Re: [tcmtf] Improved version (v8) of the TCM-TF charter draft

"Eggert, Lars" <lars@netapp.com> Thu, 21 November 2013 17:09 UTC

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From: "Eggert, Lars" <lars@netapp.com>
To: "jsaldana@unizar.es" <jsaldana@unizar.es>
Thread-Topic: [tcmtf] Improved version (v8) of the TCM-TF charter draft
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Date: Thu, 21 Nov 2013 17:09:14 +0000
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Subject: Re: [tcmtf] Improved version (v8) of the TCM-TF charter draft
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Hi,

On 2013-11-21, at 11:56, Jose Saldana <jsaldana@unizar.es> wrote:
> - in a pair of appliances creating a tunnel between two offices  of a
> company, there are a number of hops. Interesting for TCM-TF

there are multiple hops, but are there pressing resource constraints? The intranet in all companies I have worked for has worked well enough without TCM-TF. If you lease MPLS circuits, you can easily acquire more bandwidth.

> But what happens if a scenario may involve one, two or more L3 hops? This
> will  happen in a "community network": you can create a tunnel just to
> connect a village with the Internet (one hop), or to connect a village with
> another village, which is the one really connected to the Internet (more
> than one hop). See a paper about the topology of these networks here
> http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6379103.

All of these PEPs really only make sense on the resource-constrained hop. In your village example, put them on each side of the congested link. Then it's a one-hop scenario. There is little point in going through the overheads of compressing, tunneling, etc. when there is ample resource capacity.

> Perhaps we should take this into account when thinking about the "TCM-TF
> negotiation". Suppose there are two TCM-optimizers that want to create an
> optimized tunnel. During the negotiation they SHOULD check if the number of
> L3 hops between them is 1. In that case, they can avoid the tunnel, and also
> the multiplexing (and multiplexing delay in turn). This could be seen as a
> particular case of TCM-TF:
> 
> - Compression layer: ROHC
> - Multiplexing layer: send every single packet. No need for PPPMux
> - Tunneling layer: no tunnel
> 
> So perhaps we should also consider the "no multiplexing" and "no tunneling"
> options in the protocol stack, in order to cover these cases.

The point I'm trying to make is that I haven't seen *any* scenario that requires a multi-hop solution. And therefore to me what we have with ROHC seems to be just fine.

Lars