this question is with regard to the OSI model...
as far i remember, 7 layers of OSI model work in either direction i.e from top to bottom (from layer-7 to layer-1) and from bottom to top (from layer-1 to layer-7).
In the ICND-1 official module, it talks about the Encapsulation and De-Encapsulation processes. Accoring to the Encapsulation process, when sender sends the data,it is encapsulated and passed from Application layer to Physical Layer.Now when receiver receives this data,it gets De-Encapsulated and passes from Physical layer to Application Layer. Therefore in this whole process, data was passed from Layer-7 to Layer-1(Encapsulation), and then was later passed from Layer-1 to Layer-7 (De-Encapsulation).
The confusion starts when Cisco, soon after this, talks about the 'Peer to Peer Communication'.
My question is that the same 'Encapsulation and De-Encapsulation' process is followed in the P2P communication? and OSI layers always work in both directions?