I'm going to produce VoLTE packet stream on OMNET++. Which OS is recommended for installing OMNET++, Linux or Win? My laptop system is win10. If Linux is better, is there any problem if I use linux on VBox? Thanx for your kind recommendations.
Linux [1] is definitely the recommended OS for using OMNeT++. In particular, you will have the best experience with Ubuntu 18.04.1 - if you're using the latest OMNeT++ release that is. Older versions might work better on earlier Ubuntu releases.
Running it in a virtual machine should not cause any issues.
The only case that might be problematic is using the 3D integration (OSG and osgEarth). Rendering performance might be worse (or it might not work at all), but this depends on your setup. There are a few GPU/driver/config/etc. combinations where even this works quite well.
EDIT:
The reason is that even though Windows is fully supported as well, it simply performs significantly worse - especially during building either OMNeT++, or any model libraries or projects. We suspect that it is caused mostly by how NTFS works, among a variety other things.
On top of that, certain "more exotic" features in some model libraries might only be available on Linux.
[1]: Well, technically it's GNU/Linux, or more appropriately, GNU+Linux. :D