Hi Tomasz, after quite some testing and calculations, my understanding of the strange behaviour of CCID-3 over loopback is that it is due to the combination of * an application-limited sender (ie. sending rate X_send < s/RTT); * very low RTT as compared to inter-packet gap; * frequent expiry of the nofeedback timer; * the particular interpretation of "idle periods" in rfc3448bis-00. Hence as you pointed out, the Token Bucket Filter solution will indeed not cure the problem. Artificially inflating the link RTT, on the other hand, causes the computation of X to stabilise towards s/RTT. I have written up the causes etc. on http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/ccid3/ccid3_over_loopback/ This was not easy to do and so I appreciate comments if there are any errors or misinterpretations. Gerrit Quoting Tomasz Grobelny: | Dnia Monday 10 of March 2008, Gerrit Renker napisa?: | > Now I have a question: adding 1 ms delay at the interface avoided the | > hang-up, but what do you mean by "long enough"? Is this 60 seconds? | > | I tested it for something like 100 seconds and didn't encounter any problems. | | > But since the average RTT is 48 microseconds in the `outfile', I am | > assuming that the outfile was produced when the delay was not added to | > the interface? | > | Yes, that's what I thought you asked me for... | | > There is a long-standing problem (at least 1 year) with regard to CCID-3 | > over high-speed networks (and lo interface is in fact a high-speed | > interface): high link speeds are outside the control region of CCID-3. | > | > The peak limit of controllable speed is about 12 Mbps. Everything higher | > that will cause problems. I have not tested, but you may be able to | > also silence this behaviour by using a netem token-bucket filter with | > e.g. a maximum bitrate of <= 10 Mbps. | > | I somehow doubt it because setting up tbf with limit greater than the actual | traffic should have no influence at all. But let's check it... | sudo tc qdisc add dev lo root handle 1:0 tbf rate 30kbit burst 30kbit latency | 500ms | | Still the speed drops down to 1 packet per 64 seconds. | | > So I think the least thing we need to do is put a warning into the DCCP | > Wiki that people should add interface delay when using CCID-3 for | > testing over loopback. | Maybe CCID-3 could somehow disable itself when it detects it is not necessary? | -- | Regards, | Tomasz Grobelny | | -- -- To unsubscribe from this list: send the line "unsubscribe dccp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
