Editing Synchronous optical networking (section)

==Physical layer==
The physical layer refers to the first layer in the OSI networking model.<ref>Tyson, Jeff. "How OSI Works" HowStuffWorks.com. <http://computer.howstuffworks.com/osi.htm> 2 December 2011.</ref> The ATM and SDH layers are the regenerator section level, digital line level, transmission path level, virtual path level, and virtual channel level.<ref>Black, Uyless D. Emerging Communications Technologies. Englewood Cliffs, NJ: PTR Prentice Hall, 1994. 298-99. Print.</ref> The physical layer is modeled on three major entities: transmission path, digital line and the regenerator section.<ref>Hassan, Rosilah, James Irvine, and Ian Glover. "Design and Analysis of Virtual Bus Transport Using Synchronous Digital Hierarchy/Synchronous Optical Networking." Journal of Computer Science 4.12 (2008): 1003-011. Print.</ref> 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.<ref>"SONET: How Does SONET Work?" Capybara.Org. Web. 2 December 2011. <[https://web.archive.org/web/20071129010421/http://www.capybara.org/~dfraser/gaul/CS457/A1/howworks.html]>.</ref><ref>"Introduction to SONET." Networking - Computer and Wireless Networking Basics - Home Networks Tutorials. Web. 2 December 2011. <http://compnetworking.about.com/od/hardwarenetworkgear/l/aa092800a.htm {{Webarchive|url=https://web.archive.org/web/20160620193416/http://compnetworking.about.com/od/hardwarenetworkgear/l/aa092800a.htm |date=20 June 2016 }}>.</ref>