Re: [EToSat] Packet lost on last mile network?

[Christian Huitema <[e-mail]>]

On 5/20/2020 9:56 AM, Carsten Bormann wrote:
>> And, if they are only deployed in a
>> fraction of the Wi-Fi network, then the transport folks will still need
>> an end-to-end solution.
> They sure will.  But that never can be as good as local recovery.

In a nutshell, that's the entire discussion of end-to-end vs middle-boxes.

It is always possible to do a local optimization by adding some
intelligence in the network. That's the case for pretty much all middle
boxes, and it seems that the proxies envisaged in Loop fall into that
category. But there are always downsides, such as management,
flexibility, and most importantly ossification by old proxies prone to
bit rot.

Given effort, it is almost always possible to find end-to-end solutions
that are "good enough", getting you within 90% of the optimum or some
such. FEC as tail probe would be one example of that. The end-to-end
solutions also tend to get better over time, as implementers devise more
clever algorithms and update the code. All it takes is some motivation
that the effort is important.

An example of that would be support for cellular networks. Twenty years
ago, this was a niche, and TCP was not optimized for it. Hence the
deployment of middle-boxes in the cellular networks. But as this became
an ever more important scenario, TCP improved, and QUIC will improve
over that. The cellular middle-boxes become harder to justify, and will
start moving from the "optimization" to the "hindrance" category.

Satellite networks are a peculiar case. They remain very much a niche
application to this day, something like a communication media of last
resort in places that fiber or cellular cannot reach. Given the niche
status, it is unclear whether end-to-end transports will bother
implementing optimized algorithms, even when these are available. But it
is also unclear whether "mainline" networks will bother deploying
middle-boxes solely for the benefit of the satellite niche, which kinds
of rules out solutions like 'deploy a box in every Wi-Fi network'.
'Deploy a proxy at the ground station' might work, because the satellite
operator has the right business incentives, but of course that requires
nodes to still do something special for satellites, i.e., discover the
proxy and use it. Not obvious.

Hence my effort to look at end-to-end solutions covering not just the
satellite case, but also other long distance networks such as
intercontinental connections. These are still niches today, given VPN,
but they are still useful for P2P applications. Given enough niches,
there might be enough motivation for doing the effort.

-- Christian Huitema