Horizontal communication
Fig: Horizontal Communication in OSI Model.
1) The horizontal communication is the logical connection between the layers, there is no direct communication between them. 2) Information included in each protocol header by the transmitting system is a message that will be carried to the same protocol in the destination system . 3) For two computers to communicate over a n/w, the protocol used at each layer of the OSI model in the transmitting system must be duplicated at the receiving system. 4) The packet travels up through the protocol stack and each successive header is stripped of by the appropriate protocol & processed. 5) When the packet arrived at its destination, the process by which the headers are applied at the source is repeated in server.
Vertical communication:
1) In addition to communicating horizontally with the same protocol in the other system, the header information also enables each layer to communicate with the layer above & below it. 2) Eg. The n/w layer will communicate with the data link layer & transport layer. 3) This interlayer communication is called communication vertical. 4) When a system receives a packet & passes it up through various layers the data link layer protocol header includes a field which specifies the name of n/w layer protocol to be used to process the packet. 5) The n/w layer protocol header will specify the name of transport layer protocol to be used to process the packet. 6) Due to vertical communication, it becomes protocol at each layer simultaneously.
Fig:Vertical communication