Re: Round-trip delays

Jason Williams (streak@ccwf.cc.utexas.edu)
Wed, 24 Sep 1997 14:29:45 -0500 (CDT)


On Wed, 24 Sep 1997, John Ingham wrote:
> The other day I was using CU-SeeMe and PowWow to talk with a friend in the
> USA from Australia. We experienced a "round-trip" delay of some 60 seconds
> - yes that's right, it took 60 seconds for an answer to arrive to a
> question!
>
> When I used "Tracert" to check out the path between him and me there were
> about 15 hops, each varying between 150 msec to 1500 msec, but adding up to
> no more than 6 seconds total delay.

15 hops isn't bad at all... You could try pinging to see what the delay
is. I know from my own observations that a few Sprint routers are
horribly slow when handing packets off to the next router.

> Why would this measured time be so much smaller than the actual delay
> experienced by using CU-SeeMe (Chat and Video) and PowWow (Chat and Sound)?

My only comment would be to make sure your rates are set correctly. If
you are on a 28.8kbps modem, try keeping your max send around 15kbps...and
your max receive around 28kbps. Video and audio at the same time can
really eat up the bandwidth. I've watched the huge delays in the
chat when on a DC and both parties had their max send and max receive set
at 28kbps. You might also try pausing your video and see what happens
with the audio. Since you used tracert and your packets got to the
destination ok, all the routers were up between you and them. I'd try a
ping to see what happens. I normally get around 300-400ms round-trip with
pings on my system.

> Are "Ping-type" packets handled by servers more quickly than packets
> containing real data? Thankyou.

more quickly? I believe ICMP traffic is low-priority, but you also have
to consider the fact that traceroute and ping generally use very small
size packets. CU-SeeMe and PowWow use much bigger and more packets. Ping
and traceroute are just used for diagnostic purposes, not real-time data.
They help to see where the bottleneck is with your bandwidth or why you
can't get to your destination. I'd say make sure your rates are set right
and the other person has their rates set right. Other than that...who
knows :) I've had mysterious things happen as well. Perhaps redialing
your ISP would also fix it.

--
streak@ccwf.cc.utexas.edu    * Jason Williams -- Austin, Tx.  |     |
streak@mail.utexas.edu       * University of Texas at Austin  | ___ |
streak@cs.utexas.edu         * BS Computer Science             \_|_/
*************** http://ccwf.cc.utexas.edu/~streak/ **************|