17-09-2009, 12:29 AM
Optical switching enables routing of optical data signals without the need for conversion to electrical signals and, therefore, is independent of data rate and data protocol.Optical Burst Switching (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.
In an OBS network the incoming IP traffic is first assembled into bigger entities called bursts. Bursts, being substantially bigger than IP packets are easier to switch with relatively small overhead. When a burst is ready, reservation request is sent to the core network. Transmission and switching resources for each burst are reserved according to the one-pass reservation scheme, i.e. data is sent shortly after the reservation request without receiving an acknowledgement of successful reservation.
The reservation request (control packet) is sent on a dedicated wavelength some offset time prior to the transmission of the data burst. This basic offset has to be large enough to electronically process the control packet and set up the switching matrix for the data burst in all nodes. When a data burst arrives in a node the switching matrix has been already set up, i.e. the burst is kept in the optical domain. The reservation request is analysed in each core node, the routing decision is made, and sent to the next node. When the burst reaches its destination node it is disassembled, and the resulting IP packets are sent to their respective destinations.
The benefit of OBS over circuit switching is that there is no need to dedicate a wavelength for each end-to-end connection. OBS is more viable than optical packet switching because the burst data does not need to be buffered or processed at the cross-connect.
Advantages
#Greater transport channel capacity
#No O-E-O conversion
#Cost effective
Disadvantages
#Burst dropped in case of contention
#Lack of effective technology
