Re: [multipathtcp] Fw: New Version Notification for draft-hoang-mptcp-sub-rate-limit-00.txt

<mohamed.boucadair@orange.com> Fri, 12 July 2019 14:12 UTC

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From: <mohamed.boucadair@orange.com>
To: Olivier Bonaventure <olivier.bonaventure@uclouvain.be>, Viet Hoang Tran <hoang.tran@uclouvain.be>, multipathtcp <multipathtcp@ietf.org>
Thread-Topic: [multipathtcp] Fw: New Version Notification for draft-hoang-mptcp-sub-rate-limit-00.txt
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Date: Fri, 12 Jul 2019 14:12:35 +0000
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Subject: Re: [multipathtcp] Fw: New Version Notification for draft-hoang-mptcp-sub-rate-limit-00.txt
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Re-,

Please see inline. 

Cheers,
Med

> -----Message d'origine-----
> De : Olivier Bonaventure [mailto:olivier.bonaventure@uclouvain.be]
> Envoyé : vendredi 12 juillet 2019 15:00
> À : BOUCADAIR Mohamed TGI/OLN; Viet Hoang Tran; multipathtcp
> Objet : Re: [multipathtcp] Fw: New Version Notification for draft-hoang-
> mptcp-sub-rate-limit-00.txt
> 
> Med,
> 
> > Thank you for igniting this work.
> >
> > FWIW, we used to have this requirement in
> > draft-nam-mptcp-deployment-considerations (with cellular networks in
> mind):
> >
> >     “For cases where some access networks are subject to a volume quota,
> >
> >     it is desirable to support a signal to indicate to a remote peer how
> >
> >     it must place data into available subflows”.
> >
> > The rate-limit option as currently defined may not be adequate. I would
> > like an option which allows to tell a remote peer, for example:
> >
> > ·to use a given subflow only where there is a need to grab more
> > resources (that is, don’t use this subflow if data can be placed on
> > other subflows).
> 
> This would be a variation of the backup bit, with a different semantics.
> There are different possible semantics, the current one says:
> - don't use the backup subflow unless there is an active one
> Other semantics could be:
> - don't use the backup subflow as long as the delay on the active one is
> below <250msec (this is roughly what Apple does with Wifi assist)
> - don't use the backup subflow as long as the throughput of the active
> one is above 1 Mbps

[Med] Yes, the issue is how to unambiguously identify which semantic is associated with a single bit. For the sake if interoperability, more than one bit is needed to cover these cases. 

> 
> > ·“here is my suggested inbound traffic distribution ratio among
> > established subflows”.
> 
> As a percentage between the different subflows of an existing connection
> ?

[Med] Yes, typically. 

 The main difficulty of such an approach is that the number of subflows
> changes over time and client and servers might have a different view on
> the number of subflows that are active. There are many corner cases that
> make this difficult to implement in general.

[Med] For the hybrid access case or within DCs, the number of subflows is not supposed to change that much. 

> 
> I think that a rate limit (typically on the cellular interface) covers
> many of these use cases
> 
> > ·“here is the maximum data that can be placed in a given subflow”.
> 
> In bytes ? We could imagine an option that indicates that a given
> connection can receive up to x MBytes and after that it will be released.

[Med] OK, thanks.    

> 
> 
> Olivier