Re: Do we have buffer bloat on edge routers or on core routers?

On Sat, Mar 30, 2013 at 10:11:34PM +0000, Fred Baker (fred) wrote:
> Mark Allman recently published a paper, in which he says that his massively over-provisioned FIOS network doesn't seem to have this problem, so he doesn't think it's a real problem.

That's a commonly discussed misunderstanding of Marks paper
(see related discussions in the bloat and tsvwg mailing list,
e.g., posts by Mark Allman).
His paper is /not/ about measuring buffer bloat in an FTTH network.
While his /vantage point/ is indeed located in the FTTH network,
the paper actually measures buffer bloat in various remote networks.

Also Marks paper is not the only study suggesting the extend of the problem
to be modest. The presented results are in line with recent findings by
Chirichella and Rossi [1]. Based on unpublished work, I can confirm the
low magnitude of the problem. I analyzed passive measurements of
residential users traffic from multiple continents (~60 million IPs
originating from 50\% of all ASes) and rarely find excessive RTTs that,
among other problems, can indicate the presence of buffer bloat.

One reason for the outcome of these studies is that users often do not
sustainably utilize their uplink capacity and fill-up their potentially
large queues.

> The primary way that network designers can reduce buffer bloat is
> over-provisioning.

This assumes that buffer bloat mainly occurs in the core.
However, the current evidence suggest it to be a problem
in the edge: oversized buffers in hosts, 3G, cable / DSL modems
or home routers have been shown to be often oversized and
thus have the potential to inject large queueing delays
when filled.

To me, buffer bloat is more of a configuration problem than
a fundamental network problem. The first step in resolving
buffer bloat should therefore be fixing the misconfigurations
by deploying reasonable sized buffers in edge equipment.
This is an initiative that is currently taken in DOCSIS
standards to give cable operators the chance to tune the
buffer size in the deployed edge devices.

Once buffers are reasonably sized, the effect on end-user
experience might not be that large as suggested by this
work:

BufferBloat: How Relevant? A QoE Perspective on Buffer Sizing.
Oliver Hohlfeld, Enric Pujol, Florin Ciucu, Anja Feldmann, Paul Barford
http://downloads.ohohlfeld.com/paper/bufferbloat-qoe-tr.pdf

We found network workload / congestion, rather than buffer size,
to be the primary determinant of end-user experience.

In this way, I agree with you that any means to reduce congestion,
e.g., by over-provisioning links, will improve user experience.
However, this is very specific to the core and I haven't seen
much evidence of buffer bloat in the core. To me, over-provisioning
doesn't apply much to residential access lines.

Other means to improve are QoS / service differentiation, or
queue management.

Oliver