<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology . Its goal is the interoperability of diverse communication systems with standard protocols . The model partitions a communication system into abstraction layers . The original version of the model defined seven layers . </P> <P> A layer serves the layer above it and is served by the layer below it . For example, a layer that provides error - free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that comprise the contents of that path . Two instances at the same layer are visualized as connected by a horizontal connection in that layer . </P>

How many layers are there in osi networking model