JP3545632B2 - Optical packet signal transfer method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical packet signal transfer method for transferring an optical packet signal from one node to another node.
[0002]
[Prior art]
Conventionally, a packet signal transfer method is known as a method for efficiently transmitting Internet information and data information.
[0003]
As shown in FIG. 1, in a packet transfer network, a packet signal transmitted from one node (source node) 1 reaches another node (reception node) 3 via a plurality of transfer nodes 2. In each transfer node 2, an output path is set for the transmitted packet signal in accordance with the destination, and the packet signal is transmitted toward the next transfer node 2 (note that the expressions of the transmission node, the reception node, and the transfer node are: It merely indicates the role of a certain packet signal, and in fact, any node can be a transmitting node, a receiving node, or a forwarding node.)
[0004]
In such a signal transfer method, the problem is to transfer the packet signal to the receiving node without causing collision between the packet signals.
[0005]
If each node arbitrarily transmits a packet signal, a packet signal to be transmitted to a certain output path may arrive at the same time from a plurality of different input paths and collide at the transfer node. When such a collision occurs, a packet signal must be discarded, and the packet signal cannot reach the receiving node.
[0006]
Therefore, conventionally, in order to avoid collision between packets, the packet transmission time is adjusted between the transfer nodes, and when a plurality of packets arrive at the same time, one packet is made to wait in the buffer memory, and the output path becomes empty. In such a case, a method of sending the message when it has been used has been used.
[0007]
When adjustment is performed between the transfer nodes, for example, as shown in FIG. 2, a central control unit 4 for managing the entire network is prepared. Then, based on transmission requests from a plurality of transmission nodes, the transmission node transmits a packet signal after scheduling so that a collision of the packet signal does not occur in the transmission node.
[0008]
FIG. 3 shows a configuration of a node for transferring an optical packet signal in a conventional wavelength division multiplexing system in which collision of packet signals is prevented by using a buffer memory.
[0009]
Usually, in a wavelength multiplex system, the wavelength of each optical packet signal is predetermined. Therefore, a collision occurs when an optical packet to be transmitted at a certain wavelength on a certain output path arrives simultaneously from a plurality of different input paths. In order to avoid this, a procedure is adopted in which the arriving packet signals are made to wait in a temporary buffer memory, and are sequentially transmitted when a predetermined output path and wavelength become free. For that purpose, a buffer memory is required, and an optical memory for storing optical signals as light has been proposed (Japanese Patent Laid-Open No. 6-169478), but is not very practical at present.
[0010]
Therefore, as shown in FIG. 3, the transferred optical packet signal is demultiplexed by the demultiplexer 11 and is once converted into an electric signal by the optical-electrical (O / E) converter 12, respectively. After switching (path switching) and buffering (temporary storage) are performed in the unit 13 and the electrical buffer memory 14 under the control of the control unit 15, the electrical-optical (E / O conversion) converter 16 converts the optical signal again into an optical signal. However, the signal is multiplexed by the multiplexer 17 and transmitted to the output path.
[0011]
[Problems to be solved by the invention]
However, these means for avoiding collisions cause transfer delays.
[0012]
That is, when performing adjustment between transfer nodes, each transmission node exchanges control signals with the central control unit, and transmits a packet signal after transmission is OK, so that it takes time to start transmission. When the network scale is large, the load on the central control unit is large.
[0013]
In addition, when a buffer memory is used, a time for controlling which signal is transmitted first and which signal is made to wait, and a signal waiting time are required. Further, a circuit for temporarily converting an optical signal into an electric signal and then converting the signal into an optical signal again is required.
[0014]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical packet signal transfer method that can be used for transmitting a signal requiring a short time such as a telephone call or a TV conference, which has a short transfer delay time.
[0015]
[Means for Solving the Problems]
According to the present invention, in order to achieve the above object, in an optical packet signal transfer method for transferring a wavelength-multiplexed optical packet signal via a transfer node, the transmitted optical packet signal is demultiplexed at the transfer node for each wavelength. An optical packet signal transfer method for sequentially converting the wavelength of the demultiplexed optical packet signal to a preset wavelength in the order of arrival at the node and transmitting the wavelength to the next transmission path. The means for wavelength-converting the packet signal and sending it to the next transmission path has N × M (where N: number of wavelength multiplexing, M: number of output transmission paths) output terminals, An optical space switch that switches and outputs a signal to an arbitrary output terminal, a wavelength conversion unit that converts a wavelength of output light from each of the output terminals into one of a plurality of different wavelengths to be multiplexed, and the wavelength conversion unit from Multiplexing means for multiplexing N-waves of power light and sending them to M output transmission paths, respectively, and wavelength conversion for converting the demultiplexed optical packet signal to a desired wavelength corresponding to a desired output transmission path Control means for controlling the optical space switch so as to output to the output terminal to which the means is connected .
[0016]
According to the above configuration, the optical packet signal is immediately sent to the next node without being written into the buffer memory, and no coordination between nodes is required. Only by increasing the size, it is possible to realize transfer with little collision and extremely short delay time.
[0017]
Further, in the present invention, in order to achieve the above object, in an optical packet signal transfer system for transferring a wavelength-multiplexed optical packet signal via a transfer node, in the transfer node, the transmitted optical packet signal is transmitted for each wavelength. This is an optical packet signal transfer system in which a demultiplexed optical packet signal is wavelength-converted to a preset and idle wavelength in the order of arrival at the node and transmitted to the next transmission path. Means for wavelength-converting the demultiplexed optical packet signal and sending it to the next transmission path has N × M (where N: the number of wavelength multiplexing, M: the number of output transmission paths) output terminals. An optical space switch that switches and outputs a demultiplexed optical packet signal to an arbitrary output terminal, and a wavelength converter that converts a wavelength of output light from each of the output terminals to one of a plurality of different wavelengths to be multiplexed. Means Multiplexing means for multiplexing the output light from the wavelength converting means for each N wave and sending the multiplexed light to each of the M output transmission paths, and combining the demultiplexed optical packet signal with a desired output transmission path to a desired output transmission path. Control means for controlling the optical space switch so as to output to a connected output terminal a wavelength conversion means for converting the wavelength into a wavelength .
[0018]
According to the above configuration, the multiplexed wavelength can be used effectively, and the packet discard rate due to collision can be further reduced.
[0019]
Further, in the present invention, in order to achieve the above object, in an optical packet signal transfer system for transferring a wavelength-multiplexed optical packet signal via a transfer node, in the transfer node, the transmitted optical packet signal is transmitted for each wavelength. This is an optical packet signal transfer system in which a demultiplexed optical packet signal is wavelength-converted to a preset and idle wavelength in the order of arrival at the node and transmitted to the next transmission path. The wavelength in the idle state is searched from a plurality of different conversion wavelengths assigned in advance in advance in the order from the wavelength next to the wavelength assigned to the optical packet signal arriving immediately before the corresponding optical packet signal. It is characterized by the following .

[0020]
As means for wavelength-converting the above-mentioned demultiplexed optical packet signal and sending it to the next transmission path, N × M (N: number of wavelength multiplexing, M: number of output transmission paths) output terminals An optical space switch for switching and outputting a demultiplexed optical packet signal to an arbitrary output terminal, and converting a wavelength of output light from each of the output terminals into one of a plurality of different wavelengths to be multiplexed. Wavelength converting means, multiplexing means for multiplexing the output light from the wavelength converting means by N waves and sending the multiplexed light to each of M output transmission paths, and transmitting the demultiplexed optical packet signal to a desired output signal. Control means for controlling the optical space switch so as to output to the output terminal connected to the wavelength conversion means for converting to a desired wavelength corresponding to the path.
[0021]
Further, the wavelength converting means may have a signal reproducing function, and a plurality of output paths may be connected to one transfer node.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
[0023]
Embodiment 1
The present invention is directed to an optical packet signal, and furthermore, each signal is transmitted between nodes at different wavelengths by a wavelength division multiplexing transmission system. It is assumed that destination information is added to the packet signal.
[0024]
As means for adding the destination information, (1) writing in a header portion of a packet signal, (2) using a subcarrier signal, (3) transmitting a header packet prior to a signal packet, and the like are possible. When a header packet is used, the same wavelength as the main signal may be used, or a wavelength for transferring the header packet may be set.
[0025]
Each node arbitrarily transmits an optical packet signal without performing coordination between the nodes. The optical packet signal arriving at the transfer node is sorted for each wavelength and sent to an output path corresponding to each destination. The output path may correspond to the next transfer node on a one-to-one basis, or a plurality of output paths may be connected to one transfer node (a plurality of output paths are connected to one transfer node). In this case, the transfer capacity to the next node can be increased.)
[0026]
Here, since no adjustment is made between the nodes, a plurality of packets destined for a certain output path may arrive at the transfer node at the same time at the same wavelength from different input paths. Even in such a case, in order to transmit the packet without causing a collision, the present invention buffers the packet signal on the wavelength axis.
[0027]
The details will be described below with reference to FIGS.
[0028]
FIG. 4 shows an example of a transfer node according to the present invention. Here, a configuration in a case where a main signal and a control signal (destination information) have the same wavelength is shown.
[0029]
In FIG. 4, reference numeral 21 denotes a wavelength demultiplexer that demultiplexes an optical packet signal reaching a node for each wavelength. An optical space switch 22 includes N × M output terminals O ₁₁ , O ₁₂ , O ₁₃ , O ₁₄ , O ₂₁ , and O ₂₂ (where N is the number of multiplexed wavelengths and M is the number of output transmission paths). , O ₂₃ , O ₂₄ ,... (Where the first digit corresponds to a conversion wavelength described later and the second digit corresponds to an output transmission path). The output optical packet signal is switched to an arbitrary output terminal and output.
[0030]
Reference numeral 23 denotes a wavelength converter connected to each output terminal of the optical space switch 22. The wavelength converter 23 multiplexes a plurality of different wavelengths for multiplexing the wavelength of the output light from each output terminal, here, λ1, λ2, λ3, is fixedly converted to one of λ4. Numeral 24 denotes an optical multiplexer for multiplexing the wavelength-converted output lights N by N and sending them out to M output transmission paths I, II,....
[0031]
Reference numeral 25 denotes a detector that splits a part of the demultiplexed optical packet signal and extracts the destination information of the packet signal from the header portion. Reference numeral 26 denotes a control unit which determines an output transmission path and an output wavelength based on the destination information, and converts a demultiplexed optical packet signal into a desired wavelength corresponding to a desired output transmission path. The optical space switch 22 is controlled so as to output to the output terminal of the optical space switch 22 to which the device 23 is connected.
[0032]
FIG. 5 shows another example of the transfer node according to the present invention. Here, a configuration in which wavelengths are separately set for a main signal and a control signal is shown.
[0033]
In FIG. 5, reference numeral 31 denotes a wavelength demultiplexer that demultiplexes an optical packet signal reaching a node for each wavelength. Reference numeral 32 denotes an optical space switch, which is composed of N × M (where N: the number of wavelength multiplexes, M: the number of output transmission paths) output terminals O ₁₁ , O ₁₂ , O ₁₃ , O ₂₁ , O ₂₂ , and O _23. ,... (Where the first digit corresponds to the converted wavelength described later, and the second digit corresponds to the output transmission path). Switch to any output terminal and output.
[0034]
Reference numeral 33 denotes a wavelength converter connected to each output terminal of the optical space switch 32. The wavelength converter 33 multiplexes the wavelength of the output light from each output terminal into a plurality of different wavelengths to be multiplexed, here, λ1, λ2, λ3. Fixedly convert to one. Numeral 34 multiplexes the wavelength-converted output light N by N, and multiplexes a control signal light of a predetermined wavelength (λc) to M output transmission paths I, II,. These are optical multiplexers to be transmitted.
[0035]
Reference numeral 35 denotes a detector that converts the wavelength component of the control signal in the demultiplexed optical signal into an electric signal as it is and extracts the destination information of the arriving packet signal. Reference numeral 36 denotes a control unit which determines an output transmission path and an output wavelength based on the destination information, and converts a demultiplexed optical packet signal into a desired wavelength corresponding to a desired output transmission path. The optical space switch 32 is controlled to output to the output terminal of the optical space switch 32 to which the device 33 is connected, and the destination information for the next node is transmitted.
[0036]
Reference numeral 37 denotes a transmitter that converts destination information from the control unit 36 into a control signal light having a predetermined wavelength (λc) and outputs the control signal light.
[0037]
Next, a switching procedure in the device will be described.
[0038]
For example, consider a packet going to output path I. A plurality of output terminals (O ₁₁ , O ₁₂ , O ₁₃ , O _{14 in} the case of FIG. 4) are provided for the output path I, and the wavelength converters 23 of the conversion wavelengths λ1, λ2, λ3, λ4 are provided respectively. Is connected. In the optical space switch 22, as shown in FIG. 6, it outputs the arrived packet in the order of arrival terminal _{O 11, O 12, O 13} , and sequentially outputs to the _{O 14.} The output packets are converted into corresponding wavelengths, multiplexed, and transmitted to the output path I.
[0039]
When the control signal wavelength is set separately as in the case of FIG. 5, the destination information of the output packet is placed on the control signal wavelength and sent out to the transmission path together with the main signal.
[0040]
It takes some time for the detector, the control unit, and the like to read the destination information of the packet, determine the output path / output wavelength based on the information, and operate the optical space switch. The main signal needs to be input to the optical space switches 22 and 32 in accordance with these processing times. 4 and 5, optical delay lines 27 and 38 are inserted in front of the optical space switch in order to match the input timing of the main signal.
[0041]
In the above configuration / procedure, if the number of wavelengths is somewhat larger than the average number of packets arriving toward one output path, packets are transferred without causing a collision.
[0042]
For example, assume that the probabilities of the number of arriving packets are distributed around a certain average value as shown in FIG. On the other hand, a number of wavelength multiplexed lights that are somewhat larger than the average value are prepared. Then, at a certain time, since the number of arriving packets is smaller than the number of wavelengths, the arriving packets are transmitted to the output path without collision. However, with a certain probability, the number of arriving packets> the number of wavelengths occurs (the hatched portion in FIG. 7), and in this case, the packets must be discarded.
[0043]
The packet loss rate is determined by system conditions (number of nodes, packet transmission probability, etc.) and the number of wavelengths. In the above description, the case where the number of multiplexed wavelengths is 4 has been exemplified. However, if the number of wavelengths is increased according to the system conditions, the packet discard rate can be set to a sufficiently small value.
[0044]
In the above description, a wavelength converter is simply connected to the output terminal of the optical space switch. However, a wavelength converter having a signal regeneration (waveform regeneration) function is known. I have. If such a wavelength conversion / signal regenerator is used, a larger-scale optical packet signal transfer network can be realized. In a very simple manner, a method of temporarily converting an optical signal into an electric signal, reproducing the signal in an electric stage, and then converting the signal into an optical signal having a predetermined wavelength may be used.
[0045]
Embodiment 2
In the first embodiment, when the lengths of the packets being transferred are substantially the same, the occupation states of the wavelengths of the output paths are vacant sequentially in the order of wavelength. Therefore, the switching may be performed so that the converted wavelengths are sequentially assigned in the order of arrival of the optical packet signals. However, when packets of various lengths are mixed, the packets are not always empty in the order of wavelength.
[0046]
For example, as shown in FIG. 8, since the packet 1 is long, the wavelength λ2 may become empty before the wavelength λ1. It is assumed that the packet 5 arrives there at the timing of FIG. According to the procedure of the first embodiment, the conversion wavelength of the packet 5 is λ1, and in this case, collision with the packet 1 occurs. On the other hand, since the wavelength λ2 is empty, collision can be avoided if the converted wavelength of the packet 5 is set to λ2.
[0047]
Therefore, in the second embodiment, it is assumed that the destination information of the packet also includes information on the packet length, and the control unit of the transfer node recognizes which conversion wavelength is occupied in the output path. . Basically, switching is performed so that wavelengths are allocated sequentially in the order of arrival of packets. If the converted wavelength is occupied, the wavelength is allocated to the next converted wavelength. Further, if the converted wavelength is occupied, a search for the next converted wavelength is performed, and if all are blocked, the packet is discarded.
[0048]
By performing such control, it is possible to reduce the packet discard rate by effectively using the wavelengths, as compared with the case where the converted wavelengths are simply assigned in order. It is similar to the first embodiment that the wavelength converter preferably has a signal reproducing function.
[0049]
【The invention's effect】
As described above, according to the present invention, at the transfer node, the packet signal is transferred to the next transmission path without being stored in the buffer memory. Also, no coordination between nodes is performed. Therefore, a packet signal can be transferred with lower delay than in the related art.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a packet signal transfer network. FIG. 2 is a diagram showing an example of a packet signal transfer network with an inter-node adjustment function. FIG. 3 is a configuration of a transfer node in a conventional wavelength multiplexed optical packet signal transfer system. FIG. 4 is a configuration diagram illustrating an example of a transfer node according to the present invention. FIG. 5 is a configuration diagram illustrating another example of a transfer node according to the present invention. FIG. 6 is a diagram illustrating switching in the transfer node according to the first embodiment. FIG. 7 is a diagram showing a probability distribution of the number of arriving packets. FIG. 8 is a diagram showing how switching is performed in a forwarding node according to the second embodiment.
1: transmitting node, 2: forwarding node, 3: receiving node, 21, 31: wavelength demultiplexer, 22, 32: optical space switch, 23, 33: wavelength converter, 24, 34: optical multiplexer, 25, 35: detector, 26, 36: control unit, 27, 38: optical delay line, 37: transmitter.

Claims (6)

In an optical packet signal transfer method for transferring a wavelength-multiplexed optical packet signal via a transfer node,
In the forwarding node, the transmitted optical packet signal is demultiplexed for each wavelength, and the demultiplexed optical packet signal is sequentially wavelength-converted to a preset wavelength in the order of arrival at the node, and the next transmission path is performed. An optical packet signal transfer method for sending to
Means for wavelength-converting the demultiplexed optical packet signal and sending it to the next transmission path,
An optical space switch which has N × M output terminals (where N is the number of wavelength multiplexing and M is the number of output transmission paths) and switches and outputs a demultiplexed optical packet signal to an arbitrary output terminal;
Wavelength conversion means for converting the wavelength of the output light from each of the output terminals into one of a plurality of different wavelengths to be multiplexed,
Multiplexing means for multiplexing the output light from the wavelength conversion means by N waves and sending the multiplexed light to M output transmission paths,
Control means for controlling the optical space switch so as to output the demultiplexed optical packet signal to an output terminal connected to a wavelength conversion means for converting the demultiplexed optical packet signal into a desired wavelength corresponding to a desired output transmission path. An optical packet signal transfer method, characterized in that: In an optical packet signal transfer method for transferring a wavelength-multiplexed optical packet signal via a transfer node,
At the transfer node, the transmitted optical packet signal is demultiplexed for each wavelength, and the demultiplexed optical packet signal is wavelength-converted to a preset and idle wavelength in the order of arrival at the node. An optical packet signal transmission method for transmitting to the next transmission path ,
Means for wavelength-converting the demultiplexed optical packet signal and sending it to the next transmission path,
An optical space switch which has N × M output terminals (where N is the number of wavelength multiplexing and M is the number of output transmission paths) and switches and outputs a demultiplexed optical packet signal to an arbitrary output terminal;
Wavelength conversion means for converting the wavelength of the output light from each of the output terminals into one of a plurality of different wavelengths to be multiplexed,
Multiplexing means for multiplexing the output light from the wavelength conversion means by N waves and sending the multiplexed light to M output transmission paths,
Control means for controlling the optical space switch so as to output the demultiplexed optical packet signal to an output terminal connected to a wavelength conversion means for converting the demultiplexed optical packet signal into a desired wavelength corresponding to a desired output transmission path. An optical packet signal transfer method, characterized in that: In an optical packet signal transfer method for transferring a wavelength-multiplexed optical packet signal via a transfer node,
At the transfer node, the transmitted optical packet signal is demultiplexed for each wavelength, and the demultiplexed optical packet signal is wavelength-converted to a preset and idle wavelength in the order of arrival at the node. An optical packet signal transmission method for transmitting to the next transmission path ,
The wavelength in the idle state is searched according to the order from the wavelength next to the wavelength assigned to the optical packet signal arriving immediately before the corresponding optical packet signal, from among a plurality of different conversion wavelengths which are assigned in advance in advance. An optical packet signal transfer method, characterized in that: Means for wavelength-converting the demultiplexed optical packet signal and sending it to the next transmission path,
An optical space switch which has N × M output terminals (where N is the number of wavelength multiplexing and M is the number of output transmission paths) and switches and outputs a demultiplexed optical packet signal to an arbitrary output terminal;
Wavelength conversion means for converting the wavelength of the output light from each of the output terminals into one of a plurality of different wavelengths to be multiplexed,
Multiplexing means for multiplexing the output light from the wavelength conversion means by N waves and sending the multiplexed light to M output transmission paths,
Control means for controlling the optical space switch so as to output the demultiplexed optical packet signal to an output terminal connected to a wavelength conversion means for converting the demultiplexed optical packet signal into a desired wavelength corresponding to a desired output transmission path. 4. The optical packet signal transfer method according to claim 3, wherein: Wavelength conversion means optical packet signal transfer system according to claim 1 or 2 or 3 or 4, wherein that it comprises a signal regeneration function. Optical packet signal transfer system according to claim 1 or 2 or 4, wherein a plurality of output paths, characterized in that it is connected to one of the forwarding node.

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