Gerrit Renker 1435562d7e dccp ccid-2: Replace broken RTT estimator with better algorithm ... The current CCID-2 RTT estimator code is in parts broken and lags behind the suggestions in RFC2988 of using scaled variants for SRTT/RTTVAR. That code is replaced by the present patch, which reuses the Linux TCP RTT estimator code - reasons for this code duplication are given below. Further details: ---------------- 1. The minimum RTO of previously one second has been replaced with TCP's, since RFC4341, sec. 5 says that the minimum of 1 sec. (suggested in RFC2988, 2.4) is not necessary. Instead, the TCP_RTO_MIN is used, which agrees with DCCP's concept of a default RTT (RFC 4340, 3.4). 2. The maximum RTO has been set to DCCP_RTO_MAX (64 sec), which agrees with RFC2988, (2.5). 3. De-inlined the function ccid2_new_ack(). 4. Added a FIXME: the RTT is sampled several times per Ack Vector, which will give the wrong estimate. It should be replaced with one sample per Ack. However, at the moment this can not be resolved easily, since - it depends on TX history code (which also needs some work), - the cleanest solution is not to use the `sent' time at all (saves 4 bytes per entry) and use DCCP timestamps / elapsed time to estimated the RTT, which however is non-trivial to get right (but needs to be done). Reasons for reusing the Linux TCP estimator algorithm: ------------------------------------------------------ Some time was spent to find a better alternative, using basic RFC2988 as a first step. Further analysis and experimentation showed that the Linux TCP RTO estimator is superior to a basic RFC2988 implementation. A summary is on http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/ccid2/rto_estimator/ In addition, this estimator fared well in a recent empirical evaluation: Rewaskar, Sushant, Jasleen Kaur and F. Donelson Smith. A Performance Study of Loss Detection/Recovery in Real-world TCP Implementations. Proceedings of 15th IEEE International Conference on Network Protocols (ICNP-07). 2007. Thus there is significant benefit in reusing the existing TCP code. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>		2008-09-04 07:45:39 +02:00
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lib	dccp tfrc/ccid-3: Computing Loss Rate from Loss Event Rate	2008-09-04 07:45:34 +02:00
ccid2.c	dccp ccid-2: Replace broken RTT estimator with better algorithm	2008-09-04 07:45:39 +02:00
ccid2.h	dccp ccid-2: Replace broken RTT estimator with better algorithm	2008-09-04 07:45:39 +02:00
ccid3.c	dccp: Return-value convention of hc_tx_send_packet()	2008-09-04 07:45:38 +02:00
ccid3.h	dccp ccid-3: Remove dead states	2008-09-04 07:45:35 +02:00
Kconfig	dccp ccid-2: Remove old infrastructure	2008-09-04 07:45:37 +02:00
Makefile	[DCCP] CCID2: Initial CCID2 (TCP-Like) implementation	2006-03-20 17:41:47 -08:00