Editing Xerox Network Systems (section)

===Overall design===
In comparison to the [[OSI model]]'s 7 layers, XNS is a five-layer system,{{sfn|Stephens|1989|p=15}} like the later [[Internet protocol suite]].

The Physical and Data Link layers of the OSI model correspond to the Physical layer (layer 0) in XNS, which was designed to use the transport mechanism of the underlying hardware and did not separate the data link. Specifically, XNS's Physical layer is really the [[Ethernet]] [[local area network]] system, also being developed by Xerox at the same time, and a number of its design decisions reflect that fact.{{sfn|Stephens|1989|p=15}} The system was designed to allow Ethernet to be replaced by some other system, but that was not defined by the protocol (nor had to be).

The primary part of XNS is its definition of the Internal Transport layer (layer 1), which corresponds to OSI's Network layer, and it is here that the primary internetworking protocol, IDP, is defined. XNS combined the OSI's Session and Transport layers into the single Interprocess Communications layer (layer 2). Layer 3 was Resource Control, similar to the OSI's Presentation.{{sfn|Stephens|1989|p=15}}{{sfn|cisco}}

Finally, on top of both models, is the Application layer, although these layers were not defined in the XNS standard.{{sfn|Stephens|1989|p=15}}