JP2004186815A - Signal generator circuit and packet transfer apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly discard incoming packets at random with a variable possibility depending on the congesting condition by a small-scale circuit in a packet transfer apparatus. <P>SOLUTION: The signal generator circuit 100 for generating a signal at a predetermined possibility decides whether incoming packets are discarded, using a signal generator circuit having a means 101 for generating random numbers, a means 102 for holding a comparison constant for comparing with the random numbers, and a means 103 for generating a signal according to the comparison result of the random numbers with the constant. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a packet transfer device and a signal generation circuit used therefor, and more particularly, to a Random Early Detection (RED) packet transfer device that stochastically discards packets that pass when a sign of congestion starts to appear, and a signal used therefor. It relates to a generating circuit.
[0002]
[Prior art]
At the relay switching node of the Internet protocol, at the time when signs of congestion start to appear, randomly select and discard at a low discard rate from the passing packets, or by setting the congestion notification bit in the header of the packet, A congestion avoidance method using a Random Early Detection (RED) method, which is a method of notifying the occurrence of congestion to an application or a transport protocol of some hosts and inducing a reduction in the transmission amount from the host, is known (non-congestion). Patent Document 1). In the RED system, it is necessary to change the probability in accordance with the state of congestion, that is, the degree of accumulation of packets, and to randomly discard packets arriving for the dynamically changing probability.
[0003]
Conventionally, as a device for randomly generating a signal, a device having a configuration shown in FIG. 4 is known (see Patent Document 1). The figure shows a pseudo-random number generator for generating a pseudo-random number used in a cryptographic communication device or the like. A linear feedback shift register 401 for generating an m-sequence can set an initial value by an initial value setting terminal 403, The state changes in synchronization with the clock. The non-linear conversion function circuit 402 non-linearly converts each of the register values of the linear feedback shift register 401 except for a specific bit to obtain a 1-bit output. The exclusive-OR operation means 404 performs an exclusive-OR operation on a specific 1-bit and the 1-bit output from the nonlinear conversion function circuit 402, and outputs the result as a pseudo-random number. If the number of stages of the linear feedback shift register 401 is made sufficiently large by using the above-described device, occurrences of 0 and 1 output from the exclusive OR operation means 404 are equal in frequency, and pseudorandom numbers with good random number characteristics can be generated. Will be possible.
[0004]
[Non-patent document 1]
Sally Floyd, Van Jacobson. "Random Early Detection Gateways for Congestion Aidance", (IEEE / ACM Transaction on Networking, Vol. 1, No. 4, pp 1-32, August, 1993).
[Patent Document 1]
JP-A-2000-81969 (FIG. 8, abstract)
[0005]
[Problems to be solved by the invention]
However, in the above-mentioned conventional pseudo-random number generator, it is possible to generate 0 and 1 at equal frequency, but in the above-mentioned RED system, 0 and 1 are generated randomly for the probability of dynamically changing. Need to be done. For example, when a certain packet buffer is in one state, it is necessary to randomly discard the packet with a probability of 5%, and in another state, it is necessary to randomly discard the packet with a probability of 50%. If it is necessary to always discard randomly at a probability of 50%, the above-described conventional pseudo-random number generator may be used, but it cannot be used for a fluctuating probability.
[0006]
In view of the above-described problems, the present invention provides a signal generation circuit for randomly discarding an arriving packet with a high-speed and small-scale circuit in response to a probability that varies according to the congestion state. A first object is to provide a packet transfer device using the same, and a second object is to provide a packet transfer device using the same.
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a signal generating circuit for generating a signal with a predetermined probability in order to achieve the first object, wherein a random number generating means for generating a random number is compared with the random number. A signal generation circuit having a comparison constant holding unit for holding a comparison constant and a signal generation unit for generating a signal in accordance with a result of comparing the random number with the constant is used.
According to the first aspect of the present invention, the signal generation probability can be set by changing the comparison constant held by the comparison constant holding unit, and the random number generation unit generates a random number. Can output signals.
[0008]
According to a second aspect of the present invention, in order to achieve the second object, the signal generation circuit according to the first aspect, a packet receiving unit for receiving a packet, a packet holding unit for holding a received packet, A packet transmitting unit for transmitting the packet held by the packet holding unit; and a comparison constant determining unit for determining a constant to be held by the comparison constant holding unit. The packet receiving unit receives the packet and determines the arrival of the packet. Notifying the random number generating means and the comparison constant determining means, discarding the packet arriving in accordance with the signal generated by the signal generating means or transferring the packet to the packet holding means, wherein the packet holding means is Holds the number of packets to be transferred and notifies the comparison constant determining means of the amount of the held packets. A packet transfer device configured to determine the constant in accordance with the arrival notification of the packet notified from the packet receiving unit, the signal output from the signal generation circuit, and the amount of the packet notified from the packet holding unit. Is used.
According to the second aspect of the present invention, a signal can be output at random with respect to the generation probability set by the signal generation means, so that packets arriving at a dynamically fluctuating probability can be randomly discarded.
[0009]
According to a third aspect of the present invention, in the packet transfer device according to the second aspect, random number generating means having counting means for increasing an output value by one and bit order exchange means for changing the order of a plurality of bits output from the counting means. Is used.
According to the third aspect of the present invention, since the random number is generated by using the counting means for increasing the output value by one and the bit order changing means for changing the order of a plurality of bits, the pseudo random number can be generated by a relatively simple method. , Packets arriving for dynamically varying probabilities can be randomly discarded.
[0010]
According to a fourth aspect of the present invention, in the packet transfer device of the third aspect, a counting means configured to increase an output value by one in response to the arrival notification of the packet is used.
According to the fourth aspect of the present invention, the counting means increases the output value by one according to the arrival of the packet. Therefore, for a non-periodic packet flow, the packet arriving at a dynamically varying probability is randomly discarded. can do.
[0011]
According to a fifth aspect of the present invention, in the packet transfer device of the third aspect, a counting means configured to periodically increase the output value by one is used.
According to the fifth aspect of the present invention, the counting means periodically increments the output value by one, so that for a non-periodic packet flow, packets arriving at a dynamically varying probability are randomly discarded. be able to.
[0012]
According to a sixth aspect of the present invention, in the packet transfer device of the second aspect, the random number generating means includes a feedback shift register for generating an m-sequence and a bit order exchange means for exchanging the order of a plurality of bits output from the feedback shift register. Used.
According to the sixth aspect of the present invention, a random number is generated using a feedback shift register that generates an m-sequence and a bit order exchange unit that exchanges the order of a plurality of bits, so that a pseudo-random number can be generated by a relatively simple method. Packets arriving for dynamically varying probabilities can be dropped randomly.
[0013]
According to a seventh aspect of the present invention, in the packet transfer device according to the sixth aspect, a feedback shift register configured to transition an output value in response to the arrival notification of the packet is used.
According to the seventh aspect of the present invention, since the feedback shift register changes the output value according to the arrival of the packet, the packet arriving at the probability of dynamically changing the packet flow having no periodicity is randomly discarded. be able to.
[0014]
According to an eighth aspect of the present invention, in the packet transfer device according to the sixth aspect, a feedback shift register configured to periodically transition an output value is used.
According to the eighth aspect of the present invention, since the feedback shift register transitions the output value periodically, for a packet flow having no periodicity, packets arriving at the probability of dynamically fluctuating are randomly discarded. Can be.
[0015]
According to a ninth aspect of the present invention, in the packet transfer device according to any one of the sixth to eighth aspects, reset means for periodically resetting the feedback shift register to an initial value such that all the registers do not become 0 is provided. The configuration is further added.
According to the ninth aspect of the present invention, since the feedback shift register is periodically reset, even if all the registers become 0 for some reason, the m-sequence can be surely reproduced and arrives at the probability of dynamically changing. Packets can be discarded randomly.
[0016]
According to a tenth aspect of the present invention, in the packet transfer device according to the sixth to eighth aspects, when all the registers of the feedback shift register become zero, the registers are reset to initial values such that all the registers do not become zero. Reset means is further added.
According to the tenth aspect of the present invention, the feedback shift register is reset when all registers become 0 for some reason, so that the m-sequence can be reliably reproduced, and the packet arriving at the probability of dynamically fluctuating is determined. It can be randomly discarded.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
A preferred embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a configuration of a signal generation circuit 100 according to an embodiment of the present invention and a packet transfer device 110 using the same. As shown in FIG. 1, a signal generating circuit 100 of the present invention includes a random number generating means 101 for sequentially generating a random number, a comparison constant holding means 102 for holding a comparison constant for comparing with the random number, Signal generating means 103 for generating a signal according to the result of comparison with the above constant. For example, in order for the signal generation circuit 100 to output a signal uniformly with a probability of 20%, the random number generation means 101 uniformly and randomly generates an integer value of 1 or more and 1000 or less. Further, the comparison constant holding means 102 holds a value of 200 (decimal number). The signal generator 103 outputs a signal when the random number is equal to or smaller than the comparison constant, and does not output a signal when the random number is larger than the comparison constant. If the random number is 55, the signal is output because it is less than the constant. That is, the comparison constant is a value within the range of the random number, and this value is compared with each random number.
[0018]
With the above configuration, the signal generation circuit 100 uniformly and randomly generates an integer value of 1 or more and 1000 or less, so that the probability of being 200 or less is 20%, and the frequency of signal generation is also uniform. become.
[0019]
Further, the packet transfer apparatus 110 of the present invention includes the above-described signal generating circuit 100 and packet receiving means 113 for receiving a packet, packet holding means 111 for holding a received packet, and transmitting the packet held by the packet holding means 111. And a comparison constant determining unit 112 for determining a constant to be held by the comparison constant holding unit 102. The packet receiving means 113 receives a packet arriving from outside, notifies the arrival of the packet to the random number generating means 101 and the comparison constant determining means 112, and discards the packet according to the signal generated by the signal generating means 103. The packets not discarded are transferred to the packet holding unit 111 and held.
[0020]
The packet holding unit 111 holds the packet transferred by the packet receiving unit 113 and notifies the comparison constant determining unit 112 of the amount of the held packet. The comparison constant determining unit 112 receives the packet arrival notification from the packet receiving unit 113, the signal output from the signal generation unit 103 (which is also the output signal of the signal generation circuit 100), and the packet notification from the packet holding unit 111. Determine the constant according to the quantity. When the amount of packets received by the packet receiving unit 113 is larger than the amount of packets transmitted by the packet transmitting unit 114, the amount of packets held by the packet holding unit 111 increases, and a congestion state occurs.
[0021]
The comparison constant determining unit 112 determines whether the packet is discarded based on the amount of packets held by the packet holding unit 111 at a certain time, the packet arrival notification notified from the packet receiving unit 113, and the signal notified from the signal generation circuit 100. The number of packets that have been passed without being discarded continuously up to the time after the occurrence is obtained, and a constant is determined using these. When not in a congestion state, the constant is 0, no signal is generated from the signal generation circuit 100 regardless of the random number generated by the random number generation means 101, and the received packet is not discarded at all. When a sign of congestion starts to appear, a received packet is stochastically discarded by outputting a non-zero constant.
[0022]
The comparison constant determination means 112 obtains the probability of discarding the packet by the calculation method described in the above-mentioned "Random Early Detection Gateways for Congestion Aidance", and further determines the constant from the probability. With the above-described configuration, it is possible to realize a RED scheme that probabilistically discards packets that pass when signs of congestion start to appear.
[0023]
Next, a configuration example of the random number generation unit 101 in FIG. 1 is shown in FIGS. The configuration example of the random number generation unit 101 in FIG. 2 includes a counting unit 201 that increases the output value by one and a bit order exchange unit 202 that exchanges the order of a plurality of bits output from the counting unit 201. The counting means 201 outputs 10-bit data, and the bit order exchanging means 202 inverts and outputs the MSB and LSB of the data.
[0024]
The configuration example of the random number generation unit 101 in FIG. 3 includes a feedback shift register 301 that generates an m-sequence and a bit order exchange unit 302 that exchanges the order of a plurality of bits output from the feedback shift register 301. The feedback shift register 301 outputs 10-bit data, and the bit order exchange means 302 outputs the data by changing the order of some bits of the data.
[0025]
With the configuration shown in FIG. 2 and FIG. 3, random numbers between 0 and 1023 can be generated in a pseudo manner. In FIG. 2, the reason why the bit order exchange means 202 changes the bit order is to prevent the signal generation means 103 from continuously generating a signal if only the counting means 201 which increments by one is used. is there. In FIG. 3, it is known that the bit order exchange unit 302 changes the bit order, even if only the feedback shift register 301 is used, a number equal to or more than 0 and equal to or less than 1023 is generated. Since a large number or a small number may be output successively, the bit order is changed to prevent the signal generation unit 103 from generating a signal continuously. When discarding a TCP flow, if packets are discarded continuously, a problem such as global synchronization may occur. However, since discarding may be performed with some randomness, a pseudo-random number is generated with a simple configuration. The configuration is adopted.
[0026]
Further, the count-up timing of the counting means 201 in FIG. 2 may be adjusted to the arrival of the packet if the order of arrival of the packets of the plurality of TCP flows is not regular, or may be the regular period if the arrival time of the packet is not regular. You may go to. The same applies to the transition timing of the output value of the feedback shift register of the feedback shift register 301 in FIG. Normally, it is considered that the arrival of packets of the TCP flow does not have regularity, so that the same effect can be obtained in either case. When the feedback shift register 301 shown in FIG. 3 is used, if all bits that are 1 disappear for some reason, 0 is permanently output. Therefore, when all the bits become 0, or when all the bits become 0, they are not 0 periodically. By adding means for resetting the number, the m-sequence can be generated more safely.
[0027]
【The invention's effect】
According to the first aspect of the present invention, by setting the range of the random number generated by the random number generation unit and the constant held by the comparison constant holding unit, the signal generation unit compares the random number with the constant according to the result. Therefore, a signal can be generated with various probabilities.
[0028]
According to the second aspect of the present invention, the random number generating means can generate random numbers one after another in response to the arrival of the packet or periodically, and the comparison constant determining means can determine whether the packet received from the packet receiving means has been received. Since the constant is determined according to the signal output from the notification and signal generation circuit and the amount of the packet notified from the packet holding unit, the constant can be determined according to the congestion state. Can be discarded or transferred to the packet holding means in accordance with the signal generated by the communication device, so that the arriving packet can be randomly discarded according to the probability determined by the congestion state.
[0029]
According to the third aspect of the present invention, the random number generating means can be relatively easily constituted by the counting means for increasing the output value by one and the bit order changing means for changing the order of the plurality of bits output from the counting means. Since the signal generation means can generate a signal at random according to the given constant, it is possible to randomly discard packets arriving at a probability determined by the congestion state.
[0030]
According to the fourth aspect of the present invention, the counting means increases the output value by one in response to the packet arrival notification, so that the signal generating means can generate signals one by one for each packet. Packets can be randomly discarded according to the probability determined by.
According to the fifth aspect of the present invention, the counting means periodically increments the counter by one, so that the signal generating means can generate signals one after another, so that the signal arrives according to the probability determined by the congestion state. Packets can be dropped randomly.
[0031]
According to the sixth aspect of the present invention, the random number generation means can be relatively easily constituted by the feedback shift register for generating the m-sequence and the bit order exchange means for exchanging the order of a plurality of bits output from the feedback shift register. Since the generating means can generate a signal at random according to the given constant, it is possible to randomly discard the arriving packet according to the probability determined by the congestion state.
[0032]
According to the seventh aspect of the present invention, the feedback shift register changes the output value in response to the arrival notification of the packet, so that the signal generating means can generate signals one by one for each packet. Packets arriving according to the determined probability can be randomly discarded.
[0033]
According to the eighth aspect of the present invention, since the feedback shift register periodically changes the output value, the signal generating means can generate signals one after another, and arrives at a probability determined by the congestion state. Packets can be dropped randomly.
[0034]
According to the ninth aspect of the present invention, since the feedback shift register periodically transitions to an initial value other than 0, a secure packet transfer device that can recover even if all bits become 0 due to a circuit failure or the like is provided. it can.
[0035]
According to the tenth aspect of the present invention, the feedback shift register transitions to an initial value other than 0 when all the registers become 0, so that even if all bits become 0 due to a circuit failure or the like, the feedback shift register can be restored. A secure packet transfer device can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of a packet transfer device according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration example in a case where a random number generating unit according to an embodiment of the present invention is configured using a counter. FIG. 3 is a block diagram showing a configuration example when a random number generation unit according to the embodiment of the present invention is configured using a feedback shift register that generates an m-sequence; FIG. Circuit for [Description of reference symbols]
REFERENCE SIGNS LIST 100 signal generation circuit 101 random number generation means 102 comparison constant holding means 103 signal generation means 110 packet transfer device 111 packet holding means 112 comparison constant determination means 113 packet reception means 114 packet transmission means 201 counting means 202, 302 bit order exchange means 301 feedback Shift register 400 pseudorandom number generator 401 linear feedback shift register 402 nonlinear conversion function circuit 403 initial value setting terminal

Claims (10)

Random number generating means for generating a random number;
Comparison constant holding means for holding a comparison constant to be compared with the random number;
A signal generation unit that compares the random number and the comparison constant with a value within the range of the random number, and generates a signal with a probability determined in advance according to a result of the comparison between the range of the random number and the comparison constant. Means and
A signal generating circuit. Random number generating means for generating a random number, comparison constant holding means for holding a comparison constant to be compared with the random number, and the random number and the comparison constant, comparing the value within the range of the random number, the result A signal generation circuit having a signal generation unit that generates a signal at a predetermined probability according to a relationship between the range of the random number and the comparison constant,
Packet receiving means for receiving a packet;
Packet holding means for holding received packets;
Packet transmitting means for transmitting a packet held by the packet holding means;
And a comparison constant determining means for determining a constant to be held by the comparison constant holding means,
The packet receiving means receives the packet, notifies the arrival of the packet to the random number generating means and the comparison constant determining means, and discards the arriving packet in accordance with a signal generated by the signal generating circuit or holds the packet. Transfer to means,
The packet holding unit notifies the comparison constant determining unit of the amount of the packet held and held by the packet receiving unit to transfer the packet,
The comparison constant determining means is configured to determine the constant according to a packet arrival notification notified from the packet receiving means, a signal output from the signal generation circuit, and an amount of packets notified from the packet holding means. Packet forwarding equipment. 3. The packet transfer device according to claim 2, wherein said random number generating means includes a counting means for increasing an output value by one, and a bit order changing means for changing the order of a plurality of bits output from said counting means. 4. The packet transfer device according to claim 3, wherein said counting means is configured to increase an output value by one in response to the packet arrival notification. 4. The packet transfer device according to claim 3, wherein said counting means is configured to periodically increase the output value by one. 3. The packet transfer device according to claim 2, wherein said random number generating means includes a feedback shift register for generating an m-sequence and a bit order exchange means for exchanging the order of a plurality of bits output from the feedback shift register. 7. The packet transfer device according to claim 6, wherein the feedback shift register is configured to transition an output value according to the arrival notification of the packet. 7. The packet transfer device according to claim 6, wherein the feedback shift register is configured to periodically change an output value. 9. The packet transfer device according to claim 6, further comprising reset means for periodically resetting the feedback shift register to an initial value such that all registers do not become 0. 9. The packet according to claim 6, further comprising resetting means for resetting the feedback shift register to an initial value such that when all the registers become 0, all the registers do not become 0. Transfer device.

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