The high speed LAN (HSLAN) market is dominated by FDDI, but this domination is being challenged by newcomers. The most important ones are FDDI-II, DQDB and CRMA. The Laboratoire de Teleinformatique, Lausanne has developed an HSLAN OPERNET. Amongst the various applications called to use these HSLANs are backbone networks, high resolution graphics and video transmission. Therefore these HSLANs should be able to transmit asynchronous as well as isochronous traffic. The author compares the performance of the above networks for both asynchronous and isochronous transfers