choice.

- Just insert MCP into everything which doesn’t support MPTCP anyway
[Med] The problem with the second one is that MCP resources usage won’t be optimized: an operator would like to dedicate these resources to the connections it proxies. Further, because “everything doesn’t support MPTCP anyway” there will be MCPs that will strip by default MP_CAPABLE. So, having the MP_PREFER_PROXY signal will help MPTCP connections issued from endhosts to bypass this MCP.

This would potentially require DHCP to deliver the MCP address for point 1, and potential policy configuration as to what to proxy and what not to for point 2, but are these significant issues? What sort of policy would a client be able to apply which a proxy would not be able to? And are there any scenarios why the MP_PREFER_PROXY bit is the only way of achieving what you want?

Given this option is now a separate option and not a bit in the MP_CAPABLE handshake I am less concerned about its impact on the base protocol spec, since this can be kept entirely separate, but I am still puzzled as to the actual real-world requirements of this rather than the other two options.

As a side issue, and not to derail this conversation, I’d rather the term “MP_CONVERT" didn’t look quite so much like an MPTCP option when it wasn’t.


On 10 Mar 2017, at 08:43,<> wrote:

Dear all,

A new version of the draft is available online. This version integrates the comments that were raised on the mailing list.
We had many off-line discussions with Alan, this version is the outcome of those discussion. The main changes are:

* MP_CONVERT object does not consume anymore the MPTCP option codepoints space.
* A new MPTCP option (MP_PREFER_PROXY) is defined to demux native connections vs proxied one when the implicit mode is in use.
* MCPs are now able to detect if remote MCPs do not support MP_CONVERT
* Only TCP is covered
* Interference with TFO are discussed

Comments, questions, and suggestions are always welcome.


-----Message d'origine-----
De :<> []
Envoyé : vendredi 10 mars 2017 08:52
À : Wim Henderickx; Luis M. Contreras;<>; Wouter
Cloetens; Suresh Vinapamula; Denis Behaghel; BOUCADAIR Mohamed IMT/OLN;
Suresh Vinapamula; Robert Skog; Luis Contreras; JACQUENET Christian
IMT/OLN; Bart Peirens; Ullrich Meyer; Denis Behaghel; Olivier Bonaventure;
SungHoon Seo; Stefano Secci
Objet : New Version Notification for draft-boucadair-mptcp-plain-mode-

A new version of I-D, draft-boucadair-mptcp-plain-mode-10.txt
has been successfully submitted by Mohamed Boucadair and posted to the
IETF repository.

Name:                       draft-boucadair-mptcp-plain-mode
Revision:       10
Title:             Extensions for Network-Assisted MPTCP Deployment Models
Document date:        2017-03-09
Group:                      Individual Submission
Pages:                       25

  Because of the lack of Multipath TCP (MPTCP) support at the server
  side, some service providers now consider a network-assisted model
  that relies upon the activation of a dedicated function called MPTCP
  Conversion Point (MCP).  Network-Assisted MPTCP deployment models are
  designed to facilitate the adoption of MPTCP for the establishment of
  multi-path communications without making any assumption about the
  support of MPTCP by the communicating peers.  MCPs located in the
  network are responsible for establishing multi-path communications on
  behalf of endpoints, thereby taking advantage of MPTCP capabilities
  to achieve different goals that include (but are not limited to)
  optimization of resource usage (e.g., bandwidth aggregation), of
  resiliency (e.g., primary/backup communication paths), and traffic
  offload management.

  This document specifies extensions for Network-Assisted MPTCP
  deployment models.

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