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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2008-09-04 09:30:19 +0400
committerGerrit Renker <gerrit@erg.abdn.ac.uk>2008-09-04 09:45:42 +0400
commitc8f41d50adc380bfb38538ce39ca0ffea5926221 (patch)
treead2d9b674e2782b271f5ae15eb35630848055fbb /net/dccp/ccids/Kconfig
parent891e4d8a402427bc40dee4c8413213a584710372 (diff)
downloadlinux-c8f41d50adc380bfb38538ce39ca0ffea5926221.tar.xz
dccp ccid-3: Measuring the packet size s with regard to rfc3448bis-06
rfc3448bis allows three different ways of tracking the packet size `s': 1. using the MSS/MPS (at initialisation, 4.2, and in 4.1 (1)); 2. using the average of `s' (in 4.1); 3. using the maximum of `s' (in 4.2). Instead of hard-coding a single interpretation of rfc3448bis, this implements a choice of all three alternatives and suggests the first as default, since it is the option which is most consistent with other parts of the specification. The patch further deprecates the update of t_ipi whenever `s' changes. The gains of doing this are only small since a change of s takes effect at the next instant X is updated: * when the next feedback comes in (within one RTT or less); * when the nofeedback timer expires (within at most 4 RTTs). Further, there are complications caused by updating t_ipi whenever s changes: * if t_ipi had previously been updated to effect oscillation prevention (4.5), then it is impossible to make the same adjustment to t_ipi again, thus counter-acting the algorithm; * s may be updated any time and a modification of t_ipi depends on the current state (e.g. no oscillation prevention is done in the absence of feedback); * in rev-06 of rfc3448bis, there are more possible cases, depending on whether the sender is in slow-start (t_ipi <= R/W_init), or in congestion-avoidance, limited by X_recv or the throughput equation (t_ipi <= t_mbi). Thus there are side effects of always updating t_ipi as s changes. These may not be desirable. The only case I can think of where such an update makes sense is to recompute X_calc when p > 0 and when s changes (not done by this patch). Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Diffstat (limited to 'net/dccp/ccids/Kconfig')
-rw-r--r--net/dccp/ccids/Kconfig20
1 files changed, 20 insertions, 0 deletions
diff --git a/net/dccp/ccids/Kconfig b/net/dccp/ccids/Kconfig
index dc973abe03b4..fb168be2cb43 100644
--- a/net/dccp/ccids/Kconfig
+++ b/net/dccp/ccids/Kconfig
@@ -74,6 +74,26 @@ config IP_DCCP_CCID3_DEBUG
If in doubt, say N.
+choice
+ prompt "Select method for measuring the packet size s"
+ default IP_DCCP_CCID3_MEASURE_S_AS_MPS
+
+config IP_DCCP_CCID3_MEASURE_S_AS_MPS
+ bool "Always use MPS in place of s"
+ ---help---
+ This use is recommended as it is consistent with the initialisation
+ of X and suggested when s varies (rfc3448bis, (1) in section 4.1).
+config IP_DCCP_CCID3_MEASURE_S_AS_AVG
+ bool "Use moving average"
+ ---help---
+ An alternative way of tracking s, also supported by rfc3448bis.
+ This used to be the default for CCID-3 in previous kernels.
+config IP_DCCP_CCID3_MEASURE_S_AS_MAX
+ bool "Track the maximum payload length"
+ ---help---
+ An experimental method based on tracking the maximum packet size.
+endchoice
+
config IP_DCCP_CCID3_RTO
int "Use higher bound for nofeedback timer"
default 100