Thus spake "TOMSON ERIC" <Eric.Tomson@siemens.atea.be> > It IS the ISO OSI model. I see no contradiction with TCP/IP. Simply, there is no link layer in TCP/IP : it's a model that only provides higher layers and must be implemented over an existing link layer technology : > > OSI > Layer Name TCP/IP > ----------------------------------- > 7 Application ] > 6 Presentation ] APPLICATION (HTTP, FTP, DNS,...) > 5 Session ] > ----------------------------------- > 4 Transport TRANSPORT (TCP, UDP) I'd always considered TCP/UDP to cover both layers 4 and 5, and ASCII/EBCDIC/XDR to cover layer 6. S