OPTICAL PACKET SWITCHING
Kunal K Mehta(11BEC107)
Electronics and communication branch
Institute of Technology, Nirma University
Optical packet switching promises to bring the flexibility and efficiency of Internet to transparent optical networking technology with bit rate extending beyond that is currently available with electronic router technologies. New optical signal processing have been demonstrated that enable routing at bit rates from 10gb/s to beyond 40gb/s. Keywords: Wavelength Division Multiplexing(WDM), Packet switching, Router, Bandwidth, IP network, Contention Resolution . I. Introduction
Packets are the basic units of Internet data. Currently, they are directed to their final destination using electronic routers. These packets are moved from router to router using optical fiber transmission and wavelength division multiplexing (WDM) systems where data is transported over different wavelength (colors) of light that are combined onto the same fiber. Today’s fiber systems carry a typical 32-80 wavelengths modulated at 2.5 Gbps to 10 Gbps per wavelength while routers are required to handle almost 1 Terabits per second. Now facts state that data carrying potential of optical fibers continues to double every 8-12 months with a single fiber capacity exceeding 10 Tbps. Comparing this increase with that of electronic processor speeds that doubles every 18 months (Moore’s Law) and comes at the expense of increased chip power dissipation we see that there is a potential bandwidth mismatch in handling capability between fiber transmission systems and electronic routers and switching systems. The situation becomes more complex when we consider that future routers and switches will potentially terminate hundreds or thousands of optical wavelengths and the increase in bit-rate per wavelength will head out to 40 Gbps and beyond to 160 Gbps. Additionally, electronic memory access speeds only increase at the rate of approximately 5% per year, an important data point since memory plays a key role in how packets are buffered and directed through the router. It is not difficult to see that the process of moving a massive number of packets per second through the multiple layers of electronics in a router, can lead to router congestion and leading to electronic circuits failure. II. Packet Switching in today’s Optical network
Routing and transmission are the basic functions required to move packets through a networks. In Internet Protocol (IP) networks, the packet routing and transmission problems are designed to handle separately. A router moves randomly arriving packets through a network by directing them from its multiple inputs to outputs and transmitting them on a link to next router. The router uses information carried with arriving packets (e.g. IP headers, packet type and priority) to forward them from its input to output ports as efficiently as possible with minimal packet loss and disruption to packet flow. This processing of merging multiple random input packet streams onto common output is called statistical multiplexing. In smaller networks, the links between routers can be made directly using Ethernet; however in high capacity metropolitan enterprise transmission systems between routers employ synchronous framing techniques like synchronous optical network (SONET) and packet over SONET (POS). This added layer of framing is designed to simplify transmission between routers and decouple it from packet routing and forwarding process. The transport that connects routers can designed to handle the packets asynchronously or synchronously. The most commonly used approaches maintain the random nature of packet flow by only loosely aligning them with in synchronous transmission frames. So to conclude we can say the function of a router is to take randomly arriving packets on its...
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