for example in chapter 6 of optical networks a practical perspective r ramaswami and k sivarajan academic press 1998 which is hereby incorporated by reference in its entirety networks almost universally employ multiple layers of protocols a low level physical layer protocol assures the transmission and reception of a data stream between two devices data packets are constructed in a data link layer over the physical layer a network and transport layer protocol governs transmission of data through the network thereby ensuring end to end reliable data delivery as computer and transmission networks have developed various approaches have been used in the choice of communication medium network topology message format protocols for channel access and so forth some of these approaches have emerged as de facto standards but there is still no single standard for network communication however a model for network architectures has been proposed and widely accepted it is known as the international standards organization iso open systems interconnection osi reference model the osi reference model is not itself a network architecture rather it specifies a hierarchy of protocol layers and defines the function of each layer in the network each layer in one node of the network carries on a conversation with the corresponding layer in another node with which communication is taking place in accordance with a protocol defining the rules of this communication in reality information is transferred down from layer to layer in one node then through the channel medium and back up the successive layers of the.