Dear Zoha,
If I understand correctly, you have been trying to port the very old and completely outdated IPSuite to OMNeT++ 4.0. This looks utterly and completely useless to me. We do have a good TCP/IP suite, it is called the INET Framework. It has evolved from the very IPSuite that you are hacking, over years, with lots of hard work invested into its development. So, what's the point of hacking IPSuite, really???
OK, looks like you want to use the SIP model that comes with IPSuite. Fine, so why don't you just port the SIP model itself into the INET Framework? That, apart from being a lot less work, would actually be useful for the community as well. The path you're currently following leads nowhere – I sincerely suggest that you download the INET Framework, and try to port SIP into that. I am sure everyone would help be better inclined to help you then.
As for "gatesizes" and other problems: the Migration Guide is your friend. Open http://omnetpp.org/doc/omnetpp40/migration/migration.html, hit Ctrl+F and type "gatesizes". Thanks!
Regards,
Andras