# Patent

## Title
Optical packet switching system, optical packet switching device, and optical packet transmitter device

## Abstract

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

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to and the benefit of Japanese Patent Application Number 2011-025242, 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.
[Patent document No. 1] JP 2008-235986
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. Excessive optical packet signals discarded in this way causes communication quality to be decreased.
SUMMARY OF THE INVENTION
The present invention addresses the background as described above and a purpose thereof is to provide a technology capable of reducing the probability of discarding optical packets.
The optical packet switching system according to an embodiment of the present invention comprises: an optical packet transmitter device and an optical packet switching device. The optical packet transmitter device includes a packet-length detection unit configured to detect the packet length of a received client signal, a setting unit configured to set, according to the packet length, a number of divisions by which the client signal is divided and a wavelength used for an optical packet signal to be transmitted, a header generation unit configured to generate a header containing information of a wavelength in use and destination information of the client signal, a transmission processing unit configured to divide the client signal according to the set number of divisions and generate a plurality of packet signals, a header insertion unit configured to insert the generated header in at least one packet signal, and an electrical/optical converter unit configured to convert the plurality of packet signals into optical packet signals of a plurality of wavelengths according to the set wavelength in use. The optical packet switching device includes a plurality of receiver units configured to receive optical packet signals in which the optical packet signals of a plurality of wavelengths are wavelength-multiplexed, a branching unit configured to branch the received wavelength-multiplexed optical packet signals into optical packet signals of wavelengths with the header, an optical switch unit configured to route the wavelength-multiplexed optical packet signals, an analyzer unit configured to analyze the header of the branched optical packet signals so as to detect the destination information and the information of the wavelength in use, and an output competition determination unit configured to check for temporal competition of the plurality of wavelength-multiplexed optical packet signals input to the plurality of receiver units based on the destination information and to determine whether the wavelength-multiplexed optical packet signals should be transmitted or discarded based on the information of the wavelength in use when there is competition.
Even when there is temporal competition in the plurality of optical packet signals, the output competition determination unit may allow the plurality of wavelength-multiplexed optical packet signals to be transmitted altogether if no competition has occurred with regard to wavelengths.
The setting unit may set the number of divisions by which the client signal is divided and the corresponding number of wavelengths in use to a first predetermined value and set the wavelengths in use to be a predetermined first wavelength group when the packet length is less than a predetermined length, and the setting unit may set the number of divisions and the number of wavelengths in use to be a second predetermined value, which is larger than the first predetermined value, and set the wavelengths in use to a predetermined second wavelength group when the packet length is at least the predetermined length. The first wavelength group and the second wavelength group may have different wavelength allocation.
The optical packet switching system may comprise a plurality of the optical packet transmitter devices as nodes, and the wavelength allocation of the first wavelength group may be different on a node-by-node basis.
The optical packet switching system may further comprise a table associating a packet length and a wavelength group.
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 optical packet signals in which the optical packet signals of a plurality of wavelengths are wavelength-multiplexed, the optical packet signals having destination information and information of a wavelength in use; a branching unit configured to branch the received wavelength-multiplexed optical packet signals into optical packet signals of wavelengths with the header; an optical switch unit configured to route the wavelength-multiplexed optical packet signals; an analyzer unit configured to analyze the header of the branched optical packet signals so as to detect the destination information and the information of the wavelength in use; and an output competition determination unit configured to check for temporal competition of the plurality of wavelength-multiplexed optical packet signals input to the plurality of receiver units based on the destination information and to determine whether the wavelength-multiplexed optical packet signals should be transmitted or discarded based on the information of the wavelength in use when there is competition.
Yet another embodiment of the present invention relates to an optical packet transmitter device. The optical packet transmitter device for use in an optical packet switching system comprises: a packet-length detection unit configured to detect the packet length of a received client signal; a setting unit configured to set, according to the packet length, a number of divisions by which the client signal is divided and a wavelength used for an optical packet signal to be transmitted; a header generation unit configured to generate a header containing information of a wavelength in use and destination information of the client signal; a transmission processing unit configured to divide the client signal according to the set number of divisions and generate a plurality of packet signals; a header insertion unit configured to insert the generated header in at least one packet signal; and an electrical/optical converter unit configured to convert the plurality of packet signals into optical packet signals of a plurality of wavelengths according to the set wavelength in use.
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.



BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments will now be described, by way of example only, with reference to the accompanying drawings that are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several figures, in which:
FIG. 1 shows an optical packet switching system according to a comparative example;
FIG. 2 shows the configuration of an optical packet transmitter device according to the comparative example;
FIG. 3 shows the configuration of an optical packet receiver device according to the comparative example;
FIG. 4 shows the configuration of an optical packet switching device according to the comparative example;
FIGS. 5A-5C illustrate output competition determination in the optical packet switching device according to the comparative example;
FIG. 6 shows an optical packet switching system according to the embodiment of the present invention;
FIG. 7 shows the configuration of an optical packet transmitter device according to the present embodiment;
FIG. 8 shows an example of wavelength allocation;
FIG. 9 shows the configuration of an optical packet receiver device according to the present embodiment;
FIG. 10 shows the configuration of an optical packet switching device according to the present embodiment;
FIGS. 11A-11C illustrate output competition determination in the optical packet switching device according to the present embodiment;
FIG. 12 shows another example of wavelength allocation;
FIG. 13 shows an example of a bit configuration for transmitting information of wavelength in use;
FIG. 14 shows another example of the bit configuration for transmitting the information of wavelength in use; and
FIG. 15 shows an example of a table associating a group with wavelength composition.



DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention, but to exemplify 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. 1 shows an optical packet switching system 110 according to the comparative example. As shown in FIG. 1, the optical packet switching system 110 comprises an optical packet transmitter device 111, an optical packet switching device 112, an optical packet receiver device 113, a first AWG 114, a second AWG 115, a first optical amplifier 116, a second optical amplifier 117, and first through fourth optical transmission paths 118-121.
The optical packet transmitter device 111 generates 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 device 111 then 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 device 111 are multiplexed by the first AWG 114, then amplified by the first optical amplifier 116, and output to the second optical transmission path 119.
The optical packet signal propagated through the second optical transmission path 119 is input to a second input unit 163 of the optical packet switching device 112. To a first input unit 162 of the optical packet switching device 112, a wavelength-multiplexed optical packet signal from another optical packet transmitter device connected to a WDM network is input via the first optical transmission path 118.
The optical packet switching device 112 is 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 path 120 is connected to the first output unit 164 of the optical packet switching device 112, and the fourth optical transmission path 121 is connected to the second output unit 165. The optical packet signal propagated through the third optical transmission path 120 is output to the WDM network. Meanwhile, the optical packet signal propagated through the fourth optical transmission path 121 is amplified by the second optical amplifier 117 and then demultiplexed into wavelengths of λ1-λn by the second AWG 115. The optical packet signals of n wavelengths demultiplexed by the second AWG 115 are input to the optical packet receiver device 113.
The optical packet receiver device 113 restores the received optical packet signals of n wavelengths to the original Ether packet and outputs the restored Ether packet to the client.
FIG. 2 shows the configuration of the optical packet transmitter device 111 according to the comparative example. As shown in FIG. 2, the optical packet transmitter device 111 comprises an optical/electrical converter unit 130, a reception processing unit 132, a routing information extraction unit 133, a serial/parallel conversion unit 134, a frame memory 135, a transmission processing unit 136, a packet-length detection unit 137, a look-up table 138, a header generation unit 139, a header insertion unit 140, and first through nth electrical/optical converter units 141-1 through 141-n. 
In the optical packet transmitter device 111, a 10 Gigabit Ethernet signal input from the client is converted into an electrical signal by the optical/electrical converter unit 130. 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 unit 132. The routing information extraction unit 133 then extracts routing information from the Ether signal. The routing information is converted into destination information by referring to the look-up table 138 and then input to the header generation unit 139. The packet-length detection unit 137 extracts the packet length of the received Ether signal and then outputs the extracted packet length to the header generation unit 139.
The Ether signal output from the routing information extraction unit 133 is converted into a parallel signal by the serial/parallel conversion unit 134 and then stored in the frame memory 135. The Ether signal is then equally divided by n by the transmission processing unit 136 so as to generate n pieces of packet signals. Optical packet ID/copy information is output from the transmission processing unit 136 to the header generation unit 139.
The header generation unit 139 generates 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 unit 140. The n pieces of packet signals are then converted into optical signals by the first through nth electrical/optical converter units 141-1 through 141-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 λ1 in this case.
FIG. 3 shows the configuration of an optical packet receiver device 113 according to the comparative example. As shown in FIG. 3, the optical packet receiver device 113 comprises a first through nth optical/electrical converter units 150-1 through 150-n, first through nth frame memories 151-1 through 151-n, a header processing unit 152, a packet assembling unit 153, a packet identification unit 154, a MAC table 155, an output control unit 156, and an electrical/optical converter unit 158.
In the optical packet receiver device 113, 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 units 150-1 through 150-n, respectively. The header processing unit 152 extracts 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 λ1 so as to determine the normality of the packet signal.
The n pieces of packet signals output from the first through nth optical/electrical converter units 150-1 through 150-n are stored in the first through nth frame memories 151-1 through 151-n, respectively. The packet assembling unit 153 assembles a packet in reference to the packet information, the packet length, and the ECC error from the header processing unit 152. The packet identification unit 154 identifies an Ether packet from the output of the packet assembling unit 153 and extracts the Ether packet. In reference to the MAC table 155, the output control unit 156 replaces a destination MAC address in the Ether packet output from the packet identification unit 154 with a MAC address registered in the MAC table 155. The Ether packet is then input to the electrical/optical converter unit 158. The data format of an Ether signal input to the electrical/optical converter unit 158 is a MAC frame. The electrical/optical converter unit 158 converts the Ether packet into an optical signal and then output the optical signal to the client.
FIG. 4 shows the configuration of an optical packet switching device 112 according to the comparative example. As shown in FIG. 4, the optical packet switching device 112 comprises an optical switch unit 160, an optical switch control unit 161, a first input unit 162, a second input unit 163, a first input-side optical amplifier 166, a second input-side optical amplifier 167, a first demultiplexer 170, a second demultiplexer 171, a first optical delay line 172, a second optical delay line 173, a first output-side optical amplifier 168, a second output-side optical amplifier 169, a first output unit 164, and a second output unit 165. The optical switch control unit 161 comprises a first optical/electrical converter unit 174, a second optical/electrical converter unit 175, a first analyzer unit 176, a second analyzer unit 178, and an output competition determination unit 179.
The optical packet switching device 112 extracts 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 device 112 then determines an output destination based on the routing information header and switches the output destination by the optical switch unit 160.
Wavelength-multiplexed optical packet signals of n wavelengths are input to the first input unit 162 and the second input unit 163. The wavelengths of the optical packet signals input to the first input unit 162 are set to be λ1_1 through λ1—n, and the wavelengths of the optical packet signals input to the second input unit 163 are set to be λ2_1 through λ2—n. 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 in FIG. 2.
The optical packet signals that have been input are amplified by the first input-side optical amplifier 166 and second input-side optical amplifier 167 for optical level adjustment. Then, only optical packet signals of header wavelengths (in this case, λ1_1 and λ2_1) are optically branched by the first demultiplexer 170 and the second demultiplexer 171. The branched optical packet signals of wavelengths of λ11 and λ21 are input to the optical switch control unit 161. Meanwhile, wavelength-multiplexed optical packet signals are input to the optical switch unit 160 via the first optical delay line 172 and the second optical delay line 173.
The branched optical packet signals of the wavelengths of λ1_1 and λ2_1 are converted into electrical packet signals by the first optical/electrical converter unit 174 and the second optical/electrical converter unit 175, respectively. Then, routing information headers thereof are analyzed by the first analyzer unit 176 and the second analyzer unit 178 so as to detect destination information.
The output competition determination unit 179 determines 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 unit 160 based on the result of determination.
The first optical delay line 172 and the second optical delay line 173 delay the wavelength-multiplexed optical packet signals for a duration required for the optical switch control unit 161 to generate the optical switch control signal. By providing the first optical delay line 172 and the second optical delay line 173, on/off of the optical switch unit 160 can be controlled to be synchronized with the timing of arrival of the optical packet signals at the optical switch unit 160.
The optical switch unit 160 is a 2×2 optical switch and comprises first through fourth optical gate switches 180 through 183 and four optical couplers 184-187. The optical gate switches may be implemented by a semiconductor optical amplifier (SOA). The first through fourth optical gate switches 180 through 183 are controlled to be turned on or off by an optical switch control signal from the optical switch control unit 161. In the optical packet switching device 112, 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-5C illustrate output competition determination in the optical packet switching device 112. FIG. 5A shows an optical packet signal input to the first input unit 162. FIG. 5B shows an optical packet signal input to the second input unit 163. FIG. 5C shows an optical packet signal output from the first output unit 164. Optical packet signals 1-1, 1-2, and 2-1 that have been input are all directed to the first output unit 164 as an output destination.
As shown in FIG. 5, the optical packet signal 1-1 is first input to the first input unit 162, the optical packet signal 2-1 is then input to the second input unit 163, and the optical packet signal 1-2 is lastly input to the first input unit 162. Since the optical packet signal 1-1 is a signal that arrives first, the output competition determination unit 179 outputs the optical packet signal 1-1 to the first output unit 164. In other words, the output competition determination unit 179 turns on the optical gate switch 180 of the optical switch unit 160 and opens a path from the first input unit 162 to the first output unit 164 (other paths are closed).
However, the optical packet signal 2-1 input to the second input unit 163 temporally competes with the optical packet signal 1-1 input to the first input unit 162. In other words, the two optical packet signals concur in time. In this case, the output competition determination unit 179 discards the optical packet signal 2-1. In other words, the output competition determination unit 179 leaves off the optical gate switches 182 and 183 to which the optical packet signal 2-1 is input.
Although the optical packet signal 1-2 input to the first input unit 162 has an overlapping data portion with the optical packet signal 2-1, the output competition determination unit 179 outputs the optical packet signal 1-2 to the first output unit 164 since the optical packet signal 2-1 is 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, an optical packet signal received first is allowed to pass, and the following optical packet signal is discarded. In an optical packet switching system, an Ether signal is divided into optical packet signals of n wavelengths, and all the wavelengths are then routed at once. Thus, when data congestion occurs in even one wavelength, data on all the wavelengths will be discarded, increasing the probability of discarding optical packets. Thus, in an embodiment of the present invention described in the following, an optical packet switching system capable of reducing the probability of discarding optical packets is suggested.
FIG. 6 shows an optical packet switching system 10 according to the embodiment of the present invention. As shown in FIG. 6, the optical packet switching system 110 comprises an optical packet transmitter device 11, an optical packet switching device 12, an optical packet receiver device 13, a first AWG 14, a second AWG 15, a first optical amplifier 16, a second optical amplifier 17, and first through fourth optical transmission paths 18-21. The basic configuration of the optical packet switching system 10 is similar to that of the optical packet switching system 110 shown in FIG. 1. Thus, a detailed description is omitted.
FIG. 7 shows the configuration of the optical packet transmitter device 11 according to the embodiment. As shown in FIG. 7, the optical packet transmitter device 11 comprises an optical/electrical converter unit 30, a reception processing unit 32, a routing information extraction unit 33, a serial/parallel conversion unit 34, a frame memory 35, a transmission processing unit 36, a packet-length detection unit 37, a look-up table 38, a header generation unit 39, a setting unit 88, an association table 89, first through nth header insertion unit 40-1 through 40-n, and first through nth electrical/optical converter units 41-1 through 41-n. The optical packet transmitter device 11 functions as an Ether signal/optical packet converter device.
In the optical packet transmitter device 11, a 10 Gigabit Ethernet signal input from the client is converted into an electrical signal by the optical/electrical converter unit 30. 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 unit 32. The routing information extraction unit 33 then extracts routing information from the Ether signal. The routing information is converted into destination information by referring to the look-up table 38 and then input to the header generation unit 39. The packet-length detection unit 37 extracts the packet length of the received Ether signal and then outputs the extracted packet length to the header generation unit 39. In the present embodiment, the packet-length detection unit 37 outputs the packet length also to the setting unit 88.
According to the packet length, the setting unit 88 sets a number of divisions by which a received Ether signal is to be divided and a wavelength used for an optical packet signal to be transmitted. More specifically, when the packet length is less than a predetermined reference packet length, the setting unit 88 sets the number of divisions and the corresponding number of wavelengths in use to a first predetermined value m and sets the wavelengths in use to a predetermined first wavelength group (wavelengths λ1 through λm). When the packet length is at least the reference packet length, the setting unit 88 sets the number of divisions and the corresponding number of wavelengths in use to a second predetermined value n−m and sets the wavelengths in use to a predetermined second wavelength group (wavelengths λm+1 through λn). The notation n represents the maximum number of wavelengths that can be used, and the notation m represents an integer of at least 2 that satisfies m<n−m. The first wavelength group and the second wavelength group are set such that the groups have different wavelength allocation, in other words, such that no wavelength is overlapped.
FIG. 8 shows an example of wavelength allocation. In FIG. 8, the reference packet length is 1519 bytes, the maximum wavelength number n is 40, the first predetermined value m is 10, and the second predetermined value n−m is 30. As shown in FIG. 8, when the packet length of an Ether signal is less than 1519 bytes (64-1518 bytes), the setting unit 88 sets the number of divisions and the number of wavelengths in use to be 10 and sets the wavelengths in use to the first wavelength group (wavelengths λ1 through λ10). When the packet length of the Ether signal is at least 1519 bytes (1519-9600 bytes), the setting unit 88 sets the number of divisions and the number of wavelengths in use to be 30 and sets the wavelengths in use to the second wavelength group (wavelengths λ11 through λ40). In a 10 Gigabit Ethernet signal, etc., a packet of up to 1518 bytes is referred to as a “normal packet,” and a packet that is larger than this is referred to as a “jumbo packet.” In other words, the number of divisions and the number of wavelengths in use are made smaller in the case of a normal packet, and the number of divisions and the number of wavelengths in use are made larger in the case of a jumbo packet.
A table associating a packet length and a wavelength group with each other as described above is described in the association table 89. When a packet length is input, the setting unit 88 sets a wavelength group to be used, in reference to the association table 89.
The header generation unit 39 collects a packet length, destination information, a local node ID, and a wavelength in use so as to generate a routing information header.
The Ether signal output from the routing information extraction unit 33 is converted into a parallel signal by the serial/parallel conversion unit 134 and then stored in the frame memory 35. The transmission processing unit 36 then divides an Ether signal according to the number of divisions set by the setting unit 88 and generates a plurality of packet signals. In other words, the Ether signal is equally divided by m when the Ether signal is a normal packet, and the Ether signal is equally divided by n−m when the Ether signal is a jumbo packet.
When the Ether signal is a normal packet, packet signals divided into m pieces are input to first through mth header insertion unit 40-1 through 40-m, respectively. The first header insertion unit 40-1 inserts, in the input packet signal, a routing information header generated by the header generation unit 39. The second through mth header insertion unit 40-2 through 40-m insert a dummy header in the input packet signals. First through mth electrical/optical converter unit 41-1 through 41-m respectively convert the packets signals from the first through mth header insertion unit 40-1 through 40-m into optical signals and transmit optical packet signals at wavelengths λ1 through λm. The header wavelength is λ1 in this case.
Meanwhile, when the Ether signal is a normal packet, packet signals divided into n−m pieces are input to (m+1)th through nth header insertion unit 40-m+1 through 40-n, respectively. The (m+1)th header insertion unit 40-m+1 inserts, in the input packet signal, a routing information header generated by the header generation unit 39. The (m+2)th through nth header insertion unit 40-m+2 through 40-n insert a dummy header in the input packet signals. (m+1)th through nth electrical/optical converter unit 41-m+1 through 41-n respectively convert the packets signals from the (m+1)th through nth header insertion unit 40-m+1 through 40-n into optical signals and transmit optical packet signals at wavelengths λm+1 through λn. The header wavelength is λm+1 in this case.
In the present embodiment, header wavelengths are set to be the wavelengths of λ1 and λm+1. However, a header wavelength can be appropriately modified. In FIG. 7, dashed arrows are drawn that are directed from the header generation unit 39 to header insertion units other than the first header insertion unit 40-1 and the (m+1) the header insertion unit 40-m+1, in order to indicate that the header wavelength can be modified.
FIG. 9 shows the configuration of the optical packet receiver device 13 according to the embodiment. As shown in FIG. 9, the optical packet receiver device 13 comprises a first through nth optical/electrical converter units 50-1 through 50-n, first through nth frame memories 51-1 through 51-n, a header processing unit 52, a packet assembling unit 53, a packet identification unit 54, a MAC table 55, an output control unit 56, and an electrical/optical converter unit 58. The optical packet receiver device 13 functions as an optical packet/Ether signal converter device.
In the optical packet receiver device 13, optical packet signals at wavelengths λ1 through λm whose original Ether signal is a normal packet are input to first through mth optical/electrical converter units 50-1 through 50-m and converted into electrical packet signals. Meanwhile, optical packet signals at wavelengths m+1 through λn whose original Ether signal is a jumbo packet are input to (m+1)th through nth optical/electrical converter units 50-m+1 through 50-n and converted into electrical packet signals.
The header processing unit 52 extracts 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 λ1 or λm+1 and transmits these to the packet assembling unit 53.
The packet signals output from the first through nth optical/electrical converter units 50-1 through 50-n are stored in the first through nth frame memories 51-1 through 51-n, respectively. The packet assembling unit 53 assembles a packet in reference to the wavelength in use, the packet information, the packet length, and the ECC error from the header processing unit 52. The packet identification unit 54 identifies an Ether packet from the output of the packet assembling unit 53 and extracts the Ether packet. The packet identification unit 54 performs packet anomaly detection by reading a FCS (Frame Check Sequence), which is a CRC (Cyclic Redundancy Check) 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 reference to the MAC table 55, the output control unit 56 replaces a destination MAC address in the Ether packet output from the packet identification unit 54 with a MAC address registered in the MAC table 55. The Ether packet is then input to the electrical/optical converter unit 58. The data format of the Ether signal input to the electrical/optical converter unit 58 is a MAC frame. The electrical/optical converter unit 58 converts the Ether packet into an optical signal and then output the optical signal to the client.
FIG. 10 shows the configuration of the optical packet switching device 12 according to the embodiment. As shown in FIG. 10, the optical packet switching device 12 comprises an optical switch unit 60, an optical switch control unit 61, a first input unit 62, a second input unit 163, a first input-side optical amplifier 66, a second input-side optical amplifier 67, a first demultiplexer 70, a second demultiplexer 71, a third demultiplexer 90, a fourth demultiplexer 91, a first optical delay line 72, a second optical delay line 73, a first output-side optical amplifier 68, a second output-side optical amplifier 69, a first output unit 64, and a second output unit 65. The optical switch control unit 61 comprises a first optical/electrical converter unit 74, a second optical/electrical converter unit 75, a third optical/electrical converter unit 92, a fourth optical/electrical converter unit 93, a first analyzer unit 76, a second analyzer unit 78, a third analyzer unit 94, a fourth analyzer unit 95, and an output competition determination unit 79.
The optical packet switching device 12 extracts 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 device 12 then determines an output destination based on the routing information header and switches the output destination by the optical switch unit 60.
Wavelength-multiplexed optical packet signals are input to the first input unit 62 and the second input unit 63. The wavelengths of the optical packet signals input to the first input unit 62 are set to be λ1_1 through λ1—n (λ1_1 through λ1—m (the first wavelength group) in the case when the original Ether signal is a normal packet and λ1—m+1 through λ1—n (the second wavelength group) in the case when the original Ether signal is a jumbo packet). The wavelengths of the optical packet signals input to the second input unit 63 are set to be λ2_1 through λ2—n (λ2_1 through λ2—m (the first wavelength group) in the case when the original Ether signal is a normal packet and λ2—m+1 through λ2—n (the second wavelength group) in the case when the original Ether signal is a jumbo packet). 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 in FIG. 7.
When wavelength-multiplexed optical packet signals at the wavelengths λ1_1 through λ1—m and λ2_1 through λ2—m (the original Ether signal is a normal packet) are input to the first input-side optical amplifier 66 and the second input-side optical amplifier 67, the optical packet signals are amplified by the first input-side optical amplifier 66 and second input-side optical amplifier 67 for optical level adjustment. Then, only optical packet signals of header wavelengths of λ1_1 and λ2_1 are optically branched by the first demultiplexer 70 and the second demultiplexer 71. The branched optical packet signals of the wavelengths of λ1_1 and λ2_1 are input to the optical switch control unit 61. Then, the optical packet signals of the wavelengths of λ1_1 and λ2_1 are converted into electrical packet signals by the first optical/electrical converter unit 74 and the second optical/electrical converter unit 75, respectively. Then, routing information headers thereof are analyzed by the first analyzer unit 76 and the second analyzer unit 78 so as to detect destination information and information of wavelength in use. Meanwhile, wavelength-multiplexed optical packet signals passed through the first demultiplexer 70 and the second demultiplexer 71 are input to the optical switch unit 60 via the first optical delay line 72 and the second optical delay line 73.
When wavelength-multiplexed optical packet signals at the wavelengths λ1—m+1 through λ1—n and λ2—m+1 through λ2—n (the original Ether signal is a jumbo packet) are input to the first input-side optical amplifier 66 and the second input-side optical amplifier 67, the optical packet signals are amplified by the first input-side optical amplifier 66 and second input-side optical amplifier 67. Then, only optical packet signals of header wavelengths of λ1—m+1 and λ2—m+1 are optically branched by the third demultiplexer 90 and the fourth demultiplexer 91. The branched optical packet signals of the wavelengths of λ1—m+1 and λ2—m+1 are input to the optical switch control unit 61. Then, the optical packet signals of the wavelengths of λ1—m+1 and λ2—m+1 are converted into electrical packet signals by the third optical/electrical converter unit 92 and the fourth optical/electrical converter unit 93, respectively. Then, routing information headers thereof are analyzed by the third analyzer unit 94 and the fourth analyzer unit 95 so as to detect destination information and information of wavelength in use. Meanwhile, wavelength-multiplexed optical packet signals passed through the third demultiplexer 90 and the fourth demultiplexer 91 are input to the optical switch unit 60 via the first optical delay line 72 and the second optical delay line 73.
Based on the destination information detected by the analyzer units, the output competition determination unit 79 checks for temporal competition of the wavelength-multiplexed optical packet signals input to the first input-side optical amplifier 66 and the second input-side optical amplifier 67, and when competition has occurred, the output competition determination unit 79 determines whether the wavelength-multiplexed optical packet signals should be transmitted or discarded based on the information of the wavelength in use. The output competition determination unit 79 then outputs an optical switch control signal to the optical switch unit 60 based on the result of determination.
The first optical delay line 72 and the second optical delay line 73 delay the wavelength-multiplexed optical packet signals for a duration required for the optical switch control unit 61 to generate the optical switch control signal. By providing the first optical delay line 72 and the second optical delay line 73, on/off of the optical switch unit 60 can be controlled to be synchronized with the timing of arrival of the optical packet signals at the optical switch unit 60.
The optical switch unit 60 is a 2×2 optical switch and comprises first through fourth optical gate switches 80 through 83 and four optical couplers 84-87. The optical gate switches may be implemented by a semiconductor optical amplifier (SOA). The first through fourth optical gate switches 80 through 83 are controlled to be turned on or off by an optical switch control signal from the optical switch control unit 61.
FIGS. 11A-11C illustrate output competition determination in the optical packet switching device 12. FIG. 11A shows an optical packet signal 96 input to the first input unit 62. FIG. 11B shows an optical packet signal 97 input to the second input unit 63. FIG. 11C shows an optical packet signal output from the first output unit 64. Optical packet signals 96 and 97 that have been input are all directed to the first output unit 64 as an output destination.
As shown in FIG. 11, the optical packet signal 96 is first input to the first input unit 62 and the optical packet signal 97 is then input to the second input unit 63. Since the optical packet signal 96 is a signal that arrives first, the output competition determination unit 79 outputs the optical packet signal 96 to the first output unit 64.
As shown in FIG. 11, the optical packet signal 97 input to the second input unit 63 after the optical packet signal 96 temporally competes with the optical packet signal 96. This temporal competition can be determined based on the detected destination information. In the present embodiment, even when there is temporal competition in the optical packet signals 96 and 97, the output competition determination unit outputs both the optical packet signals 96 and 97 to the first output unit 64 if no competition has occurred with regard to wavelengths. The optical packet signal 96 is a wavelength-multiplexed optical packet signal of the first wavelength group (λ1_1 through λ1—m), and the optical packet signal 97 is a wavelength-multiplexed optical packet signal of the second wavelength group (λ2—m+1 through λ2—n). Therefore, the optical packet signals 96 and 97 do not compete with each other with regard to wavelengths, and it is possible for these signals to coexist even when they are multiplexed. The optical packet signal 97 is an optical packet signal to be discarded in the above comparative example. If the wavelengths in use of the optical packet signals 96 and 97 compete (the wavelengths overlap), a process if performed where the optical packet signal input first is allowed to pass and where the following optical packet is discarded.
As described, even when there is temporal competition in a plurality of optical packet signals, the optical packet signals, which are to be discarded in the above-described comparative example, can be transmitted by allowing the optical packet signals to be transmitted to a same output destination if no competition has occurred regarding wavelengths, according to the present embodiment. As a result, the probability of discarding optical packets can be reduced.
Two output routes, network output and client output, can be possible as basic output routes in an optical packet switching device. As shown in FIG. 11, when signals are output to a network, the signals are transmitted to a same output route even when the signals have been input at the same timing, if there is no wavelength competition. However, when signals are output to a client, different optical packet signals can be input to an optical packet/Ether signal converter device at the same timing, and it is thus necessary to avoid competition at the time of Ether signal conversion in the optical packet/Ether signal converter device.
There are two possible methods for avoiding competition. One method is to check the input timing of the header wavelength of each optical packet signal so as to give priority to an optical packet signal that has been input at an earlier timing and discard the following optical packet signal. Another method is to perform, when two input optical signals are input at the same timing, have no wavelength competition, and are directed to the client, only output competition determination without performing wavelength competition determination so as to output to a client an optical packet that has been input at an earlier timing in an optical packet switching device. In the above two methods, an optical packet signal that is input at an earlier timing is given priority for transmission. If there is enough space in frame memory units for respective optical packet signals in an optical packet/Ether signal converter device, a method is also possible where two input optical packet signals are stored in respective frame memory units so as to convert the signals into Ether signal in the order of the input timing.
FIG. 12 shows another example of wavelength allocation. In an actual optical packet switching system, a plurality of optical packet transmitter devices, optical packet switching devices, and optical packet receiver devices are provided as nodes, forming a network. In such an optical packet switching system comprising a plurality of nodes, wavelength allocation of a first wavelength group may be changed on a node-by-node basis. In other words, a wavelength used when an Ether signal is a normal packet is changed on a node-by-node basis.
FIG. 12 shows that, when a node number and the maximum number of wavelengths are set to be 4 and 40, respectively, a first wavelength group (λ1 through λ10) is used for transmitting a normal packet at a first node, a second wavelength group (λ11 through λ20) is used for transmitting a normal packet at a second node, a third wavelength group (λ21 through λ30) is used for transmitting a normal packet at a third node, and a fourth wavelength group (λ31 through λ40) is used for transmitting a normal packet at a fourth node.
Changing wavelength allocation on a node-by-node basis that is used when the packet length of an Ether signal is that of a normal packet as described above allows for reduction of the probability of discarding normal packets due to competition in an optical packet switching device. In other words, for example, even when an optical packet signal (first wavelength group) from the first node and an optical packet signal (second wavelength group) from the second node temporally compete in the optical packet switching device, there is no competition with regard to the wavelength since the wavelength groups being used are different, and the optical packet signals thus can be transmitted to a same output destination without discarding one of the optical packet signals. This is particularly advantageous when Ether signals used on a network are mostly normal packets.
FIG. 13 shows an example of a bit configuration for transmitting information of wavelength in use. In this example, information in units of one bit is added to all WDM wavelengths as shown in FIG. 13. If the maximum number of WDM wavelengths is 40, 40 bits are necessary. The bit of a wavelength in use is set to be “1”, and the bit of a wavelength not in use is set to be “0”. Adding such information of a wavelength in use to a header allows the information of a wavelength in use to be transmitted to an optical packet switching device and an optical packet receiver device.
FIG. 14 shows another example of a bit configuration for transmitting information of a wavelength in use. In this example, the number of wavelength groups are fixed, and the number of bits corresponding to the number of the wavelength groups is prepared. As shown in FIG. 14, if the number of wavelength groups is set to be 8, information of a wavelength in use can be transmitted in 3 bits. A table associating the name of a group with wavelengths that belong to the group is stored in a memory in each device.
FIG. 15 shows an example of a table associating a group with wavelength composition. Using a table such as the one shown in FIG. 15 allows for reduction of the number of bits for transmitting information of a wavelength in use. If there are 8 wavelength groups, it is possible to identify a wavelength in use by using information of 3 bits.
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.

## Claims

1. An optical packet switching system comprising:
an optical packet transmitter device including a packet-length detection unit configured to detect the packet length of a received client signal,
a setting unit configured to set, according to the packet length, a number of divisions by which the client signal is divided and a wavelength used for an optical packet signal to be transmitted,
a header generation unit configured to generate a header containing information of a wavelength in use and destination information of the client signal,
a transmission processing unit configured to divide the client signal according to the set number of divisions and generate a plurality of packet signals,
a header insertion unit configured to insert the generated header in at least one packet signal, and
an electrical/optical converter unit configured to convert the plurality of packet signals into optical packet signals of a plurality of wavelengths according to the set wavelength in use; and
an optical packet switching device including a plurality of receiver units configured to receive optical packet signals in which the optical packet signals of a plurality of wavelengths are wavelength-multiplexed,
a branching unit configured to branch the received wavelength-multiplexed optical packet signals into optical packet signals of wavelengths with the header,
an optical switch unit configured to route the wavelength-multiplexed optical packet signals,
an analyzer unit configured to analyze the header of the branched optical packet signals so as to detect the destination information and the information of the wavelength in use, and
an output competition determination unit configured to check for temporal competition of the plurality of wavelength-multiplexed optical packet signals input to the plurality of receiver units based on the destination information and to determine whether the wavelength-multiplexed optical packet signals should be transmitted or discarded based on the information of the wavelength in use when there is competition.

2. The optical packet switching system according to claim 1, wherein, even when there is temporal competition in the plurality of optical packet signals, the output competition determination unit allows the plurality of wavelength-multiplexed optical packet signals to be transmitted altogether if no competition has occurred with regard to wavelengths.

3. The optical packet switching system according to claim 1, wherein the setting unit sets the number of divisions by which the client signal is divided and the corresponding number of wavelengths in use to a first predetermined value and sets the wavelengths in use to be a predetermined first wavelength group when the packet length is less than a predetermined length, and wherein the setting unit sets the number of divisions and the number of wavelengths in use to be a second predetermined value, which is larger than the first predetermined value, and sets the wavelengths in use to a predetermined second wavelength group when the packet length is at least the predetermined length.

4. The optical packet switching system according to claim 3, wherein the first wavelength group and the second wavelength group have different wavelength allocation.

5. The optical packet switching system according to claim 3 comprising a plurality of the optical packet transmitter devices as nodes, wherein
the wavelength allocation of the first wavelength group is different on a node-by-node basis.

6. The optical packet switching system according to claim 1 further comprising a table associating a packet length and a wavelength group.

7. An optical packet switching device comprising:
a plurality of receiver units configured to receive optical packet signals in which the optical packet signals of a plurality of wavelengths are wavelength-multiplexed, the optical packet signals having destination information and information of a wavelength in use;
a branching unit configured to branch the received wavelength-multiplexed optical packet signals into optical packet signals of wavelengths with the header;
an optical switch unit configured to route the wavelength-multiplexed optical packet signals;
an analyzer unit configured to analyze the header of the branched optical packet signals so as to detect the destination information and the information of the wavelength in use; and
an output competition determination unit configured to check for temporal competition of the plurality of wavelength-multiplexed optical packet signals input to the plurality of receiver units based on the destination information and to determine whether the wavelength-multiplexed optical packet signals should be transmitted or discarded based on the information of the wavelength in use when there is competition.

8. The optical packet switching device according to claim 7, wherein, even when there is temporal competition in the plurality of optical packet signals, the output competition determination unit allows the plurality of wavelength-multiplexed optical packet signals to be transmitted altogether if no competition has occurred with regard to wavelengths.

9. An optical packet transmitter device for use in an optical packet switching system comprising:
a packet-length detection unit configured to detect the packet length of a received client signal;
a setting unit configured to set, according to the packet length, a number of divisions by which the client signal is divided and a wavelength used for an optical packet signal to be transmitted;
a header generation unit configured to generate a header containing information of a wavelength in use and destination information of the client signal;
a transmission processing unit configured to divide the client signal according to the set number of divisions and generate a plurality of packet signals;
a header insertion unit configured to insert the generated header in at least one packet signal; and
an electrical/optical converter unit configured to convert the plurality of packet signals into optical packet signals of a plurality of wavelengths according to the set wavelength in use.

10. The optical packet transmitter device according to claim 9, wherein the setting unit sets the number of divisions by which the client signal is divided and the corresponding number of wavelengths in use to a first predetermined value and sets the wavelengths in use to be a predetermined first wavelength group when the packet length is less than a predetermined length, and wherein the setting unit sets the number of divisions and the number of wavelengths in use to be a second predetermined value, which is larger than the first predetermined value, and sets the wavelengths in use to a predetermined second wavelength group when the packet length is at least the predetermined length.

11. The optical packet transmitter device according to claim 10, wherein the first wavelength group and the second wavelength group have different wavelength allocation.