A Linux TCP implementation for NS2 (Part of the NS-2 enhancement project) David X. Wei Prof. Pei Cao Netlab @ Caltech CS @ Stanford May 2006; Revision 1 for parameter tunings: Sep 2007. This is a patch that can run Linux TCP congestion control algorithms on NS2, with similar simulation speed and memory usages as other NS2 TCPs (e.g. Sack1). The implementation loosely follows the Linux TCP implementation, and can produce results comparable to Linux experimental results. The patch is for NS-2.31 and compatible with 2.29 and 2.30. You may need some modification if you want to install it for other versions. News (complete update records): Mar 31, 2008: TCP-Linux has been incorporated into NS-2 main distribution of ns-2.33 -- if you are using NS-2.33 or later version, you have TCP-Linux with the release automatically. Future maintenance and bugfixes will also go into the main distribution. Now the easiest way to use NS-2 TCP-Linux is to upgrade your NS-2 to 2.33 or later version. This site continues to serve for documentation purpose.Dec 2, 2007: the patch is updated with a change in tcp_compound.c to fix a discrepency between this module and the new congestion control interface on TCP_CONG_RTT_STAMP flag. Thanks to Arya Afrashteh at Virginia Tech for reporting the problem.Nov 11, 2007: the patch is updated with documentation in doc/ directory and example codes in tcl/ex/tcp-linux directory.Oct 30, 2007: Updated the patch with a new feature that allows simulation script to change Linux parameters (the parameters out side congestion control modules, such as max_burst, abc, and etc). See updated tutorial on how this works.Oct 21, 2007: Confirmed that the patch works with NS-2.31 on Cygwin.Oct 1, 2007: A new version of NS-2 TCP-Linux is released. New features include: Support changes of congestion control parameters. See the updated tutorial on how to change congestion control parameters in the simulations.Patch against latest NS-2 source code (2.31), compatible with 2.29 and 2.30.Support the new interface in recent Linux kernel (184.108.40.206), incorporating 14 congestion control algorithmsA set of NS2-compatible validation testsA script that easily updates the congestion control module source codes from linux kernel source code (on *nux platform) The old version of NS-2 TCP-Linux with 220.127.116.11 kernel is no longer supported. However, bug fixes and patches from other contributors to this project will still be published here.Aug 05, 2006: 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. BibtexJun 15, 2006: A summary of known problems in Linux TCP modules is set up in order to help users separate the Linux bugs from algorithm design problems or bugs in NS-2 TCP-Linux.A mini-tutorial for TCP Linux is written for users who want to develop their congestion control algorithms with TCP Linux. Patch for NS-2.31: The patch can be downloaded from here. It is for NS-2.31 and compatible with 2.29 and 2.30. To install the patch, you need to take the following steps, assuming you have successfully installed and run NS-2.31 in your computer: Copy the patch to ns-allinone-2.31/ns-2.31In the directory of ns-allinone-2.31/ns-2.31 , run: make cleanIn the directory of ns-allinone-2.31/ns-2.31 , run: patch -p1 < ns-linux-v2.patch(Optional) delete the patch file by rm ns-linux-v2.patchrecompile the ns2 by make and make install The patch changes the following files: tcp/tcp-linux.h, tcp/tcp-linux.cc: (new files) the NS-2 TCP Linux moduletcp/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 implementationtcp/linux/: (new files) this directory is added to hold the linkages between C++ codes in NS2 and C codes in Linuxtcp/linux/src/: (new files) this directory is added to hold source codes of Linux TCP congestion control modulesMakefile: (modifying old file) to include a list of new files to be compiledtcl/lib/ns-default.tcl: (modifying old file) to add default values to control variables in TCP-Linuxtcl/test/test-all-tcpLinux and tcl/test/test-suite-tcpLinux.tcl: (new files) added for NS-2 compatible validation teststcl/ex/tcp-linux/ (new files): two example files on running TCP-Linuxdoc/ns.bib and doc/tcp.tex (modifying old files): documentation filesThis patch also includes a scheduler improvement patch to speed up the simulation. Legacy patch for NS-2.29 with interface in Linux-2.6.16 kernels The old patch for NS-2.29 with congestion control interface for Linux 2.6.13-2.6.20 kernels can be found here. (Linux changes its congestion control interface in 2.6.22.) This old version is no longer supported. However, bug fixes and patches from other contributors to this project will still be published. Usage: This section serves as a quick reference for users who want to run different Linux TCP algorithms in the TCP Linux patch. There is a mini-tutorial for TCP Linux . Please read the mini-tutorial for details if you want to design your own algorithms or port new algorithms from Linux to NS-2. If you find some performance problem of some Linux algorithms, please check the known Linux bugs page to make sure it is really the problem of the algorithm, not a bug in Linux implementation. 1. Normal Usage: The TCP-Linux module is call "Agent/TCP/Linux". If you have an existing script that runs TCP and want to change to TCP-Linux, what you need to do is: Change the TCP Agent's name (e.g. Agent/TCP/Sack1) to Agent/TCP/Linux.Make sure the TCP Sink has Sack1 support. That is, either you are using Agent/TCPSink/Sack1 or Agent/TCPSink/Sack1/DelAck . Currently, TCP-Linux does not support receivers without SACK.Optional but recommended: change the window_ option in tcp agent to be large enough. This option is the upper bound of congestion window. It is 20 by default in NS-2. Most congestion control algorithms work the same if the congestion window is bounded by 20. The recommended value is at least bandwidth-delay-product.Before starting the simulation, add one command: $ns at 0 "$tcp select_ca $TCP_Name" where $ns is the NS-2 scheduler you are using in the script, and $TCP_Name is the congestion control algorithm you want to select. 2. Basic behavior: The patch comes with 14 different congestion control algorithms from Linux-18.104.22.168, as listed in the following table. Please see the tcl script for the simulation details; see the control shell script for the configuration of the simulations; and the gnuplot script for how the figures are generated. $TCP_Name Congestion Control Algorithm cwnd dynamic of a single flow (RTT=128ms, BW=100Mbps, buffer=220pkt) bic Binary Increase Congestion control for TCP cubic TCP CUBIC: Binary Increase Congestion control for TCP v2.0 , an extension of BIC-TCP highspeed Sally Floyd's High Speed TCP (HS-TCP RFC 3649) congestion control htcp Hamilton TCP (H-TCP) congestion control hybla TCP-HYBLA Congestion control algorithm reno TCP NewReno Note that this "NewReno" also includes implementation of SACK and Fack. scalable Tom Kelly's Scalable TCP vegas TCP Vegas congestion control westwood TCP Westwood+ veno TCP Veno lp TCP Low-Priority (TCP-LP) yeah YeAH-TCP illinois TCP Illinois compound TCP Compound (C-TCP) (Last updated for 22.214.171.124 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. 3. Advanced Usage Changing parameters in a congestion control module in the simulation You can change the parameters of a congestion control module during the simulation. Add a command to change the global value of a parameter for all flows running a congestion control module: $ns at $ChangeTime "$tcp set_ca_default_param $TCP_Name $Parameter_Name $Parameter_Value" 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_Valueis the new value of the parameter. Effect is taken on all the flows which run the $TCP_Name and without defining their own local value for this parameter. (Flows which has used set_ca_param to define a local value for this parameter will not be affected.) Add a command to change the local value of a parameter for a particular flow running a congestion control module: $ns at $ChangeTime "$tcp set_ca_param $TCP_Name $Parameter_Name $Parameter_Value" 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 $Parameter_Valueis the new value of the parameter. Effect is taken on this particular flow ($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 baseFollow 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.ocompile, 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 differenceD-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-2.29In the directory of ns-allinone-2.29/ns-2.29 , run: make cleanIn 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.patchrecompile 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 modulestcp/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 LinuxMakefile: (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-LinuxThis 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!