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Dear Alberto,

see my comments below.

Best regards
Michael

On Wednesday, January 23, 2002, at 03:19 PM, Alberto Bellettato wrote:

Hello Michael, hello Brian,

1. I modified Path.Max.Retransmits to 3 and RTO.max to 3000 millisec
As Brian Bidulock explained, granularity is caused by RTO.min set to
default value of 1000 millisec. But I don't understand how delay for the first
retransmitted packets is only 0.5 sec (and not RTO.min).
As Brian suggested (thanks!), I tried to reduce RTO.min value. I found a
stable (no false retransmits) configuration setting RTO.min to 10 millisec
and Path.Max.Retransmit to 5. So I obtained this graph:
http://spazioweb.inwind.it/stazionebase/graphbetter.jpg
Changeover is reduced to about 400 milliseconds and peak delay value is only
about 80 millisec.
I can understand linear decrementing traits, only assuming that implementation
runs a single T3-rtx timer for all chunks present in the send queue; I mean
that, after RTO expiring, implementation retransmits all chunks present in the
send queue and it restarts a T3-rtx timer only for the next set of chunks (and
not for every chunk inserted in the queue). Could you confirm if I am right?

Yes, we have only one T3 timer.

2. When a data message arrives to the upper layer of the receiving machine
(notification DataArriveNotify), it is sent back to the sender, without
any modification. When echoed message arrives to the sender, [(current time)-(timestamped sending time)]/2
gives the delay time.

OK. When we did some measurements we wanted to measure only the time from
the sender to the receiver. We reported back the time using UDP. So we could
configure network parameters (using DUMMYNET) for SCTP and did not affect
the time measurement mechanism. We first tired TCP for that which did not work.

Best regards,

Alberto

On Tue, 22 Jan 2002, you wrote:

Hello Alberto,

thank you very much for the measurement. Before making more
detailed commetents on that I have two questions:
1. Have you modified SCTP timers? The delays have a 'granularity'
of 500 ms. This is something I do not understand.
2. How do you send back the packets with the timestamps?

Best regards
Michael

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• [SCTP-Discussion] Path failure in multi-homing scenario, Alberto Bellettato, 01/22/2002
  • Re: [SCTP-Discussion] Path failure in multi-homing scenario, Brian F. G. Bidulock, 01/22/2002
  • <Possible follow-up(s)>
  • RE: [SCTP-Discussion] Path failure in multi-homing scenario, Tuexen Michael, 01/22/2002
    • RE: [SCTP-Discussion] Path failure in multi-homing scenario, Alberto Bellettato, 01/23/2002
      • Re: [SCTP-Discussion] Path failure in multi-homing scenario, Michael Tuexen, 01/23/2002
  • RE: [SCTP-Discussion] Path failure in multi-homing scenario, Tuexen Michael, 01/25/2002

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