Abstract: A system of at least one OSI transport relay ensuring cooperation between at least a first system containing at least one source system (SS), using an OSI transport profile based on a network service in connected mode, called CONS, and at least a second system including at least one target system (SD) using an OSI transport profile based on a network service in non-connected mode, called CLNS, with the information routed on the transport layer. According to the invention, the system characterized by the fact that the addresses of the transport service access points TSAP of the source and target system (TSAP.sub.S and TSAP.sub.D) are transported end to end by the transport layer, in connection requests TPDU-CR, and the addresses of the network service access points used by the network service are those of the source and relay systems (NSAP.sub.S and NSAP.sub.R). The invention is application to telecommunications networks.