Re: [multipathtcp] potential MPTCP proxy charter item

<mohamed.boucadair@orange.com> Mon, 07 November 2016 08:45 UTC

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From: <mohamed.boucadair@orange.com>
To: "Olivier.Bonaventure@uclouvain.be" <Olivier.Bonaventure@uclouvain.be>, Alan Ford <alan.ford@gmail.com>
Thread-Topic: [multipathtcp] potential MPTCP proxy charter item
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Date: Mon, 7 Nov 2016 08:45:10 +0000
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Subject: Re: [multipathtcp] potential MPTCP proxy charter item
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Re-,

In addition to what was mentioned by Olivier, and from where I sit, an answer to Alan's question is also the result of a tension between the e2e principle and deployment requirements:
1.	Favor e2e MPTCP connections (Goal 1)
2.	Optimize MCP resources usage (Goal 2)
3.	Allow for policies to determine flows eligible to the network-assisted MPTCP (Goal 3)

Requiring that every MPTCP host will be eligible to use MCP resources is not viable, IMHO. 

The solution that allows to distinguish in a deterministic manner native MPTCP connections from proxied one has the advantages:
.	to not interfere with native MPTCP connections issued from MPTCP capable host, by default (Goal 1).
.	solid signal to the MCP when it should be involved (or not) (Goal 2)
.	Native MPTCP connections can benefit from the NAM service **IF** policies provided to the CPE allow for that (Goal 3). 

Cheers,
Med

> -----Message d'origine-----
> De : Olivier Bonaventure [mailto:Olivier.Bonaventure@uclouvain.be]
> Envoyé : lundi 7 novembre 2016 08:56
> À : Alan Ford
> Cc : BOUCADAIR Mohamed IMT/OLN; multipathtcp@ietf.org
> Objet : Re: [multipathtcp] potential MPTCP proxy charter item
> 
> Alan,
> >
> >> On 6 Nov 2016, at 21:06, Olivier Bonaventure
> >> <Olivier.Bonaventure@uclouvain.be
> >> <mailto:Olivier.Bonaventure@uclouvain.be>> wrote:
> >>
> >> The implicit mode was suggested by network operators. The MCP resides
> >> on the path between the CPE and the destination server. The main
> >> benefit of the implicit mode is that the MCP does not need to perform
> >> any address translation. Given all the complications with NAT, this is
> >> a huge benefit, in particular in IPv6 deployments. In IPv4
> >> deployments, the CPE can use a single address and there is no need for
> >> a pool of IPv4 addresses on the MCP.
> >>
> >> In implicit mode, the MCP needs to distinguish between an MP_CAPABLE
> >> generated by the endhost and an MP_CAPABLE added by the CPE.
> >
> > Broad question - why?
> >
> > If the answer is simply "to know when to terminate the MPTCP connection"
> > (i.e. if the end host does it you want it to run all the way to
> > destination, but if the CPE has done it you want to handle at the
> > proxy), then thinking out loud here, could the desired behaviour not be
> > achieved by deciding to proxy only based on the SYN/ACK (i.e. based on
> > the far end's capabilities) and otherwise be transparently adding MPTCP
> > to /everything/? That way you get even greater MPTCP coverage whilst not
> > interfering with destinations which have already deployed it.
> 
> 
> The problem is more complex than this because the connecitivity on the
> CPE is not the same as connectivity on the endhost. Consider the
> following scenario :
> 
> laptop <-----------+
>                     |
> smartphone <----> cpe <-------> mcp <------> server
>      +              +
>   cellular1     cellular2
> 
> The MCP resides on the DSL path between the CPE and the server.
> 
> The laptop is connected over WiFi and the CPE converts the TCP
> connection onto an MPTCP connection to bond DSL and cellular2.
> 
> The smartphone is connected over wifi to the cpe which is connected over
> DSL to the server via the MCP. When the smartphone uses MPTCP, it wants
> to use WiFi and cellular1. It could start over WiFi and then moves and
> want to switch to cellular1. The MCP has no idea of cellular1 and cannot
> terminate an MPTCP connection created by the smartphone.
> 
> 
> 
> Olivier