There are two types of communication methods available on the IBM SP2. These are the User Space protocol(us) and the Internet protocol(ip). The User Space protocol is much quicker, but does not allow one to share the communicating nodes with other Message Passing Library (MPL) processes. This User Space protocol always uses the high performance switch. The Internet Protocol (ip) is slower, but allows communicating nodes to be shared by other MPL processes. One can use the Internet Protocol over the ethernet or the high performance switch (which you may have guessed, is quicker than using the ethernet).