Re: [Codel] [Bloat] The challenge

[Justin McCann <jneilm@gmail.com>]

On Thu, May 10, 2012 at 3:02 AM, David Woodhouse <dwmw2@infradead.org> wrote:
>
> If we overload the DSLAM, it drops one ATM cell out of N, which nixes
> fairly much *every* IP packet by dropping a tiny part of each one, and
> results in almost zero throughput. We don't let the DSLAM do
> buffering :)

<tangent>
Can't they turn on Early Packet Discard or something similar? This
seems like a no-brainer.

Dynamics of TCP Traffic over ATM Networks (1994), Allyn Romanow , Sally Floyd
     http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.30.7647

"We investigate the performance of TCP connections over ATM networks
without ATM-level congestion control, and compare it to the
performance of TCP over packet-based networks. For simulations of
congested networks, the effective throughput of TCP over ATM can be
quite low when cells are dropped at the congested ATM switch. The low
throughput is due to wasted bandwidth as the congested link transmits
cells from `corrupted' packets, i.e., packets in which at least one
cell is dropped by the switch. We investigate two packet discard
strategies which alleviate the effects of fragmentation. Partial
Packet Discard, in which remaining cells are discarded after one cell
has been dropped from a packet, somewhat improves throughput. We
introduce Early Packet Discard, a strategy in which the switch drops
whole packets prior to buffer overflow. This mechanism prevents
fragmentation and restores throughput to maximal levels."

</tangent>