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

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Date:	Wed, 22 Oct 2014 09:56:34 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Kristian Evensen <kristian.evensen@...il.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] tcp: Add TCP_FREEZE socket option

On Wed, Oct 22, 2014 at 8:36 AM, Kristian Evensen
<kristian.evensen@...il.com> wrote:
> From: Kristian Evensen <kristian.evensen@...il.com>
>
> This patch introduces support for Freeze-TCP [1].
>
> Devices that are mobile frequently experience temporary disconnects, for example
> due to signal fading or a technology change. These changes can last for a
> substantial amount of time (>10 seconds), potentially causing multiple RTOs to
> expire and the sender to enter slow start. Even though a device has
> reconnected, it can take a long time for the TCP connection to recover.
>
> Operators of mobile broadband networks mitigate this issue by placing TCP
> splitters at the edge of their networks. However, the splitters typically only
> operate on some ports (mostly only port 80) and violate the end-to-end
> principle. The operator's TCP splitter receives a notification when a temporary
> disconnect occurs and starts sending Zero Window Announcements (ZWA) to the
> remote part of the connection. When a devices regains connectivity, the window
> is reopened.

At least split TCP is transparent to applications, while your approach is not.
I don't understand why you said it typically operates on some ports, since
TCP is stateful.

BTW, AFAIK Linux doesn't support split TCP.
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