netdev - Re: [PATCH net-next] tcp: Add TCP

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Date:	Wed, 22 Oct 2014 21:50:14 +0200
From:	Hagen Paul Pfeifer <hagen@...u.net>
To:	Kristian Evensen <kristian.evensen@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] tcp: Add TCP_FREEZE socket option

On 22 October 2014 19:08, Kristian Evensen <kristian.evensen@...il.com> wrote:

> Another approach I designed was to have a separate TCP Freeze module
> and trigger the freeze/unfreeze through genetlink-messages. A user
> space application will be responsible for monitoring the devices and
> decide when to trigger the ZWAs. Would a design like that be
> acceptable?

At least better. But what userspace daemon would configure this?
Likely NetworkManager and friends. But at what conditions?

- When the WIFI signal strength is below some threshold?
- When switched to another AP?
- When switched from 802.11 to 802.3
- ...

In a NATed scenario there is no gain because IP addreses change and
the connection is lost anyway. For the signal strength thing there
might be an advantage but it has costs:

a) how long did you freeze the connection? What if NetworkManager
stops? The connection hang \infty
b) is it not better to inform the upper layer - the application - that
something happen with the link?

I mean when the application experience disruptions, the application
can decide what it do: reconnect, reconnect and resend or inform the
user. This possibility is now lost/hidden. Maybe it is no problem -
maybe it is for some applications.

I have no fundamental problems with TCP Freeze, but what is missing is
a complete story line. The use cases where it makes sense and if it is
save.

Do you have considered to bring this to the IETF (TCPM WG)?

Hagen
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