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<DIV>David Diaz replied to my comments</DIV>
<DIV> </DIV>
<DIV>Concerning latency</DIV>
<DIV><BR></DIV>
<DIV>>>>Well the bingo latency number used a lot in voice is
50ms. Im simplifing without getting into all the details, but that's an
important number. As far as VoIP goes, I think higher latency is ok, it's
more important to have "consistent" latency. Fluctuating latency really
affects VoIP more then a higher consistent latency. There are a lot of
people doing VoIP and traditional voice on satellites and the latency there is
huge.<< </DIV>
<DIV> </DIV>
<DIV>Here's an example. Without naming networks, I recently subscribed to DSL at
the Oregon coast because the local phone company, which is also a national
network provider advertised that they use a particular ISP, who we have in the
NWAX exchange in Portland. I thought, well I should be able to get a good
connection back to Oregon Health and Sciences University (OHSU), and if so this
will be a good path for the physicians in that coastal community who have wanted
to particpate in our grand rounds and other continuing medical education
programs. They also have wanted to let the public participate in our "healthy
chats" program. These events are live and interactive. So, I was very
optimistic and set up my connection. I was shocked to learn, however that the
DSL provider routes all the bits from that location to Dallas/Fort Worth, Texas
before letting them find their way to their eventual destination. Rather than a
nice direct route to OHSU, the route was 19 hops via Texas and Silicon Valley
(Palo Alto and San Francisco) before getting to Portland. The average latency,
which I duplicated consistently with multiple destinations in the Portland area
is 180 msec and I have seen packet loss hitting 30% every minute or two. There
is absolutely no way that this connection would be able to handle an interactive
application.</DIV>
<DIV> </DIV>
<DIV>Yes, people have tolerated 500 msec latency on satellite links — but only
because they really had no choice.</DIV>
<DIV> </DIV>
<DIV>Dave Diaz continued</DIV>
<DIV> </DIV>
<DIV>>>>Fewer hops = less packet loss? There has been a lot of
discussion on the list about that. I still dont see it although it does
push latency up a bit. Truth is that there are a lot of tunnels or express
routes build in, so we arent seeing all the hops nowadays. I think that's
more for sales and marketing as people keep judging networks by hops in a
traceroute.<<<</DIV>
<DIV> </DIV>
<DIV>See above. Partly, I think it is just the odds of encountering congestion
goes up exponentially with the number of hops. No engineering reason other
than if you have 5% likelihood of hitting congestion on any one hop and
then you have 19 your odds of hitting congestion are much higher. Combine that
with a persistent connection for an interactive video session and you will find,
as I did that every couple minutes you have a spike that causes fits with your
video.</DIV>
<DIV><BR><BR></DIV>
<DIV>Dave Diaz continued</DIV>
<DIV> </DIV>
<DIV><BR></DIV>
<DIV>>>>An IP backbone is a bad place for live TV. Delayed or on
demand tv yes. Live tv plays to the benefits of One to Many broadcast
ability of satellite as Doug Humphrey will tell you. So a feed from a DSS
dish into your local cache would work well. It still can be done at a per
city peering point to better feed the broadband users. <<<</DIV>
<DIV> </DIV>
<DIV>If we fix the IP backbones for interactive TV then broadcast should be a
piece of cake. While I agree with a later post that questioned convergence
for the sake of convergence, the benefits of IP+Ethernet are that it is an order
of magnitude cheaper and you eliminate the need for any local "head end"
equipment, manipulation by local stations, etc, etc. Ultimately, the only stuff
that will originate locally is local news and content.</DIV>
<DIV> </DIV>
<DIV>Jere</DIV></BODY></HTML>