[e2e] TCP, retransmissions, and ISPs with byte caps

[Philippe Strauss]

On Tue, Jun 18, 2002 at 12:01:53PM -0400, David P. Reed wrote:
> 
> At 05:34 PM 6/18/2002 +0200, Philippe Strauss wrote:
> >then came the LANcity. my colleagues tried it and shipped it back due
> >to a terribly long time for the modem to reconnect after
> >a plant outage or noise burst (several hours for ~ 500 modems)
> >modulation and access to the return path was close to the docsis1.0
> >standard I think.
> 
> As a customer, I have never observed the several hour case, and there are 
> several hundred LANCity modems on our branch of the tree.   Minutes, 
> yes.  Hours, no.   But who knows what your plant looks like.

I thinks it was simply a bug, misfeature of their first software
release. it was either in early 98 or end of 97.

> >terayon and it's teracomm 1000, a well designed system on
> >the transission side: spread spectrum CDMA, good performance even
> >on noisy plant.
> >it's allocation scheme on the upstream path, most of the time,
> >impose a 20ms min RTT for the basic UBR traffic contracts.
> >with a non UBR you get better RTT, same values as you
> >see with the LANcity.
> 
> Bad design.   Must have been designed for ATM bigots.  20 ms is enough time 

yes the headend use ATM internally.
all the IT side of teracomm 1000 is rather weak, but the RF/modulation/encoding
is beautifull.

> for a signal to travel 4,000 miles.   You can do arbitration orders of 
> magnitude faster than that on a radio channel in freespace, which is much 
> harder to work over than a coax plant, which is like a cleanroom in 
> comparison.

granularity of this scheduling seems 10ms.. hmm remind me of a
quiet famous family of operating system clock granularity :)

> This is what you get when your engineers only think about bitrate and not 
> about latency.  They probably drive cars that go from 0-60 in 5 seconds, 
> after waiting 7 seconds for the turbocharger lag.

:-)) excellent point!

all of these paquet-over-CATV equipement smells firtish design.
Docsis 2 maybe will be mature, at least a good step in that direction.

-- 
Philippe Strauss
http://philou.ch/

L'indifférence est le plus grand risque de notre temps,
la forme civilisée de la cruauté.  -- Zenta Maurina
--