Optical packet switching system and optical packet switching device

An optical packet switching device is provided with: a first input unit and a second input unit for receiving an optical packet signal having destination information and priority information; a first demultiplexer and a second demultiplexer for branching the optical packet signal; an optical switch unit for routing one of branched optical packet signals; a first analyzer unit and a second analyzer unit for analyzing the header of the other branched optical packet signal so as to detect the destination information and the priority information; and an output competition determination unit for checking for temporal competition of a plurality of optical packet signals based on destination information and for determining whether the optical packet signals should be transmitted or discarded based on priority information when there is competition.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Japanese Patent Application Number 2011-025243, filed on Feb. 8, 2011, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical packet switching method in which packet-by-packet optical packet switching is enabled by driving an optical switch according to destination information assigned to an optical packet signal.

2. Description of the Related Art

The technology of switching the path depending on the wavelength in an optical transmission system based on wavelength division multiplexing (WDM) and by employing a wavelength selective switch (WSS) is in practical use. One of the next-generation technologies studied is an optical packet switching system in which the path is switched in smaller units, namely, IP packets (10 Gigabit Ethernet (registered trademark) signals, etc.). Each packet is converted in format into an optical packet and routed by using an ultrahigh-speed optical switch (see e.g., patent document No. 1).

When the transmission is based on IP packets, no significant information is transmitted absent any data so that the bandwidth is wasted accordingly. If the optical packet switching system is realized, however, any idle time in which data is absent can be occupied by another packet. Therefore, the optical packet switching system promises the possibility of dramatically increasing the bandwidth usage efficiency of the transmission path and is envisaged as a technology of the future.

In an optical packet switching device, there are occasions when a plurality of optical packet signals received at the same time by a plurality of input units request output to a same output unit. In such a case, the optical packet switching device performs switching using an optical packet signal received first as a valid optical packet signal and discards the following optical packet.

However, the degree of priority for transmission may be set for a client signal such as, e.g., an Ether signal according to the type of data. In this situation, it is preferred to efficiently transmit a client signal with a high degree of priority.

SUMMARY OF THE INVENTION

The present invention addresses the background as described above, and a purpose thereof is to provide a technology capable of efficiently transmitting a client signal with a high degree of priority in an optical packet switching system.

An optical packet switching system according to one embodiment of the present invention comprises: an optical packet transmitter device including a detection unit configured to detect destination information and predetermined priority information from a received client signal, a header generation unit configured to generate a header containing the destination information and the priority information, a header insertion unit configured to insert the header in the client signal so as to generate a packet signal, and an electrical/optical converter unit configured to convert the packet signal into an optical packet signal; and an optical packet switching device including a plurality of receiver units configured to receive an optical packet signal, a branching unit configured to branch the optical packet signal, an optical switch unit configured to route one of branched optical packet signals, an analyzer unit configured to analyze the header of the other branched optical packet signal so as to detect the destination information and the priority information, and an output competition determination unit configured to check for temporal competition of a plurality of optical packet signals input to the plurality of receiver units based on destination information and to determine whether the optical packet signals should be transmitted or discarded based on priority information when there is competition.

The output competition determination unit may compare the degree of priority of competing optical packet signals when there is temporal competition in the plurality of optical packet signals and allow an optical packet signal input first to pass and discards the following optical packet when the optical packet signals have equal degree of priority.

The output competition determination unit may compare the degree of priority of competing optical packet signals when there is temporal competition in the plurality of optical packet signals and allow an optical packet signal having a high degree of priority to pass and discards an optical packet having a low degree of priority when the optical packet signals have different degree of priority.

When a second optical packet signal whose degree of priority is higher than that of a given first optical packet signal is input while the first optical packet signal is being transmitted, the output competition determination unit may stop the transmission of the first optical packet signal and allow the second optical packet signal to pass.

The optical packet switching system may further comprise: an optical packet receiver device configured to receive an optical signal output from the optical packet switching device. When the optical packet receiver device receives the optical packet signal stopped in the middle by the output competition determination unit from being transmitted, the optical receiver device may discard the optical packet signal.

Another embodiment of the present invention relates to an optical packet switching device. The optical packet switching device comprises: a plurality of receiver units configured to receive an optical packet signal having a header containing destination information and priority information; a branching unit configured to branch the optical packet signal; an optical switch unit configured to route one of branched optical packet signals; an analyzer unit configured to analyze the header of the other branched optical packet signal so as to detect the destination information and the priority information; and an output competition determination unit configured to check for temporal competition of a plurality of optical packet signals input to the plurality of receiver units based on destination information and to determine whether the optical packet signals should be transmitted or discarded based on priority information when there is competition.

Optional combinations of the aforementioned constituent elements, or implementations of the invention in the form of apparatuses, methods, systems, programs, and recording mediums storing programs may also be practiced as additional modes of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A description will now be given of an optical packet switching system according to an embodiment of the present invention. Prior to an explanation of the optical packet switching system according to the embodiment of the present invention, an explanation is given as a comparative example regarding an optical packet switching system conventionally developed by the present inventors.

FIG. 1shows an optical packet switching system110according to the comparative example. As shown inFIG. 1, the optical packet switching system110comprises an optical packet transmitter device111, an optical packet switching device112, an optical packet receiver device113, a first AWG114, a second AWG115, a first optical amplifier116, a second optical amplifier117, and first through fourth optical transmission paths118-121.

The optical packet transmitter device111generates a routing information header (including a packet length, destination information, and a local node ID) that indicates a forwarding destination of a 10 Gigabit Ethernet packet received from a client, adds the routing information header to the head of the packet, and then divides the data of the packet by n. The optical packet transmitter device111then adds the divided n pieces of data to optical signals at wavelengths λ1-λn and outputs the optical signals as optical packet signals of n wavelengths. Regardless of the packet length of an Ether signal, the number by which an Ether packet is divided is fixed to n (the maximum number of wavelengths that can be used in a system, e.g., n=40).

The optical packet signals of n wavelengths (at wavelengths λ1-λn) output from the optical packet transmitter device111are multiplexed by the first AWG114, then amplified by the first optical amplifier116, and output to the second optical transmission path119.

The optical packet signal propagated through the second optical transmission path119is input to a second input unit163of the optical packet switching device112. To a first input unit162of the optical packet switching device112, a wavelength-multiplexed optical packet signal from another optical packet transmitter device connected to a WDM network is input via the first optical transmission path118.

The optical packet switching device112is a 2-input×2-output optical packet switching device that switches a route of an optical packet signal in accordance with destination information assigned to the optical packet signal. The third optical transmission path120is connected to the first output unit164of the optical packet switching device112, and the fourth optical transmission path121is connected to the second output unit165. The optical packet signal propagated through the third optical transmission path120is output to the WDM network. Meanwhile, the optical packet signal propagated through the fourth optical transmission path121is amplified by the second optical amplifier117and then demultiplexed into wavelengths of λ1-λn by the second AWG115. The optical packet signals of n wavelengths demultiplexed by the second AWG115are input to the optical packet receiver device113.

The optical packet receiver device113restores the received optical packet signals of n wavelengths to the original Ether packet and outputs the restored Ether packet to the client.

FIG. 2shows the configuration of the optical packet transmitter device111according to the comparative example. As shown inFIG. 2, the optical packet transmitter device111comprises an optical/electrical converter unit130, a reception processing unit132, a routing information extraction unit133, a serial/parallel conversion unit134, a frame memory135, a transmission processing unit136, a packet-length detection unit137, a look-up table138, a header generation unit139, a header insertion unit140, and first through nth electrical/optical converter units141-1through141-n.

In the optical packet transmitter device111, a 10 Gigabit Ethernet signal input from the client is converted into an electrical signal by the optical/electrical converter unit130. The data format of this electrical Ether signal is a MAC frame. A predetermined reception process is then performed on the Ether signal in the reception processing unit132. The routing information extraction unit133then extracts routing information from the Ether signal. The routing information is converted into destination information by referring to the look-up table138and then input to the header generation unit139. The packet-length detection unit137extracts the packet length of the received Ether signal and then outputs the extracted packet length to the header generation unit139.

The Ether signal output from the routing information extraction unit133is converted into a parallel signal by the serial/parallel conversion unit134and then stored in the frame memory135. The Ether signal is then equally divided by n by the transmission processing unit136so as to generate n pieces of packet signals. Optical packet ID/copy information is output from the transmission processing unit136to the header generation unit139.

The header generation unit139generates a routing information header based on the packet length, the destination information, the local node ID, and the optical packet ID/copy information. The generated routing information header is inserted in one packet signal among the n pieces of packet signals divided by the header insertion unit140. The n pieces of packet signals are then converted into optical signals by the first through nth electrical/optical converter units141-1through141-n and then output as optical packet signals of n wavelengths (λ1-λn). The wavelength of an optical packet signal in which the routing information header is inserted is referred to as a “header wavelength.” The header wavelength is λ1in this case.

FIG. 3shows the configuration of an optical packet receiver device113according to the comparative example. As shown inFIG. 3, the optical packet receiver device113comprises a first through nth optical/electrical converter units150-1through150-n, first through nth frame memories151-1through151-n, a header processing unit152, a packet assembling unit153, a packet identification unit154, a MAC table155, an output control unit156, and an electrical/optical converter unit158.

In the optical packet receiver device113, the optical packet signals of n wavelengths (λ1-λn) that have been input are converted into electrical packet signals by the first through nth optical/electrical converter units150-1through150-n, respectively. The header processing unit152extracts packet information, a packet length, and an ECC (Error Check Code) error from the routing information header of a packet signal that corresponds to the optical packet signal of the header wavelength of λ1so as to determine the normality of the packet signal.

The n pieces of packet signals output from the first through nth optical/electrical converter units150-1through150-n are stored in the first through nth frame memories151-1through151-n, respectively. The packet assembling unit153assembles a packet in reference to the packet information, the packet length, and the ECC error from the header processing unit152. The packet identification unit154identifies an Ether packet from the output of the packet assembling unit153and extracts the Ether packet. In reference to the MAC table155, the output control unit156replaces a destination MAC address in the Ether packet output from the packet identification unit154with a MAC address registered in the MAC table155. The Ether packet is then input to the electrical/optical converter unit158. The data format of an Ether signal input to the electrical/optical converter unit158is a MAC frame. The electrical/optical converter unit158converts the Ether packet into an optical signal and then output the optical signal to the client.

FIG. 4shows the configuration of an optical packet switching device112according to the comparative example. As shown inFIG. 4, the optical packet switching device112comprises an optical switch unit160, an optical switch control unit161, a first input unit162, a second input unit163, a first input-side optical amplifier166, a second input-side optical amplifier167, a first demultiplexer170, a second demultiplexer171, a first optical delay line172, a second optical delay line173, a first output-side optical amplifier168, a second output-side optical amplifier169, a first output unit164, and a second output unit165. The optical switch control unit161comprises a first optical/electrical converter unit174, a second optical/electrical converter unit175, a first analyzer unit176, a second analyzer unit178, and an output competition determination unit179.

The optical packet switching device112extracts the routing information header from an optical packet signal that has been input as a WDM signal from the client or the network. The optical packet switching device112then determines an output destination based on the routing information header and switches the output destination by the optical switch unit160.

Wavelength-multiplexed optical packet signals of n wavelengths are input to the first input unit162and the second input unit163. The optical packet signals that are input are obtained by converting an Ether signal from a client unit of the local node or a client unit of another node in an optical packet transmitter device such as the one shown inFIG. 2.

The optical packet signals that have been input are amplified by the first input-side optical amplifier166and second input-side optical amplifier167for optical level adjustment. Then, only optical packet signals of header wavelengths are optically branched by the first demultiplexer170and the second demultiplexer171. The branched optical packet signals of header wavelengths are input to the optical switch control unit161. Meanwhile, wavelength-multiplexed optical packet signals are input to the optical switch unit160via the first optical delay line172and the second optical delay line173.

The branched optical packet signals of the header wavelengths are converted into electrical packet signals by the first optical/electrical converter unit174and the second optical/electrical converter unit175, respectively. Then, routing information headers thereof are analyzed by the first analyzer unit176and the second analyzer unit178so as to detect destination information.

The output competition determination unit179determines whether the optical packet signals should be transmitted or discarded based on the detected destination information and outputs an optical switch control signal to the optical switch unit160based on the result of determination.

The first optical delay line172and the second optical delay line173delay the wavelength-multiplexed optical packet signals for a duration required for the optical switch control unit161to generate the optical switch control signal. By providing the first optical delay line172and the second optical delay line173, on/off of the optical switch unit160can be controlled to be synchronized with the timing of arrival of the optical packet signals at the optical switch unit160.

The optical switch unit160is a 2×2 optical switch and comprises first through fourth optical gate switches180through183and four optical couplers184-187. The optical gate switches may be implemented by a semiconductor optical amplifier (SOA). The first through fourth optical gate switches180through183are controlled to be turned on or off by an optical switch control signal from the optical switch control unit161. In the optical packet switching device112, the wavelength-multiplexed optical packet signals of n wavelengths are routed all at once based on the destination information extracted from an optical packet signal of one header wavelength.

FIGS. 5A-5Cillustrate output competition determination in the optical packet switching device112.FIG. 5Ashows an optical packet signal input to the first input unit162.FIG. 5Bshows an optical packet signal input to the second input unit163.FIG. 5Cshows an optical packet signal output from the first output unit164. Optical packet signals1-1,1-2, and2-1that have been input are all directed to the first output unit164as an output destination.

As shown inFIG. 5, the optical packet signal1-1is first input to the first input unit162, the optical packet signal2-1is then input to the second input unit163, and the optical packet signal1-2is lastly input to the first input unit162. Since the optical packet signal1-1is a signal that arrives first, the output competition determination unit179outputs the optical packet signal1-1to the first output unit164. In other words, the output competition determination unit179turns on the optical gate switch180of the optical switch unit160and opens a path from the first input unit162to the first output unit164.

However, the optical packet signal2-1input to the second input unit163temporally competes with the optical packet signal1-1input to the first input unit162. In other words, the two optical packet signals concur in time. In this case, the output competition determination unit179discards the optical packet signal2-1. In other words, the output competition determination unit179leaves off the optical gate switches182and183to which the optical packet signal2-1is input.

Although the optical packet signal1-2input to the first input unit162has an overlapping data portion with the optical packet signal2-1, the output competition determination unit179outputs the optical packet signal1-2to the first output unit164since the optical packet signal2-1is already discarded.

As described, if congestion occurs in some optical packet signals when optical packet signals are received at the same timing from a plurality of input units with output requests for a same output route in the optical packet switching device according to the comparative example, a process is performed where an optical packet signal received first is allowed to pass and where the following optical packet signal is discarded.

Meanwhile, the degree of priority for transmission may be set for a client signal such as, e.g., an Ether signal according to the type (emails, phones, video images, etc.) of data. In this situation, it is preferred to perform routing in consideration of the degree of priority of the client signal. A description will now be given of an optical packet switching system capable of performing routing according to the degree of priority of a client signal.

FIG. 6shows an optical packet switching system10according to the embodiment of the present invention. As shown inFIG. 6, the optical packet switching system10comprises an optical packet transmitter device11, an optical packet switching device12, an optical packet receiver device13, a first AWG14, a second AWG15, a first optical amplifier16, a second optical amplifier17, and first through fourth optical transmission paths18-21. The basic configuration of the optical packet switching system10is similar to that of the optical packet switching system110shown inFIG. 1. Thus, a detailed description is omitted.

FIG. 7shows the configuration of the optical packet transmitter device11according to the embodiment. As shown inFIG. 7, the optical packet transmitter device11comprises an optical/electrical converter unit30, a reception processing unit32, a routing information extraction unit33, a serial/parallel conversion unit34, a frame memory35, a transmission processing unit36, a detection unit37, a look-up table38, a header generation unit39, a header insertion unit40, and first through nth electrical/optical converter units41-1through41-n. The optical packet transmitter device11functions as an Ether signal/optical packet converter device.

A 10 Gigabit Ethernet signal is input to the optical packet transmitter device11from the client. Priority information determined by the client managing data according to the type of the data is included in the Ether signal. The priority information represents the degree of importance of the Ether signal, and an Ether signal with a high degree of propriety is transmitted preferentially over a signal with a low degree of priority. An example of data with a high degree of priority includes, for example, data for Video On Demand that continuously transmits large volumes of video data.

The 10 Gigabit Ethernet signal input from the client is converted into an electrical signal by the optical/electrical converter unit30. The data format of this electrical Ether signal is a MAC frame. A predetermined reception process is then performed on the Ether signal in the reception processing unit32. The routing information extraction unit33then extracts routing information from the Ether signal. The routing information is converted into destination information by referring to the look-up table38and then input to the header generation unit39. The detection unit37detects packet length information and priority information in the received Ether signal and then outputs the detected packet length information and priority information to the header generation unit39.

The Ether signal output from the routing information extraction unit33is converted into a parallel signal by the serial/parallel conversion unit134and then stored in the frame memory35. The Ether signal is then equally divided by n by the transmission processing unit36so as to generate n pieces of packet signals. Optical packet ID/copy information is output from the transmission processing unit36to the header generation unit39.

The header generation unit39generates a routing information header based on the packet length, the destination information, the priority information, the local node ID, and the optical packet ID/copy information. The generated routing information header is inserted in one packet signal among the n pieces of packet signals divided by the header insertion unit40. The n pieces of packet signals are then converted into optical signals by the first through nth electrical/optical converter units41-1through41-n and then output as optical packet signals of n wavelengths (λ1-λn). The wavelength of an optical packet signal in which the routing information header is inserted is referred to as a “header wavelength.” The header wavelength is λ1in this case.

FIG. 8shows the configuration of the optical packet receiver device13according to the embodiment. As shown inFIG. 8, the optical packet receiver device13comprises a first through nth optical/electrical converter units50-1through50-n, first through nth frame memories51-1through51-n, a header processing unit52, a packet assembling unit53, a packet identification unit54, a MAC table55, an output control unit56, and an electrical/optical converter unit58. The optical packet receiver device13functions as an optical packet/Ether signal converter device.

In the optical packet receiver device13, the optical packet signals of n wavelengths (λ1-λn) that have been input are converted into electrical packet signals by the first through nth optical/electrical converter units50-1through50-n, respectively.

The header processing unit52extracts a wavelength in use, packet information, a packet length, and an ECC (Error Check Code) error from the routing information header of a packet signal converted from an optical packet signal of a header wavelength of λ1and transmits these to the packet assembling unit53.

The n pieces of packet signals output from the first through nth optical/electrical converter units50-1through50-n are stored in the first through nth frame memories51-1through51-n, respectively. The packet assembling unit53assembles a packet in reference to the packet information, the packet length, and the ECC error from the header processing unit52.

The packet identification unit54identifies an Ether packet from the output of the packet assembling unit53and extracts the Ether packet. The packet identification unit54performs packet anomaly detection by reading a FCS (Frame Check Sequence), which is a CRC (Cyclic Redundancy Check) value calculated from the respective fields of a destination address, transmission source address, length/type, and data of the Ether signal, and by making comparison with a CRC value calculated in a local station. In the case of anomaly, the packet identification unit54discards the data.

In reference to the MAC table55, the output control unit56replaces a destination MAC address in the Ether packet output from the packet identification unit54with a MAC address registered in the MAC table55. The Ether packet is then input to the electrical/optical converter unit58. The data format of the Ether signal input to the electrical/optical converter unit58is a MAC frame. The electrical/optical converter unit58converts the Ether packet into an optical signal and then output the optical signal to the client.

FIG. 9shows the configuration of the optical packet switching device12according to the embodiment. As shown inFIG. 9, the optical packet switching device12comprises an optical switch unit60, an optical switch control unit61, a first input unit62, a second input unit63, a first input-side optical amplifier66, a second input-side optical amplifier67, a first demultiplexer70, a second demultiplexer71, a first optical delay line72, a second optical delay line73, a first output-side optical amplifier68, a second output-side optical amplifier69, a first output unit64, and a second output unit65. The optical switch control unit61comprises a first optical/electrical converter unit74, a second optical/electrical converter unit75, a first analyzer unit76, a second analyzer unit78, and an output competition determination unit79.

The optical packet switching device12extracts the routing information header from an optical packet signal that has been input as a WDM signal from the client or the network. The optical packet switching device12then determines an output destination based on the routing information header and switches the output destination by the optical switch unit60.

Wavelength-multiplexed optical packet signals are input to the first input unit62and the second input unit63. The optical packet signals that are input are obtained by converting an Ether signal from a client unit of the local node or a client unit of another node in an optical packet transmitter device such as the one shown inFIG. 7.

The optical packet signals that have been input to the first input unit62and the second input unit63are amplified by the first input-side optical amplifier66and second input-side optical amplifier67for optical level adjustment. Then, only optical packet signals of header wavelengths are optically branched by the first demultiplexer70and the second demultiplexer71. The branched optical packet signals of header wavelengths are input to the optical switch control unit61. Then, the optical packet signals of the header wavelengths are converted into electrical packet signals by the first optical/electrical converter unit74and the second optical/electrical converter unit75, respectively. Then, routing information headers thereof are analyzed by the first analyzer unit76and the second analyzer unit78so as to detect destination information, priority information, and packet length information. Meanwhile, wavelength-multiplexed optical packet signals passed through the first demultiplexer70and the second demultiplexer71are input to the optical switch unit60via the first optical delay line72and the second optical delay line73.

Based on the destination information and packet length information detected by the first analyzer unit76and the second analyzer unit78, the output competition determination unit79checks for temporal competition of the optical packet signals input to the first input unit62and the second input unit63, and when competition has occurred, the output competition determination unit79determines whether the optical packet signals should be transmitted or discarded based on the priority information. The output competition determination unit79then outputs an optical switch control signal to the optical switch unit60based on the result of determination.

The first optical delay line72and the second optical delay line73delay the wavelength-multiplexed optical packet signals for a duration required for the optical switch control unit61to generate the optical switch control signal. By providing the first optical delay line72and the second optical delay line73, on/off of the optical switch unit60can be controlled to be synchronized with the timing of arrival of the optical packet signals at the optical switch unit60.

The optical switch unit60is a 2×2 optical switch and comprises first through fourth optical gate switches80through83and four optical couplers84-87. The optical gate switches may be implemented by a semiconductor optical amplifier (SOA). The first through fourth optical gate switches80through83are controlled to be turned on or off by an optical switch control signal from the optical switch control unit61.

FIGS. 10A-10Cillustrate output competition determination in the optical packet switching device12.FIG. 10Ashows a first optical packet signal P1input to the first input unit62.FIG. 10Bshows a second optical packet signal P2input to the second input unit63.FIG. 10Cshows an optical packet signal output from the first output unit64.

As shown inFIGS. 10A and 10B, the first optical packet signal P1is first input to the first input unit62, and the second optical packet signal P2is then input to the second input unit63. The optical packet signals P1and P2are all directed to the first output unit64as an output destination. The first optical packet signal P1and the second optical packet signal P2are optical packet signals having the same level of priority (in this case, the degree of priority is low for both).

As shown inFIGS. 10A and 10B, the first optical packet signal P1and the second optical packet signal P2temporally compete (in other words, there is overlap in time). This temporal competition can be determined based on the destination information and the packet length information regarding the first optical packet signal P1and the second optical packet signal P2. In the optical packet switching device12according to the present embodiment, when a plurality of optical packet signals temporally compete as described above, the output competition determination unit79compares the degree of priority of the competing optical packet signals. When the optical packet signals have equal degree of priority, it is determined to allow the optical packet signal input first to pass and to discard the following optical packet. More specifically, in the examples shown inFIGS. 10A-10C, since the degree of priority is “low” for both first optical packet signal P1and second optical packet signal P2that are competing, the output competition determination unit79allows the first optical packet signal P1that has been input first to pass and discards the second optical packet signal P2that has been input subsequently. In the examples shown inFIGS. 10A-10C, an explanation is given for the case when the degree of priority of two optical packet signals is “low.” However, the same applies for the case when the degree of priority is “high” for both.

FIGS. 11A-11Calso illustrate output competition determination in the optical packet switching device12. FIG.11A shows a first optical packet signal P1and a third optical packet signal P3that are input to the first input unit62.FIG. 11Bshows a second optical packet signal P2input to the second input unit63.FIG. 11Cshows an optical packet signal output from the first output unit64.

As shown inFIGS. 11A and 11B, the first optical packet signal P1is first input to the first input unit62, the second optical packet signal P2is then input to the second input unit63, and the third optical packet signal P3is lastly input to the first input unit62. The first through third optical packet signals P1through P3are all directed to the first output unit64as an output destination. The first optical packet signal P1and the third optical packet signal P3both have a “low” degree of priority, and the second optical packet signal P2has a “high” degree of propriety.

In the optical packet switching device12according to the present embodiment, when a plurality of optical packet signals temporally compete, the output competition determination unit79compares the degree of priority of the competing optical packet signals. When the optical packet signals have different degree of priority, the output competition determination unit79performs a process of allowing an optical packet having a high degree of priority to pass and discarding an optical packet having a low degree of priority.

A detailed description is now given of the above process in reference toFIGS. 11A-11C. The first optical packet signal P1is output to the first output unit64since the first optical packet signal P1has been input first. It is then assumed that the second optical packet signal P2, whose degree of priority is higher than that of the first optical packet signal P1, is input to the second input unit63while the first optical packet signal is being transmitted. In this case, the output competition determination unit79stops the transmission of the first optical packet signal P1having a low degree of priority and allows the second optical packet signal P2having a high degree of priority to pass. In other words, a third optical gate switch82of the optical switch unit60is turned off while the first optical packet signal P1is being output to the first output unit64, and a first optical gate switch80is then turned on. A no-signal period called predetermined “guard time” is provided between time in which the third optical gate switch82is turned off and time in which the first optical gate switch80is turned on. The guard time is for recognizing that the second optical packet signal P2is normal data in a receiver in the subsequent stage. Then, the third optical packet signal P3having a low degree of priority is input to the first input unit62. The third optical packet signal P3and the second optical packet signal P2concur in time, and the third optical packet signal P3is discarded since the degree of priority thereof is lower than that of the second optical packet signal P2.

In the example shown inFIGS. 11A-11C, the first optical packet signal P1is output from the first output unit64while missing a part of data. The first optical packet signal P1is input to the optical packet receiver device13shown inFIG. 8. In the optical packet receiver device13, anomaly detection is performed on a received packet by the packet identification unit54, as described above. Thus, a packet signal, such as the first optical packet signal P1, that is missing a part of data is discarded. Therefore, the optical packet receiver device13does not get affected even when the outputting of an optical packet signal having a low degree of priority is stopped in the middle.

As described above, the optical packet switching system10according to the present embodiment allows a signal with a high degree of priority to be efficiently transmitted by using priority information in output competition determination.

In the above-stated embodiment, the degree of priority is defined in two levels: “high” and “low.” However, the degree of priority is not limited to these, and a plurality of levels may be set for the degree of priority. In this case, an optical packet signal with a highest degree of priority is preferentially output in output competition determination.

Described above is an explanation of the present invention based on the embodiments. These embodiments are intended to be illustrative only, and it will be obvious to those skilled in the art that various modifications to constituting elements and processes could be developed and that such modifications are also within the scope of the present invention.