[sctp-dev] (no subject)

[Jens Carlberg]

Hi again!

Now that we have managed to run SCTP between different servers, we have continued troubleshooting our original problem - bad SCTP throughput on localhost.


- Scenario 1: using loopback interface

We connect a server sending messages over SCTP to a client. Both run on the same machine, connecting over localhost. The traffic starts OK, the messages are sent one by one and usually SACKed after two of them, but after a while the server starts to bundle the messages and the client starts sending a SACK only once every 200 ms. We get a throughput on about 185 messages per second. We have assumed the 200 ms is the standard SCTP SACK timeout, and by setting it to 1 we have been able to see about 14000 messages/s.


- Scenario 2: using standard network interface

We connect a server sending messages over SCTP to a client. The server and the client runs on two different machines, connecting over a gigabit network card. The traffic starts OK, the messages are sent one by one and usually SACKed after two of them, after a while the server starts to bundle the messages but in this case the client is OK with this and keeps sending SACKs in a timely manner. We get a throughput around 50000 messages/s.


Once more we are at a loss to explain this behaviour.
* What differences is there between a real network and the loopback interface?
* Can the SACK timeout be set to 0 for better performance, or a fraction like 0.1?
* We have a dump of the traffic with a SACK for a TSN, that there is no corresponding DATA chunk. Is the dump missing data, is there a bug in the clinet SCTP stack, or is there scenarios where this is OK?



//Best regards,
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JENS CARLBERG
Software Designer

Ericsson AB
FU Radio System I&V, LI/EAB/FJZ/TE
Datalinjen 4
SE-58112 Linköping, Sweden
Phone +46 107114141
SMS/MMS +46 761497941
jens.carlberg at ericsson.com
www.ericsson.com


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