Can P2P applications learn to play fair on networks?

Tue Oct 23 02:31:39 UTC 2007

Here's a few downstream/upstream numbers and ratios:
    ADSL2+: 24/1.5 = 16:1 (sans Annex.M)
DOCSIS 1.1: 38/9 = 4.2:1 (best case up and downstream modulations and
carrier widths)
      BPON: 622/155 = 4:1
      GPON: 2488/1244 = 2:1

Only the first is non-shared, so that even though the ratio is poor, a
person can fill their upstream pipe up without impacting their neighbors.

It's an interesting question to ask how much engineering decisions have led
to the point where we are today with bandwidth-throttling products, or if
that would have happened in an entirely symmetrical environment.

DOCSIS 2.0 adds support for higher levels of modulation on the upstream,
plus wider bandwidth
(http://i.cmpnet.com/commsdesign/csd/2002/jun02/imedia-fig1.gif), but still
not enough to compensate for the higher downstreams possible with channel
bonding in DOCSIS 3.0.

Frank

-----Original Message-----
From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu] On Behalf Of Jack
Bates
Sent: Monday, October 22, 2007 12:35 PM
To: Bora Akyol
Cc: Sean Donelan; nanog at merit.edu
Subject: Re: Can P2P applications learn to play fair on networks?

Bora Akyol wrote:
> 1) Legal Liability due to the content being swapped. This is not a
technical
> matter IMHO.

Instead of sending an icmp host unreachable, they are closing the connection
via
spoofing. I think it's kinder than just dropping the packets all together.

> 2) The breakdown of network engineering assumptions that are made when
> network operators are designing networks.
>
> I think network operators that are using boxes like the Sandvine box are
> doing this due to (2). This is because P2P traffic hits them where it
hurts,
> aka the pocketbook. I am sure there are some altruistic network operators
> out there, but I would be sincerely surprised if anyone else was concerned
> about "fairness"
>

As has been pointed out a few times, there are issues with CMTS systems,
including maximum upstream bandwidth allotted versus maximum downstream
bandwidth. I agree that there is an engineering problem, but it is not on
the
part of network operators. DSL fits in it's own little world, but until
VDSL2
was designed, there were hard caps set to down speed versus up speed. This
has
been how many last mile systems were designed, even in shared bandwidth
mediums.
More downstream capacity will be needed than upstream. As traffic patterns
have
changed, the equipment and the standards it is built upon have become
antiquated.

As a tactical response, many companies do not support the operation of
servers
for last mile, which has been defined to include p2p seeding. This is their
right, and it allows them to protect the precious upstream bandwidth until
technology can adapt to a high capacity upstream as well as downstream for
the
last mile.

Currently I show an average 2.5:1-4:1 ratio at each of my pops. Luckily, I
run a
DSL network. I waste a lot of upstream bandwidth on my backbone. Most
downstream/upstream ratios I see on last mile standards and equipment
derived
from such standards isn't even close to 4:1. I'd expect such ratio's if I
filtered out the p2p traffic on my network. If I ran a shared bandwidth last
mile system, I'd definitely be filtering unless my overall customer base was
small enough to not care about maximums on the CMTS.

Fixed downstream/upstream ratios must die in all standards and
implementations.
It seems a few newer CMTS are moving that direction (though I note one I
quickly
found mentions it's flexible ratio as beyond DOCSIS 3.0 features which
implies
the standard is still fixed ratio), but I suspect it will be years before
networks can adapt.

Jack Bates