seven layers are there in osi networking model.
how many layers are there in osi networking model?
seven
the services and protocols specified in ieee 802 map to the lower two layers (data link and physical) of the seven-layer osi networking reference model. in fact, ieee 802 splits the osi data link layer into two sub-layers named logical link control (llc) and media access control (mac), so the layers can be listed like this: 





























bullet::::- data link layer





























bullet::::- llc sublayer





























bullet::::- mac sublayer





























bullet::::- physical layer
ieee 802
the physical layer refers to the first layer in the osi networking model. the atm and sdh layers are the regenerator section level, digital line level, transmission path level, virtual path level, and virtual channel level. the physical layer is modeled on three major entities: transmission path, digital line and the regenerator section. the regenerator section refers to the section and photonic layers. the photonic layer is the lowest sonet layer and it is responsible for transmitting the bits to the physical medium. the section layer is responsible for generating the proper sts-n frames which are to be transmitted across the physical medium. it deals with issues such as proper framing, error monitoring, section maintenance, and orderwire. the line layer ensures reliable transport of the payload and overhead generated by the path layer. it provides synchronization and multiplexing for multiple paths. it modifies overhead bits relating to quality control. the path layer is sonet's highest level layer. it takes data to be transmitted and transforms them into signals required by the line layer, and adds or modifies the path overhead bits for performance monitoring and protection switching.
synchronous optical networking