In many replies, not just this thread, a lot of replies argue that the correct solution "depends on the application". I am now arguing that there are a finite number of communication portals to use and as such they are pre-defined and may or may not match an application. Instead of always relaying the same boring answer with no informative response maybe a more helpful approach would be to write a FAQ or create a tutorial on all the communication portals that could be potentially used. Implementing a parametric table would be greatly helpful to seasoned veterans who continously need communications which describe which portals would allow master-slave.... master-multi-slave.... master-master-slave... etc etc... and possibly implementing common properties as speed. If this has been done successfully on the internet, then obviously that link should be posted so that the OP knows the method to use with their application. The application chooses the communication portal, but the communication portal has already been defined. Of course, there might be the chance that none of the communication portals match the application, then what do you do?