JP4684920B2 - Handover method, handover system, base station, and access router - Google Patents

Description

  The present invention relates to a handover method used when a mobile terminal apparatus performs handover between communication systems, and more particularly to a handover method for handover of a mobile terminal apparatus between different types of communication systems, a handover system, and a communication system. The present invention relates to a base station and an access router.

  In recent years, with the development of the mobile Internet, there is a problem that communication quality (for example, communication rate) deteriorates due to handover processing in which a mobile terminal device switches connection points.

  For example, at the time of handover, a flow of a mobile terminal apparatus that performs handover (hereinafter referred to as a handover terminal apparatus) is transferred to the handover destination base station. The packet of the mobile terminal apparatus that was originally connected to the handover destination base station is lost due to the flow into the mobile station, thereby causing a deterioration in communication quality.

  This will be described in detail with reference to FIG. 4. Here, a mobile node (MN) 11 is connected to a base station (BS) 12, and the BS 12 is an access router (AR). The MN 11 is downloading a file from an FTP (File Transfer Protocol) server 13 (indicated by reference numeral F1), while the four existing MNs 14-1 to 14-4 are connected to the BS 15, and the BS 15 Are connected to the AR 15a, and each of the MNs 14-1 to 14-4 downloads a file from the FTP server 16 (indicated by reference numeral F2). Here, when the MN 11 moves and is handed over to the BS 15, the traffic to the MN 11 is directed to the BS 15 (indicated by the symbol F3).

  Then, in contrast to the state where the four existing MNs 14-1 to 14-4 share network resources, new traffic destined for the MN 11 is added to the BS 15, so that congestion occurs temporarily in the BS 15, and the handover terminal apparatus There is a possibility that not only the packets of the MN11, but also the packets of the existing MNs 14-1 to 14-4 may be lost.

  In particular, in TCP (Transmission Control Protocol), in many versions including TCP Reno, the communication rate is greatly lowered by the occurrence of packet loss as a trigger, so the communication rate of the existing mobile terminal device is greatly lowered together with the handover terminal device. It will be.

  By the way, conventionally, for example, most handovers are performed in the same wireless system such as a cellular network, but in the future, different types of wireless systems (communication systems) such as a handover from a wireless MAN (Metropolitan Area Network) to a cellular network will be used. ) Is expected to become popular. For example, as shown in FIG. 7, when the MN 11 communicates with another MN 11a via the Internet NET and the communication system X, the MN 11 moves and communicates via another type of communication system Y. Needs to be handed over between different types of communication systems.

  However, there are many cases in which the characteristics differ greatly between different types of wireless systems. For example, the communication speed of so-called third-generation mobile phones such as W-CDMA and CDMA 2000 1x is several hundred kbps at maximum, whereas IEEE 802.16-2004, which is one of wireless MANs, has a maximum of several tens of Mbps. Then, the communication speed is increased by about 100 times.

  In such a handover between different types of communication systems, the above-described problems such as deterioration in communication quality are considered to be more prominent. Referring to FIG. 5, it is assumed that the MN 11 is connected to a wireless system 21 capable of high-speed communication and downloads a file from the FTP server 13 at high speed.

  Here, when the MN 11 moves and hands over to the radio system 22 that can only perform low-speed communication, a large amount of traffic when connected to the radio system 21 flows into the radio system 22 at once. In the wireless system 22, since the BS 15 can only deliver packets to the mobile terminal device (MN) at a low speed, there is a high possibility that the BS 15 (the buffer of the BS 15) overflows all at once with the packet addressed to the MN 11. The effect is greater than handover between wireless systems.

  In order to prevent such inconveniences, there is one that performs traffic control during handover between BSs under the BR (Border Router) that supervises subdomains when the hierarchical mobility protocol is used ( (See Non-Patent Document 1, hereinafter referred to as a conventional example).

  Referring to FIG. 6, in the conventional example, the BR 23 has a buffer called a cache buffer in addition to a normal buffer, and the BR 23 transfers a flow addressed to the MN 11 after the handover of the MN 11 which is a handover terminal apparatus. Cache it and send it to a normal buffer in small increments. At this time, the BR 23 uses a so-called window control method to adjust the sending speed, and sends a packet buffered by the window size.

  The initial value of the window size is “1”, and when receiving an ACK (response signal) from the MN 11, the BR 23 increases the window size by “1”. When the BR 23 receives a duplicate ACK or detects a packet loss such as not receiving an ACK within a predetermined time, the BR 23 sets the window size to “1” again.

  When a preset time has elapsed after the flow cache is started, the BR 23 sends out the packets in the cache all at once to the normal buffer and ends the processing. By performing such processing, the flow destined for the handover terminal device is gradually added to the handover destination network, and the congestion state in the BS 15 can be avoided.

Graceful Degradation of Transport Layer in Mobile Internet, “2nd International Conference on Wired / Wireless Internet Communications (WWIC 2004), 200-131, pp. 120-131.

  However, in the conventional example, it is necessary to create a cache buffer for each mobile terminal device every time the mobile terminal device is handed over. In a BR that supervises a subdomain in which a plurality of BSs exist, a large number of mobile terminal apparatuses are managed, and there is not a high possibility that handover within the subdomain will frequently occur. In addition, frequent creation and deletion of the cache buffer requires an extra processing load on the BR.

  Also, the cost required for the memory space increases, such as the need to prepare a large amount of memory space for the cache buffer in advance. In addition, since window control is performed for each cache buffer, the processing load also increases.

  Furthermore, even if there is a margin in the bandwidth of the handover destination BS, all packets addressed to the handover terminal apparatus are cached, and packets are sent out gradually by window control as in the slow start of TCP. Network resources may not be used effectively. Since the TCP retransmission timer is not so long, when the packet is cached in the cache buffer, the retransmission timer may expire on the TCP transmission side, and unnecessary retransmission processing may occur.

  In addition, in the conventional example, handover between the same wireless systems is assumed, but considering handover between different types of wireless systems (especially, only low-speed communication from a wireless system capable of high-speed communication as shown in FIG. 5). Considering handover to an unsupported wireless system), a large amount of packets are cached in the cache buffer, and as described above, the retransmission timer on the TCP transmission side may expire and retransmission processing may occur Becomes higher.

  Since the retransmitted packet is queued at the end of the cache buffer, the retransmission timer expires again on the TCP transmission side before the retransmission packet is sent out due to the queuing delay, and the retransmission process is repeated. Is more likely.

  In addition, when a preset time has elapsed after the flow cache is started in the above-described state, the packets in the cache are sent out at once, causing congestion and causing problems due to the above-described handover. On the other hand, if the timer (preset time) is set longer, congestion is less likely to occur, but the flow of the handover terminal apparatus may be repeatedly retransmitted for a long time and exposed to a decrease in throughput for a long time.

  The present invention has been made in order to solve such a problem, and the object thereof is to reduce the processing load at the time of handover, reduce the throughput, and cause retransmission processing. It is an object of the present invention to provide extremely few handover methods, handover systems, base stations, and access routers.

  The present invention is a handover method for a mobile terminal apparatus selectively connected to any one of a plurality of communication systems to perform handover between the communication systems, and when the mobile terminal apparatus performs the handover, The first step of estimating the amount of packets destined for the device staying in the network as the amount of staying packets according to the moving average value of the throughput and the round-trip delay amount, and the packet discard rate based on the amount of staying packets and the remaining buffer amount There is provided a handover method comprising: a second step to be obtained; and a third step of discarding the received packet addressed to the mobile terminal apparatus according to the packet discard rate.

  In the present invention, in the third step, each time a packet is received, the size of the packet is subtracted from the amount of staying packets.

  Further, the present invention is a handover system used when a mobile terminal apparatus selectively connected to any of a plurality of communication systems via a base station and an access router is used for handover between the communication systems, In the mobile terminal device, when performing handover between the communication systems, the staying packet estimation means for estimating the amount of packets destined for the own device staying in the network as the staying packet amount according to the moving average value of the throughput and the round-trip delay amount; The base station or the access router is used as a selection station, and notification means for notifying the selection station of the amount of staying packets is provided. The selection station includes the amount of staying packets and the remaining amount of buffer. Based on the packet discard rate calculating means for obtaining the packet discard rate, and receiving the packet discard rate according to the packet discard rate. Providing a handover system characterized by packet discarding means for discarding a packet addressed to the mobile terminal device is provided.

  In the present invention, each time a packet is received, the packet discarding unit subtracts the size of the packet from the amount of staying packets.

  The present invention is also provided for a communication system, and is a base station for connecting a mobile terminal apparatus to the communication system, and when the mobile terminal apparatus performs handover between the communication systems, the mobile terminal Receiving means for receiving, from the device, a staying packet amount representing the amount of packets destined for the device staying in the network estimated according to the moving average value of the throughput and the round-trip delay amount; And a packet discarding unit for discarding a packet addressed to the mobile terminal device according to the packet discarding rate.

  In the present invention, in the base station, when the packet discard rate calculation means receives the amount of staying packets, the mobile terminal apparatus has at least the staying packet amount and the packet discard rate in association with the terminal identifier of the mobile terminal device A first means for generating a terminal entry and storing the entry in a handover node list; and when a packet is received, if the terminal identifier associated with the packet does not exist in the handover node list, the packet is stored in a packet buffer. And second means for storing, and third means for passing the packet to the packet discarding means when a terminal identifier related to the packet is present in the handover node list when the packet is received.

In the present invention, the round trip delay time is transmitted together with the amount of staying packets from the mobile terminal device, and in the base station, the first means is based on the round trip delay time when generating the handover terminal entry. Each time the packet discarding unit receives a packet, the packet discarding unit subtracts the packet size from the amount of staying packets in the handover terminal entry, and the timer expires or the amount of staying packets is When it reaches zero, the handover terminal entry is deleted.

  In addition, the present invention is an access router that is provided corresponding to a communication system and connects the mobile terminal apparatus to the communication system to define an access route, and the mobile terminal apparatus performs handover between the communication systems. Receiving means for receiving, from the mobile terminal device, a staying packet amount representing a packet amount destined for the device staying in the network estimated according to a moving average value of throughput and a round-trip delay amount, and the staying packet amount And a packet discard rate calculating means for obtaining a packet discard rate based on the remaining buffer capacity and a packet discard means for discarding a packet destined for the mobile terminal according to the packet discard rate. Provide a router.

  Also in this access router, when the packet discard rate calculation means receives the amount of staying packets, the mobile terminal device associates with the terminal identifier for the mobile terminal device a handover terminal entry having at least the amount of staying packets and the packet discard rate. A first means for generating and storing the entry in a handover node list; and a first means for storing the packet in a packet buffer when a packet identifier is not present in the handover node list when the packet is received. And a third means for passing the packet to the packet discarding means when the terminal identifier associated with the packet exists in the handover node list when the packet is received.

Further, the round trip delay time is transmitted together with the amount of staying packets from the mobile terminal device, and in the access router, the first means measures the time based on the round trip delay time when generating the handover terminal entry. Each time the packet discarding unit receives a packet, the packet discarding unit subtracts the size of the packet from the amount of staying packets in the handover terminal entry, and the timer expires or the amount of staying packets is When it reaches zero, the handover terminal entry is deleted.

  As described above, in the present invention, the amount of packets staying in the network at the time of handover is obtained as the amount of staying packets, and the mobile terminal device (mobile terminal device that performs handover (handover terminal device) according to this staying packet amount ) Is discarded, so that it is possible to prevent a drop in communication rate at the handover destination.

  Further, in the present invention, the amount of staying packets is estimated according to the moving average value of the throughput and the round-trip delay amount, the packet discard rate is obtained based on the amount of staying packets and the remaining amount of buffer, Since the packets are discarded in accordance with the packet discard rate, for example, when performing handover between communication systems of different types, there is an effect that it is possible to avoid a drop in throughput at the handover destination.

  In the present invention, since packets destined for the handover terminal apparatus are discarded according to the packet discard rate at the time of handover, it is possible not only to reduce the processing load at the time of handover but also to cause retransmission processing. There is an effect that it can be reduced, and there is an effect that the throughput of the handover terminal apparatus can be recovered early.

  Next, embodiments of the present invention will be described with reference to the drawings. First, referring to FIG. 1, in the illustrated network system, the MN 11 is connected to a wireless system 21 capable of high-speed communication via the BS 12 and downloads a file from the FTP server 13 (indicated by reference numeral F1). On the other hand, the MNs 14-1 to 14-3 are connected to the wireless system 22 that supports only low-speed communication via the BS 15, and download files from the FTP server 16 (indicated by reference numeral F2). In the illustrated example, BSs 11 and 15 are connected to ARs 31 and 32, respectively.

  FIG. 2 is a block diagram showing the configuration of the AR according to the present embodiment to the limit necessary for this embodiment. In the figure, ARs 31 and 32 are a packet classification unit 41 (the packet classification unit 41 has a function as a packet discard rate calculation means), a memory unit 42, and a packet dropper unit. 43 (packet discarding means), a packet buffer (Packet Buffer) unit 44, and a lower layer (Lower Layer) unit 45. The packet classification unit 41 sorts received packets as described later.

  The memory unit 42 stores a handover node list (Handover Node List (HONL)) shown in FIG. 3, and an entry (handover terminal entry) for each handover terminal device is stored in the HONL as described later. Accumulated. The handover terminal entry includes, for each IP address (IP Address (terminal identifier)) field, a staying packet amount (Amount of Flying Packets) field, an RTT (Round Trip Time (msec)) field, and a discard. A rate (Drop Rate (%)) field is defined, and the packet discard unit 43 performs packet discard according to HONL (that is, handover terminal entry). The packet buffer unit 44 queues the packets from the packet classification unit 41 and the packet discard unit 43, and transmits the packets queued by the lower layer unit 45.

  Referring to FIGS. 1 and 2, MN 11 holds a maximum RTT and a moving average value of throughput for each predetermined period. In FIG. 1, it is assumed that MN 11 moves and a handover occurs. At this time, the MN 11 receives a trigger signal for announcing the occurrence of a handover, as described in, for example, IEEE 802.21. Thereby, the MN 11 estimates the amount of packets addressed to the MN 11 currently staying in the network as the staying packet amount. This estimate is calculated by, for example, Equation 1 (Equation 1 represents the maximum amount of packets that stay in the network).

(Equation 1)
Residual packet amount (B) = 125 × [moving average of throughput (Mb / s)] [round trip delay time (ms)]

  Using Equation 1, when the MN 11 estimates the amount of staying packets remaining in the network, the MN 11 notifies the AR32 connected to the handover destination BS 15 together with the maximum RTT value. This notification is performed using, for example, a message that conforms to an MIH (Media Independent Handover) message format that is scheduled to be standardized by IEEE 802.21.

  In addition, when the BS 12 measures the throughput of the MN 11, the BS 12 may transmit the moving average value of the throughput to the MN 11 using an MIH message or the like. In this case, the MN 11 does not need to hold a moving average value of throughput.

  When the amount of staying packets and the maximum RTT value are received from the MN 11 that is the handover terminal device, in the AR 32, for example, the packet classification unit 41 creates an entry (handover terminal entry) related to the handover terminal device in the HONL shown in FIG. 3 (HONL An entry is created for each mobile terminal apparatus that performs the handover). As described above, in the HONL (that is, the handover terminal entry), the IP address field for registering the IP address of the MN 11 (the handover terminal apparatus that has notified the AR 32), and the stay packet for registering the notified stay packet amount An amount field, an RTT field for registering the notified maximum RTT value, and a discard rate field for registering a packet discard rate are defined.

In AR32, for example, the discard rate is calculated using Equation 2.
(Equation 2)
Discard rate (%) = IF (AFP−ROB × MAR) / AFP ≦ 0,0
Otherwise, (AFP-ROB × MAR) / AFP
However, AFP: staying packet amount (B), ROB: remaining buffer capacity (B) of the packet buffer unit, MAR: ratio for taking a safety margin (0 <MAR ≦ 1).

  When the discard rate (%) is zero, the entry related to the handover terminal device is deleted from the HONL. Note that before creating an entry in the HONL, the discard rate may be calculated first, and the entry may be created when the discard rate is other than zero.

  Hereinafter, a case where the discard rate of entries related to MN 11 is other than zero will be described. In AR32, when a packet is received, the packet classification unit 41 first checks the source address field of the received packet. If the transmission source address is not registered in the IP address field of any entry in HONL, the packet classification unit 41 queues the packet directly in the packet buffer unit 44.

  On the other hand, if the source address is registered in the IP address field of any entry in the HONL, the packet classification unit 41 passes the packet to the packet discard unit 43. The packet discard unit 43 randomly discards the packet according to the discard rate described in the discard rate field in the entry in which the source address of the packet is registered.

  The packet discard unit 43 queues the packet that has not been discarded in the packet buffer 44. Then, every time a packet is received, the packet discard unit 43 subtracts this packet size from the value described in the staying packet amount field in the entry.

  When the value of the staying packet amount field becomes zero or when α (parameter) times as long as the value described in the RTT field elapses from the creation time of the entry, the packet discard unit 43 deletes the entry. Note that when a new entry is created when there is an existing entry for the handover terminal apparatus in the HONL, or when another entry remains when deleting the existing entry, the discard rate is calculated according to Equation 3.

(Equation 3)
Discard rate (%) = IFΣ (AFP) − (ROB × MAR) / ΣAFP ≦ 0,0
Otherwise, Σ (AFP) − (ROB × MAR) / Σ (AFP)
In Equation 3, the discard rate in all entries is changed uniformly.

On the other hand, the discard rate shown in Equation 4 may be used.
(Equation 4)
Discard rate (%) = IFΣ (AFP) − (ROB × MAR) / ΣAFP ≦ 0,0
Otherwise, Σ (AFP) − (ROB × MAR) / AFP
Here, Equation 4 is executed for each entry, and a different discard rate is set for each entry.

  In the above example, the AR has been described as having a function (packet discard function) such as a packet discard process, but the BS may have this packet discard function.

  In this way, in this embodiment, the handover terminal apparatus estimates the amount of staying packets according to the moving average value of throughput and the RTT, and the amount of staying packets and the remaining buffer capacity (free space) at the handover destination base station or access router. The packet discard rate is calculated based on the buffer amount), and the handover destination base station or access router discards the packet addressed to the handover terminal apparatus according to the packet discard rate. As a result, when performing handover between different types of communication systems, it is possible not only to avoid a drop in throughput at the handover destination, but also to reduce the processing load at the time of handover, and retransmission processing occurs. This can be extremely reduced.

  As is clear from the above description, the mobile terminal device is provided with a staying packet estimation function and a notification function, and either the access router or the base station is provided with a packet discard rate calculation function and a packet discard function. Will be.

  It can be suitably used as a handover method between communication systems of different types.

1 is a diagram showing a network configuration in which an example of a handover system according to an embodiment of the present invention is used. FIG. It is a figure which shows the structure of the access router shown in FIG. 1 only by the part relevant to this Embodiment. FIG. 3 is a diagram illustrating an example of a handover node list held by the access router illustrated in FIG. 1. It is a figure for demonstrating the malfunction caused by a hand-over. It is a figure for demonstrating the malfunction caused by the handover between different types of communication systems. It is a figure for demonstrating the conventional handover method. It is a figure for demonstrating the hand-over between different types of communication systems.

Explanation of symbols

11, 14-1 to 14-4 Mobile terminal equipment (MN)
12, 15 Base station (BS)
13, 16 FTP server 21, 22 Communication system 31, 32 Access router (AR)
41 Packet classification unit 42 Memory unit 43 Packet discard unit 44 Packet buffer unit 45 Lower layer unit

Claims (10)

A mobile terminal apparatus selectively connected to any of a plurality of communication systems is a handover method for performing handover between the communication systems,
A first step of estimating the amount of staying packets, which is the amount of packets destined for the device staying in the network when the mobile terminal device performs the handover , based on a product of a moving average value of throughput and a round-trip delay amount;
A second step of determining a packet discard rate based on the amount of staying packets and the remaining amount of buffer, so that a portion of the amount of staying packets that exceeds the remaining amount of buffer is discarded ;
A third step of discarding the received packet addressed to the mobile terminal device according to the packet discard rate;
A handover method characterized by comprising:   2. The handover method according to claim 1, wherein in the third step, each time a packet is received, the size of the packet is subtracted from the amount of staying packets. A handover system used when a mobile terminal apparatus selectively connected to any one of a plurality of communication systems via a base station and an access router performs handover between the communication systems,
In the mobile terminal device, when performing handover between the communication systems , a stay packet that estimates a stay packet amount that is a packet amount destined for the own device staying in the network based on a product of a moving average value of throughput and a round-trip delay amount A means of estimation,
With any one of the base station and the access router as a selected station, a notification means for notifying the selected station of the amount of staying packets is provided,
Based on the amount of staying packets and the remaining amount of buffer, the selected station calculates a packet discarding rate for obtaining a packet discarding rate so that packets exceeding the remaining amount of buffering out of the amount of staying packets are discarded. Means,
A handover system comprising packet discarding means for discarding the received packet destined for the mobile terminal apparatus in accordance with the packet discard rate.   4. The handover system according to claim 3, wherein the packet discarding unit subtracts the size of the packet from the amount of staying packets every time a packet is received. A base station provided corresponding to a communication system for connecting a mobile terminal device to the communication system,
When the mobile terminal apparatus performs handover between the communication systems, the mobile terminal apparatus represents the amount of packets destined for the apparatus that stays in the network estimated based on the product of the moving average value of throughput and the round-trip delay amount. Receiving means for receiving the amount of staying packets;
Based on the amount of staying packets and the remaining amount of buffer, a packet discarding rate calculating means for obtaining a packet discarding rate so that a portion of the staying packet amount exceeding the remaining amount of buffering is discarded ,
Packet discarding means for discarding packets addressed to the mobile terminal device in accordance with the packet discard rate;
A base station characterized by comprising: The packet discard rate calculating means includes:
When the staying packet amount during the handover is received, a handover terminal entry that associates the previous SL residence packet amount and the packet loss rate to the terminal identifier for the mobile terminal device, as a component of the handover node list first means for adding and storing to the handover node list,
A second means for storing the packet in a packet buffer when a packet identifier is not present in the handover node list when the packet is received;
A third means for passing the packet to the packet discarding means when a terminal identifier associated with the packet is present in the handover node list when the packet is received;
The base station according to claim 5, comprising: The round trip delay time is transmitted from the mobile terminal device together with the amount of staying packets,
The first means, when adding the handover terminal entry to the handover node list, activates a timer that counts a time measured based on the round trip delay time;
The packet discarding unit subtracts the size of the packet from the amount of staying packets in the handover terminal entry each time a packet is received, and when the timer expires or the amount of staying packets becomes zero, The base station according to claim 6, wherein a terminal entry is deleted from the handover node list . An access router provided corresponding to a communication system and defining an access route by connecting a mobile terminal device to the communication system,
When the mobile terminal apparatus performs handover between the communication systems, the mobile terminal apparatus represents the amount of packets destined for the apparatus that stays in the network estimated based on the product of the moving average value of throughput and the round-trip delay amount. Receiving means for receiving the amount of staying packets;
Based on the amount of staying packets and the remaining amount of buffer, a packet discarding rate calculating means for obtaining a packet discarding rate so that a portion of the staying packet amount exceeding the remaining amount of buffering is discarded ,
Packet discarding means for discarding packets addressed to the mobile terminal device in accordance with the packet discard rate;
An access router characterized by comprising: The packet discard rate calculating means includes:
When the staying packet amount during the handover is received, a handover terminal entry that associates the previous SL residence packet amount and the packet loss rate to the terminal identifier for the mobile terminal device, as a component of the handover node list first means for adding and storing to the handover node list,
A second means for storing the packet in a packet buffer when a packet identifier is not present in the handover node list when the packet is received;
A third means for passing the packet to the packet discarding means when a terminal identifier associated with the packet is present in the handover node list when the packet is received;
9. The access router according to claim 8, further comprising: The round trip delay time is transmitted from the mobile terminal device together with the amount of staying packets,
The first means, when adding the handover terminal entry to the handover node list, activates a timer that counts a time measured based on the round trip delay time;
The packet discarding unit subtracts the size of the packet from the amount of staying packets in the handover terminal entry each time a packet is received, and when the timer expires or the amount of staying packets becomes zero, The access router according to claim 9, wherein a terminal entry is deleted from the handover node list .

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