Michel, your drawing of TCP/IP is NOT the model I used in the design of TCP/IP. At the time Bob Kahn and I were working on this design, there were three networks being used to support the Internet: ARPANET, Packet Radio net and Packet Satellite net. These networks were packet switched and they had physical and link layers as well as network layers. so we had IP/network/link/physical layers IP was a layer above the nominal "network" layer. Things got more complex as routers were implemented that ran IP over dedicated links rather than servings as gateways between packet nets. However, even with routers operating at IP layer primarily, there were lower layer networks such as frame relay, ATM, over which IP operated. If there was any confusion, it was that packet radio, arpanet and packet satellite networks had both layer two and layer three elements while Frame Relay and ATM tended to be characterized as layer 2 networks. vint At 04:29 PM 10/6/2002 -0700, Michel Py wrote: >If I had to design a model it would be: > > Michel's TCP/IP OSI > model model model >+--------------+ +---------------+ +---+--------------+ >! ! ! ! ! 7 ! Application ! >! ! ! ! +---+--------------+ >! Application ! ! Application ! ! 6 ! Presentation ! >! ! ! ! +---+--------------+ >! ! ! ! ! 5 ! Session ! >+--------------+ +---------------+ +---+--------------+ >! Transport ! ! Transport ! ! 4 ! Transport ! >+--------------+ +---------------+ +---+--------------+ >! Network ! ! Internet ! ! 3 ! Network ! >+--------------+ +---------------+ +---+------+-------+ >! Logical Link ! ! ! ! ! Data ! LLC ! >+--------------+ ! Network ! ! 2 ! Link +-------+ >! Media Access ! ! Interface ! ! ! ! MAC ! >+--------------+ ! ! +---+------+-------+ >! Physical ! ! ! ! 1 ! Physical ! >+--------------+ +---------------+ +---+--------------+ > >I understand that people that have used the TCP/IP model don't care much >of what's inside the Network Interface layer, but there is a bunch of >stuff there that could use layering. That's why, short of having my very >own model drawn above, I keep using the OSI one for >explanatory/educational purposes. > >Michel. Vint Cerf SVP Architecture & Technology WorldCom 22001 Loudoun County Parkway, F2-4115 Ashburn, VA 20147 703 886 1690 (v806 1690) 703 886 0047 fax