Research progress of optical burst switching technology in optical fiber communication and its advantages
1. Introduction
With the rapid growth of IP services worldwide, the demand for transport network bandwidth and switching system capacity is increasing at an unprecedented rate. At present, DWDM technology is used in the optical layer. It can make the available bandwidth of an optical fiber reach about 10Tbit/s, which can meet the requirements of the transmission network bandwidth in a long period of time. However, the exchange rate using the usual circuit switching technology (time division, space division and wavelength switching) is much lower than this value. In this way, the development of mismatch exchange technology between the two puts forward new requirements.
In the long run, OPS(OpticalPacketSwitching) is the development direction of optical switching, but OPS has two obstacles that are difficult to overcome in the near future: First, the optical cache technology is not mature, and the fiber delay line (FDL, FiberDelayLine) used in the current experimental system is often bulky, inflexible, and the storage depth is limited; Second, it is difficult to achieve accurate synchronization of multiple input groups at OPS nodes. Therefore, the commercial application prospect of optical packet switching is not optimistic in a short period of time.
In this case, ChunmingQiao and JsTurnor et al proposed a new optical switching technology —-OBS(optical burst switching) as a transition technology from circuit switching to packet switching. The bandwidth granularity used by 0BS is between circuit switching and packet switching, which is more flexible than circuit switching, has higher bandwidth utilization, and is closer to practical than optical packet switching. It can be said that it combines the advantages of both and overcomes some disadvantages of both, and is a balanced choice between the two, so it has gradually attracted the attention of many experts and scholars.
2. Principle of OBS technology
The “burst” in OBS is an ultra-long IP packet composed of IP packets with the same egress edge router address and the same QoS requirements, which can come from different electrical IP routers in the traditional IP network. Burst data is the basic switching unit in optical burst switching network. In OBS, BCP(Burstcontrol packet, control packet, equivalent to the packet header of packet switching) and burst data (net load) are separated on the physical channel, and each control packet corresponds to a burst data. For example, in a WDM system, control packets occupy one or several wavelengths, and burst data occupies all other wavelengths.
In OBS, the burst data is always in the optical domain from the source node to the destination node, while the control information needs O/E/O transformation and electrical processing at each node. The rate of the control channel (wavelength) and the burst data channel (wavelength) can be the same or different. OBS network is composed of optical core router and electric edge router. The edge router is responsible for encapsulating the data in the traditional IP network into optical burst data and reverse unpacking. The core router is responsible for forwarding and exchanging optical burst data. Data information is not O/E, E/O transformation in 0BS network.
3. Key technologies of OBS
3.1 Assembly Algorithm
The edge router Assembler collates the packets into the corresponding Burst buffer heap based on the destination address and QoS of the packets entered from the port channel. The assembly of burst packets generally needs to consider two parameters, one is the assembly time, the other is the maximum length of burst packets. Also, consider whether the length of the burst packet is fixed or variable. There are currently several assembly algorithms.