OSI Layers working in both directions?

hassaan_st · ‎09-04-2008

Hello friends,

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?

Regards

Calin C. · ‎09-04-2008

Hi there!

It has been a while since I got CCNA, but for me P2P communication is describing the way that 2 peers communicate (as an example P2P is opposite to hub-and-spoke). Of course that encapsulation and de-encapsulation of the packets take place no matter if the communication in P2P or another type (eg. hub-and-spooke).

For me OSI layer and type of communication are 2 different things. L1-L7 or L7-L1 take place no matter of the method of communication.

Please tell me if you need more info.

Cheers,

Calin

ahmednaas · ‎09-05-2008

P2P is a form network communications and therefore follows the OSI model. Please note that:

- The OSI model is an idealized model and that the TCP/IP stack doesn't follow the OSI model to the letter since it has less than seven layers and some protocols are not confined to a single OSI layer.

- P2P is an alternative to the client-server model of networking. The [en/de]-encapsulation you refer to is applicable in both cases.

Ahmed Naas