Using your in-kernel protocol implementation

There are a number of protocols implemented in kernel space, like many transport protocols (e.g., TCP, UDP, SCTP), Layer-3 forwarding plane (IPv4, v6 with related protocols ARP, Neighbor Discovery, etc). DCE can simulate these protocols with ns-3.

This document describes an example when we supported new protocol, Stream Control Transmission Protcool (SCTP), with DCE. Although other protocols may not adapt this patterns as-is, you will see what’s needed to implement for your purpose.

1. Extend net-next-sim kernel (make menuconfig in Linux)

In Linux kernel, there is a configuration system in Linux kernel to enable/disable features. This is typically done by make menuconfig command, and it writes a file (.config) at the kernel source directory. Build system (e.g., make bzImage) refers the file which source files are compiled.

In our DCE Linux kernel module (i.e. net-next-sim available at github.com), we have arch/sim/defconfig file to store the default configuration of kernel features. You may need to add proper configuration parameters (e.g., CONFIG_IP_SCTP) to build the protocol by default.

For the Linux SCTP implementation, we need at least the following configuration parameters.

• CONFIG_IP_SCTP=y
• CONFIG_SCTP_DEFAULT_COOKIE_HMAC_NONE=y
• CONFIG_CRYPTO_CRC32C=y
• CONFIG_CRC32=y

These should be added to the file (arch/sim/defconfig).

Note

These configuration options SHOULD be minimized at the beginning since adding new option may require new functions which DCE doesn’t support at the time and need to implement glue code.

2. Build liblinux.so

To build the liblinux.so, DCE version of Linux kernel,

make defconfig
make library ARCH=sim

You can use make menuconfig command (below) instead of editing the defconfig file. If everything is fine, you will see liblinux.so linked to libsim-linuxv.y.z.so file at the root directory of Linux kernel.

make menuconfig ARCH=sim

3. Write user space application to use this protocol

Then, we need to write userspace applications using new feature of kernel protocol. In case of SCTP, we wrote sctp-client.cc and sctp-server.cc.

Optional You may optinally need external libraries to build/run the applications. In this case, the applications need lksctp-tools, so that applications fully benefit the features of SCTP, rather than only using standard POSIX socket API.

Moreover, adding system dependency to bake configuration file (i.e., bakeconf.xml) would be nice to assist build procedure. The following is an example of lksctp-tools, which above applications use.

<module name="lksctp-dev">
  <source type="system_dependency">
    <attribute name="dependency_test" value="sctp.h"/>
    <attribute name="try_to_install" value="True"/>
    <attribute name="name_apt-get" value="lksctp-dev"/>
    <attribute name="name_yum" value="lksctp-tools-devel"/>
    <attribute name="more_information" value="Didn't find:   lksctp-dev package; please install it."/>
  </source>
  <build type="none" objdir="no">
  </build>
</module>

4. Write ns-3 scenario to use above applications.

The next step would be writing ns-3 simulation scenario to use the applications you prepared. dce-sctp-simple.cc is the script that we prepared. In the script, you may need to load the applications by using DceApplicationHelper as follows.

DceApplicationHelper process;
ApplicationContainer apps;

process.SetBinary ("sctp-server");
process.ResetArguments ();
process.SetStackSize (1<<16);
apps = process.Install (nodes.Get (0));
apps.Start (Seconds (1.0));

process.SetBinary ("sctp-client");
process.ResetArguments ();
process.ParseArguments ("10.0.0.1");
apps = process.Install (nodes.Get (1));
apps.Start (Seconds (1.5));

5. run it !

./waf --run dce-simple-sctp

If you’re lucky, it’s done.

If you aren’t lucky, you may face errors of DCE, such as unresolved symbols in system calls (called by userspace applications) or missing kernel functions (used by newly added CONFIG_IP_SCTP option), or invalid memory access causing segmentation fault. In that case, adding missing functions, so called glue-code would be the next step.