Emulation¶

In INET, the word emulation is used in a broad sense to describe a system which is partially implemented in the real world and partially in simulation. Emulation is often used for testing and validating a simulation model with its real-world counterparts. It may also be used out of necessity, because some part of the system only exists in the real world or only as a simulation model.

Developing a protocol, a protocol implementation, or an application that heavily relies on network communication is often less expensive, more practical, and safer using simulation than directly performing experiments in the real world. However, there are potential pitfalls: porting simulation code to the target device may be costly and error prone, and also, a model that performs well in simulation does not necessarily work equally well when deployed in the real world. INET helps reducing these risks by allowing the researcher to mix simulation and real world in various ways, thereby reducing the need for porting, and offering more possibilities for testing out the code.

INET provides modules that act as bridges between the simulated and real domains, therefore it is possible to leave one part of the simulation unchanged, while simply extracting the other into the real world. Several setups are possible when one can take advantage of the emulation capabilities of INET:

simulated node in a real network
a simulated subnet in real network
real-world node in simulated network
simulated protocol in a real network node
real application in a simulated network node
etc.

For the simulation to act as a network emulator, two major problems need to be solved. On one hand, the simulation must run in real time, or the real clock must be configured according to the simulation time (synchronization). On the other hand, the simulation must be able to communicate with the real world (communication). This is achieved in INET as the following:

Synchronization:
- RealTimeScheduler: It is a socket-aware real-time scheduler class responsible for synchronization. Using this method, the simulation is run according to real time.
Communication:
- The interface between the real (an interface of the OS) and the simulated parts of the model are represented by Ext modules, with names beginning with Ext~ prefix in the simulation (ExtLowerUdp, ExtUpperEthernetInterface, etc.).
  
  Ext modules communicate both internally in the simulation and externally in the host OS. Packets sent to these modules in the simulation will be sent out on the host OS interface, and packets received by the host OS interface (or rather, the appropriate subset of them) will appear in the simulation as if received on an Ext~ module.
  
  There are several possible ways to maintain the external communication:
  - File
  - Pipe
  - Socket
  - Shared memory
  - TUN/TAP interfaces
  - Message Passing Interface (MPI)

In order to run any emulation example, INET must be compiled with the “Network Emulation” feature enabled. Enabling this feature can be done by checking the IDE‣Project‣Properties‣OMNeT++/Project Features‣Network Emulation options.

In order to be able to send packets through raw sockets applications require special permissions. There are two ways to achieve this under linux.

The suggested solution is to use setcap to set the application permissions:

$ sudo setcap cap_net_raw,cap_net_admin=eip /*fullpath*/opp_run
$ sudo setcap cap_net_raw,cap_net_admin=eip /*fullpath*/opp_run_dbg
$ sudo setcap cap_net_raw,cap_net_admin=eip /*fullpath*/opp_run_release

This solution makes running the examples from the IDE possible. Alternatively, the application can be started with root privileges from command line:

$ sudo `inet_dbg -p -u Cmdenv`

Note

In any case, it’s generally a bad idea to start the IDE as superuser. Doing so may silently change the file ownership for certain IDE configuration files, and it may prevent the IDE to start up for the normal user afterwards.

The following showcases demonstrate several such emulation examples: