Hi Stephen,
Thanks for the implementation. I have checked the codes, and I have the
following comments:
1, The math is basically correct in computing alpha and beta from da.
2, In the computation of da, you implicitly set d1=0. Setting d1=0 is a
conservative approach, although it also works well (it may lead to a longer
convergence time than a positive d1). The reason is that, even if far from
congestion, there are some burstiness in RTT measurements, and we get
dad_min. This way, we have an alphaalpha_max even if congestion is far
away. We choose d1 to be close to 0 in our simulations for conservativeness,
but we believe even if d1 is non-trivial positive, like 0.05*dm, it should
work, and it might work better.
3, There is one more feature in TCP-Illinois: to avoid setting alpha to be
alpha_max if actually the congestion level is high and the small queueing
delay is due to noise. We have explained that in our updated version of the
paper, available at
http://www.ews.uiuc.edu/~shaoliu/papersandslides/liubassri06perf.pdf
We have also implemented this feature in our ns-2 code. The basic idea of
this feature is that, once da exceeds d1 and alphaalpha_max, we know that
congestion level is not very low. Once this happen, the congestion level
should not drop unless some user has experienced a packet loss and backed
off its window size. If that is the case, da should drop to below d1 for a
long time. If, however, da drops to below d1 suddenly, but increases back to
above d1 soon, we predict that congestion is not alleviated, and the small
da measurement comes from noise. Under this case, we should not set
alpha=alpha_max, but should set it to be its previous legitimate value.
We believe that this feature is important if there is noise in delay
measurement and if d1 is set to be nonzero. Even if d1 is set to be zero, we
think this feature should be included if the noise is delay measurement is
significant. Under this case, we can modify the feature a little bit: alpha
is initially computed to be around alpha_max when congestion is far. As da
increases, alpha decreases. But alpha cannot be increased as soon as da
drops. Alpha can only be increased if the decrease trend of da last for a
certain period.
4, In your implementation, you set alpha_max=10 and alpha_min=0.1. Although
this parameter setting is chosen by our paper, we suggest you try some
different values, especially for alpha_min. An alpha_min from 0.2 to 0.5
might be a better choice, as this will make the convergence time faster.
Please feel free to tell me if you have any related questions.
Thanks!
Best regards!
Yours sincerely,
Shao Liu (Julian)
University of Illinois at Urbana Champaign
Coordinated Science Laboratory and Department of Electrical and Computer
Engineering
www.ews.uiuc.edu/~shaoliu
-Original Message-
From: Stephen Hemminger [mailto:[EMAIL PROTECTED]
Sent: Tuesday, April 03, 2007 11:17 AM
To: David Miller
Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED];
[EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED];
netdev@vger.kernel.org
Subject: [PATCH] TCP Illinois congestion control
This is a new implementation of TCP Illinois invented by Shao Liu at
University of Illinois. It is a another variant of Reno which adapts the
alpha and beta parameters based on RTT. The basic idea is to increase window
less rapidly as delay approaches the maximum. See the papers and talks to
get a more complete description.
Please consider for 2.6.22.
Signed-off-by: Stephen Hemminger [EMAIL PROTECTED]
---
net/ipv4/Kconfig| 13 +++
net/ipv4/Makefile |1 +
net/ipv4/tcp_illinois.c | 212
+++
3 files changed, 226 insertions(+), 0 deletions(-) create mode 100644
net/ipv4/tcp_illinois.c
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig index dc61e66..e62aee0
100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -588,6 +588,19 @@ config TCP_CONG_YEAH
For further details look here:
http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
+config TCP_CONG_ILLINOIS
+ tristate TCP Illinois
+ depends on EXPERIMENTAL
+ default n
+ ---help---
+ TCP-Illinois is a sender-side modificatio of TCP Reno for
+ high speed long delay links. It uses round-trip-time to
+ adjust the alpha and beta parameters to achieve a higher average
+ throughput and maintain fairness.
+
+ For further details see:
+ http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html
+
choice
prompt Default TCP congestion control
default DEFAULT_CUBIC
diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile index eeb94d5..4ff6c15
100644
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -50,6 +50,7 @@ obj-$(CONFIG_TCP_CONG_VENO) += tcp_veno.o
obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o
obj-$(CONFIG_TCP_CONG_LP) += tcp_lp.o
obj-$(CONFIG_TCP_CONG_YEAH) += tcp_yeah.o
+obj-$(CONFIG_TCP_CONG_ILLINOIS) +=
