Optical Burst Switching

According to recent rapid increase of internet traffic, researches on high-speed and huge volume data transmission method and switching technology have been made. WDM(Wavelength Division Multiplexing) technology that piles some wavelength up into an optical fiber is remarkable as a core technology to carry out a next generation IP backbone network. However, When IP backbone is built up by using electrical router and WDM network, poor electric processing speed becomes a bottleneck of speed-up and huge capacity of the network. So OBS(Optical Burst Switching) multi-transfer IP packet that has the same address and the same quality requirements to IP packet row which has a burst is remarked to remove the bottleneck.

Research Introduction

QoS differentiation in OCBS
OBS becomes a problem of a burst signal confliction caused by multi burst signals aiming at the same out-put port at a core router, because it doesn’t reserve a wavelength at end-to-end. OBS rejects all burst signals reaching after burst signal’s confliction. To reduce an influence of the burst signal’s confliction, OCBS(Optical Composite Burst Switching) is suggested, which reject front part of duplicated burst signals that have already passed through the out-put port, and transfer the rest part among the burst signals which reached there later. But in OCBS, burst signals that have a lot of hop numbers to the addressed edge router go through a core router many times. And a possibility which rejects packets multiplexed by the burst signals comparing with that have low hop number increases. Therefore, QoS which is independent of hop number is uncontrollable, because possibility of rejecting packets waiting QoS demand is different low hop numbers from many hop numbers on the conventional method. To control QoS independent of hop number, the burst signal production method has been created, which changes a ratio depending on the hop numbers that has various demanded packets.

Reduce the burst loss by route study
The conventional OBS, the burst signal is always transmitted through the shortest path route, and it cause increase of a burst loss when traffics concentrate at a certain link. So we suggested a new method to change a transmission route of burst signals by route study. This method includes a feed back packet telling success or failure of transmission, and a search packet that examine a traffic situation on the unused route. The transmission router does a route study based on the information got by using a feedback packet and a search packet when the burst signals are transmitted. This suggested method prohibits an overloading at a certain link, and distributes the load in OBS networks, because the each router does a route study distributely.

Realization of QoS(Quality of Service)
With a spread of Internet, various traffic services will appear on the network. To satisfy various service demands will be a theme on optical burst exchange. The conventional QoS control method suggests to change an offset time (transmission intervals between a header and a burst signal) depending on the priority. But there is a problem that a packet delays depend on a priority for rejecting ratio. A differentiating method of QoS mapping a priority depending on the order of IP packet low in the burst signals has been suggested as a method to control a priority for packet rejecting ratio without deterioration of the delay.

Contention avoidance
The three method including a time axis, a wavelength axis and a space axis are created to avoid a confliction among the burst signals. As a time axis, a method using optical buffer for example fiber delaying line was suggested, but it has a problem that has less of flexibility and increase a size of switch. A wavelength axis that is a method of a wavelength axis has a cost problem, and it is difficult to mount it on all nodes. And detour routing as a space axis increase the delay. Yamanaka lab proposes a high reliability OBS ring network without being rejected at a relay node, because an upstream priority switch is arranged nodes like a ring. The proposed ring achieves an impartial access among nodes in the ring using dispersed impartial controlling mechanism, and improvement of a throughput.

Scheduling algorithm
TSOBS(Time sliced Optical Burst Switching) network that builds a TDM domain and does a efficient burst transmission is paid attention. Yamanaka lab has an aim to improve a throughput time, and is suggesting a scheduling algorithm to reduce unused time slot by examining newly produced head gap and tail gap by allocating burst signals.


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