Abstract:
Disclosed is a mobile communication system preventing the transmission of acknowledgements at a burst leading to a decrease in throughput caused by detecting the retransmission and the congestion of packets at the protocol of a transport layer. In a mobile communication system including a mobile terminal and gateway equipment for relaying a packet between a communication partner and the mobile terminal, if the gateway equipment receives the acknowledgement from the mobile terminal, the gateway equipment waits the transmission of the received acknowledgement to the communication partner until the estimated transmission time passes from the time at which the gateway equipment receives the previous acknowledgement from the mobile terminal.

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese patent application JP 2010-064443 filed on Mar. 19, 2010, the content of which is hereby incorporated by reference into this application. 
     FIELD OF THE INVENTION 
     The present invention relates to a mobile communication system for communicating a packet between gateway equipment and a mobile terminal and, in particular, to a mobile communication system in which the gateway equipment causes the mobile terminal to wait the transmission of an acknowledgement for a packet. 
     BACKGROUND OF THE INVENTION 
     At present, a mobile communication system called the third and a half generation has prevailed. An environment has further been improved in which a mobile terminal is connected to the Internet to use an electronic mail and the Web access. 
     On the other hand, the next generation radio communication service with a broader bandwidth (5 MHz or higher) and a high transmission rate of 10 Mbps or higher has been standardized and developed. The next generation radio communication service is known as the 3.9 generation mobile communication system called worldwide interoperability for microwave access (WiMAX) and long term evolution (LTE) using orthogonal frequency division multiplexing access (OFDMA). 
     In general, a transmission control protocol (TOP) used as a transport protocol between a mobile terminal and a server system has a retransmission control function using a sequence number (control number) and an acknowledgement. Thereby, the TOP can provide a high reliability communication. The TOP has a rate control function to transmit the next packet in conformity with a timing in which the acknowledgement arrives in order to transmit a packet in conformity with the bandwidth of a network. 
     In general, the transmission rate of a radio access is network between a mobile terminal and a base station is lower than that of a network between a server system and a wireless access gateway. For this reason, if congestion in which a buffering packet increases is detected in the entity of a link layer in the radio access network, gateway equipment (a node) (or a base station or a wireless access gateway) adjusts the pacing of transmission of an acknowledgement by buffering a packet of the acknowledgement (refer to JP-T-2002-527936, for example). 
     SUMMARY OF THE INVENTION 
     The 3.9 generation mobile communication system such as the WiMAX and the LTE has presently been studied. It is expected that a radio communication system with a transmission rare of 10 Mbps or higher per user is available. 
     Fading and shadowing caused by the movement of a mobile terminal between the mobile terminal and a base station can cause an error in a radio link layer between the mobile terminal and the base station. An automatic repeat request (ARQ) for automatically retransmitting a link layer between the mobile terminal and the base station, a radio base station control apparatus, or a wireless access gateway is used as a unit for recovering the error of the radio link layer. 
     On the other hand, for the speed of an interface of a server system used for a data center, the speed of a gigabit interface has been generalized. In recent years, an interface with a transmission rate of as high as 10 Gbps has been introduced to a server system. For this reason, even though the next generation mobile communication system is introduced, the speed of the interface of a mobile terminal tends to deviate from that of the interface of the server system. 
     In general, a transport protocol such as the TCP used between a mobile terminal and a server includes a congestion control function to control the transmission rate of a packet to prevent the packet from being dropped due to a failure of storing queues (queue overflow) for transmitting a packet at a router or a switch and a base station in a network attributed to the reception capacity of a mobile terminal and the transmission bandwidth in a network. The TOP includes a function called a self clocking for a server transmitting a packet in conformity with a timing in which an acknowledgement arrives at the server as a function to control the transmission rate of the packet in conformity with the bandwidth of a network. 
     A radio resource divided by a frequency and a time base between the mobile terminal and the base station is allocated to each mobile terminal. For a packet whose length is shorter than that of a predetermined packet, a packet transmitted from the base station to the server may be transmitted at a burst by transmitting a plurality of packets buffered at the base station until the transmission timing of the allocated resource in one transmission timing. 
     If the ARQ is introduced between the mobile terminal and the base station, an error is caused in the block of a part of the ARQ. If a subsequent block is normally received and buffered and the error in the block is recovered by retransmission, the block buffered on the reception side and the block in which the error is recovered can be transmitted at a burst. 
     A case where a block is transmitted at a burst in the ARQ is described below with reference to  FIG. 10 . 
       FIG. 10  is a conventional diagram of the present invention. 
     A self clocking for transmitting the next packet when an acknowledgement is received is implemented in a transport protocol between a server  101  and a mobile terminal  104 . 
     When the server  101  receives the acknowledgement from the mobile terminal  104 , the mobile terminal  104  transmits a data packet to be transmitted next to the data packet corresponding to the received acknowledgement to the mobile terminal  104 . 
     In  FIG. 10 , the server  10  initially transmits a data packet for a transmittable window size without waiting an acknowledgement. 
     When the base station  103  receives the data packet for a transmittable window size, the base station  103  divides the received data packet into four blocks of a sequence number (SN) ( 0  to  3 ) and relays the blocks to the mobile terminal  104 . 
     When the mobile terminal  104  receives the blocks from the base station  103 , the mobile terminal  104  transmits the acknowledgement provided with the same number as the received blocks to the base station  103 . 
     In  FIG. 10 , the base station  103  detects an error in an ARQ block of an acknowledgement with a sequence number of  0  and cancels the ARQ block of an acknowledgement ( 1001 ). The base station  103  normally receives the ARQ block of an acknowledgement of sequence numbers ( 1  to  3 ) ( 1002  to  1004 ). 
     The base station  103  requests the ARQ block of an acknowledgement of a control number  0  for retransmission. The ARQ blocks of all acknowledgements corresponding to the data packet for a window size are not completed, so that the ARQ blocks of acknowledgements of control numbers  1  to  3  received in steps  1002  to  1004  are buffered. 
     When the base station  103  normally receives the ARQ block of an acknowledgement of a control number  0  ( 1005 ), the ARQ blocks of all acknowledgements corresponding to the data packet for one window size are completed, so that the base station  103  transmits these four acknowledgements at a burst ( 1006 ). 
     When the server  101  receives the acknowledgements transmitted from the base station  103 , the server  101  transmits the next packet. Since the acknowledgements have been transmitted at a burst from the base station  103 , the server  101  transmits packets at a burst ( 1007 ). 
     Since the transmission rate of a radio access network is lower than that of the server network between the server  101  and a wireless access gateway  102 , if there is insufficient space in queue of a router and a switch composing the radio access network between the wireless access gateway  102  and the base station  103 , the router and the switch cannot completely buffer the queue to cause the overflow of the queue, thereby the transmission of packets at a burst breaks packets to be transmitted ( 1008 ). 
     Since the transmission rate of the radio network between the base station  103  and the mobile terminal  104  is lower than that of the server network, if there is insufficient space in queue at the base station  103 , the overflow of the queue is caused to break the packet to be transmitted ( 1009 ). 
     Thus, throughput is lowered by losing packets at the router and the switch which configure the radio access network and the base station  103 . 
     Even if packets are not lost at the router, the switch, and the base station  103  configuring the radio access network, packets are incorrectly retransmitted at the protocol of a transport layer. 
     The present invention has an object to provide a mobile communication system preventing the transmission of acknowledgements at a burst leading to a decrease in throughput caused by detecting the retransmission and the congestion of packets at the protocol of such a transport layer. 
     According to one aspect of the present invention, a mobile communication system includes a mobile terminal and gateway equipment for relaying a packet between a communication partner and the mobile terminal, wherein the gateway equipment stores information about a transmission rate between the mobile terminal, and the gateway equipment; stores a packet length of a packet relayed from the communication partner to the mobile terminal and the time at which an acknowledgement corresponding to the packet transmitted from the mobile terminal to the communication partner is received in a process related to a transport protocol used between the mobile terminal and the communication partner in a case where the packet is relayed from the mobile terminal to the gateway equipment; estimates a transmission time required for transmitting the packet from the gateway equipment to the mobile terminal based on the length of a packet and the transmission rate to the mobile terminal; and takes a relay time interval at which the acknowledgement from the mobile terminal is relayed to communication partner as the estimated transmission time interval by waiting, if the gateway equipment receives the acknowledgement from the mobile terminal, the transmission of the received acknowledgement to the communication partner until the estimated transmission time passes from the time at which the gateway equipment receives the previous acknowledgement from the mobile terminal. 
     According to the present invention, the transmission of acknowledgements at a burst can be prevented, so that the lowering of throughput caused by detecting the retransmission and the congestion of packets at the protocol of the transport layer can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a configuration of a mobile communication system according to a first embodiment of the present invention; 
         FIG. 2  is a schematic diagram showing a configuration of a wireless access gateway according to the first embodiment of the present invention; 
         FIG. 3  is an operational diagram in a case where a TOP is used as a transport protocol between the mobile terminal and the server in the first embodiment of the present invention; 
         FIG. 4  is a diagram showing the transmission of a data packet by a sliding window of the TOP according to the first embodiment of the present invention; 
         FIG. 5  is a flow chart for data packet relay processing executed by the wireless access gateway according to the first embodiment of the present invention; 
         FIG. 6  is a diagram showing communication in the mobile communication system of the first embodiment of the present invention; 
         FIG. 7  is a diagram showing a configuration of the base station in a second embodiment of the present invention; 
         FIG. 8  is a flow chart for a data packet relay process executed by the base station according to the second embodiment of the present invention; 
         FIG. 9  is a diagram showing communication in the mobile communication system of a third embodiment of the present invention; and 
         FIG. 10  is a conventional diagram of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First to third embodiments of the present invention are described below with reference to  FIGS. 1 to 9 . 
     First Embodiment 
     The first embodiment of the present invention is described below with reference to  FIGS. 1 to 6 . 
       FIG. 1  is a schematic diagram showing a configuration of a mobile communication system according to the first embodiment of the present invention. 
     The mobile communication system includes a server  101 , a wireless access gateway  102 , a base station  103 , and a mobile terminal  104 . The wireless access gateway  102  and the base station  103  are generically referred to as gateway equipment. 
     The server  101  communicates with the wireless access gateway  102  via an IP network  105 . Communication is made via a radio access network  106  between the wireless access gateway  102  and the base station  103  and between the base station  103  and the mobile terminal  104 . 
     The transmission rate (a guaranteed bit rate for each bearer used by the mobile terminal  104  or a maximum bit rate of an individual or collective bearers) of the radio access network  106  is lower than that of the IP network  105 . 
     The server  101  is a communication partner of the mobile terminal  104  and transmits a packet to the mobile terminal  104 . When the server  101  transmits data to the mobile terminal  104 , the server  101  first transmits a packet for a window size transmittable without waiting an acknowledgement and then transmits the next packet to the mobile terminal  104  each time an acknowledgement is received. 
     The wireless access gateway  102  is installed between the IP network  105  and the radio access network  106  and relays a packet between the server  101  and the base station  103 . 
     The wireless access gateway  102  is described in detail below. 
     The wireless access gateway  102  manages the moving status of the mobile terminal  104  in the radio access network  106 . The wireless access gateway  102  executes paging for the mobile terminal  104  in the radio access network  106 . Furthermore, the wireless access gateway  102  executes processing for incoming/outgoing call setup control of the mobile terminal  104  and for switching the base station  103  (handoff) in a case where the mobile terminal  104  is in communication. 
     Other than that, the wireless access gateway  102  has a function to relay a packet between the mobile terminal  104  and the server  101  while following the base station  103  subordinating the mobile terminal  104 . The wireless access gateway  102  executes processing for the mobile terminal  104  receiving the service of the IP network  105  (the terminal authentication of the mobile terminal  104 , service authentication, and the allocation of IP address). 
     If the LTE of the 3.9 generation mobile communication system is introduced, the wireless access gateway  102  corresponds to mobility management entity (MME), service gateway (S-GW), and packet data network gateway (P-GW). 
     If the WiMAX of the 3.9 generation mobile communication system is introduced, the wireless access gateway  102  corresponds to access service gateway (ASN-GW). 
     The base station  103  communicates with the mobile terminal  104  by radio and relays communication between the mobile terminal  104  and the server  101 . 
     The mobile terminal  104  corresponds to a cellular phone or a portable personal computer, for example. 
       FIG. 2  is a schematic diagram showing a configuration of the wireless access gateway  102  according to the first embodiment of the present invention. 
     The wireless access gateway  102  includes a CPU  201 , a memory  202 , a storage  203 , and a network interface card (NIC)  204 . The CPU  201 , the memory  202 , the storage  203 , and the network interface card (NIC)  204  are connected with one another via a bus  205 . 
     The CPU  201  executes calculation processing such as the execution of a program stored in the memory  202 . 
     The memory  202  stores program groups for operating the wireless access gateway  102 . Specifically, the memory  202  stores program groups for executing the mobility management of the mobile terminal  104 , the paging for the mobile terminal  104 , the incoming/outgoing call setup control of the mobile terminal  104 , and the call processing for the mobile terminal  104  switching the base station  103  in communication. Furthermore, the memory  202  stores various table groups used by the CPU  201  when the program groups are executed. 
     The memory  202  further includes a queue  208  for receiving and buffering a packet addressed to the mobile terminal  104  or the server  101 , a scheduler  207  for extracting the packet from the queue  208  and transmitting the packet to a network via the NIC  204 , and a scheduler table  209  to which the scheduler  207  refers in extracting the packet from the queue  208 . 
     The storage  203  is a storage for the memory  202 . 
     The NIC  204  is an interface for connecting the wireless access gateway  102  to an external network  206  communicable with the server  101  and the base station  103 . 
       FIG. 3  is an operational diagram in a case where the TCP is used as a transport protocol between the mobile terminal  104  and the server  101  in the first embodiment of the present invention. 
     The server  101  transmits a data packet to the mobile terminal  104  ( 301 ). The mobile terminal  104  receives the data packet and transmits an acknowledgement to the server  101  ( 302 ). 
     The TCP header of the data packet transmitted from the server  101  stores a sequence number (Seq) and a packet length data (LEN) indicating the packet length of the data packet ( 303 ). The sequence number is incremented by one each time 1-byte packet is transmitted. 
     The TCP header of the acknowledgement transmitted from the mobile terminal  104  stores the sequence number included in the data packet received by the mobile terminal  104  as a confirmation number ( 304 ). 
     The wireless access gateway  102  capsules the data packet transmitted from the server  101  in the IP packet to transmit the encapsulated data packet to the base station  103  housing the mobile terminal  104  to which the data packet is addressed ( 305 ). The IP packet for encapsulating the data packet is referred to as a generic routing encapsulation (GRE) or a GPRS tunneling protocol (GTP). Similarly, the base station  103  encapsulates the acknowledgement transmitted from the mobile terminal  104  by the IP packet ( 305 ). In other words, communication is made by the encapsulated data packet between the wireless access gateway  102  and the base station  103 . 
     The repeat request of a radio link layer called the ARQ or a Hybrid ARQ is used between the mobile terminal  104  and the base station  103 . In this case, if the capacity of the packet transmitted and received by the mobile terminal  104  is larger than that of a block used by the ARQ, the packet is divided into a block capacity (block size) and transmitted ( 306  to  308 ). The packet divided into the block capacity is reconstructed on the reception side. If the capacity of the packet transmitted and received by the mobile terminal  104  is smaller than that of a block used by the ARQ, a plurality of data packets is stored in a block processed by one-time ARQ ( 310 ). 
     In  310  of  FIG. 3 , the acknowledgement (UL ARQ=2) transmitted by the mobile terminal  104  stores acknowledgements corresponding to sequence numbers  2920  and  4380 . 
     In the TCP as a transport protocol, a sequence number for providing a high reliability communication is stored in the TCP header transmitted from the server  101 . The sequence number of a data packet received by the mobile terminal  104  is stored in the TOP header of the acknowledgement transmitted from the mobile terminal  104 . For this reason, the reception side detects whether a number is missing in a sequence number or a confirmation number of the received data packet to allow detecting that the data packet is lost and the data packet is discarded in communication. If the reception side detects that a number is missing in a sequence number or a confirmation number of the received data packet, the reception side requests the transmission side to retransmit the data packet in which a number is missing. 
     In the TOP as a transport protocol, the server  101  transmits only a sliding window size (or the data capacity of a sliding window) transmittable without waiting an acknowledgement and transmits the next data packet when the server  101  receives one acknowledgement. This enables communication in conformity with the bandwidth of the mobile terminal  104 . The transmission of a data packet by the sliding window of the TOP is described in detail in  FIG. 4 . 
       FIG. 4  is a diagram showing the transmission of a data packet by the sliding window of the TOP according to the first embodiment of the present invention. 
     The server  101  transmits data packet for the sliding window size transmittable without waiting an acknowledgement ( 401  to  404 ). 
     In step  401 , the server  101  transmits the data packet with a packet length of 1460 bytes and control numbers of  0  to  1459 . In step  402 , the server  101  transmits the data packet with a packet length of 1460 bytes and control numbers of  1460  to  2919 . In step  403 , the server  101  transmits the data packet with a packet length of 1460 bytes and control numbers of  2920  to  4379 . 
     A step  404  shows that the server  101  transmits the data packet up to the sliding window size transmittable without waiting an acknowledgement. The data packet transmitted in step  404  has a packet length of 1460 bytes and a control number of xxxx to xxxx+1459. 
     When the server  101  completes the transmission in which the capacity of the data packet whose acknowledgement is not received reaches the sliding window size, the server  101  interrupts the transmission of the data packet ( 405 ). 
     When the server  101  receives the acknowledgement corresponding to the data packet transmitted in step  401 , the server  101  transmits the net data packet ( 406 ). In step  406  and the subsequent steps, the server  101  transmits data packets in timing in which the server  101  receives an acknowledgement ( 407 ). More specifically, the server  101  can transmit data packets in conformity with the bandwidth of a network on the side of the mobile terminal  104  and cause through-put to conform to the bandwidth of a network on the side of the mobile terminal  104 . 
       FIG. 5  is a flow chart for data packet relay processing executed by the wireless access gateway  102  according to the first embodiment of the present invention. 
     When the wireless access gateway  102  creates a bearer used by the mobile terminal  104  between the mobile terminal  104  and the wireless access gateway  102 , the wireless access gateway  102  stores the transmission rate of the radio access network  106  between the mobile terminal  104  and the wireless access gateway  102  in the scheduler table  209  ( 501 ). 
     The transmission rate stored in the scheduler table  209  may be a guaranteed bit rate for each bearer used by the mobile terminal  104  or a maximum bit rate of an individual or a collective bearer, for example. 
     The wireless access gateway  102  stores the association of the transport protocol of a bearer transmitting a data packet to the mobile terminal  104  with a bearer transmitting the acknowledgement for the data packet from the mobile terminal  104  in the scheduler table  209  ( 502 ). 
     In step  502 , the wireless access gateway  102  may also store the association of the transport protocol of a bearer transmitting an acknowledgement to the server  101  with the transport protocol of a bearer transmitting a data packet from the server  101 . 
     When the wireless access gateway  102  receives a packet related to the transport protocol (the data packet transmitted from the server  101  or the acknowledgement transmitted from the mobile terminal  104 ) ( 503 ), the wireless access gateway  102  determines whether the received packet is the data packet transmitted from the server  101  to the mobile terminal  104  ( 504 ). 
     In step  504 , if it is determined that the received packet is the data packet transmitted from the server  101  to the mobile terminal  104 , the wireless access gateway  102  stores the packet length and the sequence number of the received data packet in the scheduler table  209  ( 505 ) and the processing returns to step  503 . 
     On the other hand, if it is determined that the received packet is not the data packet transmitted from the server  101  to the mobile terminal  104 , in other words, if it is determined that the received packet is the acknowledgement transmitted from the mobile terminal  104  to the server  101 , the wireless access gateway  102  identifies the transmission, rate at which the data packet transmitted from the server  101  corresponding to the received acknowledgement is transmitted to the mobile terminal  104  ( 506 ). 
     A method of identifying a transmission rate is specifically described below. 
     The wireless access gateway  102  identifies a bearer transmitting the data packet transmitted from the server  101  corresponding to the received acknowledgement with reference to the association, stored in the scheduler table  209  in step  502 , of the transport protocol of the bearer transmitting a data packet to the mobile terminal  104  and the bearer in which an acknowledgement for the data packet is transmitted from the mobile terminal  104 . The wireless access gateway  102  identifies the transmission rate of the identified bearer used by the mobile terminal  104  with reference to the transmission rate between the wireless access gateway  102  and the mobile terminal  104  stored in the scheduler table  209  in step  501 . 
     The wireless access gateway  102  acquires the packet length of the data packet with the control number corresponding to the confirmation number of the received acknowledgement with reference to the packet length and the control number of the data packet transmitted to the mobile terminal  104 , stored in the scheduler table  209  in step  505 . The wireless access gateway  102  estimates the time spent until the data packet corresponding to the received acknowledgement reaches the mobile terminal  104  (transmission delay time) based on the packet length of the acquired data packet and the transmission rate used by the mobile terminal  104  identified in step  506  ( 507 ). 
     The wireless access gateway  102  buffers the acknowledgement received this time until the transmission delay time estimated in step  507  passes from the time when the last acknowledgement is transmitted among the time when the acknowledgement of the transport protocol of the bearer similar to the received acknowledgement is transmitted to the server  101  ( 508 ). The wireless access gateway  102  transmits the acknowledgement received this time to the server  101  when the transmission delay time estimated in step  507  passes from the time when the last acknowledgement is transmitted and stores the time when the acknowledgement received this time is transmitted to the server  101  ( 509 ) and the processing returns to step  503 . 
     As described above, the wireless access gateway  102  relays the previous acknowledgement to the server  101 , then delays the acknowledgement transmitted from the mobile terminal  104  by the time spent until the data packet transmitted from the server  101  corresponding to the acknowledgement is transferred to the mobile terminal  104  and relays the delayed acknowledgement to the server  101 . For this reason, even if the acknowledgement is transmitted at a burst, the wireless access gateway  102  delays the acknowledgement by the transmission delay time from the time when the previous acknowledgement is transmitted and transmits the delayed acknowledgement to the server  101 , allowing preventing the server  101  from receiving the acknowledgement at a burst. 
     Since the period during which the wireless access gateway  102  transmits an acknowledgement takes the delay time of acknowledgement as the time spent until the data packet transmitted from the server  101  is transferred to the mobile terminal  104 , when the mobile terminal  104  receives the data packet next to the data packet corresponding to the acknowledgement received this time by the wireless access gateway  102 , the server  101  receives the acknowledgement received this time by the wireless access gateway  102  and transmits the next data packet to the mobile terminal  104 . Therefore, the packet for a window size is communicated via the network between the server  101  and the mobile terminal  104  to allow the packet to be effectively communicated between the server  101  and the mobile terminal  104 . 
     In the present embodiment, the wireless access gateway  102  stores the confirmation number of the acknowledgement received from the mobile terminal  104  instead of storing the packet length of the data packet transmitted to the mobile terminal  104  in step  505 . In step  507 , the wireless access gateway  102  estimates the packet length of the data packet transmitted from the server  101  corresponding to the acknowledgement received this time based on the difference value between the confirmation number of the acknowledgement received this time and the confirmation number of the acknowledgement received last time. 
     In the present embodiment, although the transmission delay time is estimated in steps  506  and  507  when the acknowledgement transmitted from the mobile terminal  104  is transmitted to the server  101 , the transmission delay time is previously estimated when the data packet transmitted from the server  101  is transmitted to the mobile terminal  104  and the estimated transmission delay time may be stored. 
     The wireless access gateway  102  further stores the time at which the data packet transmitted form the server  101  is transmitted to the mobile terminal  104 , the sequence number of the data packet, and the packet length of the data packet. The wireless access gateway  102  identifies the data packet with the sequence number corresponding to the confirmation number of the received acknowledgement. The wireless access gateway  102  cumulatively calculates the difference between the time at which the identified data packet is transmitted and the time at which the acknowledgement is received as a round-trip time. The wireless access gateway  102  divides the calculated cumulative round-trip time by the sum of the packet length of the data packet and the packet length of the acknowledgement and multiplies the divided value by the packet length of the data packet to estimate the transmission delay time. 
     If the confirmation request received from the mobile terminal  104  is a retransmission request acknowledgement indicating a retransmission request for a data packet in step  508 , the wireless access gateway  102  instantly transmits the retransmission request acknowledgement for only the transmission delay time to the server  101  without waiting. 
     If the confirmation number of the received acknowledgement precedes that of the acknowledgement received in advance of the received acknowledgement, the wireless access gateway  102  determines that the received acknowledgement is the retransmission request acknowledgement in other words, if the control number of the data packet corresponding to the received acknowledgement precedes that of the data packet corresponding to the acknowledgement received in advance of the received acknowledgement, the wireless access gateway  102  determines that the received acknowledgement is the retransmission request acknowledgement. 
       FIG. 6  is a diagram showing communication in the mobile communication system of the first embodiment of the present invention. The processes similar to those in  FIG. 10  are denoted by the same reference numerals and the description thereof is omitted. 
     In step  1006 , if the base station  103  transmits four acknowledgements at a burst, the wireless access gateway  102  receives the four acknowledgements and takes the interval of transmission of the received acknowledgement to the server  101  as a transmission delay time interval described in  FIG. 5 . 
     The server  101 , therefore, receives the acknowledgement in the transmission delay time interval ( 601 ). For this reason, the server  101  newly transmits data packets in the transmission delay time interval ( 602 ). 
     The wireless access gateway  102  and the base station  103  transmit each packet and then receive the next packet, allowing preventing the discard of the packet due to queue overflow ( 603 ). 
     As described above, in the present embodiment, the wireless access gateway  102  delays the acknowledgement transmitted from the mobile terminal  104  by the time spent until the data packet transmitted from the server  101  (transmission delay time) corresponding to the acknowledgement is transferred to the mobile terminal  104  and relays the delayed acknowledgement to the server  101  after the wireless access gateway  102  relays an acknowledgement previous to the acknowledgement to the server  101 . For this reason, even if the acknowledgement is transmitted at a burst, the wireless access gateway  102  delays the acknowledgement by the transmission delay time from the time when the previous acknowledgement is transmitted and transmits the delayed acknowledgement to the server  101 , allowing preventing the server  101  from receiving the acknowledgement at a burst and from transmitting data packets at a burst. Accordingly, in the wireless access gateway  102  and the base station  103 , the discard of the packet due to queue overflow can be prevented. 
     Second Embodiment 
     In the second embodiment, the base station  103  has a function, which the wireless access gateway  102  has in the first embodiment, to relay an acknowledgement with the acknowledgement delayed. 
       FIG. 7  is a diagram showing a configuration of the base station  103  in the second embodiment of the present invention. 
     The base station  103  includes a TRX  701 , a MODEM  702 , a MAC process unit  703 , an ARQ process unit  704 , a queue  705 , a scheduler  706 , a network interface card NIC  707 , a scheduler table  708 , and a resource management unit  709 . 
     The TRX  701  digital-to-analog converts a packet to be transmitted and analog-to-digital converts the received packet. The MODEM  702  subjects a signal to be transmitted to and received from an antenna to a modulation-demodulation process. The MAC process unit  703  allocates resources such as a band, frequency, and time frame used for transmission to and reception from the mobile terminal  104  to the mobile terminal  104 . The ARC) process unit  704  executes the ARQ process of a radio link layer between the mobile terminal  104  and the base station  103 . The ARQ process is sometimes executed by a radio base station control device (RNC and BSC) for controlling the base station  103 . 
     The queue  705  is the one in which a packet addressed to the mobile terminal  104  or the server  101  is received and buffered. The scheduler  706  extracts a packet from the queue  705  and transmits the packet to a network via the NIC  707 . The scheduler table  708  is the one to which the scheduler  706  refers when extracting a packet from the queue  705 . 
     The NIC  707  is an interface for connecting the base station  103  with the wireless access gateway  102 . 
     The resource management unit  709  is the one to which the MAC process unit  703  refers when allocating a resource to the mobile terminal  104 . 
       FIG. 8  is a flow chart for a data packet relay process executed by the base station  103  according to the second embodiment of the present invention. 
     When the base station  103  receives a packet to data packet transmitted from the server  101  or an acknowledgement transmitted from the mobile terminal  104 ) related to a transport protocol ( 801 ), the base station  103  determines whether the received packet is the data packet transmitted from the server  101  to the mobile terminal  104  ( 802 ). 
     In step S 802 , if the base station  103  determines that the received packet is the data packet transmitted from the server  101  to the mobile terminal  104 , the base station  103  estimates the bandwidth of a bearer used for communication with the mobile terminal  104  with reference to the resource management unit  709 . The base station  103  stores the packet length of the received data packet, the sequence number of the received data packet, and the bandwidth of the estimated bearer ( 803 ). The processing returns to step  801 . 
     In step  803 , the base station  103  stores association of the transport protocol of the bearer transmitting a data packet to the mobile terminal  104  and the bearer transmitting the acknowledgement for the data packet from the mobile terminal  104  in the scheduler table  708 . 
     In step  803 , the base station  103  may store also association of the transport protocol of the bearer transmitting an acknowledgement to the server  101  and the transport protocol of the bearer transmitting a data packet from the server  101 . 
     On the other hand, in step  802 , if the base station  103  determines that the received packet is not the data packet transmitted from the server  101  to the mobile terminal  104 , in other words, if the base station  103  determines that the received packet is the acknowledgement transmitted from the mobile terminal  104  to the server  101 , the base station  103  identifies a transmission rate at which the data packet transmitted from the server  101  corresponding to the received acknowledgement is transmitted to the mobile terminal  104  ( 804 ). 
     A method of identifying a transmission rate is described in detail below. 
     The base station  103  identifies the bearer transmitting the data packet transmitted from the server  101  corresponding to the received acknowledgement with reference to the association of the transport protocol of the bearer transmitting a data packet to the mobile terminal  104  and the bearer transmitting the acknowledgement for the data packet from the mobile terminal  104  stored in the scheduler table  708  in step  803 . The base station  103  identifies the bandwidth of the identified bearer (transmission rate) used by the mobile terminal  104  with reference to the bandwidth of the bearer stored in the scheduler table  708  in step  803  ( 804 ). 
     The base station  103  acquires the packet length of the data packet with the control number corresponding to the confirmation number of the received acknowledgement with reference to the packet length and the control number of the data packet transmitted to the mobile terminal  104  stored in the scheduler table  708  in step  803 . The base station  103  estimates the time spent until the data packet corresponding to the received acknowledgement is transferred to the mobile terminal  104  (transmission delay time based on the acquired packet length of the data packet and the transmission rate of the bearer used by the mobile terminal  104  identified in step  804  ( 805 ). 
     The base station  103  buffers the acknowledgement received this time until the transmission delay time estimated in step  805  passes from the time at which the last acknowledgement is transmitted among the time during which the acknowledgement of the transport protocol belonging the seine bearer as the acknowledgement received this time is transmitted to the server  101  ( 806 ). When the transmission delay time estimated in step  805  passes from the time at which the last acknowledgement is transmitted the base station  103  transmits the acknowledgement received this time to the server  101  and stores the time at which the acknowledgement received this time is transmitted to the server  101  ( 807 ). The processing returns to step  801 . 
     In step  807 , if the confirmation request received from the mobile terminal  104  is a retransmission request acknowledgement indicating a retransmission request for a data packet, the base station  103  instantly transmits the retransmission request acknowledgement for only the transmission delay time to the server  101  without waiting. 
     If the confirmation number of the received acknowledgement precedes that of the acknowledgement received in advance of the received acknowledgement, the base station  103  determines that the received acknowledgement is the retransmission request acknowledgement. In other words, if the control number of the data packet corresponding to the received acknowledgement precedes that of the data packet corresponding to the acknowledgement received in advance of the received acknowledgement, the base station  103  determines that the received acknowledgement is the retransmission request acknowledgement. 
     The transmission delay time may be estimated using a plurality of methods described in the first embodiment. 
     As described above, the base station  103  delays the acknowledgement transmitted from the mobile terminal  104  by the time spent until the data packet transmitted from the server  101  (transmission delay time) corresponding to the acknowledgement is transferred to the mobile terminal  104  and relays the delayed acknowledgement to the server  101  after the base station  103  relays an acknowledgement previous to the acknowledgement to the server  101 . For this reason, even if the acknowledgement is transmitted at a burst, the base station  103  delays the acknowledgement by the transmission delay time from the time when the previous acknowledgement is transmitted and transmits the delayed acknowledgement to the server  101 , allowing preventing the server  101  from receiving the acknowledgement at a burst. 
     Since the delay time of the acknowledgement is taken as the time spent until the data packet transmitted from the server  101  is transferred to the mobile terminal  104 , when the mobile terminal  104  receives the data packet next to the data packet corresponding to the acknowledgement received this time by the base station  103 , the server  101  receives the acknowledgement received this time by the base station  103  and transmits the next data packet to the mobile terminal  104 . Therefore, the packet for a window size is communicated via the network between the server  101  and the mobile terminal  104  to allow the packet to be effectively communicated between the server  101  and the mobile terminal  104 . 
     Third Embodiment 
     In the first and second embodiments, the base station  103  divides a first data packet transmitted from the server  101  into a plurality of data blocks, provides the data blocks with control numbers, and transmits the data blocks to the mobile terminal  104 . When the base station  103  receives the acknowledgements of all the data blocks into which the first data packet is divided, the base station  103  transmits the acknowledgement corresponding to the first data packet to the server  101  in other words, the base station  103  does not transmit the acknowledgement corresponding to the first data packet until the acknowledgements of all the data blocks into which the first data packet is divided are completed. 
     In the third embodiment, when the base station  103  receives the acknowledgement data block of a first data block to which a first data packet is divided, the base station  103  transmits the acknowledgement data block to the server  101  without waiting the acknowledgements of all of the data blocks to which a first data packet is divided. 
     When the base station  103  receives the acknowledgement transmitted corresponding to the mobile terminal  104  receiving the data block, the base station  103  stores the confirmation number of the received acknowledgement. 
     The base station  103  detects whether a number is missing in the confirmation number of the received acknowledgement is missing. 
     More specifically, the base station  103  calculates a difference between the sequence numbers till the confirmation number stored last among the sequence numbers of the data blocks already transmitted and all the stored confirmation numbers to detect that a number is missing in the confirmation number of the received acknowledgement if there is a difference if the base station  103  detects that a number is missing in the confirmation number of the received acknowledgement, the base station  103  transmits the acknowledgement, to the server  101 , indicating that the acknowledgement of the confirmation number of the difference between the sequence numbers till the confirmation number stored last among the sequence numbers of the data blocks already transmitted and all the stored confirmation numbers is not received. 
     If the base station  103  receives all the acknowledgements of the confirmation number in which a number is missing, the base station  103  transmits the acknowledgement indicating that all the acknowledgements of all the data blocks to which the first data block is divided are received to the server  101 . 
     The third embodiment is described in detail with reference to  FIG. 9 . 
       FIG. 9  is a diagram showing communication in the mobile communication system of the third embodiment of the present invention. The processes similar to those in  FIG. 10  are denoted by the same reference numerals and the description thereof is omitted. 
     In step  1001 , the base station  103  fails to receive the acknowledgement of a confirmation number  100 . In step  1002 , when the base station  103  normally receives the acknowledgement of a confirmation number  1560 , the base station  103  detects whether a number is missing in the confirmation number. 
     More specifically, since there is a difference ( 100 ) between the sequence numbers ( 100  and  1560 ) till the confirmation number ( 1560 ) stored last among the sequence numbers of the data blocks already transmitted and all the stored confirmation numbers ( 1560 ), the base station  103  detects that a number is missing in the acknowledgement of the confirmation number ( 1560 ). 
     The base station  103  transmits a selection acknowledgement including the confirmation number of the received acknowledgement and the confirmation number in which a number is missing to the server  101  ( 901 ). The confirmation number ( 1560 ) of the received acknowledgement is stored in the SACK block of the selection acknowledgement and the confirmation number ( 100 ) in which a number is missing is stored in the ACK block of the selection acknowledgement. 
     In step  1003 , when the base station  103  normally receives the acknowledgement of a confirmation number  3120 , the base station  103  detects whether a number is missing in a confirmation number. The base station  103  detects that the confirmation number  100  is missing herein, so that the base station  103  transmits the selection acknowledgement to the server  101  ( 902 ). The SACK block of the selection acknowledgement stores the confirmation numbers  1560  and  3120 . The ACK block of the selection acknowledgement stores the confirmation number  100 . 
     In step  1005 , when the base station  103  receives the acknowledgement of the confirmation number  100  in which a number is missing, the base station  103  receives all the acknowledgements corresponding to all the data blocks to which the first data packet is divided, so that the base station  103  transmits the acknowledgement indicating that all the acknowledgements are wholly received to the server  101  ( 903 ). 
     On the other hand, in step  901 , when the server  101  receives the transmitted selection acknowledgement, the server  101  transmits the next data packet ( 904 ). 
     As described above, even though the base station  103  detects that a number is missing, the base station  103  transmits a selection acknowledgement to the server  101 , so that the server  101  can transmit a data packet in conformity with the transmission rate between the base station  103  and the mobile terminal  104 . 
     This prevents the server  101  from receiving acknowledgements at a burst and transmitting data packets at a burst and packets from being discarded due to queue overflow at the router and the switch in the radio access network  106  and at the base station  103 . 
     The mobile terminal and the gateway equipment the base station or the wireless access gateway) can be applied to a mobile communication system.