Mumbai University > Electronics Engineering > Sem 8 > Advanced Networking Technologies

Marks: 5M

Year: Dec 13, May 12, Dec 15, May 15, Dec 12, Dec 11, May 14

1. Figure below shows the SONET layers with respect to the functional layers of OSI model. Data link layer function of OSI model is divided according to devices of SONET architecture and followed by three distinct layers of SONET. While function of Physical layer of OSI model is performed by Photonic Layer.

   • Path Layer: The path layer is responsible for the movement of a signal from its optical source to its optical destination. At the optical source signal is changed from an electronic form into optical form, multiplexed with other signal, and encapsulated in a frame. At the optical destination, the received frame is demultiplexed, and the individual optical signals are changed into their electronic forms.
   • Line Layer: The line layer is responsible for the movement of a signal across a physical line. Line layer overhead is added to the frame at this layer. Multiplexers provide line layer functions.
   • Section Layer: The section layer is responsible for the movement of a signal across a physical section. It handles framing, scrambling and error control.
   • Photonic Layer: The photonic layer corresponds to the physical layer. It includes physical specifications for the optical fibre channel, the sensitivity of the receiver, multiplexing functions etc. SONET uses NRZ coding where presence of light representing 1 and absence of light representing 0.
2. When we compare above mentioned functions with that of OSI Layers it can be observe that Data Link Layer whose main function is to set up connection between transmitter and receiver in a network as well as route the data through that path is divided among the Path layer, Line layer and Section layer. Where section is optical link connecting two neighbouring devices. A line is a portion of network between two multiplexers. A path is end to end portion of a network between two terminals.