[e2e] Skype and congestion collapse.

[RJ Atkinson]

On Mar 5, 2005, at 16:30, David P. Reed wrote:
> The "512 kb limit" upstream on cable plants seems a bit bogus to me, 
> as I just ran a test and got sustained 741 kb/s upstream to Los 
> Angeles.

It does not seem bogus to me, since often more than 100 active users are
sharing a 1.5 Mbps upstream channel; reasonable people might have a 
range
of differing views on this topic.

> A small correction about cable modem nets (Ran knows a fair bit so he 
> may correct me).   Cable modems sit on networks with an architecture 
> called HFC, Hybrid Fiber Coax, which is designed so the number of 
> homes passed is dependent on where in the cable distribution tree the 
> plant turns from fiber to coax.  In advanced operators (Comcast and 
> RCN out here) the fiber goes
> out very close to the users, and has moved closer as the upstream 
> demand
> has increased.

This varies widely market-by-market.  The Boston area is very unusual 
because
RCN "over-built" Comcast. Many households in the Boston area can choose 
from
either RCN or Comcast for wired cable-TV.  Boston has more fibre and 
fibre
much closer to the house than is typical for most markets in North 
America because of the competition -- so it is more like Europe in that 
respect.

A "good" fibre node might encompass 500 homes/addresses.  Typical fibre
nodes might run to 1500 homes/addresses.  Fibre nodes with up to 3000
homes/addresses are not yet unusual.  Some markets are still all copper
or worse.

> I happen to have a fair amount of contact with Comcast execs, and their
> plan is to move fiber even closer to the users, reducing the number of
> homes per coax segment.

This is true of most cable operators that I'm familiar with, but the 
rate
of increased fibre deployment varies widely with the economics of the
particular market.

>  In recent conversations with CableLabs execs (my namesake, David P. 
> Reed,
> and Richard Green) regarding the DOCSIS capabilities indicate that 
> they are
> quite aware of the need for more upstream bandwidth, because they see 
> the
> asymmetry going down as more and more bittorrent, etc. is deployed.   
> So
> while YMMV depending on how sluggish your operator is, HFC is generally
> pursuing a strategic direction to go well beyond the current upstream 
> limits.
> Thus, the upstream link share level seems likely to go down.

All that is true, but the situation varies widely from one market to 
another.
In a previous life we tried to get QAM to work upstream on several 
different
HFC deployments, but QAM really didn't work anyplace other than Europe 
because
of upstream noise implosion (at that time).

> Ran may have other data that contradicts this, and I have to admit 
> today I've *only* got 784 Kb/s upstream and 7 Mb/s downstream on RCN, 
> so it might be a year or so before I get past a megabit upstream for 
> my $50 per month.  [happening to live in a place where RCN and Comcast 
> compete head-to-head has strong benefits... especially since Verizon 
> DSL has so far refused to be competitive anywhere in Massachusetts].

I don't think anything I have contradicts your data, but maybe it 
suggests
that your market is not typical of most markets around the globe.

Cheers,

Ran