Table Of Contents

Direct Code Execution (DCE) Manual

This is the manual of Direct Code Execution (DCE).

This document is written in reStructuredText for Sphinx and is maintained in the doc/ directory of ns-3-dce’s source code.



Direct Code Execution (DCE) is a module for ns-3 that provides facilities to execute, within ns-3, existing implementations of userspace and kernelspace network protocols or applications without source code changes. For example instead of using the pseudo application provided by ns-3 V4PingHelper you can use the true ping.

Manual Structure

This document consists of the following parts:

  1. Quick Start: The document describes a quick instruction of DCE.
  2. User’s Guide: The document is for people who will use DCE to experiment.

DCE Outlook

  • To run an application using DCE, it is not necessary to change its sources. However you will need to recompile them.
  • The simulation is executed wholly within a single process which greatly facilitates the debugging.
  • DCE is very memory-efficient, thanks to the way it loads the executables similarly to shared libraries.

Supported Features

  • Simulation with POSIX socket application (no manual modifications)
  • C/C++ applications
  • Simulation with Linux kernel implemented network protocol
  • IPv4/IPv6
  • running with POSIX socket applications and ns-3 socket applications
  • configuration via sysctl-like interface
  • multiple nodes debugging with single gdb interface
  • memory analysis by single valgrind execution with multiple nodes
  • Variance of network stacks
  • ns-3 native stack (IPv4/IPv6, partially)
  • Network simulation cradle network stack (IPv4 TCP only)
  • Linux network stack (IPv4/IPv6/others)
  • Per-node configuration/stdin input
  • Per-node syslog/stdout/stderr files output

Tested Applications

  • CCNx
  • Quagga
  • iperf
  • ping/ping6
  • ip (iproute2 package)
  • Mobilt IPv6 daemon (umip)
  • Linux kernel (from 2.6.36 to 3.7 versions)
  • http server (thttpd)
  • torrent (libtorrent from rasterbar + opentracker)

Tested Environment

Currently, DCE only supports Linux-based operating system. DCE has been tested on the following distributions:

  • Ubuntu 10.04 64bit
  • Ubuntu 12.04 32bit/64bit
  • Ubuntu 12.10 64bit
  • Ubuntu 13.04 64bit
  • Fedora 18 32bit
  • CentOS 6.2 64bit
  • CentOS 6.4 64bit

but you can try on the others (e.g., CentOS, RHEL). If you got run on another distribution, please let us know.

Quick Start


The DCE ns-3 module provides facilities to execute within ns-3 existing implementations of userspace and kernelspace network protocols.

As of today, the Quagga routing protocol implementation, the CCNx CCN implementation, and recent versions of the Linux kernel network stack are known to run within DCE, hence allowing network protocol experimenters and researchers to use the unmodified implementation of their protocols for real-world deployments and simulations.

Build DCE

DCE offers two major modes of operation:
  1. The basic mode, where DCE use the ns-3 TCP stacks,
  2. The advanced mode, where DCE uses a Linux network stack instead.

Building DCE basic mode

First you need to download Bake using Mercurial and set some variables:

hg clone bake
export BAKE_HOME=`pwd`/bake

then you must to create a directory for DCE and install it using bake:

mkdir dce
cd dce configure -e dce-ns3-|version| download build

note that dce-ns3-1.2 is the DCE version 1.2 module. If you would like to use the development version of DCE module, you can specify dce-ns3-dev as a module name for bake.

the output should look likes this:

Installing selected module and dependencies.
Please, be patient, this may take a while!
>> Downloading ccnx
>> Download ccnx - OK
>> Downloading iperf
>> Download iperf - OK
>> Downloading ns-3-dev-dce
>> Download ns-3-dev-dce - OK
>> Downloading dce-ns3
>> Download dce-ns3 - OK
>> Building ccnx
>> Built ccnx - OK
>> Building iperf
>> Built iperf - OK
>> Building ns-3-dev-dce
>> Built ns-3-dev-dce - OK
>> Building dce-ns3
>> Built dce-ns3 - OK

Building DCE advanced mode (with Linux kernel)

If you would like to try Linux network stack instead of ns-3 network stack, you can try the advanced mode. The difference to build the advanced mode is the different module name dce-linux instead of dce-ns3 (basic mode).

mkdir dce
cd dce configure -e dce-linux-|version| download build

note that dce-linux-1.2 is the DCE version 1.2 module. If you would like to use the development version of DCE module, you can specify dce-linux-dev as a module name for bake.

Building DCE using WAF

While Bake is the best option, another one is the configuration and build using WAF. WAF is a Python-based framework for configuring, compiling and installing applications. The configuration scripts are coded in Python files named wscript, calling the WAF framework, and called by the waf executable.

In this case you need to install the single packages one by one. You may want to start with ns-3:

# Download ns-3
hg clone

# Configure
./waf configure --enable-examples -d optimized --prefix=$HOME/dce/build \

# Build and install in the directory specified by
# --prefix parameter
./waf build
./waf install

Then you can download and install net-next-sim and DCE (net-next-sim includes the linux stack module):

# Clone net-next-sim
git clone
cd net-next-sim
# Select a kernel version
git checkout sim-ns3-3.10.0-branch
# Configure and build
make defconfig OPT=yes ARCH=sim
make library OPT=yes ARCH=sim
cd ..

# Download, configure, build and install DCE
hg clone
./waf configure --with-ns3=$HOME/dce/build --enable-opt \
                --enable-kernel-stack=$HOME/dce/net-next-sim/arch \
./waf build
./waf install


If you got succeed to build DCE, you can try an example script which is already included in DCE package.

Example: Simple UDP socket application

This example execute the binaries named udp-client and udp-server under ns-3 using DCE. These 2 binaries are written using POSIX socket API in order to send and receive UDP packets.

If you would like to see what is going on this script, please refer to the user’s guide.

$ cd source/ns-3-dce
$ ./waf --run dce-udp-simple
$ ls
  elf-cache  files-0 exitprocs
$ ls -lR files-0
  total 4
  drwxr-x--- 3 furbani planete 4096 Sep  2 17:02 var

  total 4
  drwxr-x--- 4 furbani planete 4096 Sep  2 17:02 log

  total 8
  drwxr-x--- 2 furbani planete 4096 Sep  2 17:02 53512
  drwxr-x--- 2 furbani planete 4096 Sep  2 17:02 53513

  total 12
  -rw------- 1 furbani planete  12 Sep  2 17:02 cmdline
  -rw------- 1 furbani planete 185 Sep  2 17:02 status
  -rw------- 1 furbani planete   0 Sep  2 17:02 stderr
  -rw------- 1 furbani planete  21 Sep  2 17:02 stdout

  total 12
  -rw------- 1 furbani planete  22 Sep  2 17:02 cmdline
  -rw------- 1 furbani planete 185 Sep  2 17:02 status
  -rw------- 1 furbani planete   0 Sep  2 17:02 stderr
  -rw------- 1 furbani planete  22 Sep  2 17:02 stdout

This simulation produces two directories, the content of elf-cache is not important now for us, but files-0 is. files-0 contains first node’s file system, it also contains the output files of the dce applications launched on this node. In the /var/log directory there are some directories named with the virtual pid of corresponding DCE applications. Under these directories there is always 4 files:

  1. cmdline: which contains the command line of the corresponding DCE application, in order to help you to retrieve what is it,
  2. stdout: contains the stdout produced by the execution of the corresponding application,
  3. stderr: contains the stderr produced by the execution of the corresponding application.
  4. status: contains a status of the corresponding process with its start time. This file also contains the end time and exit code if applicable.

Before launching a simulation, you may also create files-xx directories and provide files required by the applications to be executed correctly.

Example: iperf

This example shows the usage of iperf with DCE. You are able to generate traffic by well-known traffic generator iperf in your simulation. For more detail of the scenario description, please refer to the user’s guide.

Once you successfully installed DCE with bake, you can execute the example using iperf.

cd source/ns-3-dce
./waf --run dce-iperf

As we saw in the previous example the experience creates directories containing the outputs of different executables, take a look at the server (node 1) output:

$ cat files-1/var/log/*/stdout
Server listening on TCP port 5001
TCP window size:  124 KByte (default)
[  4] local port 5001 connected with port 49153
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-11.2 sec  5.75 MBytes  4.30 Mbits/sec

the client (node-0) output bellow:

$ cat files-0/var/log/*/stdout
Client connecting to, TCP port 5001
TCP window size:  124 KByte (default)
[  3] local port 49153 connected with port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 1.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  1.0- 2.0 sec   512 KBytes  4.19 Mbits/sec
[  3]  2.0- 3.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  3.0- 4.0 sec   512 KBytes  4.19 Mbits/sec
[  3]  4.0- 5.0 sec   512 KBytes  4.19 Mbits/sec
[  3]  5.0- 6.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  6.0- 7.0 sec   512 KBytes  4.19 Mbits/sec
[  3]  7.0- 8.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  8.0- 9.0 sec   512 KBytes  4.19 Mbits/sec
[  3]  9.0-10.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  0.0-10.2 sec  5.75 MBytes  4.72 Mbits/sec

if you have already built the advanced mode, you can use Linux network stack over iperf.

cd source/ns-3-dce
./waf --run "dce-iperf --kernel=1"

the command line option –kernel=1 makes the simulation use the Linux kernel stack instead of ns-3 network stack.

$ cat files-1/var/log/*/stdout
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
[  4] local port 5001 connected with port 60120
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-11.2 sec  5.88 MBytes  4.41 Mbits/sec
$ cat files-0/var/log/*/stdout
Client connecting to, TCP port 5001
TCP window size: 16.0 KByte (default)
[  3] local port 60120 connected with port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 1.0 sec   512 KBytes  4.19 Mbits/sec
[  3]  1.0- 2.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  2.0- 3.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  3.0- 4.0 sec   512 KBytes  4.19 Mbits/sec
[  3]  4.0- 5.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  5.0- 6.0 sec   512 KBytes  4.19 Mbits/sec
[  3]  6.0- 7.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  7.0- 8.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  8.0- 9.0 sec   512 KBytes  4.19 Mbits/sec
[  3]  9.0-10.0 sec   640 KBytes  5.24 Mbits/sec
[  3]  0.0-10.2 sec  5.88 MBytes  4.84 Mbits/sec

Interestingly, the two results between two network stacks are slightly different, though the difference is out of scope of this document.

User’s Guide

This document is for the people who want to use your application in ns-3 using DCE.

Direct Code Execution (DCE) allows us to use POSIX socket-based applications as well as Linux kernel network stack.

Setup Guide

In order to install DCE you must follow the tutorial Build DCE.

Installation result

The result of the installation process is the creation of libraries from source of DCE and that of ns-3 and also some tools and sources of an optional Linux kernel if you have also chosen to use the stack of a Linux kernel. Below you will find the main directories:

|── bakefile.xml          Bake internal configuration file (generated by configure command).
|──         Bake generated file used to configure environmental variable.
|── build                 Target directory of |ns3| Core and DCE compilation.
│   |── bin
│   |── bin_dce
│   |── etc
│   |── include
│   |── lib
│   |── sbin
│   |── share
│   |── usr
│   +── var
+── source                 Source directory during ' download'. Listed files below depend on the configuration of bake.
    |── ccnx
    |── ccnx-0.6.2.tar.gz
    |── ns-3-dce
    │   |── build
    │   |── doc            Documentation source
    │   |── elf-cache
    │   |── example        Example scenarios using DCE
    │   |── files-0
    │   |── files-1
    │   |── files-2
    │   |── files-3
    │   |── files-5
    │   |── helper         The source code directory for helper library
    │   |── model          The source code directory for DCE core
    │   |── myscripts      Sub-module and ad-hoc script directory
    │   |── netlink        Netlink module
    │   |── ns3waf         waf extension used by DCE
    │   |── test           Test script directory
    │   |── testpy-output  Directory used for test results
    │   +── utils          Utilities used by DCE
    |── elf-loader
    |── iperf
    |── iperf-2.0.5-source.tar.gz
    |── iproute
    |── iproute2-2.6.38.tar.bz2
    |── iputils
    |── iputils-s20101006.tar.bz2
    |── mptcp
    |── net-next-sim-2.6.36
    |── ns-3-dev-dce
    |── pybindgen-user
    |── quagga
    |── quagga-0.99.20.tar.gz
    |── thttpd
    |── thttpd-2.25b.tar.gz
    |── umip
    |── wget
    +── wget-1.14.tar.gz

Basic Use Cases

Using your userspace protocol implementation

As explained in How It Works, DCE needs to relocate the executable binary in memory, and these binary files need to be built with specific compile/link options.

In order to this you should follow the two following rules:

  1. Compile your objects using this gcc flag: -fPIC for exemple: gcc -fPIC -c foo.c
  1. (option) Some application needs to be compile with -U_FORTIFY_SOURCE so that the application doesn’t use alternative symbols including __chk (like memcpy_chk).
  1. Link your executable using this gcc flag: -pie for exemple: gcc -o foo -pie foo.o
  2. Verify the produced executable using readelf utility in order to display the ELF file header and to verify that your exe is of type DYN indicating that DCE should be able to relocate and virtualize it under ns-3 virtual world and network. For exemple: readelf -h foo|grep Type: ==> Type: DYN (Shared object file)
  3. Check also that your executable runs as expected outside of ns-3 and DCE.
Install the target executable

Copy the executable file produced in a specified directory in the variable environment DCE_PATH so that DCE can find it. (FIXME: to be updated)

Write a ns-3 script

Now that you have compiled your executable you can use it within ns-3 script with the help of a set of DCE Helper Class:

DceManagerHelper ns3/dce-manager-helper.h A DceManager is a DCE internal class which manage the execution of the executable you will declare to run within ns-3; The DceManagerHelper is the tool you will use within your script to parameter and install DceManager on the ns-3 nodes where you plan to run binaries.
DceApplicationHelper ns3/dce-application-helper.h

You will use this helper in order to define which application you want to run within ns-3 by setting the name of the binary its optionals arguments, its environment variables, and also optionally if it take its input from a file instead of stdin.

This class can be derived if you need to do more preparation before running your application. Often applications need configuration file to work properly, for example if you look at the contents of the helper named CcnClientHelper you will see that his job is to create the key files needed for the operation of CCNx’s applications.

LinuxStackHelper ns3/linux-stack-helper.h This helper is used to configure parameters of Linux kernel when we are using the advanced mode.
CcnClientHelper ns3/ccn-client-helper.h This helper is a subclass of DceApplicationHelper, its jobs is to create keys files used by ccnx executables in order to run them correctly within NS3.
QuaggaHelper ns3/quagga-helper.h This helper is a subclass of DceApplicationHelper. It will help you to setup Quagga applications.

Note that the table above indicates the name of includes, so you can look at the comments in them, but in reality for DCE use you need to include only the file ns3/dce-module.h.

The directory named myscripts is a good place to place your scripts. To create a new script you should create a new directory under myscripts, and put your sources and a configuration file for waf build system, this file should be named wscript. For starters, you may refer to the contents of the directory myscripts/ping.

For more detail, please refer DCE API (doxygen) document.

Compile the script

To compile simply execute the command waf. The result must be under the directory named build/bin/myscripts/foo/bar where foo is your directory and bar your executable according to the content of your wscript file.

Launch the script

Simply launch your script like any other program.

$ ./waf --run bar

The execution of the apps using DCE generates special files which reflect the execution thereof. On each node DCE creates a directory /var/log, this directory will contain subdirectory whose name is a number. This number is the pid of a process. Each of these directories contains the following files cmdline, status, stdout, stderr. The file cmdline recalls the name of the executable run followed arguments. The file status contains an account of the execution and dating of the start; optionally if the execution is completed there is the date of the stop and the return code. The files stdout and stderr correspond to the standard output of the process in question.

Example: DCE Simple UDP (dce-udp-simple)

The example uses two POSIX socket-based application in a simulation. Please take time to look at the source

int main (int argc, char *argv[])
  CommandLine cmd;
  cmd.Parse (argc, argv);

  NodeContainer nodes;
  nodes.Create (1);

  InternetStackHelper stack;
  stack.Install (nodes);

  DceManagerHelper dceManager;
  dceManager.Install (nodes);

  DceApplicationHelper dce;
  ApplicationContainer apps;

  dce.SetStackSize (1<<20);

  dce.SetBinary ("udp-server");
  apps = dce.Install (nodes.Get (0));
  apps.Start (Seconds (4.0));

  dce.SetBinary ("udp-client");
  dce.AddArgument ("");
  apps = dce.Install (nodes.Get (0));
  apps.Start (Seconds (4.5));

  Simulator::Stop (Seconds(1000100.0));
  Simulator::Run ();
  Simulator::Destroy ();

  return 0;

You can notice that we create a ns-3 Node with an Internet Stack (please refer to ns-3 doc. for more info), and we can also see 2 new Helpers:

  1. DceManagerHelper which is used to Manage DCE loading system in each node where DCE will be used.
  2. DceApplicationHelper which is used to describe real application to be launched by DCE within ns-3 simulation environment.
Example: DCE with iperf(dce-iperf)

The example uses iperf traffic generator in a simulation. The scenario is here:

#include "ns3/network-module.h"
#include "ns3/core-module.h"
#include "ns3/internet-module.h"
#include "ns3/dce-module.h"
#include "ns3/point-to-point-module.h"
#include "ns3/applications-module.h"
#include "ns3/netanim-module.h"
#include "ns3/constant-position-mobility-model.h"
#include "ccnx/misc-tools.h"

using namespace ns3;
// ===========================================================================
//         node 0                 node 1
//   +----------------+    +----------------+
//   |                |    |                |
//   +----------------+    +----------------+
//   |    |    |    |
//   +----------------+    +----------------+
//   | point-to-point |    | point-to-point |
//   +----------------+    +----------------+
//           |                     |
//           +---------------------+
//                5 Mbps, 2 ms
// 2 nodes : iperf client en iperf server ....
// Note : Tested with iperf 2.0.5, you need to modify iperf source in order to
//        allow DCE to have a chance to end an endless loop in iperf as follow:
//        in source named Thread.c at line 412 in method named thread_rest
//        you must add a sleep (1); to break the infinite loop....
// ===========================================================================
int main (int argc, char *argv[])
  bool useKernel = 0;
  bool useUdp = 0;
  std::string bandWidth = "1m";
  CommandLine cmd;
  cmd.AddValue ("kernel", "Use kernel linux IP stack.", useKernel);
  cmd.AddValue ("udp", "Use UDP. Default false (0)", useUdp);
  cmd.AddValue ("bw", "BandWidth. Default 1m.", bandWidth);
  cmd.Parse (argc, argv);

  NodeContainer nodes;
  nodes.Create (2);

  PointToPointHelper pointToPoint;
  pointToPoint.SetDeviceAttribute ("DataRate", StringValue ("5Mbps"));
  pointToPoint.SetChannelAttribute ("Delay", StringValue ("1ms"));

  NetDeviceContainer devices;
  devices = pointToPoint.Install (nodes);

  DceManagerHelper dceManager;
  dceManager.SetTaskManagerAttribute( "FiberManagerType", StringValue ( "UcontextFiberManager" ) );

  if (!useKernel)
      InternetStackHelper stack;
      stack.Install (nodes);
      dceManager.SetNetworkStack ("ns3::LinuxSocketFdFactory", "Library", StringValue (""));
      LinuxStackHelper stack;
      stack.Install (nodes);

  Ipv4AddressHelper address;
  address.SetBase ("", "");
  Ipv4InterfaceContainer interfaces = address.Assign (devices);

  // setup ip routes
  Ipv4GlobalRoutingHelper::PopulateRoutingTables ();

  dceManager.Install (nodes);

  DceApplicationHelper dce;
  ApplicationContainer apps;

  dce.SetStackSize (1<<20);

  // Launch iperf client on node 0
  dce.SetBinary ("iperf");
  dce.AddArgument ("-c");
  dce.AddArgument ("");
  dce.AddArgument ("-i");
  dce.AddArgument ("1");
  dce.AddArgument ("--time");
  dce.AddArgument ("10");
  if (useUdp)
      dce.AddArgument ("-u");
      dce.AddArgument ("-b");
      dce.AddArgument (bandWidth);

  apps = dce.Install (nodes.Get (0));
  apps.Start (Seconds (0.7));
  apps.Stop (Seconds (20));

  // Launch iperf server on node 1
  dce.SetBinary ("iperf");
  dce.AddArgument ("-s");
  dce.AddArgument ("-P");
  dce.AddArgument ("1");
  if (useUdp)
      dce.AddArgument ("-u");

  apps = dce.Install (nodes.Get (1));

  pointToPoint.EnablePcapAll (useKernel?"iperf-kernel":"iperf-ns3", false);

  apps.Start (Seconds (0.6));

  setPos (nodes.Get (0), 1, 10, 0);
  setPos (nodes.Get (1), 50,10, 0);

  Simulator::Stop (Seconds(40.0));
  Simulator::Run ();
  Simulator::Destroy ();

  return 0;

This scenario is simple there is 2 nodes linked by a point 2 point link, the node 0 launch iperf as a client via the command iperf -c -i 1 –time 10 and the node 1 launch iperf as a server via the command iperf -s -P 1. You can follow this to launch the experiment:

Using your in-kernel protocol implementation


How to add system calls ?


If your applications running with DCE are not able to run due to missing function symbols, you need to add the function call or system call to DCE by hand. The POSIX API coverage of DCE is growing day by day, but your contribution is definitely helpful not only for your case, but also for someone will use in future.

More specifically, if you faced the following error when you executed, you need to add a function call to DCE. In the following case, a symbol strfry not defined in DCE is detected during the execution of the simulation.

% ./waf --run dce-udp-perf
'build' finished successfully (0.704s)
/home/tazaki/hgworks/dce-dev/source/ns-3-dce/build/bin/dce-udp-perf: **relocation error: elf-cache/0/udp-perf: symbol strfry**, version GLIBC_2.2.5 not defined in file with link time reference
Command ['/home/tazaki/hgworks/dce-dev/source/ns-3-dce/build/bin/dce-udp-perf'] exited with code 127
Types of symbol

There are two types of symbols that is defined in DCE.

NATIVE symbol is a symbol that DCE doesn’t care about the behavior. So this type of symbol is redirected to the one provided by underlying host operating system (i.e., glibc).
  • DCE
DCE symbol is a symbol that DCE reimplements its behavior instead of using the underlying system’s one. For instance, socket() call used in an application redirected to DCE to cooperate with ns-3 or Linux network stack managed by DCE. malloc() is also this kind.
Files should be modified

In order to add function calls or system calls that DCE can handle, you need to modify the following files.

  • model/libc-ns3.h

This is the first file that you need to edit. You may lookup the symbol that you’re going to add and once you can’t find it, add the following line.

NATIVE (strfry)

This is the case of the symbol strfry(), which we don’t have to reimplement. But you may need to add include file that defines the symbol (strfry()) at model/

If the symbol needs to reimplemented for DCE, you may add as follows.

DCE (socket)

  • model/

In case of DCE symbol, you’re going to introduce DCE redirected function. We use naming convention with prefix of dce_ to the symbol (i.e., dce_socket) to define new symbol and add the implementation in a .cc file. The following is the example of dce_socket() implementation.

We implemented dce_socket() function in the file model/

int dce_socket (int domain, int type, int protocol)

In the function, we carefully fill the function contents to cooperate with ns-3. The below line is creating DCE specific socket instance (i.e., ns-3 or DCE Linux) instead of calling system call allocating kernel space socket resources.

UnixFd *socket = factory->CreateSocket (domain, type, protocol);

Other function calls such as file system related functions (e.g., read, fopen), time reheated features (e.g., gettimeofday, clock_gettime), signal/process utilities (e.g., getpid, sigaction), and thread library (e.g., pthread_create). All these functions should be DCE since DCE core reimplements these feature instead of using underlying host system.

  • model/dce-abc.h
Once you got implemented the new redirected function, you may add the function prototype declaration to refer from other source files. dce_socket() is added to model/sys/dce-socket.h.

Creating your protocol implementation as a DCE sub-module

If your application has a configuration file to modify the behavior of applications, introducing a particular Helper class will be helpful to handle your application. In this section, we will give you an advanced way of using your application with DCE.

Some of existing submodule are following this way. You can find ns-3-dce-quagga and ns-3-dce-umip as examples to add sub-module.

Obtaining DCE sub-module template

First of all, you could start with referring sub module template available as follows.

hg clone (your module name)

The template consists of, wscript, helper, test and documentation. You could rename all/some of them for your module. Then, put ns-3-dce-submodule directory under ns-3-dce/myscripts/. This will be required to build under ns-3-dce module as an extension (sub-module) of dce.

Writing wscript
Writing bakeconf.xml (optional)
Implementing helper class (optional)
Writing examples (optional)

Global DCE Configurations


The DCE specifics variables are essentially two PATH like variables: so within them you may put paths separated by ‘:’ character.

DCE_PATH is used by DCE to find the executable you want to launch within ns-3 simulated network. This variable is used when you reference the executable using a relative form like ‘ping’.

DCE_ROOT is similar to DCE_PATH but it is used when you use an absolute form for exemple ‘/bin/bash’.

Please pay attention that executables that you will place in the directories indicated in the previous variables should be recompiled accordingly to the rules defined in the next chapter.

(FIXME: to be updated)


DCE is configurable with NS3 Attributes. Refer to the following table:

FiberManagerType The TaskManager is used to switch the execution context between threads and processes.

UcontextFiberManager the more efficient.

PthreadFiberManager helpful with gdb to see the threads. This is the de fault.


dceManager.SetTaskManagerAttribute("FiberManagerType", StringValue("UcontextFiberManager"));


LoaderFactory The LoaderFactory is used to load the hosted binaries.

CoojaLoaderFactory is the default and the only one that supports fork.

DlmLoaderFactory is the more efficient. To use it you have two ways:

  • use dce-runner
  • link using ldso as

default interpreter.


$ dce-runner my-dce-ns3-script


gcc -o  my-dce-ns3-script Wl,--dynamic-linker=PATH2LDSO/ldso ...

$ my-dce-ns3-script --ns3::DceManagerHelper::LoaderFactory=ns3::Dl mLoaderFactory[]


DCE Cradle

This document describes what DCE Cradle is, how we can use it, how we extend it.

Tutorials and how to reproduce the experiment of WNS3 2013 paper is available DCE Cradle Tutorial.

What is DCE Cradle?

DCE Cradle enables us to use Linux kernel via Direct Code Execution from the ns-3 native socket application. Applications can access it via ns-3 socket API. Currently (20th Nov. 2012) the following sockets are available:

  • IPv4 UDP
  • IPv4 TCP
  • IPv4 RAW socket
  • IPv4 DCCP
Installing DCE Cradle

DCE Cradle is already integrated in ns-3-dce module. You can just build and install DCE as instructed in the parent document.

How to use it
OnOffHelper onoff = OnOffHelper ("ns3::LinuxTcpSocketFactory",
                                 InetSocketAddress (interfaces.GetAddress (1), 9));
How to extend it

(To be added)


The project originally started during GSoC project 2012

the paper (to be added if it will be published)

Aspect-based Tracing

Aspect-based tracing, provided by libaspect, allows us to use tracing facility with unmodified code.

One of contradictions when we use DCE is, tracing, how to put trace sources into unmodified code. While DCE gives an opportunity to use unmodified codes as simulation protocols, one might want to investigate which function is called or how many messages of a particular protocol are exchanged.

ns-3 originally has a nice feature of tracing with such a purpose, with on-demand trace connector to obtain additional information. Instead of inserting TraceSource into the original code, DCE gives dynamic trace points with this library, based on the idea of aspect-based tracing.

For more detail, see the Chapter 6.3.2 of the thesis.

Quick Start

To put trace sources without modifying the original code, aspcpp::HookManager gives trace hooks into arbitrary source codes and functions.

#include <hook-manager.h>

HookManager hooks;
hooks.AddHookBySourceAndFunction ("ip_input.c", "::ip_rcv", &IpRcv);
hooks.AddHookByFunction ("::process_backlog", &ProcBacklog);
hooks.AddHookByFunction ("::arp_xmit", &ArpXmit);

The above examples specifies file name and functions with callback functions in the simulation script.

  • July 10th, 2013: aspect-based tracing (libaspect) is in the alpha release state. It might be updated frequently.
  • Callback function has no argument that it can investigate the contents of buffer that each function handles.

Advanced Use Cases

Using Alternative, Fast Loader

DCE optionally supports an alternative ELF loader/linker, so-called elf-loader, in order to replace system-provided linker/loader module. The intention of the loader is to support unlimited number of instances used by dlmopen call, which provides DCE to load a single ELF binary to multiple different memory space. dlmopen-based loader (ns3::DlmLoaderFactory) is much faster than another default one (ns3::CoojaLOaderFactory), but few issues are remain so, this is optional.

To Speedup Run-time

In order to use DlmLoaderFactory, you can add command-line argument of waf.

./waf --run dce-tcp-simple --dlm

if you are in the ./waf shell mode, the following command should be used instead.

./build/bin/dce-runner ./build/bin/dce-tcp-simple

Debugging your protocols with DCE


It is possible to use gdb to debug a script DCE/ns-3. As explained somewhere in the execution of a script is monoprocess, then you can put breakpoints in both sources of DCE and those of binaries hosted by DCE.


Although it is not strictly necessary, it is recommended that you recompile a CVS Gdb for use with ns-3-dce. First, download:

cvs -d login {enter “anoncvs” as the password} cvs -d co gdb

Note that you might consider looking at to obtain more efficient (cpu/bandwidth-wise) download instructions.

Anyway, now, you can build:

cd gdb

And, then, invoke the version of gdb located in gdb/gdb instead of your system-installed gdb whenever you need to debug a DCE-based program.


If you use gdb (a CVS or stable version), do not forget to execute the following command prior to running any DCE-based program:

(gdb) handle SIGUSR1 nostop
Signal        StopPrintPass to programDescription
SIGUSR1       NoYesYesUser defined signal 1

An alternate way to do this and avoid having to repeat this command ad-nauseam involves creating a .gdbinit file in your ns-3-dce directory and putting this inside:

handle SIGUSR1 nostop
Setup Eclipse Remote Debugging Environment

To remotely debug a DCE script you can use gdbserver as in the following example, changing the host name and port (localhost:1234):

./waf --run dce-httpd --command-template="gdbserver localhost:1234 %s <args>"

Then you can point a gdb client to your server. For example, in the following figure is reported an Eclipse debug configuration:


Once you start the debug session, you can use the usual Eclipse/gdb commands.

Helpful debugging hints

There are a couple of functions which are useful to put breakpoints into:

  • ns3::DceManager::StartProcessDebugHook
Put a breakpoint in a specific node in a simulation

If you got a trouble in your protocol during interactions between distributed nodes, you want to investigate a specific state of the protocol in a specific node. In a usual system, this is a typical case of using distributed debugger (e.g., ddt, or mpirun xterm -e gdb –args xxx), but it is annoying task in general due to the difficulty of controlling distributed nodes and processes.

DCE gives an easy interface to debug distributed applications/protocols by the single-process model of its architecture.

The following is an example of debugging Mobile IPv6 stack (of Linux) in a specific node (i.e., home agent). A special function dce_debug_nodeid() is useful if you put a break condition in a gdb session.

(gdb) b mip6_mh_filter if dce_debug_nodeid()==0
Breakpoint 1 at 0x7ffff287c569: file net/ipv6/mip6.c, line 88.
(gdb) bt 4
#0  mip6_mh_filter (sk=0x7ffff7f69e10, skb=0x7ffff7cde8b0)
    at net/ipv6/mip6.c:109
#1  0x00007ffff2831418 in ipv6_raw_deliver (skb=0x7ffff7cde8b0,
    at net/ipv6/raw.c:199
#2  0x00007ffff2831697 in raw6_local_deliver (skb=0x7ffff7cde8b0,
    at net/ipv6/raw.c:232
#3  0x00007ffff27e6068 in ip6_input_finish (skb=0x7ffff7cde8b0)
    at net/ipv6/ip6_input.c:197
(More stack frames follow...)

(FIXME: simple session using valgrind)

Testing your protocols with DCE

Since DCE allows protocol implementations to expose network conditions (packet losses, reordering, and errors) with the interactions among distributed nodes, which is not easily available by traditional user-mode virtualization tools, exercising your code is easily done with a single simulation script.

Coverage Test

Improving code coverage with writing test programs is one of headache; - writing test program is annoying, - preparing test network tends to be short-term, and - the result is not reproducible.

This text describes how to measure code coverage of protocol implementations with DCE.

  1. build target implementations (applications, kernel stack) with profile option
  2. run test program with DCE
  3. parse the result of test coverage

First, you need to compile your application with additional flags. -fprofile-arcs -ftest-coverage is used for a compilation flag (CFLAGS/CXXFLAGS), and -fprofile-arcs is used for a linker flag (LDFLAGS).

gcc -fprofile-arcs -ftest-coverage -fPIC -c foo.c
gcc -fprofile-arcs -pie foo.o -o newapp
Write Test Program

Next, write a test program like ns-3 simulation script for your application (i.e., newapp).

$ cat myscripts/

int main (int argc, char *argv[])
  CommandLine cmd;
  cmd.Parse (argc, argv);

  NodeContainer nodes;
  nodes.Create (2);

  InternetStackHelper stack;
  stack.Install (nodes);

  DceManagerHelper dceManager;
  dceManager.Install (nodes);

  DceApplicationHelper dce;
  ApplicationContainer apps;

  // application on node 0
  dce.SetBinary ("newapp");
  apps = dce.Install (nodes.Get (0));
  apps.Start (Seconds (4.0));

  // application on node 1
  dce.SetBinary ("newapp");
  apps = dce.Install (nodes.Get (1));
  apps.Start (Seconds (4.5));

  Simulator::Stop (Seconds(100.0));
  Simulator::Run ();
  Simulator::Destroy ();

  return 0;
Run Test

Then, test your application as normal ns-3 (and DCE) simulation execution.

./waf --run dce-newapp

If you successfully finish your test, you will see the coverage data files (i.e., gcov data files) with a file extension .gcda.

$ find ./ -name "*.gcda"

Parse Test Result

We use lcov utilities as a parse of coverage test result.

Put the compiler (gcc) generated files (*.gcno) in the result directory,

cp *.gcno ./files-0/home/you/are/here/ns-3-dce/
cp *.gcno ./files-1/home/you/are/here/ns-3-dce/

then run the lcov and genhtml command to generate coverage information of your test program.

lcov -c -d .-b . -o
genhtml -o html

You will see the following output and generated html pages.

Reading data file
Found 8 entries.
Writing .css and .png files.
Generating output.
Processing file ns-3-dce/example/
genhtml: Use of uninitialized value in subtraction (-) at /usr/bin/genhtml line 4313.
Processing file ns-3-dce/example/
genhtml: Use of uninitialized value in subtraction (-) at /usr/bin/genhtml line 4313.
Processing file /usr/include/c++/4.4/iostream
Processing file /usr/include/c++/4.4/ostream
Processing file /usr/include/c++/4.4/bits/ios_base.h
Processing file /usr/include/c++/4.4/bits/locale_facets.h
Processing file /usr/include/c++/4.4/bits/char_traits.h
Processing file /usr/include/c++/4.4/bits/basic_ios.h
Writing directory view page.
Overall coverage rate:
  lines......: 49.3% (35 of 71 lines)
  functions..: 31.6% (6 of 19 functions)
Fuzz Test

(TBA, about integration of trinity)

Regression Test


Technical Information

DCE in a Nutshell

File System

To start a program in the world of ns-3 you must indicate on which node it will be launched. Once launched this program will have access only to the file system corresponding to the node that corresponds to a directory on your machine called file-X where X is the decimal number of the corresponding node. The file-X directories are created by DCE, only when they do not already exist. Also note that the contents of this directory is not cleared when starting the script. So you can copy the files required for the operation of your executables in the tree nodes. If possible it is best that you create these files from the script itself in order to simplify maintenance. DCE provides some helpers for creating configuration files necessary to the execution of certain apps like CCNx and Quagga.


Your program running in a ns-3 node views the network defined by the script for this node.


Time perceived by your executable is the simulated time of ns-3. Also note that DCE supports real time scheduler of ns-3 with the same limitations.


  • Currently the POSIX API (libc) is not fully supported by DCE. However there are already about 400 methods supported. As the goal of DCE is to allow to execute network applications, many methods related to the network are supported for example socket, connect, bind, listen, read, write, poll, select. The next chapter list the applications well tested using DCE.
  • Some methods are not usable with all options of DCE. For more details refer to chapter Coverage API that lists all the supported methods.
  • The scheduler is not as advanced as that of a kernel, for example if an infinite loop in a hosted application, DCE can not get out, but this should not happen in applications written correctly.

API Coverage

Below there is the list of the systems calls supported by DCE, the column named Type represents how the system call is implemented ie:

  1. DCE the method is fully rewritten,
  2. NATIVE the real corresponding system call is used.
API Coverage
System Call Name Domain Include file Type Remarks
gettimeofday Date & Time sys/time.h DCE  
time Date & Time time.h DCE  
asctime, ctime, gmtime, localtime Date & Time time.h DCE  
asctime_r, ctime_r, gmtime_r, localtime_r, mktime, strftime Date & Time time.h NATIVE  
clock_gettime Date & Time time.h NATIVE Should not be NATIVE, do not use for now.
read IO unistd.h DCE  
write IO unistd.h DCE  
writev IO sys/uio.h DCE  
clearerr IO stdio.h DCE  
setbuf, setbuffer, setlinebuf, setvbuf IO stdio.h DCE  
fseek, ftell, rewind, fgetpos, fsetpos IO stdio.h DCE  
printf IO stdio.h DCE  
fprintf IO stdio.h NATIVE  
sprintf, snprintf IO stdio.h NATIVE  
asprintf, vasprintf IO stdio.h NATIVE  
dprintf, vdprintf IO stdio.h NATIVE  
fgetc, fgetc_unlocked IO stdio.h DCE  
getc, getc_unlocked IO stdio.h NATIVE  
getchar, getchar_unlocked IO stdio.h DCE  
_IO_getc IO stdio.h DCE  
fputc, fputc_unlocked IO stdio.h DCE  
putc, putc_unlocked IO stdio.h NATIVE  
putchar, putchar_unlocked IO stdio.h DCE  
_IO_putc IO stdio.h DCE  
fgets, fgets_unlocked IO stdio.h DCE  
fputs, fputs_unlocked IO stdio.h DCE  
puts IO stdio.h DCE  
ungetc IO stdio.h DCE  
fclose IO stdio.h DCE  
fcloseall IO stdio.h DCE  
fopen, fdopen64, fdopen, freopen IO stdio.h DCE  
fflush, fflush_unlocked IO stdio.h DCE  
fread, fread_unlocked IO stdio.h DCE  
fwrite, fwrite_unlocked IO stdio.h DCE  
ferror, ferror_unlocked IO stdio.h DCE  
feof, feof_unlocked IO stdio.h DCE  
fileno, fileno_unlocked IO stdio.h DCE  
perror IO stdlib.h DCE  
vprintf IO stdarg.h DCE  
vfprintf, vsprintf, vsnprintf IO stdarg.h NATIVE  
fcntl IO fcntl.h DCE  
dup, dup2 IO unistd.h DCE  
open, open64 IO fcntl.h DCE  
close IO unistd.h DCE  
unlink IO unistd.h DCE  
remove IO stdio.h DCE  
mkdir IO sys/stat.h DCE  
rmdir IO unistd.h DCE  
select IO unistd.h DCE  
isatty IO unistd.h DCE  
ioctl IO sys/ioctl.h DCE  
poll IO poll.h DCE  
getcwd, getwd, get_current_dir_name IO unistd.h DCE  
chdir, fchdir IO unistd.h DCE  
alphasort, alphasort64, versionsort IO dirent.h NATIVE  
umask IO sys/stat.h DCE  
truncate, ftruncate IO unistd.h DCE  
ttyname IO unistd.h DCE  
lseek IO unistd.h DCE  
euidaccess, eaccess IO unistd.h DCE  
pathconf IO unistd.h NATIVE  
getpwnam, getpwuid, endpwent IO pwd.h DCE  
opendir, fdopendir IO dirent.h DCE  
readdir, readdir_r IO dirent.h DCE  
closedir IO dirent.h DCE  
dirfd IO dirent.h DCE  
rewinddir IO dirent.h DCE  
scandir IO dirent.h DCE  
unlinkat IO fcntl.h DCE  
pread, pwrite IO unistd.h DCE  
uname Kernel sys/utsname.h DCE  
sysconf Kernel unistd.h NATIVE  
calloc, malloc, free, realloc Memory Allocation stdlib.h DCE  
mmap, mmap64, munmap Memory Mappings sys/map.h DCE  
htonl Networking arpa/inet.h NATIVE  
htons Networking arpa/inet.h NATIVE  
ntohl Networking arpa/inet.h NATIVE  
htonl Networking arpa/inet.h NATIVE  
ntohs Networking arpa/inet.h NATIVE  
socket Networking sys/socket.h DCE Not all flavour are supported pleaselook at the doxygen doc.
getsockname Networking sys/socket.h DCE  
getpeername Networking sys/socket.h DCE  
bind Networking sys/socket.h DCE  
connect Networking sys/socket.h DCE  
inet_aton, inet_addr, inet_network, inet_ntoa, inet_makeaddr, inet_lnaof, inet_netof Networking arpa/inet.h NATIVE  
inet_ntop Networking arpa/inet.h DCE  
inet_pton Networking arpa/inet.h NATIVE  
getsockopt, setsockopt Networking sys/socket.h DCE  
listen Networking sys/socket.h DCE  
accept Networking sys/socket.h DCE  
shutdown Networking sys/socket.h DCE  
send, sendto, sendmsg Networking sys/socket.h DCE  
recv, recvfrom, recvmsg Networking sys/socket.h DCE  
gethostbyname, gethostbyname2 Networking netdb.h DCE  
getaddrinfo, freeaddrinfo, gai_strerror Networking netdb.h DCE  
gethostent, sethostent, endhostset, hstrerror Networking netdb.h NATIVE  
herror Networking netdb.h DCE  
getprotoent, getprotobyname, getprotonumber, setprotoent, endprotoent Networking netdb.h NATIVE  
getservent, getservbyname, getservbyport, setservent, endservent Networking netdb.h NATIVE  
if_nametoindex Networking net/if.h DCE  
getnameinfo Networking sys/socket.h DCE  
ether_aton_r Networking netinet/ether.h NATIVE  
atexit Process stdlib.h DCE  
getpid, getppid Process unistd.h DCE  
getuid, geteuid Process unistd.h DCE  
setuid Process unistd.h DCE  
setgid Process unistd.h DCE  
seteuid, setegid Process unistd.h DCE  
setreuid, setregid Process unistd.h DCE  
setresuid, setresgid Process unistd.h DCE  
sched_yield Process sched.h DCE  
exit Process unistd.h DCE  
getenv Process stdlib.h DCE  
putenv Process stdlib.h DCE  
setenv, unsetenv Process stdlib.h DCE  
clearenv Process stdlib.h DCE  
fork Process unistd.h DCE Supported only with the Cooja Loader.
abort Process stdlib.h DCE  
execl, execlp, execle, execv, execvp, execve Process unistd.h DCE Supported only with the pthread fiber manager.
wait, waitpid Process sys/wait.h DCE  
sbrk Process unistd.h DCE  
getpagesize Process unistd.h DCE  
getgid, getegid Process unistd.h DCE  
gethostname Process unistd.h DCE  
getpgrp Process unistd.h DCE  
pipe Process unistd.h DCE  
__sigsetjmp, siglongjmp Process setjmp.h NATIVE Experimental, please do not use them.
getdtablesize Process unistd.h NATIVE  
random, srandom Random stdlib.h DCE  
rand, srand Random stdlib.h DCE  
drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48 Random stdlib.h DCE  
drand48_r, erand48_r, lrand48_r, nrand48_r, mrand48_r, jrand48_r, srand48_r, seed48_r, lcong48_r Random stdlib.h DCE  
signal Signal signal.h DCE  
sigaction Signal signal.h DCE  
sigemptyset, sigfillset, sigaddset, sigdelset, sigismember Signal signal.h NATIVE  
sigprocmask Signal signal.h DCE  
qsort Sort stdlib.h NATIVE  
strerror, strerror_h String string.h NATIVE  
setlocale String locale.h DCE Do nothing at all
strcoll String string.h NATIVE  
uselocale String locale.h NATIVE  
newlocale String locale.h NATIVE  
wctob String wchar.h NATIVE  
btowc String wchar.h NATIVE  
memset String string.h NATIVE  
memcpy String string.h NATIVE  
bcopy String string.h NATIVE  
memcmp String string.h NATIVE  
memmove String string.h NATIVE  
memchr String string.h NATIVE  
strcpy, strncpy String string.h NATIVE  
strcat, strncat String string.h NATIVE  
strcmp, strncmp String string.h NATIVE  
strlen, strnlen String string.h NATIVE  
strspn, strcspn String string.h NATIVE  
strchr, strrchr String string.h NATIVE  
strcasecmp, strncasecmp String string.h NATIVE  
strdup, strndup String string.h DCE  
getopt, getopt_long String unistd.h DCE  
atoi, atol, atoll, atof String stdlib.h NATIVE  
strtol, strtoll String stdlib.h DCE  
strtoul, strtoull String stdlib.h DCE  
strtod String stdlib.h DCE  
toupper, tolower String ctype.h NATIVE  
index, rindex String strings.h NATIVE  
strtok, strtok_r String string.h NATIVE  
sscanf String stdio.h NATIVE  
basename, dirname String libgen.h NATIVE  
bindtextdomain, textdomain, gettext String libintl.h NATIVE  
mbrlen String wchar.h NATIVE  
strtoimax, strtoumax String inttypes.h NATIVE  
openlog, syslog, closelog, vsyslog, setlogmask Syslog syslog.h DCE  
pthread_create Thread pthread.h DCE  
pthread_exit Thread pthread.h DCE  
pthread_self Thread pthread.h DCE  
pthread_once Thread pthread.h DCE  
pthread_getspecific, pthread_setspecific Thread pthread.h DCE  
pthread_key_create Thread pthread.h DCE  
pthread_key_delete Thread pthread.h DCE  
pthread_mutex_destroy, pthread_mutex_init Thread pthread.h DCE  
pthread_mutex_lock, pthread_mutex_trylock, pthread_mutex_unlock Thread pthread.h DCE  
pthread_mutexattr_destroy, pthread_mutexattr_init Thread pthread.h DCE  
pthread_mutexattr_settype Thread pthread.h DCE  
pthread_cancel Thread pthread.h DCE  
pthread_kill Thread pthread.h DCE  
pthread_join Thread pthread.h DCE  
pthread_detach Thread pthread.h DCE  
pthread_cond_destroy, pthread_cond_init Thread pthread.h DCE  
pthread_cond_broadcast, pthread_cond_signal Thread pthread.h DCE  
pthread_cond_timedwait, pthread_cond_wait Thread pthread.h DCE  
pthread_condattr_destroy, pthread_condattr_init Thread pthread.h DCE  
sem_init Thread Synchronization semaphore.h DCE  
sem_destroy Thread Synchronization semaphore.h DCE  
sem_post Thread Synchronization semaphore.h DCE  
sem_wait, sem_trywait, sem_timedwait Thread Synchronization semaphore.h DCE  
sem_getvalue Thread Synchronization semaphore.h DCE  
sleep, usleep Timer unistd.h DCE  
nanosleep Timer time.h DCE  
getitimer, setitimer Timer sys/time.h DCE  
timerfd_create, timerfd_settime, timerfd_gettime Timer sys/timerfd.h DCE  
getgrnam Users & Groups grp.h NATIVE  
getrusage Users & Groups sys/resource.h NATIVE  

Developer’s Guide

This document is for the people who want to develop DCE itself.

Kernel Developer Information

This technical documentation is intended for developers who want to build a Linux kernel in order to use with DCE. A first part will describe the architecture and the second will show how we went from a net-next kernel 2.6 has a Linux kernel-stable 3.4.5.


You must be familiar with ns-3, DCE and Linux Kernel Developpement.


The source code can be found in the following repository: You must use mercurial to download the source code.


The goal of this work is to use the real implementation of the Linux Network Stack within the Simulation environment furnished by ns-3.


The solution chosen was to use the Linux kernel source, compile the Net part and make a dynamic library and interface the result with DCE.

The following schema shows the different parts between a software user space application and the hardware network.


The following schema show the same application running under DCE and ns-3 and using a real kernel network stack:


The green parts are implemented in ns-3-linux source files, the grays parts comes from the Linux kernel sources and are not modified at all or with only few changes. Application should not be modified at all.


If you need a more theoretical documentation you can read the chapter 4.5 of this Ph.D. thesis Experimentation Tools for Networking Research.

List of files and usage

After doing the cloning of the source,

$ hg clone
destination directory: ns-3-linux
requesting all changes
adding changesets
adding manifests
adding file changes
added 62 changesets with 274 changes to 130 files
updating to branch default
125 files updated, 0 files merged, 0 files removed, 0 files unresolved

Below are the files delivered under the directory ns-3-linux:

$ ls ns-3-linux/  kernel-dsmip6.patch  kernel.patch  Makefile  Makefile.print  README  sim

The main file is the Makefile its role is to recover the kernel source, compile the NET part of the kernel and all that is necessary for the operation, the end result is a shared library that can be loaded by DCE.

$ ls ns-3-linux/sim
cred.c     glue.c     Kconfig    pid.c    random.c    seq.c         sim-socket.c  softirq.c  tasklet.c          timer.c
defconfig  hrtimer.c  Makefile   print.c  sched.c     sim.c         slab.c        sysctl.c   tasklet-hrtimer.c  workqueue.c
fs.c       include    modules.c  proc.c   security.c  sim-device.c  socket.c      sysfs.c    time.c

$ ls ns-3-linux/sim/include
asm  generated  sim-assert.h  sim.h  sim-init.h  sim-printf.h  sim-types.h

These directories contains the architecture specific code and the code doing the interface between the kernel and DCE and ns-3. Ideally we should not change a line of code outside the kernel arch portion, but in practice we make small changes : see the patchs files.

Recall: the code of Linux source is mainly C so it is very easy to port to new architecture, the architecture specific code is contained in a specific directory under arch/XXX directory where XXX name recall the processor used. In our case we have chosen to create a special architecture for our environment NS3 + DCE, we called sim.

Interfaces between Kernel and DCE

In order to install a kernel on a Node DCE do the following steps:

  1. Load the shared library containing the kernel compilation result,
  2. Call the init function called sim_init, this method is located in the just loaded library,
  3. This sim_init method is called with a parameter which is a struct containing functions pointers to DCE methods able to be callable from the kernel part,
  4. in return the sim_init fill a struct containing function pointers in kernel part which will be used by DCE to interract with the kernel part.
  5. before finish sim_init must initialize the kernel to put it in a running state ready to be usable.
Kernel -> DCE

Methods (there is also one variable) of DCE called by the kernels are the following:

  • LinuxSocketFdFactory::Vprintf
  • LinuxSocketFdFactory::Malloc
  • LinuxSocketFdFactory::Free
  • LinuxSocketFdFactory::Memcpy
  • LinuxSocketFdFactory::Memset
  • LinuxSocketFdFactory::Random
  • LinuxSocketFdFactory::EventScheduleNs
  • LinuxSocketFdFactory::EventCancel
  • CurrentNs
  • LinuxSocketFdFactory::TaskStart
  • LinuxSocketFdFactory::TaskWait
  • LinuxSocketFdFactory::TaskCurrent
  • LinuxSocketFdFactory::TaskWakeup
  • LinuxSocketFdFactory::TaskYield
  • LinuxSocketFdFactory::DevXmit
  • LinuxSocketFdFactory::SignalRaised
  • LinuxSocketFdFactory::PollEvent

there are located in the source file of DCE.

DCE -> Kernel

Methods of Kernel (sim part) called by DCE are the following:

  • task_create
  • task_destroy
  • task_get_private
  • sock_socket
  • sock_close
  • sock_recvmsg
  • sock_sendmsg
  • sock_getsockname
  • sock_getpeername
  • sock_bind
  • sock_connect
  • sock_listen
  • sock_shutdown
  • sock_accept
  • sock_ioctl
  • sock_setsockopt
  • sock_getsockopt
  • sock_poll
  • sock_pollfreewait
  • dev_create
  • dev_destroy
  • dev_get_private
  • dev_set_address
  • dev_set_mtu
  • dev_create_packet
  • dev_rx
  • sys_iterate_files
  • sys_file_read
  • sys_file_write

the corresponding sources are located in the sim directory.

Build net-next 2.6 kernel

All build operations are done using the make command with the Makefile file under the directory ns-3-linux.

Make Setup

First you should call make setup in order to download the source of the kernel:

$ make setup
git clone git:// net-next-2.6; \
          cd net-next-2.6 && git reset --hard fed66381d65a35198639f564365e61a7f256bf79
Cloning into net-next-2.6...
remote: Counting objects: 2441000, done.
remote: Compressing objects: 100% (377669/377669), done.
Receiving objects: 100% (2441000/2441000), 493.28 MiB | 28.45 MiB/s, done.
remote: Total 2441000 (delta 2043525), reused 2436782 (delta 2039307)
Resolving deltas: 100% (2043525/2043525), done.
Checking out files: 100% (33319/33319), done.

This sources correspond to a specific version well tested with DCE the net-next 2.6 and git tag = fed66381d65a35198639f564365e61a7f256bf79.

Now the directory net-next-2.6 contains the kernel sources.

Make Menuconfig

Use make menuconfig to configure your kernel, note that modules are not supported by our architecture so options chosen as modules will not be included in the result kernel.


Finally make will compile all the needed sources and produce a file named this is the library contains our net-next kernel suitable for DCE usage.


To use this kernel you should:

1. configure DCE in order to compile using the includes under sim directories to have the good interfaces between DCE and the kernel. For this you should give to the waf configure the path to the ns-3-linux directory i.e.:

$ ./waf configure ----enable-kernel-stack=/ABSOLUTE-PATH-TO/ns-3-linux
  1. In your ns-3 scenario you should indicate the good kernel file: (the file should be located in a directory presents in the DCE_PATH env. variable)
dceManager.SetNetworkStack("ns3::LinuxSocketFdFactory", "Library",
                           StringValue (""));

Use DCE unit test:

$ ./waf --run "test-runner --verbose"
PASS process-manager 9.470ms
PASS Check that process "test-empty" completes correctly. 0.920ms
PASS Check that process "test-sleep" completes correctly. 0.080ms
PASS Check that process "test-pthread" completes correctly. 0.110ms
PASS Check that process "test-mutex" completes correctly. 0.200ms
PASS Check that process "test-once" completes correctly. 0.070ms
PASS Check that process "test-pthread-key" completes correctly. 0.070ms
PASS Check that process "test-sem" completes correctly. 0.080ms
PASS Check that process "test-malloc" completes correctly. 0.060ms
PASS Check that process "test-malloc-2" completes correctly. 0.060ms
PASS Check that process "test-fd-simple" completes correctly. 0.070ms
PASS Check that process "test-strerror" completes correctly. 0.070ms
PASS Check that process "test-stdio" completes correctly. 0.240ms
PASS Check that process "test-string" completes correctly. 0.060ms
PASS Check that process "test-netdb" completes correctly. 3.940ms
PASS Check that process "test-env" completes correctly. 0.050ms
PASS Check that process "test-cond" completes correctly. 0.160ms
PASS Check that process "test-timer-fd" completes correctly. 0.060ms
PASS Check that process "test-stdlib" completes correctly. 0.060ms
PASS Check that process "test-fork" completes correctly. 0.120ms
PASS Check that process "test-select" completes correctly. 0.320ms
PASS Check that process "test-nanosleep" completes correctly. 0.070ms
PASS Check that process "test-random" completes correctly. 0.090ms
PASS Check that process "test-local-socket" completes correctly. 0.820ms
PASS Check that process "test-poll" completes correctly. 0.320ms
PASS Check that process "test-exec" completes correctly. 0.380ms
PASS Check that process "test-iperf" completes correctly. 0.070ms
PASS Check that process "test-name" completes correctly. 0.080ms
PASS Check that process "test-pipe" completes correctly. 0.160ms
PASS Check that process "test-dirent" completes correctly. 0.070ms
PASS Check that process "test-socket" completes correctly. 0.270ms
PASS Check that process "test-bug-multi-select" completes correctly. 0.260ms
PASS Check that process "test-tsearch" completes correctly. 0.080ms

All is OK.

net-next 2.6 to linux-stable 3.4.5

Now we will try to use a more recent linux kernel. We start with a fresh clone of the ns-3-linux sources.


First we need to modify the makefile in order to change the kernel downloaded. For that we need to modify the value of 2 variables:

  1. KERNEL_DIR=linux-stable
  2. KERNEL_VERSION=763c71b1319c56272e42cf6ada6994131f0193a7

Also we need to remove the patch target named .target.ts because the patch will not pass for this newer version of kernel.

First Build

Now we can try to build:

$ make defconfig
$ make menuconfig
$ make
mkdir -p sim
cc -O0 -g3 -D__KERNEL__ -Wall -Wstrict-prototypes -Wno-trigraphs -fno-inline \
           -iwithprefix ./linux-stable/include -DKBUILD_BASENAME=\"clnt\"    \
           -fno-strict-aliasing -fno-common -fno-delete-null-pointer-checks  \
           -fno-stack-protector -DKBUILD_MODNAME=\"nsc\" -DMODVERSIONS       \
           -DEXPORT_SYMTAB -include autoconf.h -U__FreeBSD__ -D__linux__=1   \
           -Dlinux=1 -D__linux=1 -I./sim/include -I./linux-stable/include    \
           -fpic -DPIC -D_DEBUG \
           -I/home/furbani/dev/dce/dev/etude_kernel/V3/ns-3-linux            \
           -DCONFIG_64BIT -c sim/fs.c -o sim/fs.o
In file included from ./linux-stable/include/asm-generic/bitops.h:12:0,
                 from ./sim/include/asm/bitops.h:4,
                 from ./linux-stable/include/linux/bitops.h:22,
                 from ./linux-stable/include/linux/thread_info.h:52,
                 from ./linux-stable/include/linux/preempt.h:9,
                 from ./linux-stable/include/linux/spinlock.h:50,
                 from ./linux-stable/include/linux/wait.h:24,
                 from ./linux-stable/include/linux/fs.h:385,
                 from sim/fs.c:1:
./linux-stable/include/linux/irqflags.h:66:0: warning: "raw_local_irq_restore" redefined
./sim/include/asm/irqflags.h:8:0: note: this is the location of the previous definition
In file included from ./linux-stable/include/linux/wait.h:24:0,
                 from ./linux-stable/include/linux/fs.h:385,
                 from sim/fs.c:1:
./linux-stable/include/linux/spinlock.h:58:25: fatal error: asm/barrier.h: No such file or directory
compilation terminated.
make: *** [sim/fs.o] Error 1

Ok now we will try to fix the compilation errors trying not to change too the kernel source. In the following we will list the main difficulties encountered.

First Error

Recall: the linux source directory include/asm-generic contains a C reference implementation of some code that should be written in assembly langage for the target architecture. So this code is intented to help the developper to port to new architectures. So our sim implementation use many of these asm-generic include files. The first warning show that our code redefine a method defined elsewhere in kernel sources, so the fix is to remove our definition of this function in opur file named sim/include/asm/irqflags.h.

Second Error

The file asm/barrier.h is missing, we just create under sim/include/asm directory and the implementation is to include the generic one ie: include/asm-generic/barrier.h.

Change in sim method

Another problem arise the function named kern_mount_data defined in sim/fs.c do not compile any more. So we need to investigate about this function:

  1. Where this function is located in the real code: in linux/fs/namespace.c
  2. Why it is reimplemented in sim/fs.c: if you look at our Makefile why try to not compile all the kernel we focus on the net part only, you can see this line in the Makefile :
dirs=kernel/ mm/ crypto/ lib/ drivers/base/ drivers/net/ net/

in fact we include only this directories. So at this time we can comment the failing line and insert a sim_assert (false); in order to continue to fix the compilation errors, and then when we will do the first run test we will see if this method is called and if yes we will need to do a better fix. Remark: sim_assert (false); is a macro used to crash the execution, we often place it in functions that we need to emulate because required by the linker but that should never be called.

Change in our makefile

After we have the following problem while compiling sim/glue.c the macro IS_ENABLED is not defined. After some search we found that we need to include linux/kconfig.h in many files. So we modify our makefile to fix like this:

  -fno-stack-protector \
- -include autoconf.h \
+ -include $(SRCDIR)$(KERNEL_DIR)/include/linux/kconfig.h \
  -U__FreeBSD__ -D__linux__=1 -Dlinux=1 -D__linux=1 \
  -I$(SRCDIR)sim/include -I$(SRCDIR)$(KERNEL_DIR)/include \
  $(AUTOCONF): $(KERNEL_DIR)/.config timeconst.h
  ./ $(KERNEL_DIR)/.config > $@
+ cp autoconf.h sim/include/generated/autoconf.h
  timeconst.h: $(KERNEL_DIR)/.config
      perl $(SRCDIR)$(KERNEL_DIR)/kernel/ $(CONFIG_HZ) > $@
Change in kernel source

Our sim/slab.c do not compile, in this case we want to use our implementation of memory allocation and to do this it is easier to modify slightly an include file in the kernel sources include/linux/slab.h :

--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -185,6 +185,8 @@ size_t ksize(const void *);
 #include <linux/slub_def.h>
 #elif defined(CONFIG_SLOB)
 #include <linux/slob_def.h>
+#elif defined(CONFIG_SIM)
+#include <asm/slab.h>
 #include <linux/slab_def.h>

As we have already written we do not recommend to change the kernel sources to facilitate future upgrades.

First Launch

After a few corrections we finally get a library containing the kernel named At this moment we need to try it using DCE. For the beginning we will try with test-runner executable.

assert failed. cond="handle != 0", msg="Could not open elf-cache/0/ elf-cache/0/ undefined symbol: noop_llseek", file=../model/, line=225
terminate called without an active exception
Aborted (core dumped)

We can see that a symbol is not defined : noop_llseek. We find this symbol defined in the kernel source named fs/ We need to choose a way to add this symbol in our kernel library, we can:

  • rewrite it in a source under our sim directory,
  • or add it in our makefile.

In this case we choose the second solution so we need to modify our makefile, first we see that the directory fs is not present in the dirs entry, so we need to add it in the write order (order is the same as found in the kernel Makefile defined by the variable named vmlinux-main); we also need to indicate that we want only the object read_write.o:

@@ -51,7 +52,7 @@
# note: the directory order below matters to ensure that we match the kernel order
-dirs=kernel/ mm/ crypto/ lib/ drivers/base/ drivers/net/ net/
+dirs=kernel/ mm/ fs/ crypto/ lib/ drivers/base/ drivers/net/ net/
 space:= $(empty) $(empty)
 colon:= :
@@ -67,11 +68,12 @@
 ctype.o string.o kasprintf.o rbtree.o sha1.o textsearch.o vsprintf.o \
 rwsem-spinlock.o scatterlist.o ratelimit.o hexdump.o dec_and_lock.o \
Fake Function

We continue to try our kernel library, now another symbol is missing generic_file_aio_read, this symbol is defined in the source mm/, it is referenced at least by read_write.c. In this case we decided to create a fake function because the source mm/ is voluminous and we do not want to take all the kernel sources. So we create a new source under sim directory named sim/filemap.c the body of the function is sim_assert (false); so if this function called sometimes we will be warned and we will write a more accurate version.


Later we meet again the function kern_mount_data, thanks to the presence of the sim_assert:

0x00007ffff5c8c572 in kern_mount_data (fs=<optimized out>, data=<optimized out>) at sim/fs.c:52
52      sim_assert (false);
(gdb) bt
#0  0x00007ffff5c8c572 in kern_mount_data (fs=<optimized out>, data=<optimized out>) at sim/fs.c:52
#1  0x00007ffff5d85923 in sock_init () at linux-stable/net/socket.c:2548
#2  0x00007ffff5c8d3aa in sim_init (exported=<optimized out>, imported=<optimized out>, kernel=<optimized out>) at sim/sim.c:169
#3  0x00007ffff7d9151b in ns3::LinuxSocketFdFactory::InitializeStack (this=0x65bde0) at ../model/
#4  0x00007ffff7d95ce4 in ns3::EventMemberImpl0::Notify (this=0x6597a0) at /home/furbani/dev/dce/dev/build/include/ns3-dev/ns3/make-event.h:94
#5  0x00007ffff76b10a8 in ns3::EventImpl::Invoke (this=0x6597a0) at ../src/core/model/
#6  0x00007ffff7d8ff7c in ns3::LinuxSocketFdFactory::ScheduleTaskTrampoline (context=0x6597a0) at ../model/
#7  0x00007ffff7d3b7d4 in ns3::TaskManager::Trampoline (context=0x65d170) at ../model/
#8  0x00007ffff7d37acd in ns3::PthreadFiberManager::Run (arg=0x65d5d0) at ../model/
#9  0x00000034be206ccb in start_thread () from /lib64/
#10 0x00000034bd6e0c2d in clone () from /lib64/

So this function is called by the initialisation, we must provide an implementation for it:

// Implementation taken from vfs_kern_mount from linux/namespace.c
struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
      static struct mount local_mnt;
      struct mount *mnt = &local_mnt;
      struct dentry *root = 0;

      memset (mnt,0,sizeof (struct mount));
      if (!type)
              return ERR_PTR(-ENODEV);
      int flags = MS_KERNMOUNT;
      char *name = type->name;
      if (flags & MS_KERNMOUNT)
              mnt->mnt.mnt_flags = MNT_INTERNAL;

      root = type->mount(type, flags, name, data);
      if (IS_ERR(root)) {
              return ERR_CAST(root);

      mnt->mnt.mnt_root = root;
      mnt->mnt.mnt_sb = root->d_sb;
      mnt->mnt_mountpoint = mnt->mnt.mnt_root;
      mnt->mnt_parent = mnt;
//    br_write_lock(vfsmount_lock);   DCE is monothreaded , so we do not care of lock here
      list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
//    br_write_unlock(vfsmount_lock);  DCE is monothreaded , so we do not care of lock here

      return &mnt->mnt;

Here we do not want to integrate all the code namespace.c, so we copy and paste the function named kern_mount_data. This solution has the advantage of minimizing code size, the disadvantage is that it can introduce problems if the next version of the kernel need changes in this function.


We will not describe the rest of the port here. But after some iteration we end up with a version that works correctly. Sometimes we should not hesitate to use gdb to trace the actual execution and correct accordingly code. The rules that we can gain from this experience’s are as follows:

  1. Be patient,
  2. Try to not modify the kernel sources,
  3. Be pragmatic,
  4. Try to not import all the kernel code into our library,
  5. Do not hesitate to go back and test other alternatives.



The implementation of the poll system call is inspired by the Linux kernel, therefore we well study first the kernel poll implementation.

Kernel implementation

Firstly in the kernel every type of file descriptor (file, socket, pipe ...) must provide a function named poll and conform to this prototype:

int poll(struct file *file, poll_table *pwait);

Where file is a pointer to a structure representing the file (it looks like this in C++) and pwait is a pointer to a poll table, pwait may be NULL, we will see later why. The return integer of this function is a mask of poll events which have already occured on the corresponding file descriptor. The behavior of this function is as follows: 1. It is not a blocking function, it immediately returns the mask of events regardless of event desired by the caller of poll. 2. if pwait is not NULL then it add pwait in the wait queue of file, and secondly a pointer to the wait queue is stored in the poll table pwait.

Thus an event on the file will ascend to the poll, and in the opposite direction when the poll ends it can de-register itself from the wait queue of the file.

Now that we know the function poll of file, we can study the poll system call, here the following pseudo code commented:

POLL( .... )
   poll_table table; // This table will contain essentially the list of wait queues that need to wake me,
                     // and also information about the current thread in order to be awakened.
   poll_table *pwait=&table; // pointer to current poll table.

   while (true)
      foreach( fd ) // For each file descriptor ...
             file *file = get_file(fd); // Retrieve **file** data structure corresponding to fd.

         if (!file)
           mask = POLLNVAL; // fd does not correspond to an open file.
               mask = file->poll (file, pwait); // During the first loop pwait is not NULL.

         if (mask)
               count++; // Increases the number of responses
           pwait = NULL; // Once we have at least one response POLL should not be blocking,
                         // so we nullify the pointer to the poll table in order to not register the poll table to more file descriptors.
      pwait = NULL; // For the next loops we must not re-register to the wait queue of files.

      if (count) break; // we have a result.
      if (timeout) break; // it is too late.

      Wait(timeout); // Put to sleep until awakening from a file or because of the time limit.
   poll_freewait(&table); // Removes the reference to the poll table from each file's wait queue.

   return count;
DCE implementation

As we have already seen, the poll will look like that of the kernel. Firstly we create a virtual method named Poll in the class UnixFd. This method will do the same job that the function poll seen early in the struct file of the kernel linux implementation. Before writing the function dce_poll which is our implementation of poll we need to create some classes for mimic the role of the poll table and the wait queues.

So we add 2 sources files named wait-queue.h and in order to implements poll table and wait queue.

It is also on this occasion that I deleted all the objects used to wait which was allocated on the stack, and I replaced by objects allocated in the heap. Concerning the dce-poll function it looks like the kernel one with some differences. The more important difference is that the PollTable cannot be allocated on the stack so it cannot be a local variable, so the PollTable object is allocated with a C++ new. I guess you’re wondering why the poll table cannot be allocated on the stack, it is because of the fork implementation of DCE. Indeed, if a process makes a fork, this creates another stack which use the same memory addresses, thus another thread of the same process cannot use an object allocated on this stack, and when a event of a file want to wake up the poll thread it will use especially this poll table. So allocating the Poll Table in the heap generates a side effect which is that we need to release this memory if another thread call exit while we are within the dce-poll. So we need to register the Poll Table somewhere in a DCE data, and the DCE place choosen is the thread struct (in file model/process.h), because each thread can be in doing a poll. Thus there is a new field in struct thread which is:

PollTable *pollTable; // No 0 if a poll is running on this thread

There is another reason to have this field, this reason arises from the fact that a file descriptor can be shared by multiple processes (thanks to dup fork ...), thus when a process exit while doing a poll, we need to deregister from the corresponding wait queues referred by the poll table.

Poll kernel implementation

Concerning the kernel implementation the dce-poll method is the same but the difference comes from the Poll method specialized implementation of the class inherited from UnixFd and which correspond to a File Descriptor open with the help of the Kernel Linux. For example the class LinuxSocketFd represents a socket which is opened in the kernel, therefore the method poll of LinuxSocketFdFactory will do much work.

Now look at the interface between DCE and the kernel, in the direction DCE to kernel, we use 2 functions which are sock_poll and sock_pollfreewait, and in the other direction there is sim_poll_event. sock_poll obviously has the same semantics as the kernel poll. sock_poll has the following signature:

void sock_poll (struct SimSocket *s, void *ret);

where s represents the socket int the kernel and ret is a pointer to a data structure of type struct poll_table_ref:

struct poll_table_ref
  int ret;
  void *opaque;

This structure allows the kernel to pass a reference to the poll table DCE via the opaque field. This reference will be used by the kernel only to warn DCE that event just happened on socket, this using the function sim_poll_event (void *ref). In return this function modifies the value of opaque and assign it a pointer to a core structure which represents an entry in the wait queue of the socket. This value will be used by DCE for unregister it from the wait queue using the function sock_pollfreewait function (void * ref). The field ret is also affected in return and it contain the mask of poll events which have already occurred on the corresponding socket. Most of the kernel code is in the file sim-socket.c it consists of two structures, and the following functions:

sim_pollwake Function called by the kernel when the arrival of an event on the socket, if the event is expected by DCE, the function forwards it to DCE.
sim_pollwait Function called by the kernel, its role is to register the poll table in the wait queue.
sim_sock_poll Function called by DCE, it is the interface between the DCE’s poll and the kernel’s poll.
sim_sock_pollfreewait Function called by DCE allows it to unregister from the wait queue.
struct poll_table_ref This is the same struct as that of DCE.
struct sim_ptable_entry This is used for the entry in the wait queue of the socket.

# TODO add example , gdb breakpoint to follow the behavior in live

How It Works

If you are interested to know why DCE exists and how it can work, you should read this document Experimentation Tools for Networking Research (and in particular the chapter 4) written by the principal author of DCE, Mathieu Lacage. Also you can read the sources too.


You know that the goal of DCE is to execute actual binaries within ns-3. More precisely a binary executed by DCE perceives time and space of ns-3, rather than the real environment.

To do this, DCE does a job equivalent to an operating system like:

  1. DCE loads in memory the code and data of executable,
  2. DCE plays the role of intermediary between the executable and the environment through the systems functions called by executables,
  3. DCE manages and monitors the execution of processes and handles liberate the memory and close open files when the stop process.
  4. DCE manages the scheduling of the various virtual processes and threads.

Main classes and main data structures


The DceManager is somewhat the entry point of DCE. It will create virtual processes and manages their execution. There is an instance of DceManager which is associated to each node which need to virtualize the execution of a process. In reality, the developer uses the classes DceManagerHelper and DceApplicationHelper.

I invite you to look at the source code and dce-manager.h and particularly the public methods Start, Stop, Exit, Wakeup, Wait and Yield; the following private methods are also important: CreateProcess, PrepareDoStartProcess, DoStartProcess, AllocatePid, TaskSwitch, CleanupThread and LoadMain. The Start method is called when starting the executable, if you look at, it begins by initializing an object of type struct Process. struct Process is very important, it contains information about the virtual processes that DCE creates, this type is described below. Start then also initializes a structure of type struct thread, it represents the principal thread in which the main entry of the executable will run. Finally Start asks the TaskManager to create a new Task and to start this one using the method DceManager::DoStartProcess as the entry point.

Class TaskManager is a major class of DCE, it is described below.


struct process contains everything you need to describe a process, I invite you to study the source code in the file process.h.

This structure contains references to standard objects for example a list of open files via a vector of FILE *, but it contains also the references to objects useful to manage DCE threads, the memory allocated by the process...

Field openFiles represents the open file descriptors of the process, the key is the fd and the value a pointer to an object of type DCE FileUsage. The field threads contains all the threads in the process see description below. Field loader is a pointer to the Loader used to load the corresponding code.

The alloc field is important it is a pointer to the memory allocator used to allocate the memory used by this process, at the end of the process it will liberate all the memory allocated so as simple and efficient.


struct thread represents a thread, It contains various fields including a pointer to the process to which it belongs, and also a pointer to Task object described later.

Taskmanager and Task

The TaskManager manages the Tasks, ie the threads of virtualized processes by DCE. It allows you to create new task. It controls the activity of the task by the following methods: Stop, Wakeup, Sleep and Yield. A Task possesses a stack which contains the call stack functions. There is one instance of TaskManager per node. The implementation of TaskManager is based on a class of type FiberManager described below.


FiberManager actually implements the creation of the execution contexts. These contexts are called fiber. FiberManager offers the following:

  1. Create a context, it returns a fiber
  2. Delete a fiber
  3. Yield hand to another fiber

DCE provides two implementations:

  1. PthreadFiberManager, which is based on the pthread library,
  2. UcontextFiberManager which is based on the POSIX API functions offered by ucontext.h: makecontext, getcontext and setcontext.

I invite you to watch the corresponding man.

LoaderFactory and Loader

The Loader is a very important object of DCE. A DCE Loader loads the executable code in memory of a special way, load several times the same executable, while isolating each of the other executable. The Loader must link the executable loaded with the 3 emulated libraries, i.e., lib C, lib pthread and lib rt. The same way the libraries used by the executable must also be linked with the emulated libraries.

DCE offers several actually Loader:

  1. CoojaLoader: it has the following characteristics: it loads into memory only a copy of the code, by cons it duplicates data (i.e., global variables and static). For each change of context there are 2 memory copies: backup data of the current context then restoration of context memory that will take control. Comment: it is rather reliable, the size of the copied memory size depends on the total static and global variables, and in general there is little, in a well-designed executable.
  2. DlmLoader: Uses a specialized loader to not duplicate the code but only the data but without special operations to do when changing context. Comment: offers the best performance in memory and cpu, but not very reliable especially during the unloading phase.

Follow a very simple example

After theory, do a bit of practice. Follow the execution of very simple example.

You can find the used sample under the directory named myscripts/sleep. This executable used by the scenario do only a sleep of ten seconds:

#include <unistd.h>

int main(int c, char **v)
  sleep (10);

  return 1;

The ns-3/DCE scenario execute tenseconds one time starting at time zero:

#include "ns3/core-module.h"
#include "ns3/dce-module.h"

using namespace ns3;

int main (int argc, char *argv[])
  NodeContainer nodes;
  nodes.Create (1);

  DceManagerHelper dceManager;
  dceManager.Install (nodes);

  DceApplicationHelper dce;
  ApplicationContainer apps;

  dce.SetStackSize (1<<20);

  dce.SetBinary ("tenseconds");
  dce.ResetArguments ();
  apps = dce.Install (nodes.Get (0));
  apps.Start (Seconds (0.0));

  Simulator::Stop (Seconds(30.0));
  Simulator::Run ();
  Simulator::Destroy ();

First we can launch tenseconds binary:

$ ./build/bin_dce/tenseconds

after 10 seconds you retrieve the prompt.

Then we can try the DCE scenario:

$ ./build/myscripts/sleep/bin/dce-sleep

This time the test is almost instantaneous, because the scenario is very simple and it uses the simulated time.

Same test by activating logs:

$ NS_LOG=DefaultSimulatorImpl ./build/myscripts/sleep/bin/dce-sleep
DefaultSimulatorImpl:SetScheduler(0x6928c0, ns3::MapScheduler[])
0s -1 DefaultSimulatorImpl:ScheduleWithContext(0x6928c0, 0, 0, 0x692ab0)
0s -1 DefaultSimulatorImpl:ScheduleWithContext(0x6928c0, 0, 0, 0x695220)
0s -1 DefaultSimulatorImpl:Stop(0x6928c0, 30000000000)
0s -1 DefaultSimulatorImpl:Schedule(0x6928c0, 30000000000, 0x692c10)
0s -1 DefaultSimulatorImpl:Run(0x6928c0)
0s -1 DefaultSimulatorImpl:ProcessOneEvent(): [LOGIC] handle 0
0s 0 DefaultSimulatorImpl:Schedule(0x6928c0, 0, 0x695630)
0s 0 DefaultSimulatorImpl:ProcessOneEvent(): [LOGIC] handle 0
0s 0 DefaultSimulatorImpl:ProcessOneEvent(): [LOGIC] handle 0
0s 0 DefaultSimulatorImpl:ProcessOneEvent(): [LOGIC] handle 0
0s 0 DefaultSimulatorImpl:Schedule(0x6928c0, 10000000000, 0x6954c0)
0s 0 DefaultSimulatorImpl:ProcessOneEvent(): [LOGIC] handle 10000000000
10s 0 DefaultSimulatorImpl:ProcessOneEvent(): [LOGIC] handle 10000000000
10s 0 DefaultSimulatorImpl:ProcessOneEvent(): [LOGIC] handle 30000000000
30s -1 DefaultSimulatorImpl:Stop(0x6928c0)
DefaultSimulatorImpl:Destroy(): [LOGIC] handle destroy 0x6928a0

We can see that an event occurs at 30s it is the end of the simulation corresponding to the line:

Simulator::Stop (Seconds(30.0));

We can also see that at 10s an event occurs, this is the end of our sleep(10).

Now we do the same experiment using the debugger:

$ gdb ./build/myscripts/sleep/bin/dce-sleep
(gdb) b ns3::DceManager::DoStartProcess
(gdb) b ns3::DceManager::Start
(gdb) run
Breakpoint 4, ns3::DceManager::Start (this=0x630c50, name=..., ....  at ../model/
403     NS_LOG_FUNCTION (this << name << stackSize << args.size () << envs.size ());
(gdb) bt
#0  ns3::DceManager::Start (this=0x630c50, name=.....) at ../model/
#1  0x00007ffff7cb5e19 in ns3::DceApplication::StartApplication (this=0x633520) at ../model/
#2  0x00007ffff71dea6e in ns3::EventMemberImpl0::Notify (this=0x633650) at ./ns3/make-event.h:94
#3  0x00007ffff76148af in ns3::EventImpl::Invoke (this=0x633650) at ../src/core/model/
#4  0x00007ffff76194c3 in ns3::DefaultSimulatorImpl::ProcessOneEvent (this=0x6308e0) at ../src/core/model/
#5  0x00007ffff761986a in ns3::DefaultSimulatorImpl::Run (this=0x6308e0) at ../src/core/model/
#6  0x00007ffff76155dd in ns3::Simulator::Run () at ../src/core/model/
#7  0x00000000004075af in main (argc=1, argv=0x7fffffffdaa8) at ../myscripts/sleep/
  (gdb) info thread
  Id   Target Id         Frame
* 1    Thread 0x7ffff6600740 (LWP 7977) "dce-sleep" ns3::DceManager::Start (this=0x630c50, .... ) at ../model/

You can notice that:

  1. We have two breakpoints.
  2. After run the first stop is in ns3::DceManager:Start.
  3. At this time there is only one thread.
  4. We are currently processing an event, this event was scheduled by the call apps.Start (Seconds (0.0)); of our scenario.

Now we continue our execution:

(gdb) continue
[New Thread 0x7ffff65fc700 (LWP 8159)]
[Switching to Thread 0x7ffff65fc700 (LWP 8159)]

Breakpoint 3, ns3::DceManager::DoStartProcess (context=0x633d50) at ../model/
274     Thread *current = (Thread *)context;
(gdb) info thread
  Id   Target Id         Frame
* 2    Thread 0x7ffff65fc700 (LWP 8159) "dce-sleep" ns3::DceManager::DoStartProcess (context=0x633d50) at ../model/
  1    Thread 0x7ffff6600740 (LWP 7977) "dce-sleep" pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:162
(gdb) bt
#0  ns3::DceManager::DoStartProcess (context=0x633d50) at ../model/
#1  0x00007ffff7d21b90 in ns3::TaskManager::Trampoline (context=0x633bd0) at ../model/
#2  0x00007ffff7d1da87 in ns3::PthreadFiberManager::Run (arg=0x634040) at ../model/
#3  0x00000034be206ccb in start_thread (arg=0x7ffff65fc700) at pthread_create.c:301
#4  0x00000034bd6e0c2d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:115

You can notice that:

  1. Now there is a second thread
  2. Gdb break execution in ns3::DceManager::DoStartProcess in the context of the second thread

This second thread is the thread corresponding to the main thread of our hosted executable tenseconds, if you look at ns3::DceManager::DoStartProcess you can notice that we are on the point of calling the main of tenseconds:

DceManager::DoStartProcess (void *context)
  Thread *current = (Thread *)context;
  int (*main)(int, char **) = PrepareDoStartProcess (current);
  int retval = 127;

  if (main)
      StartProcessDebugHook ();
      retval = main (current->process->originalArgc, current->process->originalArgv);
  dce_exit (retval);

You can also see that the pointer to the main is the result of the method ns3::DceManager::PrepareDoStartProcess. Now we can put a breakpoint before the sleep of tenseconds and follow the code of sleep:

(gdb) break tenseconds.c:5
(gdb) continue
Breakpoint 1, main (c=1, v=0x630b30) at ../myscripts/sleep/tenseconds.c:5
5       sleep (10);
(gdb) list
(gdb) step
sleep () at ../model/libc-ns3.h:193
193   DCE (sleep)
(gdb) step
dce_sleep (seconds=10) at ../model/
226     Thread *current = Current ();
(gdb) list
224   unsigned int dce_sleep (unsigned int seconds)
225   {
226     Thread *current = Current ();
227     NS_LOG_FUNCTION (current << UtilsGetNodeId ());
228     NS_ASSERT (current != 0);
229     current->process->manager->Wait (Seconds (seconds));
230     return 0;
231   }
(gdb)  bt
#0  dce_sleep (seconds=10) at ../model/
#1  0x00007ffff62cdcb9 in sleep () at ../model/libc-ns3.h:193
#2  0x00007ffff5c36725 in main (c=1, v=0x630b30) at ../myscripts/sleep/tenseconds.c:5
#3  0x00007ffff7c9b0bb in ns3::DceManager::DoStartProcess (context=0x633d50) at ../model/
#4  0x00007ffff7d21b90 in ns3::TaskManager::Trampoline (context=0x633bd0) at ../model/
#5  0x00007ffff7d1da87 in ns3::PthreadFiberManager::Run (arg=0x634040) at ../model/
#6  0x00000034be206ccb in start_thread (arg=0x7ffff65fc700) at pthread_create.c:301
#7  0x00000034bd6e0c2d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:115
(gdb) info thread
  Id   Target Id         Frame
* 2    Thread 0x7ffff65fc700 (LWP 15233) "dce-sleep" dce_sleep (seconds=10) at ../model/
  1    Thread 0x7ffff6600740 (LWP 15230) "dce-sleep" pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:162

We can notice that sleep call dce_sleep which call Wait, this Wait method is from the class TaskManager. TaskManager is a major class of DCE and we will detail it below. Basically Wait schedules and event in ns-3 event queue (in order to be woken up after sleep time) and give the control to another Task. Now we can put a breakpoint in ns3::DefaultSimulatorImpl::ProcessOneEvent and see the time advance up to 10s:

gdb) b ns3::DefaultSimulatorImpl::ProcessOneEvent
Breakpoint 2 at 0x7ffff7619207: file ../src/core/model/, line 131.
(gdb) c
[Switching to Thread 0x7ffff6600740 (LWP 3942)]
Breakpoint 2, ns3::DefaultSimulatorImpl::ProcessOneEvent (this=0x6308e0) at ../src/core/model/
warning: Source file is more recent than executable.
131     Scheduler::Event next = m_events->RemoveNext ();
(gdb) n
133     NS_ASSERT (next.key.m_ts >= m_currentTs);
(gdb) n
134     m_unscheduledEvents--;
(gdb) n
136     NS_LOG_LOGIC ("handle " << next.key.m_ts);
(gdb) n
137     m_currentTs = next.key.m_ts;
(gdb) n
138     m_currentContext = next.key.m_context;
(gdb) p m_currentTs
$1 = 10000000000

This next event will wake the thread 2 will therefore complete the sleep of our scenario.

In summary we saw briefly that DCE uses the events of ns-3 to schedule the execution between different tasks.

Subprojects of DCE

Below are the list of the tested applications with DCE.


CCNx is an open source implementation of Content Centric Networking. All the C written executables are supported and none of the Java ones. The versions tested are those between 0.4.0 and 0.6.1 included.

For more detail document, see CCNx examples.


Quagga is a routing software suite, providing implementations of OSPFv2, OSPFv3, RIP v1 and v2, RIPng and BGP-4 for Unix platforms, particularly FreeBSD, Linux, Solaris and NetBSD. For more information, see the latest support document.


iperf from the following archive as been tested. It is the exception that proves the rule. That is to say that this particular example requires a change in its code. In the source file named Thread.c at line 412 in the function named thread_rest you must add a sleep(1) in order to help DCE to break the infinite loop.


Ping from the following archive is supported.

umip (Mobilt IPv6 daemon)

The umip (Usagi-Patched Mobile IPv6 stack) support on DCE enables the users to reuse routing protocol implementations of Mobile IPv6. UMIP now supports Mobile IPv6 (RFC3775), Network Mobility (RFC3963), Proxy Mobile Ipv6 (RFC5213), etc, and can be used these protocols implementation as models of network simulation.

For more information, see the latest support document.






The creator of DCE is Mathieu Lacage.

The current maintainers and developers are Hajime Tazaki and Frédéric Urbani.


tazaki AT
mathieu.lacage AT