All Optical Switching Architectures

Introduction Optical switches are necessary for achieving reliable, fast and flexible modular communication means in future systems. At present, more and more communication transmission infrastructures are based on optical fiber links, while communication switching remains entirely electronic. This combination has two main flaws,

the first being the necessity to convert photons to electrons and vice versa, while the second is the limitation of the electronic devices in terms of throughput and bit rate as opposed to the very high capabilities of optical fibers. The unprecedented demand for optical network capacity has fueled the development of long-haul optical network systems which employ wavelength-division multiplexing (WDM) to achieve tremendous capacities. Such

systems transport tens to hundreds of wavelengths per fiber, with each wavelength modulated at 10 Gb/s or more. Up to now, the switching burden in such systems has been laid almost entirely on electronics. In every switching node, optical signals are converted to electrical form (O/E conversion), buffered electronically, and subsequently forwarded to their next hop after being converted to optical form again (E/O conversion).

Electronic switching is a mature and sophisticated technology that has been studied extensively. Apart from that, electronic equipment is strongly dependent on the data rate and protocol, and thus,any system upgrade results in the addition and/or replacement of electronic switching

If optical signals could be switched without conversion to electrical form, these drawbacks would be eliminated. This is the promise of optical switching. The main attraction of optical switching is that it enables routing of optical data signals without the need for conversion to electrical signals and, therefore, is independent of data rate and data protocol. The transfer of the switching function from electronics to optics will result in a reduction in the network equipment

switching speed, and thus network throughput, and a decrease in the operating power. In addition, the elimination of E/O and O/E conversions will result in a major decrease in the overall system cost, since the equipment associated with these conversions represents the lion ’ s share of cost in today ’ s networks.

1.Optical packet switching(OPS). 2. Generalized multiprotocol label switching (GMPLS). 3. Optical burst switching (OBS). There is a three main approaches that seem promising for the gradual migration of the switching functions from electronics to optics are:

Using pure WDM only provides granularity at the level of one Wavelength.Packet streams Can be multiplexed together statistically 1.Optical packet switching(OPS). making more efficient use of capacity and providing increased flexibility over pure WDM The wavelength dimension is also used,packet switches analyze the information contained in the packet headers and thus determine where to forward the packets. In addition, optical packet switching offers high-speed data rate & can be divided in to two categories:

1.slotted (synchronous) 2. unspotted (asynchronous) In a slotted network, all packets have the same size. They are placed together with the header inside a fixed time slot, Packets in an unspotted network do not necessarily have the same size.

2.Generalized Multiprotocol Lable Switching (GMPLS) is a technology that provides enhancements to Multiprotocol Label Switching (MPLS) to support network switching for time, wavelength, and space switching as well as for packet switching. In particular, GMPLS will provide support for photonic networking, also known as optical communications.

3. OPTICAL BURST SWITCHING(OBS) OBS is an attempt at a new synthesis of optical and electronic technologies that seeks to exploit the tremendous bandwidth of optical technology, while using electronics for management and control. Burst switching is designed to facilitate switching of the user data channels entirely in the optical domain.

This approach divides the entire network in two regions: edge and core. *ALL-OPTICAL BROADCASTING SWITCH FABRIC ARCHITECTURE The switch fabric in a router is responsible for transferring packets between the other functional blocks. In particular, it routes user packets from the input ports to theappropriate output ports. The design of the switch fabric is complicated by other requirements such as multicasting…