JP2009278256A - Relay device and relay method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress overflow of a transmission buffer for accumulating packets to be transmitted to a terminal device and to prevent unfairness of throughput of flow between upstream and downstream and unfairness of a throughput among upstream flows, in a relay device connected to one or more terminal device through a network using a random access system. <P>SOLUTION: A transmission buffer occupation state monitoring means 209 of a wireless LAN base station device 103 to be a relay device, monitors a use state of a transmission side buffer means 210. A reception side abandonment possibility determining means 208 and a packet abandoning means 206 probabilistically abandon data received from the terminal device via the wireless LAN in accordance with the use state of the transmission side buffer means 210 monitored. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a relay device such as an access point connected to one or more terminal devices through a network using a random access method such as a wireless LAN.

  In recent years, with the spread of mobile terminals such as laptop PCs and mobile phones, wireless LAN communication networks have been born. Due to its simplicity and high speed compared to mobile phones, it will continue to spread. In addition, TCP is widely used as a transport protocol that guarantees communication reliability between nodes. It is said that 80% of the current traffic is TCP communication. However, it was assumed that the TCP specification would be used on a wired network. Under such circumstances, problems have been reported when TCP traffic communication is performed on a wireless LAN.

  The problem is that when a wireless LAN terminal device performs upstream TCP flow communication, an overflow occurs in the transmission buffer on the wireless LAN side of the wireless LAN access point (wireless LAN base station device). This overflow problem occurs when there is an upstream TCP flow. Examples of upstream TCP flow communication include P2P communication, video conference, and communication by a thin client terminal. Since these are traffics that will increase in the future, the influence of upstream TCP flows cannot be ignored.

  There are two causes of overflow in the transmission buffer on the wireless LAN side in the wireless LAN base station device. The first point is that a TCP ACK packet corresponding to a TCP data packet transmitted by a wireless LAN terminal device is accumulated in the transmission buffer. In TCP, the receiving terminal returns a TCP ACK packet for arrival confirmation. Also, in TCP, multiple packets are sent at once when sending. A group of these multiple packets is called a window. The source TCP that receives the acknowledgment increases this window. Furthermore, when there are multiple wireless LAN terminal devices that perform TCP upstream communication, TCP ACK packets for all terminal devices are buffered in the transmission buffer of the wireless LAN base station device, which causes an overflow. . If buffered TCP ACK packets are efficiently transmitted over the air, buffer overflow will not occur. However, the wireless LAN base station apparatus cannot perform highly efficient transmission due to the random access control of the wireless LAN. That is the second cause. That is, another cause of buffer overflow is that buffered TCP ACK packet transmission becomes inefficient as the number of terminals increases due to the wireless LAN access method.

  The wireless access method is a random access method called CSMA / CA defined by IEEE 802.11. In CSMA / CA, a wireless LAN base station device and a terminal device share a wireless bandwidth equally. The specific procedure is as follows. If the terminal device and the base station device that have detected the end of packet communication by another terminal device in the wireless LAN have a transmission packet, each of them generates a random number. A timer is set for the output value multiplied by a certain time, and transmission is waited for. The wireless LAN device whose timer expires first acquires the transmission right. If transmission of another terminal is detected during the waiting time, the timer is temporarily stopped. In this procedure, since the result of random number distribution is stochastically scattered between terminals, collision can be avoided. Since this random access procedure is used, packet transmission right acquisition is equally given to both the wireless LAN terminal device and the base station device. However, since the transmission time interval increases as the number of wireless LAN terminal devices increases, the time interval for acquiring the transmission right of the base station device increases accordingly. This is a major cause of overflow of the transmission buffer.

  The send buffer overflow described above adversely affects performance. That is two types of throughput unfairness. One is the unfairness of TCP flow throughput between upstream and downstream. The second is the unfairness of throughput between upstream flows.

  The first unfairness of throughput between the upstream and downstream TCP flows is caused by a TCP buffer being lost due to overflow of the transmission buffer and reducing the TCP window size. For this reason, the proportion of the downstream flow occupying the radio band decreases, and the upstream TCP flow increases the transmission window size accordingly. This causes upstream and downstream unfairness. This is the result of buffer overflows promoting the throughput unfairness seen at the link level described above. According to Non-Patent Document 1, it is known that this state is maintained for at least several minutes by past simulation evaluation. This is a serious problem with video streaming, which is one of the downstream TCP traffic that requires bandwidth.

  Further, the buffer overflow also causes unfairness in throughput between upstream TCP flows as described above. Losses due to buffer overflow are bursty. For this reason, in the case of an upstream TCP flow whose window has become smaller due to a collision, all the TCP ACK packets are lost due to buffer overflow. Then, the TCP transmission side determines that a timeout has occurred and reduces the window size to the minimum value, resulting in almost no throughput. This flow is referred to herein as a low throughput flow.

  Once the window is reduced to the minimum value, a timeout may occur at the next opportunity. If there is no reply of the TCP ACK packet to the retransmission packet after the timeout, an exponential backoff state is entered, and the transmission interval is doubled. Therefore, this low throughput state continues to be maintained. According to simulation evaluation, this state lasts at least about 2 minutes. When video conferencing is performed using TCP, a delay of 2 minutes is fatal because real-time performance is required. The same state is also obtained when a new upstream TCP flow starts communication in a state where the wireless bandwidth is occupied by such an upstream TCP flow.

  On the other hand, flows that maintain a high TCP window size are less susceptible to loss due to buffer overflow. This is because if one of the packets in the window can receive a TCP ACK, the window will not be reduced. Therefore, the window size is increased until the upper limit is reached, and the radio bandwidth occupation rate is increased. This flow is referred to herein as a high throughput flow.

  Thus, when there are a plurality of upstream TCP flows, an overflow of the TCP ACK packet occurs in the transmission buffer in the base station apparatus of the wireless LAN, and there is a flow with extremely low throughput.

  Various measures have been proposed as countermeasures against the above two unfairness. In Non-Patent Document 1, assuming a necessary bandwidth from the buffer size and the number of flows, the base station device of the wireless LAN rewrites the value of the advertisement window header to suppress the overflow. Non-Patent Document 2 solves this problem by transmitting a downstream frame preferentially over an upstream packet using the IEEE802.11e standard. Patent Document 1 monitors the throughput of each TCP flow in an access router that connects a wireless LAN base station and the Internet, and discards a received packet when burst communication exceeding a threshold is detected. .

  On the other hand, in Patent Document 2, in the relay device, a first direction buffer that temporarily stores a packet transferred from one terminal to the other terminal and a second direction that temporarily stores a packet transferred from the other terminal to one terminal A technique is described in which each queue length of a buffer is monitored, and when a queue length in one buffer reaches a predetermined length, a congestion is controlled by inserting a predetermined delay time into the other buffer. Also, in the prior art section of this document, the average queue length in the buffer is monitored, and data packets in the buffer are lost with a probability corresponding to this length, so that it is explicit for the terminal. A congestion control method called red (RED: Random Early Detection gateway) for notifying congestion is described.

Japanese Patent Laid-Open No. 2004-165844 JP 2000-307634 A S. Pilosof, R. Ramjee, Y. Shavitt, P. Sinha, Understanding TCP fairness over Wireless LAN ”, INFOCOM 2003, 13 April 2003. D.J. Leith, P. Clifford, “Using the 802.11e EDCF to Achieve TCP Upload Fairness over WLAN Links”, WiOpt, April 2005.

  Each of the above techniques has problems. In Non-Patent Document 1, the control in the wireless LAN base station apparatus is complicated. Implementing multiple operations for each packet, such as monitoring the traffic and the number of flows with a wireless LAN base station device, calculating the optimum throughput value, rewriting the advertisement window size in the TCP header, etc. costly. There is also a serious problem that the radio band cannot be effectively used when the required flow rate is lower than the rate set in the advertisement window. In addition, in the control using IEEE802.11e as seen in Non-Patent Document 2, it is essential to implement IEEE802.11e in both the wireless LAN terminal and the base station. Further, in Patent Document 1, since regulation is applied after burst communication is performed, it is impossible to detect an unfairness of throughput and prevent it from occurring.

  On the other hand, in Patent Document 2, if it is detected that the occupied state of the transmission buffer of the wireless LAN exceeds the threshold and a delay time is inserted into the reception buffer, the reception buffer is likely to overflow. When the TCP ACK packet for the downstream TCP flow overflows from the reception buffer, the downstream TCP flow source reduces the transmission window, so the downstream TCP flow throughput is further reduced, and the upstream and downstream TCP flow throughput is unfair. Is encouraged. On the other hand, if it is detected that the wireless LAN reception buffer occupancy exceeds the threshold and a delay time is inserted into the transmission buffer, the transmission buffer is likely to overflow, and the TCP ACK packet overflows to the upstream TCP flow. Inequalities in throughput between flows are encouraged. In addition, when the TCP data packet of the downstream TCP flow overflows, the throughput of the downstream TCP flow further decreases, and the unfairness of the upstream and downstream TCP flow throughput is promoted.

  Red also detects that the transmission buffer occupancy exceeds the threshold value and discards the data packet in the transmission buffer, which further reduces the throughput of the downstream TCP flow and increases the throughput of the upstream and downstream TCP flows. Unfairness is encouraged. On the other hand, if it is detected that the occupancy state of the reception buffer exceeds the threshold and the data packet in the reception buffer is discarded, the bandwidth occupancy rate of the upstream TCP flow may be reduced unnecessarily. The reason is that even if the reception buffer occupation state exceeds the threshold value, the transmission buffer is not necessarily likely to overflow.

  The present invention eliminates the problems as described above, and suppresses the overflow of the transmission buffer, and can prevent the unfairness of the throughput between the upstream and downstream flows and the unfairness of the throughput between the upstream flows. The purpose is to provide.

  The relay device of the present invention is a relay device connected to one or more terminal devices through a network using a random access method, and relays packets exchanged between the terminal device and its communication partner. First means for monitoring the use state of the first and second means for stochastically discarding the data packet received from the terminal device according to the use state of the transmission buffer monitored by the first means. Prepare.

  According to the present invention, it is possible to prevent the unfairness of the throughput between the upstream and downstream flows and the unfairness of the throughput between the upstream flows. The reason for this is that the data packet received from the terminal device is stochastically discarded according to the usage state of the transmission buffer, thereby inducing congestion control on the transmission side and prompting a decrease in the bandwidth occupancy rate of the upstream flow. This is because the flow rate of the acknowledgment packet that flows into the channel is reduced to prevent the overflow of the transmission buffer.

[Embodiment 1]
Embodiment 1 of the present invention will be described in detail with reference to the drawings.

  The first embodiment is characterized in that, in a communication system using a random access scheme, the packet relay device monitors the use state of its own transmission buffer and discards the received packet if necessary. In the following description, a wireless LAN network using CSMA / CA will be described as an example of a typical communication system using a random access method, but the present invention is not limited to this as long as it is a random access method. Other examples of communication using the random access method include PLC (Power Line Communication), IEEE 802.15.3, IEEE 802.15.4, and the like.

  FIG. 1 is a configuration diagram of a network in which relay devices according to Embodiment 1 of the present invention are arranged. The wireless LAN base station (wireless base station) is connected to an external network 102 such as the Internet. Here, the wireless LAN terminal devices 104 to 107 perform packet transmission / reception with the communication device 101 via the wireless LAN base station device 103 and the external network 102.

  In FIG. 1, wireless LAN terminal devices 104 to 107 are upstream TCP flow transmission sources. Here, it is assumed that the communication partner communicates with a terminal on the external network 102. In this case, a wireless LAN frame encapsulating the upstream TCP data packet is transmitted from the wireless LAN terminal devices 104 to 107 to the wireless LAN base station device 103, and the wireless LAN base station device 103 passes the external network 102 to the communication partner. Sent. The receiving side communication device 101 connected to the external network 102 returns a TCP ACK packet as a reception confirmation response of the TCP data packet. The transmitted TCP ACK packet is buffered in the transmission buffer on the wireless LAN side of the wireless LAN base station device 103 via the external network 102. When the wireless LAN base station device 103 acquires the transmission right, the TCP ACK packet is output from the transmission buffer and transmitted to the wireless LAN terminal devices 104 to 107 that are the transmission sources.

  The downstream flow transmission path is the reverse of the above. When the communication device 101 connected to the external network 102 transmits the downlink data packet, it is stored in the transmission buffer on the wireless LAN side of the wireless LAN base station device 103 via the external network 102. The transmission buffer on the wireless LAN side in wireless LAN base station apparatus 103 in this embodiment is shared by TCP ACK packets and downlink data packets, and both are stored in the same buffer in the order of input.

  Here, the communication partner of the wireless LAN terminal devices 104 to 107 is the communication device 101 connected to the external network 102. However, when the communication partner is in the same wireless LAN cell, only the wireless LAN base station device 103 is used. A TCP data packet is delivered to the receiver. Even in such a case, the present invention is applicable.

  FIG. 2 is a block diagram showing a configuration of wireless LAN base station apparatus 103 as an example of a relay apparatus according to Embodiment 1 of the present invention.

  The wireless LAN base station device 103 includes a wireless LAN I / F (interface) 202 and an external NW I / F 201 that perform a wireless LAN base station function. The external NW I / F 201 is an interface with the external network 102 and includes a transmission function unit 203 that transmits a packet to the external network 102 and a reception function unit 211 that receives a packet from the external network 102. The wireless LAN I / F 202 is an interface between the wireless LAN, the reception function unit 204 that receives wireless LAN frames from the wireless LAN terminal devices 104 to 107 through the wireless LAN, and the wireless LAN to the wireless LAN terminal devices 104 to 107. And a transmission function unit 205 that transmits a wireless LAN frame through the network.

  The transmission function unit 205 of the wireless LAN I / F 202 includes transmission-side buffer means 210 that temporarily accumulates TCP packets to be transmitted to the wireless LAN terminal devices 104 to 107 through the wireless LAN.

  The reception function unit 204 of the wireless LAN I / F 202 includes a packet identification unit 207, a reception-side discard possibility determination unit 208, a packet discard unit 206, and a transmission buffer occupation state monitoring unit 209.

  The transmission buffer occupation state monitoring unit 209 monitors the buffer state of the transmission side buffer unit 210 of the transmission function unit 205 and notifies the reception side discard possibility determination unit 208 of the information. In the present embodiment, the buffer occupancy rate of the TCP ACK packet in the transmission side buffer means 210 is monitored as the buffer usage state. However, the occupancy rate of the downstream flow packet, the buffer delay of the packet, and the like may be monitored as the buffer usage state.

  The packet identification unit 207 acquires the flow information and notifies the reception side discard possibility determination unit 208. In the present embodiment, the packet identification unit 207 identifies whether the transport protocol is TCP or other. However, the flow information may be any information indicating a flow, such as a flow identification, for example, a destination node or a port number.

  The reception-side discard possibility determination unit 208 acquires the flow state and the transmission buffer occupation state from the packet identification unit 207 and the transmission buffer occupation state monitoring unit 209, respectively, and the received packet is an upstream TCP data packet and has a buffer occupation rate. If the threshold is exceeded, the received packet is determined as a discard packet candidate, and the received packet is determined as a discarded packet with a certain probability.

  The packet discarding unit 206 discards the received packet that the receiving side discard possibility determination unit 208 determines to be a discard packet. The packet discarding unit 206 transmits to the transmission function unit 203 of the external NW I / F 201 to transfer the received packet that the receiving side discard possibility determination unit 208 did not determine to be a discarded packet in the same manner as a normal operation. .

  The operation of wireless LAN base station apparatus 103 in the present embodiment will be described using the flowchart of FIG. FIG. 3 is a flowchart showing an operation when the wireless LAN base station apparatus 103 receives a wireless LAN frame.

  When the wireless LAN I / F 202 of the wireless LAN base station device 103 receives wireless LAN frames from the wireless LAN terminal devices 104 to 107 to which it belongs, it first transmits a WLAN ACK frame to the wireless LAN terminal device of the transmission source (F301 ). Thus, reception of the wireless LAN frame between the transmission source wireless LAN terminal device and the received wireless LAN base station device 103 is completed. This WLAN ACK transmission is a normal operation.

  Next, the packet identification means 207 in the reception function unit 204 identifies the information of the received packet and identifies whether it is a TCP data packet (F302). As a result, if the received packet is not a TCP data packet, it is forwarded to the transmission function unit 203 of the external NW I / F 201 as usual without undergoing the processing of the receiving side discard possibility judging means 208 and the packet discarding means 206 (F307) Finally, it is delivered to the communication partner via the external network 102.

  On the other hand, when the received packet is a TCP data packet, the receiving side discard possibility judging unit 208 checks the TCP ACK occupancy rate of the transmitting side buffer unit 210 from the transmission buffer occupation state monitoring unit 209 (F303). As a result, if the TCP ACK occupancy is equal to or less than the threshold value, the TCP data packet is transferred to the transmission function unit 203 as usual without being discarded by the packet discard unit 206 (F307). However, if the TCP ACK occupancy is equal to or greater than the threshold, the receiving-side discard possibility determination unit 208 assigns a random number (F304) and determines probabilistically whether to discard it (F305). In the present embodiment, data packets of all flows are discarded with a uniform probability without specifying a transmission source or a flow. The threshold value may be a fixed value or may be determined in consideration of radio congestion status and traffic status. If it is determined to be discarded, the received TCP data packet is discarded by the packet discarding means 206 (F306).

  Here, it is assumed that a one-way TCP data packet is transmitted in one connection. However, if the TCP flow is in both upstream and downstream directions with a single TCP connection, the upstream TCP data packet is an acknowledgment to the downstream TCP data packet, and the downstream TCP data packet is an acknowledgment to the upstream TCP data packet. Sometimes. In that case, the TCP data packet and the TCP ACK packet are not distinguished. When calculating the buffer size occupancy rate, the occupancy rate includes not only TCP ACK packets but also TCP data packets.

  Next, Example 1 in the case where there is one buffer occupancy threshold for packet discard in Embodiment 1 will be described. The maximum capacity of the transmission side buffer means 210 of the wireless LAN base station device 103 is 256 packets. If the TCP ACK packet occupancy exceeds 80% that is the threshold, that is, if the number of TCP ACK packets stored in the transmission side buffer means 210 of the wireless LAN base station device 103 exceeds the threshold 205 packets, Discard the received packet with a probability of 1%. For example, a random number is assigned with a value from 0 to 999. If the output value is 0 to 9, the random number is discarded, and the other values are transferred as usual without being discarded. Here, the unit representing the size of the buffer is a packet, but the unit may be a bit.

  Next, a second embodiment in which the discard rate of the upstream TCP data packet is determined based on the buffer occupancy rate of the TCP ACK packet will be described. For example, the reception-side discard possibility determination unit 208 of the wireless LAN base station device 103 determines the discard rate with reference to a table as shown in FIG. When the TCP ACK packet buffer occupancy is 80-90%, the upstream TCP data packet is discarded at a rate of 0.2%. Similarly, when the buffer occupancy rate of the TCP ACK packet is less than 90 to 100%, 0.5% is discarded, and when it reaches 100%, 1.0% is discarded. Here, the unit representing the size of the buffer is a packet, but the unit may be a bit.

  Next, a third embodiment in which the buffer occupancy threshold for packet discard varies with traffic will be described. Here, the number of upper and lower flows is used as an example of traffic as information for determining a threshold. When there is a downstream flow, the transmission side buffer means 210 needs room for a downstream data packet. For this reason, it is necessary to change the buffer occupancy threshold of the TCP ACK packet according to the case where there is no downlink flow, the case where there is a downlink flow, or the number of downlink flows. The number of downstream flows is acquired from the transmission side buffer means 210 of the transmission function unit 205. In this case, FIG. 5 shows an example of a table held by the reception-side discard possibility determination unit 208 of the wireless LAN base station device 103.

  In FIG. 5, even if the buffer occupancy rate of TCP ACK packets is equal, the packet discard rate increases as the number of downstream flows increases. This is because the buffer space is required as the downstream flow increases. The necessary space is realized by lowering the total throughput of the upstream TCP flow. As a realization method, the wireless LAN base station device 103 probabilistically discards an upstream TCP data packet when it is received. Here, the number of downlink flows is used as an index for threshold determination, but traffic-related indexes such as the input data bit rate and packet rate of downlink flow packets to the transmission side buffer means 210, the total number of flows regardless of uplink and downlink, etc. Anything is fine.

  As described above, in this embodiment, the fairness of each flow throughput can be maintained by performing both of the following two operations. The first operation is to monitor the TCP ACK packet occupancy rate in the transmission side buffer means 210 in the wireless LAN base station apparatus 103 when receiving an upstream TCP data packet. The second operation is to discard all the upstream flow TCP data packets at a certain rate when the buffer occupancy exceeds the threshold. As an effect of the above two operations, the total throughput of the upstream TCP flow can be intentionally reduced. Then, the occupancy rate of the TCP ACK packet in the transmission side buffer unit 210 of the wireless LAN base station apparatus 103 is lowered, and the buffer overflow of the TCP ACK packet can be prevented. As a result, it is possible to avoid the situation where an extremely low throughput flow occurs in the upstream TCP flow as shown in the problem and the situation where the throughput of the downstream TCP flow becomes extremely low, and achieve fairness between the flows. Can do.

[Embodiment 2]
Next, Embodiment 2 of the present invention will be described. In the second embodiment, when the reception side discard possibility determination means 208 in the wireless LAN base station device 103 in the first embodiment described above determines whether or not to discard the TCP data packet, each flow or terminal device This is a form in which the throughput is not fair and a certain amount of intentional difference is given, that is, a point of priority is discarded. A method of giving a difference in throughput between flows or between terminals is realized by making a difference in the discard rate.

  FIG. 6 shows the configuration of wireless LAN base station apparatus 103 in the second embodiment. Referring to FIG. 6, packet identifying means 207 in receiving function section 204 of wireless LAN base station apparatus 103 in Embodiment 1 shown in FIG. 2 has application identifying means 601 for identifying application information of received packets. It is different.

  When receiving a packet from the wireless LAN, the packet identification unit 207 in the present embodiment notifies the reception side discard possibility determination unit 208 of the application information of the received packet identified by the application identification unit 601. The receiving side discard possibility determination means 208 determines the priority order between the upstream flows that are currently communicating from the acquired application information, and determines whether or not to discard using the TCP data packet discard rate for each priority order. decide.

  Next, of the internal operations of wireless LAN base station apparatus 103 according to Embodiment 2, differences from Embodiment 1 will be described in detail with reference to FIGS.

  FIG. 7 shows a flowchart of the operation for determining the priority when a new TCP flow starts communication. When receiving the TCP packet, the packet identification unit 207 determines whether it is a new upstream TCP flow by the following procedure, and determines the priority class of the corresponding flow. TCP exchanges SYN packets when establishing a TCP connection. It is determined whether or not a new TCP flow is received by receiving this SYN packet (F701). Whether it is a SYN packet can be detected from the SYN bit in the TCP header. At this time, the flow is identified from the IP address of the transmission / reception terminal or the port number in the TCP header. Then, the application information is acquired from the port number, the TCP data packet following the SYN packet, etc. (F702). Thereafter, the priority information is determined by comparing the application information with the already entered application information (F703), and is entered (registered) in the flow and priority class mapping table as shown in FIG. 8 (F704). In the example of the mapping table in FIG. 8, a flow is specified by a set of session ID, transmission source port number, reception source port number, transmission source IP address, and reception source IP address.

  A specific application will be described as an example. Assume that the application of the flow that has already started communication is a video conference, and the newly started communication is e-mail. In this case, in the case of a teleconference TCP flow, the required bandwidth is at least as large as several hundred kBps communication. On the other hand, in the case of e-mail, even if there is a large attached file, the transmission rate is small and the time until completion of transmission of all packets is relatively long. Therefore, the priority class of the video conference TCP flow is set higher than that of the e-mail TCP flow.

  The flowchart shown in FIG. 10 shows the internal operation of radio base station apparatus 103 when discarding during actual communication. The operation until the occupation rate of the transmission side buffer means 210 is acquired is the same as that in the first embodiment (F301 to F303). At the time of reception, the packet identification unit 207 identifies the priority class from the application information identified by the application identification unit 601 using FIG. 8 and notifies the reception side discard possibility determination unit 208 of the priority class. The reception-side discard possibility determination unit 208 determines a discard rate according to the buffer occupancy rate using the table of FIG. In the table of FIG. 9, the discard rate of class 2 is higher than class 1 and class 3 is higher than class 2 for each buffer occupancy rate of TCP ACK packets. This is because the greater the discard rate, the greater the degree of throughput reduction. Since the subsequent operations are the same as those in the first embodiment, the description is omitted (F304 to F307).

  Note that, as shown in the first embodiment, even if the priority classes are the same, the discard rate may be determined in consideration of the traffic state.

  Here, application information is used as an index for determining the throughput difference between each flow or wireless terminal, but the priority order may be determined by a network design policy such as a communication partner apparatus or a transmission terminal apparatus.

  As described above, in the second embodiment, throughput priority control can also be realized by determining the discard rate for each flow in consideration of application information and the like. In addition, since the control is performed only by the wireless LAN base station device 103, the introduction cost can be reduced.

[Embodiment 3]
Next, Embodiment 3 of the present invention will be described.

  In the third embodiment, the reception side discard possibility determination means 208 in the wireless LAN base station apparatus 103 in the first and second embodiments described above considers the wireless state when determining whether to discard the TCP data packet. It is different in point to do.

  FIG. 11 shows the configuration of wireless LAN base station apparatus 103 in the third embodiment. Referring to FIG. 11, the difference is that reception function section 204 of wireless LAN base station apparatus 103 in Embodiments 1 and 2 shown in FIGS. The wireless state identification means 1101 determines whether the wireless LAN wireless state is a temporary bit error state, a congestion state, a normal state that is neither a temporary bit error state nor a congestion state, and whether or not the receiving side can be discarded. The determination unit 208 is notified.

  FIG. 12 shows a flowchart of the operation of the wireless LAN base station apparatus 103 of the third embodiment. The third embodiment is the same as the first and second embodiments until the buffer occupancy is acquired (F301 to F303). Thereafter, the wireless state identification unit 1101 determines the wireless state, and determines whether the wireless link is in a temporary bit error state or other state (F1201). For example, if the retry bit of the wireless LAN MAC header of the received frame is investigated and the retry bit is set for a certain period of time, not temporarily, and there is no difference between terminals, the radio state is frequently retransmitted due to congestion. Judge that On the other hand, if the retry bit is set temporarily or only the retry bit of a specific terminal is set, it is determined that the wireless state is a temporary bit error state. The receiving side discard possibility determination means 208 does not discard a packet received from a wireless link determined to be in a temporary bit error state. For a state other than a temporary bit error state, that is, a packet received from a radio link determined to be normal or congested, the same processing as in Embodiment 1 or Embodiment 2 is performed.

  In the third embodiment, by referring to the radio link state and determining whether to discard the TCP data packet, it is not necessary to unnecessarily reduce the throughput of the upstream TCP flow. The reason is to avoid the inconvenience of reducing the TCP transmission window unnecessarily when the bit error of the radio link is temporarily large, because the radio band cannot be effectively used when recovering from the bit error. .

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various additions and changes such as the following are possible.

In each of the above-described embodiments, the buffer occupancy rate of the TCP ACK packet in the transmission side buffer unit 210 is monitored as the buffer usage state. However, an embodiment in which the following situation is monitored as the buffer usage state is also conceivable.
(A) Occupancy rate of packets other than TCP ACK packets in the transmission side buffer means 210. As a packet other than the TCP ACK packet, there is a TCP data packet of a downstream TCP flow. If the occupancy of this packet increases, there is a risk of buffer overflow.
(B) Occupancy ratio of all packets in the downstream flow in the transmission side buffer means 210.
(C) One or more combinations of a bit rate at which a packet is input to the transmission side buffer unit 210, a bit rate at which a packet is output from the transmission side buffer unit 210, and a buffer delay in the transmission side buffer unit 210 . There is a risk of buffer overflow when the input bit rate exceeds a certain rate, the output bit rate falls below a certain rate, or the buffer delay exceeds a certain amount.

  Further, the relay device of the present invention can be realized by a computer and a program, in addition to being able to realize the functions of the relay device by hardware. The program is stored in a magnetic disk, a semiconductor memory, or the like, and by controlling the operation of the computer, the packet discarding unit 206, the packet identifying unit 207, the receiving side discard possibility determining unit 208, the transmission buffer occupation state monitoring unit on the computer 209, application identification means 601, wireless status identification means 1101, etc., implement functional means necessary for the relay apparatus of the present invention.

It is a figure which shows the system configuration example of the network by which the relay apparatus of this invention is distribute | arranged. FIG. 2 is a diagram illustrating a configuration example of a wireless LAN base station apparatus according to Embodiment 1 of the present invention. 6 is a flowchart showing an operation of the wireless LAN base station apparatus in the first embodiment of the present invention. FIG. 10 is an example of a management table when changing the discard rate of an upstream TCP data packet according to the buffer occupancy rate of a TCP ACK packet in Embodiment 1 of the present invention. 6 is an example of a management table in the case where the discard rate of an upstream TCP data packet is changed according to the buffer occupancy rate of the TCP ACK packet and the number of downstream flows in the first embodiment of the present invention. FIG. 7 is a diagram illustrating a configuration example of a wireless LAN base station device according to a second embodiment of the present invention. 7 is a flowchart showing an operation of a wireless LAN base station apparatus when a new TCP flow communication is started in Embodiment 2 of the present invention. In Embodiment 2 of this invention, it is an example of the mapping table of flow ID and priority class which the application identification means in a wireless LAN base station apparatus has. FIG. 11 is an example of a management table when changing the discard rate of an uplink TCP data packet according to the buffer occupancy rate of a TCP ACK packet and the application class in Embodiment 2 of the present invention. 9 is a flowchart showing a procedure for determining a discard rate of a TCP data packet in Embodiment 2 of the present invention. FIG. 11 is a diagram illustrating a configuration example of a wireless LAN base station device according to a third embodiment of the present invention. 10 is a flowchart showing an operation of the wireless LAN base station apparatus according to the third embodiment of the present invention.

Explanation of symbols

101 ... Communication device
102 ... External network
103 ... Wireless LAN base station equipment
104-107… Wireless LAN terminal
201 ... External NW I / F
202 ... Wireless LAN I / F
203… Transmission function part
204: Reception function section
205: Transmission function
206: Packet discarding means
207 ... Packet identification means
208: Means for determining whether or not the receiving side can be discarded
209 ... Transmission buffer occupation state monitoring means
210 ... Transmission side buffer means
211 ... Receiving function section
601 ... Application identification means
1101 ... Radio state identification means

Claims (12)

  A relay device that is connected to one or more terminal devices through a network using a random access method and relays packets exchanged between the terminal device and its communication partner, and monitors the use state of the transmission buffer on the network side. And a second means for stochastically discarding a data packet received from the terminal device in accordance with a use state of the transmission buffer monitored by the first means. apparatus.   The relay apparatus according to claim 1, wherein an occupancy rate of an acknowledgment packet for a TCP data packet in the transmission buffer is used as a use state of the transmission buffer.   The relay apparatus according to claim 1, wherein an occupancy rate of packets other than an acknowledgment packet for a TCP data packet in the transmission buffer is used as a use state of the transmission buffer.   The relay apparatus according to claim 1, wherein an occupancy ratio of all packets in the transmission buffer is used as a use state of the transmission buffer.   As a use state of the transmission buffer, any one or a combination of a bit rate at which a packet is input to the transmission buffer, a bit rate at which a packet is output from the transmission buffer, and a buffer delay in the transmission buffer is used. The relay device according to claim 1, wherein the relay device is used.   6. The relay apparatus according to claim 1, wherein the second means discards all received data packets with a uniform probability.   6. The relay apparatus according to claim 1, wherein the second means determines a discard rate according to a rule for the received data packet, and discards the received data packet at the determined discard rate.   8. The discarding rate according to claim 7, wherein the second means determines the discard rate in consideration of any one or a combination of an application type, a receiving packet transmitting terminal, and a receiving packet receiving terminal. Relay device.   The network is a wireless network, and includes third means for monitoring a wireless state of the wireless network, and the second means determines a discard rate according to the wireless state monitored by the first means. The relay apparatus according to claim 7 or 8, wherein   The relay apparatus according to claim 1, wherein the relay apparatus functions as an access router.   In a relay method in a relay device that is connected to one or more terminal devices through a network using a random access method and relays packets exchanged between the terminal device and its communication partner, the use state of the transmission buffer on the network side A first step of monitoring, and a second step of stochastically discarding a data packet received from the terminal device in accordance with a use state of the transmission buffer monitored in the first step. Relay method.   A computer that is connected to one or more terminal devices through a network that uses a random access method and that constitutes a relay device that relays packets exchanged between the terminal device and its communication partner, the use state of the transmission buffer on the network side And a second means for stochastically discarding a data packet received from the terminal device in accordance with a use state of the transmission buffer monitored by the first means. program.

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