MPI5000 is a communication layer between the application (MPI for example) and the transport protocol (TCP) which improves communications of distributed applications over wide area network in grids. For instance, MPI5000 reduces the impact of retransmissions and the impact of congestion window in such a context. MPI5000 is automatically and transparently executed without modifying the application. The general principle is to introduce proxies at the interface between the local network and the long- distance network to differentiate communications. These proxies allows to put forward the split of TCP connections in order to avoid losses and retransmissions on the long-distance links. This mechanism also allows to keep the congestion window closer to available throughput on the long-distance network. This work is detailled and evaluated in  , and shows which applications can benefit from these optimisations.