Improving node inter-cluster point-to-point communication by using the UDP protocol and the NAT service

In the context of multi-site parallel applications where a single MPI program is executed on several clusters linked with grid technologies (i.e. the Globus toolkit and MPICH-G2) a problem can arise in the presence of clusters with private networks. In such an environment two nodes belonging to different clusters with no public IP address cannot communicate directly. We have seen how this problem can be solved in a portable manner by introducing user MPI processes, running on the front-end, whose only purpose is to route messages among clusters. In this work we have improved private node inter-cluster point-to-point communication by using the UDP protocol and a NAT service on the front-end. The first enhancement improves network performance by reducing the transport protocol overheads while the second enhancement avoids useless memory copies for the message on the forwarding host. Performance comparison is resented with the user MPI process solution and the impact of the two enhancements is separately evaluated.