where
$ns is the NS-2 scheduler you are using in the script,
$TCP_Name is the congestion control algorithm in concern,
$Parameter_Name is the variable name of the parameter, and
$Parameter_Value is the new value of the parameter.
Effect is taken on this particular flow (
$tcp). Other flows are not affected. And the value of this parameter for this particular flow (
$tcp)
will not be affected by any future command of
set_ca_default_param.
For details, please refer to
the tutorial.
Adding your own congestion control module
You can add your own congestion control module once you develop the module in Linux.
If you decide to do so, take the following steps:
- Make sure your implementation is compliant to the congestion control structure in Linux (struct tcp_congestion_ops);
- Make sure this patch has been applied to your NS2 code base
- Follow the migration step in tutorial to migrate your whole Linux congestion control modules (including your own) to NS-2 code base.
- add a record in Makefile by adding an item to let compiler know your code:
tcp/linux/YourCode.o
- compile, run and compare the simulation results with Linux experiments results
You might encounter one of the following problems in the last step:
- If your algorithm requires access to many new fields in Linux TCP structure, you might need to add more fields to struct tcp_sock in tcp/linux/ns-linux-util.h .
WARNING: After adding a new congestion control algorithm, please verify the simulation results
extensively and carefully to make sure the simulation is running as expected.
Known Problems:
Here is a list of known problems:
- The implementation does not change receiver part. The delayed ack implementation in Linux might be different from the one in NS-2. This may results in some performance difference
- D-SACK: This may leads to performance difference in scenarios with packet reordering.
- F-RTO: Not yet implemented. Will be included very soon.
- ECN: The implementation is not extensively verified.
- TCP Segmentation: Not implemented. Will NOT be covered in the near future.
- Buffer tuning: Not implemented. Will NOT be covered in the near future.
Paper
NS-2 TCP-Linux: An NS-2 TCP Implementation with Congestion Control Algorithms from Linux ;
D. X. Wei and P. Cao; in proceedings of ValueTool'06 -- Workshop of NS-2, Oct, 2006.
PDF
Bibtex
Result comparison between TCP-Linux simulations and Linux experiments:
See the comparison results in
the first version of NS-2 TCP-Linux.
Note that the problems with cubic that we found have been resolved by the new kernel of 2.6.20.
Code Structure:
The following figure shows the code structure of TCP-Linux
.
The whole modules include four parts, corresponding to the four white blocks in the figure. Yellow blocks are from outside source codes such as NS-2 or Linux:
- TCPLinuxAgent (in tcp-linux.h and tcp-linux.cc): this is the main component which loosely follows the Linux implementation in packet receiving, ack processing and congestion control.
- ScoreBoard1 (in scoreboard1.h and scoreboard1.cc): this is a new packet SACK/Loss/Retransmission control module which combines Scoreboard-rq in NS-2 and Linux's ACK/SACK processes. It loosely follows the steps in tcp_clean_rtx_queue and tcp_sacktag_write_queue in tcp_input.c in Linux.
- Interface between NS-2 and Linux (in linux/ns-linux-util.h and .cc): this part redefines the data structure in Linux TCP and provide interfaces between the NS-2's C++ code and Linux's C code.
- Shortcuts for other Linux system calls (in linux/ns-linux-c.h and .c): this part redefines many system calls in Linux (to void) and allows Linux source code to be compiled with very minor changes.
Patch for NS-2.29:
The patch can be downloaded from here.
It is for NS-2.29.
It is also confirmed to be compatible with NS-2.30.
You may need some modification if you want to install it for other versions.
To install the patch, you need to take the following steps, assuming you
have successfully
installed and run NS-2.29 in your computer:
- Copy the patch to ns-allinone-2.29/ns-2.29
- In the directory of ns-allinone-2.29/ns-2.29 , run: make clean
- In the directory of ns-allinone-2.29/ns-2.29 , run: patch
-p1 < ns-linux.patch
- (Optional) delete the patch file by rm ns-linux.patch
- recompile the ns2 by make and make install
The patch changes the following files:
- tcp/tcp-linux.h and tcp/tcp-linux.cc: (new files) the TCP Linux
modules
- tcp/tcp.cc: (modifiying old file) fixed a bug in sending timestamp array (for delay-based algorithms)
- tcp/scoreboard1.h and tcp/scoreboard1.cc: (new files) the
Linux-like scoreboard implementation
- tcp/linux/: (new files) this directory is added to hold source
codes from Linux TCP congestion control modules and the linkages
between C++ codes in NS2 and C codes in Linux
- Makefile: (modifying old file) to include a list of new files to
be compiled
- tcl/lib/ns-default.tcl: (modifying old file) to add default
values to control
variables in TCP-Linux
- This patch also includes
a scheduler improvement patch to speed up the simulation.
Acknowledgment:
The Linux+Dummynet experiments were carried out with WAN-in-Lab (WIL) facilities and greatly helped by Dr. Lachlan Andrew at Caltech.
The work is inspired and greatly helped by Prof. Pei Cao at
Stanford and by Prof.
Steven Low at Caltech.
Many thanks to them!
(Last updated for 2.6.22.9 kernel.)
Please be very careful about compound module as this module has been discontinued in the kernel code base since 2.6.17. It is here for research purpose only and the interface of this module might be out-dated for the latest kernel. We do try our best to keep the module's interface up-to-date. Extra care is still recommended for validating the results with this module. And please let us know if there is any problem.