[Iccrg] Can TCP stay in slow start 'for ever'?

[Yuchung Cheng]

On Fri, Sep 9, 2011 at 8:18 AM, Tim Shepard <shep at alum.mit.edu> wrote:
>
>
> A thread on the tcpm mailing list from 2007 seems relevent.
>
> Here is a message in the middle of that thread... walk the tree of
> followups to see messages which discuss the status (as of 2007) of
> this stuff in a couple of widely-used TCP implementations:
>
>     http://www.ietf.org/mail-archive/web/tcpm/current/msg02868.html
>
>
> I don't know if the code that is out there now adequately handles the
> particular issue you raisd (connection never goes idle but is not
> fully making use of the cwnd it is rapidly growing).

The Linux 2.6 or later fully implements this RFC.

For app-limit part, an ACK does not increase cwnd in SS unless the
cwnd was fully utilized.

For idle connection part, Linux halves the cwnd every RTO after last
transmission. But the kernel offers a system knob to disable this.

Interestingly, some systems turning off the cwnd restart after idle
feature (in Linux or other OSes). This may generate unpleasant
line-rate bursts like Bob's video-download example.
http://www.cs.princeton.edu/~jrex/papers/snap10.pdf