We all use the layered structure in our daily life if we send things..
So here as an example .. if we want to send a message from a person to another .. (follow the chart)
In networking, we use also the layered architecture .. we use The OSI model as a reference, and all the of the model are just an implementation to the osi model. In the osi model, the message is forwarded to the application layer, where it will put its own header, and then forward the whole data to the underneath layer as a black box. This layer will do the same thing, it will receive a black box, and then add its own header, and forwards it to the next layer and so on. This process is called encapsulation and happens at the sender. At the receiver we have the opposite process, the de-capsulation. The data is received from the physical layer, which will forward the data to the upper layer. The upper layer (data-link layer) will remove its own header, and forwards its payload (data) to the next layer. And so on. As we can see, that the communication style is that a protocol in a certain layer cares or communicates only with protocols which is underneath (at sender), or above ( at receiver) .. and that made a problem .. so the protocol at the higher layer will never care or communicate with layers at bottom layer .. for an example the tcp protocol (transport layer) does not care if the transmission was wifi or 3g or dialup (data-link and physical layer) … and this is a problem witch led to a better architecture witch is the cross – layer design with