[53560] in North American Network Operators' Group
Re: PAIX
daemon@ATHENA.MIT.EDU (Jere Retzer)
Mon Nov 18 13:14:15 2002
Date: Mon, 18 Nov 2002 10:06:40 -0800
From: "Jere Retzer" <retzerj@ohsu.edu>
To: <nanog@merit.edu>
Errors-To: owner-nanog-outgoing@merit.edu
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David Diaz replied to my comments
Concerning latency
>>>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.<< =20
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.
Yes, people have tolerated 500 msec latency on satellite links =AF but =
only because they really had no choice.
Dave Diaz continued
>>>Fewer hops =3D 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=
.<<<
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.
Dave Diaz continued
>>>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. <<<
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.
Jere
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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=20
50ms. Im simplifing without getting into all the details, but that's =
an=20
important number. As far as VoIP goes, I think higher latency is ok, =
it's=20
more important to have "consistent" latency. Fluctuating latency =
really=20
affects VoIP more then a higher consistent latency. There are a lot =
of=20
people doing VoIP and traditional voice on satellites and the latency =
there is=20
huge.<< </DIV>
<DIV> </DIV>
<DIV>Here's an example. Without naming networks, I recently subscribed to =
DSL at=20
the Oregon coast because the local phone company, which is also a =
national=20
network provider advertised that they use a particular ISP, who we have in =
the=20
NWAX exchange in Portland. I thought, well I should be able to get a =
good=20
connection back to Oregon Health and Sciences University (OHSU), and if so =
this=20
will be a good path for the physicians in that coastal community who have =
wanted=20
to particpate in our grand rounds and other continuing medical education=20=
programs. They also have wanted to let the public participate in our =
"healthy=20
chats" program. These events are live and interactive. So, I was =
very=20
optimistic and set up my connection. I was shocked to learn, however that =
the=20
DSL provider routes all the bits from that location to Dallas/Fort Worth, =
Texas=20
before letting them find their way to their eventual destination. Rather =
than a=20
nice direct route to OHSU, the route was 19 hops via Texas and Silicon =
Valley=20
(Palo Alto and San Francisco) before getting to Portland. The average =
latency,=20
which I duplicated consistently with multiple destinations in the Portland =
area=20
is 180 msec and I have seen packet loss hitting 30% every minute or two. =
There=20
is absolutely no way that this connection would be able to handle an =
interactive=20
application.</DIV>
<DIV> </DIV>
<DIV>Yes, people have tolerated 500 msec latency on satellite links =
— but only=20
because they really had no choice.</DIV>
<DIV> </DIV>
<DIV>Dave Diaz continued</DIV>
<DIV> </DIV>
<DIV>>>>Fewer hops =3D less packet loss? There has been a =
lot of=20
discussion on the list about that. I still dont see it although it =
does=20
push latency up a bit. Truth is that there are a lot of tunnels or =
express=20
routes build in, so we arent seeing all the hops nowadays. I think =
that's=20
more for sales and marketing as people keep judging networks by hops in =
a=20
traceroute.<<<</DIV>
<DIV> </DIV>
<DIV>See above. Partly, I think it is just the odds of encountering =
congestion=20
goes up exponentially with the number of hops. No engineering reason =
other=20
than if you have 5% likelihood of hitting congestion on any one hop =
and=20
then you have 19 your odds of hitting congestion are much higher. Combine =
that=20
with a persistent connection for an interactive video session and you will =
find,=20
as I did that every couple minutes you have a spike that causes fits with =
your=20
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=20
demand tv yes. Live tv plays to the benefits of One to Many =
broadcast=20
ability of satellite as Doug Humphrey will tell you. So a feed from =
a DSS=20
dish into your local cache would work well. It still can be done at =
a per=20
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=20
piece of cake. While I agree with a later post that questioned =
convergence=20
for the sake of convergence, the benefits of IP+Ethernet are that it is an =
order=20
of magnitude cheaper and you eliminate the need for any local "head =
end"=20
equipment, manipulation by local stations, etc, etc. Ultimately, the only =
stuff=20
that will originate locally is local news and content.</DIV>
<DIV> </DIV>
<DIV>Jere</DIV></BODY></HTML>
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