JP2000270017A - Packet buffer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a packet buffer circuit which can improve transmission efficiency. SOLUTION: This packet buffer circuit writes packets sent from a terminal to a transmitting buffer memory 2 composed of transmitting buffers 21 to 25, packet by packet, by a transmitting buffer control part 6, selecting the written packets by a selector 3 and sending them out to a packet sending-out part 5, monitors a band allocation request from a subscriber device and the band assigned by a station device by a band allocation control part 7, compares an excessive band quantity with respective packet sizes stored in the transmitting buffer memory 2 by a band assignment control part 7 when a band is assigned exceeding the transmission final frame request of one packet, outputs a packet which can be sent out in the excessive band in such a case, and interrupts the band assignment during the transmission of a 2nd packet, thereby avoiding retransmission carried out to discard the 2nd sent out packet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet buffer circuit mounted in a subscriber device that communicates while presenting a necessary bandwidth capacity and securing a bandwidth allocation to the bandwidth in a transmission system sharing the bandwidth of two transmission paths.

[0002]

2. Description of the Related Art In a bandwidth sharing system of a time division multiple access system, a plurality of subscribers are connected to one station apparatus. Normal operation is to output a band allocation request from the subscriber device, to receive the request, the station device allocates a band, and the assigned subscriber device outputs a packet. Also, as a control of the station device, even if a certain subscriber device makes a band allocation request and the subscriber device completes the transmission of the packet, the station device ends last unless another subscriber device requests the band allocation. Generally, control is performed to continue the band allocation for the subscriber device that has requested the band allocation.

In the case where the second and third packets are received from the terminal during the transmission of the first packet and the bandwidth allocation is continued without further requesting the bandwidth allocation by another subscriber unit, If the second and third packets are immediately transmitted without performing the procedure for newly requesting a bandwidth allocation, the transmission efficiency is improved. Here, if an attempt is made to transmit a packet that is larger than necessary in the last frame of the first packet transmission over the next frame following the previous packet, When there is a bandwidth allocation request from a subscriber device, the station device performs bandwidth allocation to the subscriber device that has made the bandwidth allocation request.

[0004]

However, as a result, the packet being transmitted is discarded on the receiving side and retransmitted, which causes a problem that the transmission efficiency is reduced. Japanese Patent Application Laid-Open No. 08-340336 discloses a method for effectively using a necessary and sufficient bandwidth in multipoint communication or multiconnection communication in which a plurality of virtual channel connections are set for one call. (ATM
In an ATM network in which a plurality of virtual channel connections are set up for one call, a band shared by a predetermined combination of the virtual channel connections making up the call at the time of call setup is included in a network allocation method. It is disclosed that the reserved shared band is allocated to each channel connection of the same combination in accordance with the actual communication state of each channel connection under a predetermined allocation condition.

Further, a band shared circuit for collecting and outputting information cells of a plurality of input lines for each output line and a transmission system including the band shared circuit are disclosed in Japanese Patent Laid-Open No. 11-4 / 1999.
No. 227 gazette. In the case of this publication, the difference between the cell amount stored in the cell buffer circuit and the set threshold value is monitored, and the cell transmission is restricted to the information source transmitting the information cell according to the monitoring result. Is generated and transmitted, and the information source is provided with means for adjusting the amount of information cells transmitted to the band shared circuit.

However, these publications do not provide a solution to the problem of preventing transmission efficiency from being reduced due to retransmission of a packet in the middle of transmission, which is a conventional problem. In addition, as an approximation technique, for example, JP-A-10-145424 (information communication method) and JP-A-10-336186 (band allocation circuit) can be cited.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and a band is allocated more than required.
When there is a packet in the transmission buffer having a size that fits in the extra band, the packet is transmitted following the preceding packet, thereby avoiding retransmission of the packet due to the interruption of the band allocation during the transmission of the second packet and transmitting the packet. An object of the present invention is to provide a packet buffer circuit capable of improving efficiency.

[0008]

In order to achieve the above object, a packet buffer circuit according to the present invention comprises a plurality of transmission buffer memories for storing packets transmitted by a terminal in a subscriber unit for each packet; A transmission buffer control unit that controls writing / reading to / from the buffer memory, recognizes the size of each packet written to the transmission buffer memory, and outputs a packet read from the transmission buffer memory to a packet transmission unit;
A bandwidth allocation control unit that monitors a bandwidth allocation request of the terminal and a bandwidth allocated from a station device. Therefore, when the bandwidth allocation control unit recognizes that a bandwidth equal to or larger than the transmission packet data size has been allocated to the last transmission frame of one packet, the bandwidth allocation control unit obtains an unnecessarily allocated bandwidth capacity, and reports this to the transmission buffer. Notifying the control unit, the transmission buffer control unit compares the packet sizes stored in the plurality of transmission buffer memories, determines a packet that can be transmitted to an unnecessarily allocated band, and receives a packet transmission permission signal. In the meantime, by transmitting a packet selected from a plurality of packets following the preceding packet to the shared band, the bandwidth allocation is interrupted during the transmission of the second packet, and the retransmission performed because the second transmitted packet is discarded. To avoid
The transmission rate can be improved.

[0009]

Embodiments of a packet buffer circuit according to the present invention will be described below with reference to the drawings. FIG. 1 shows a first example of a packet buffer circuit according to the present invention.
FIG. 2 is a block diagram showing a configuration of the embodiment. In FIG. 1, a case will be described where the transmission buffer memory 2 is composed of five transmission buffers of a first transmission buffer 21 to a fifth transmission buffer 25 for convenience of explanation. The first transmission buffer 21 is a first-in first-out buffer memory in which a packet transmitted by a terminal (not shown in FIG. 1) received by the terminal interface unit 1 is written. Second transmission buffer 22 to fifth transmission buffer 2
5 is a similar buffer memory.

The selector 3 selects one packet output from the five transmission buffers of the first transmission buffer 21 to the fifth transmission buffer 25 under the control of the transmission buffer control unit 6 and outputs the selected packet to the packet transmission unit 4. Has the function of The packet transmitting unit 4 has a function of outputting the packet output by the selector 3 to the station device interface unit 5.
When notified by the terminal interface unit 1 that the packet transmitted by the terminal has arrived, the transmission buffer control unit 6 controls the plurality of transmission buffers 21 to 25 and writes the packet into one transmission buffer for each packet.

The transmission buffer control section 6 stores the packet size written in the first transmission buffer 21 to the fifth transmission buffer 25 and, when a transmission permission signal is given from the station interface section 5, It has a function of controlling the first to fifth transmission buffers 21 to 25 and the selector 3 to output packet data from the selector 3 to the packet transmission unit 4. Band allocation control unit 7
Is notified by the transmission buffer control unit 6 that a packet transmitted by the terminal has been received, calculates the number of block bandwidth allocation requests to be made, and calculates the following based on the bandwidth allocation information received via the station interface unit 5. It has a function to calculate how many blocks should be requested in one frame.

Next, the operation of the first embodiment will be described with reference to the sequence diagram of FIG. 2, the frame configuration diagram of FIG.
This will be described with reference to the system configuration diagram of FIG. In the frame configuration shown in FIG. 3, one frame includes a downlink area Fd and an uplink area Fu.
Further, the upstream region Fu is composed of a fixed band (first half) Fu1, a fixed band (second half) Fu2, a shared band (block “1”) Fu3, and a shared band (block “2”) Fu.
4, a shared band (block "3") Fu5, and a shared band (block "4") Fu6.

FIG. 4 shows a communication system in which a plurality of terminals using the optical splitter 8 share a band of one transmission line. The packet buffer circuit of the present invention is applied to the subscriber units 9a to 9n. I have. Each subscriber device 9a-
A plurality of terminals 10a to 10n are connected to 9n. In FIG. 4, each of the subscriber units 9a to 9
n shows a state where one is connected to each.

The following conditions and parameters are set for explanation. In the subscriber devices 9a to 9n of FIG.
Continuous 3 only from terminal 10a connected to subscriber unit 9a
One packet is transmitted, and during that time, no packet is transmitted from a terminal connected to another subscriber device. The frame of the station device 8 and each of the subscriber devices 9a to 9n has the frame configuration shown in FIG. 3, and the shared band has four blocks in the upstream band. Size of first packet arriving at subscriber unit 9a: 120 Size of second packet arriving at subscriber unit 9a: 100 Size of third packet arriving at subscriber unit 9a: 40 shared in frame Band block size: 20

Further, it is assumed that the following rules are applied to the allocation of the upstream shared band of the station device 8. In the allocation of the upstream shared band from the station device 8, one subscriber device is selected from the requested subscriber devices, and the band is continuously allocated until data transmission from the subscriber device is completed. . At the time when the data transmission of one subscriber device is completed, if there is no bandwidth allocation request from another subscriber device, the station device keeps allocating the bandwidth to the subscriber device that has been requested last. However, if another subscriber device makes an upstream bandwidth allocation request, even during communication, the bandwidth allocation to this subscriber device is stopped,
The bandwidth allocation to the requested subscriber device is started.

Under the above conditions and parameter settings and rules, the operation is as follows. First, the subscriber device 9a in FIG. 4 receives the first packet transmitted by the terminal 10a (time T1 in FIG. 2). The terminal interface unit 1 of FIG. 1 receives the packet transmitted from the terminal 10a,
The transmission buffer control unit 6 is notified that the terminal interface unit 1 has received it. The transmission buffer control unit 6 recognizes the state of the transmission buffer memory 2 including a plurality of transmission buffers of the first transmission buffer 21 to the fifth transmission buffer 25.

The transmission buffer controller 6 writes the received first packet into the first transmission buffer 21. At the same time, it notifies the bandwidth allocation control unit 7 of the size of the first packet. The band allocation control unit 7 outputs a request for the required number of blocks of the upstream shared band to the station device interface unit 5 (step S1 in FIG. 2). In the first embodiment, since the size of the first packet is “120” and the size of one shared band is “20” as in the setting of the parameter, the shared band is required to transmit all the packets. Although six blocks are required, one frame has only four blocks at maximum, so four blocks are requested.

The station device interface unit 5 transmits the information of the band request to the station device 8. The subscriber device 9a in FIG. 4 transmits the information of the bandwidth request to the station device 8 (frame N in FIG. 2).
O. 1). The station device 8 that has received the four-block bandwidth allocation request from the subscriber device 9a in FIG. 4 permits the four-block bandwidth allocation to the subscriber device 9a, and
The bandwidth allocation information is transmitted to a. The band allocation information is stored in the station interface unit 5 in the subscriber unit 9a.
And the band allocation information is transmitted to the band allocation control unit 7.

Further, a packet transmission permission signal is generated from the band allocation information in the station interface unit 5,
It is sent to the transmission buffer control unit 6 (step S in FIG. 2).
2). Upon receiving the band allocation information, the band allocation control unit 7 of FIG. 1 recognizes that four blocks have been allocated to the shared band, and calculates how many more blocks should be requested to transmit the first packet. I do. In the first embodiment, four blocks are allocated to the first request, and the remaining request is "40"("120"-"80"), so two blocks are requested.

The transmission buffer control unit 6 of FIG. 1 that has received the packet transmission permission signal reads the first packet from the first transmission buffer 21 of the transmission buffer memory 2 while transmission is permitted, and controls the selector 3. Then, the first packet data read out is transmitted to the packet transmitting section 4.
In the first embodiment, only “80” of the entire size “120” is read and sent to the packet sending unit 4. Frame NO. It is assumed that the second and third packets arrive from the terminal 10a connected to the subscriber device 9a in FIG. 4 during the time 2 (time T2 and time T3 in FIG. 2).

The respective packet sizes are "100" and "40". The transmission buffer control unit 6 of FIG.
Since the first packet is stored in the transmission buffer 21, the second packet is stored in the second transmission buffer 22 of the transmission buffer memory 2, and the third packet is stored in the third transmission buffer 23 of the transmission buffer memory 2. To control. The transmission buffer control unit 6 stores the second and third packet sizes. The two blocks of band allocation request information calculated by the band allocation controller 7 and the first packet data sent to the packet transmitter 4 are output from the station interface 5 to the station 8.

The subscriber unit 9a shown in FIG. 4 transmits the two blocks of band allocation request information and the first packet data to the station unit 8.
(Frame No. 2 in FIG. 2). The station device 8 in FIG. 4 receives the first packet and receives a bandwidth allocation request of two blocks. Here, if there is no bandwidth allocation request from another subscriber device, the station device 8
Even if only a block has a bandwidth allocation request, bandwidth allocation for four blocks is performed (step S3 in FIG. 2).

In the next frame, the station device 8 sends the subscriber device 9a.
, And sends four blocks of band allocation information. The band allocation information is sent to the band allocation control unit 7 in FIG. 1 similarly to the previous frame. The band allocation control unit 7, which has received the band allocation information, requests that only two blocks have been allocated, and that four blocks have been allocated and that the extra allocated band is "40". Notify section 6.

After transmitting the first packet, the transmission buffer control unit 6 confirms the size of the second packet when recognizing that an available bandwidth of "40" is further allocated. In the first embodiment, the size of the second packet is “100”, and transmission cannot be performed using only the free bandwidth of “40”. Subsequently, the transmission buffer control unit 6 checks the size of the third packet. In the first embodiment, the size of the third packet is "40", and transmission is possible in an available band. Transmission buffer controller 6
Decides to transmit the third packet to the free band following the first packet (step S in FIG. 2).
4).

The transmission buffer control unit 6, which has received the packet transmission permission signal, reads the first packet from the first transmission buffer 21 of the transmission buffer memory 2 while transmission is permitted, controls the selector, and controls the packet transmission unit. The first packet data read out is transmitted. After the transmission of the first packet is completed, the third packet is read from the third transmission buffer 23 of the transmission buffer memory 2,
The selector 3 is switched to transmit the third packet data to the packet transmitting unit 4.

At the same time, the band allocation control unit 7
It outputs a bandwidth allocation request to transmit the second packet. In the first embodiment, since the second packet is "100", five shared band blocks are required to transmit all the packets, but one frame has only a maximum of four shared band blocks. Therefore, four blocks are requested. The first and third packet data read from the transmission buffer memory 2 and the band assignment information output by the band assignment control unit 7 are transmitted to the station device 8 via the station device interface unit 5 (FIG. 2). Frame N
O. 3).

As described above, in the first embodiment, when a band is allocated to the last transmission frame of one packet more than required, the extra bandwidth and the respective transmission buffers stored in the plurality of transmission buffers are used. The packet size is compared, and if there is a packet that can be transmitted in an extra band, the packet is output (step S5 in FIG. 2), whereby the band allocation is interrupted during the transmission of the second packet, and the second packet is transmitted. Can be prevented from being retransmitted due to the discarded packet sent to the server. Accordingly, it is possible to improve the transmission rate.

Next, a second embodiment of the present invention will be described. FIG. 5 is a block diagram showing the configuration of the second embodiment. In the second embodiment, one transmission buffer memory 2 is divided into a plurality of blocks, and the transmission buffer control unit 6 writes each packet in a separate block,
It has a function of storing the address of the block and the packet size, reading each stored packet for each address, and transmitting the packet to the packet transmitting unit 4. Accordingly, the selector 3 shown in FIG. 1 is omitted, and the function of the selector 3 is also performed by the transmission buffer control unit 6.

[0029]

As described above, according to the present invention, in a communication system in which a plurality of terminals share the bandwidth of one transmission line, communication is performed while presenting a necessary bandwidth capacity and securing a bandwidth allocation to the required bandwidth capacity. In the terminal device, the packet transmitted by the terminal in the subscriber device is stored in the transmission buffer memory for each packet, and the transmission buffer memory is controlled by the transmission buffer control unit, and the size of the packet in the transmission buffer is stored. The band allocation control unit monitors the band information allocated from the station device so that it is possible to detect that the band has been allocated more than the request and its size, so that the band can be allocated more than the request and the extra If there is a packet in the transmission buffer that fits in the proper bandwidth, send the packet following the preceding packet. , It is possible to avoid the retransmission of the packet according to the band allocation interruption during transmission the second packet, thus it is possible to improve the transmission efficiency.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of a packet buffer circuit according to the present invention.

FIG. 2 is a sequence diagram illustrating an operation of the packet buffer circuit according to the first embodiment of the present invention;

FIG. 3 is an explanatory diagram showing a frame configuration applied to the first embodiment of the packet buffer circuit according to the present invention;

FIG. 4 is an explanatory diagram of a configuration of a communication system in which a plurality of terminals share the bandwidth of one transmission line to which the first embodiment of the packet buffer circuit according to the present invention is applied;

FIG. 5 is a block diagram showing a configuration of a packet buffer circuit according to a second embodiment of the present invention;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Terminal interface part, 2 ... Transmission buffer memory, 3 ... Selector, 4 ... Packet transmission part, 5 ... Station device interface part, 6 ... Transmission buffer control part, 7
... band allocation control unit, 8 ... station devices, 9a to 9n ...
... subscriber devices, 10a to 10n ... terminals, 21 ... first
Transmission buffer, 22: second transmission buffer, 23: third transmission buffer, 24: fourth transmission buffer, 25:
Fifth transmission buffer.

Claims (10)

[Claims] 1. A plurality of transmission buffer memories for storing a packet transmitted by a terminal in a subscriber unit for each packet, writing / reading control to the transmission buffer memory, and writing to the transmission buffer memory A transmission buffer control unit for recognizing a size of each packet and outputting a packet read from the transmission buffer memory to a packet transmission unit; and a band allocation control for monitoring a band allocation request of the terminal and a band allocated from a station device. A packet buffer circuit, comprising: 2. The packet transmission unit according to claim 1, wherein the packet read out by the transmission buffer control unit from a transmission buffer memory composed of a plurality of transmission buffers is switched by a selector and input. Packet buffer circuit. 3. The packet buffer circuit according to claim 1, wherein said transmission buffer memory is constituted by one and divided into a plurality of blocks. 4. The transmission buffer control unit writes the packet separately for each block of the transmission buffer memory, stores the address of the block and the packet size, reads out the packet, and transmits the packet to the packet transmission unit. The packet buffer circuit according to claim 3, wherein: 5. The transmission buffer control unit, when notified from the terminal interface unit that a packet transmitted by the terminal has arrived, controls a plurality of transmission buffers constituting the transmission buffer memory to packetize the packet. 2. The packet buffer circuit according to claim 1, wherein the data is written into one transmission buffer every time. 6. The transmission buffer memory, wherein when a bandwidth is allocated by the station device more than the terminal's request for transmission of the last frame of one packet, the transmission buffer memory stores the packet that can be transmitted to the extra bandwidth. , The packet is output,
2. The packet buffer circuit according to claim 1, wherein the bandwidth allocation by the station device is interrupted during transmission of the second packet, and the second transmitted packet is discarded. 7. The terminal according to claim 1, wherein:
2. The packet buffer circuit according to claim 1, wherein three consecutive packets are transmitted only from one terminal connected to the other subscriber terminal, and no packets are transmitted from a terminal connected to another subscriber device during that time. 8. The station device selects one subscriber device from the subscriber devices for which an uplink shared band allocation request has been made, and continues until data transmission from the selected subscriber is completed. 2. The packet buffer circuit according to claim 1, wherein a band is continuously allocated. 9. The above-mentioned station device, if there is no bandwidth allocation request from another subscriber device at the time when the data transmission of one subscriber device has been completed, sends a request to the subscriber who last made the bandwidth allocation request. 2. The packet buffer circuit according to claim 1, wherein a band is continuously allocated by using the packet buffer circuit. 10. The station device, when a subscriber device issues an upstream band allocation request, suspends band allocation to a currently communicating subscriber and starts band allocation to the requested subscriber device. 2. The packet buffer circuit according to claim 1, wherein: