Abstract:
An object is to provide a frame receiving apparatus capable of reducing establishment of radio protocol connections, while improving communication quality and performance of mobile equipment and network. In order to achieve this object, a frame receiving apparatus has a QoS reference part for identifying whether a frame is an acknowledgement type frame, based on a QoS identifier provided for each frame, and a sequence number reference part for determining whether a frame is lost, only for each acknowledgement type frame, and requesting retransmission of a lost frame.

Description:
[0001]     This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2003-207593 filed Aug. 14, 2003, the entire content of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a frame transmission/reception system, a frame transmitting apparatus, a frame receiving apparatus, and a frame transmission/reception method.  
         [0004]     2. Related Background Art  
         [0005]     As a third-generation mobile communication system there is the UMTS (Universal Mobile Telecommunication System) standardized by 3GPP (3rd Generation Partnership Project). In the radio access method of UMTS, communication using a unique radio protocol is carried out between a physical layer and an application layer. The radio protocol is set between a mobile station and a radio network control station (RNC), and consists of sublayers of PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), and MAC (Medium Access Control). Among these the RLC sublayer (cf. Non-patent Document 1 cited below) establishes a connection at a time of a start of communication to permit acknowledgement type and unacknowledgement type communication. The RLC sublayer determines one of three modes: TM (Transparent Mode), UM (Unacknowledgement Mode), and AM (Acknowledgement Mode) at the time of establishing the RLC connection. TM has a function of only dividing upper-layer data and transferring it to a lower sublayer (or the reverse). UM and AM enable upper-layer data to be loaded in a divided or multiplexed state on RLC-PDU, and are suitable for transfer of variable-length data such as IP (Internet Protocol) packets. UM has no retransmission function, while AM has a function of correcting an error due to degradation of quality in a radio section by retransmission control. These modes are set on a connection-by-connection basis and it is necessary to independently set a connection for a case of handling a data flow with need for retransmission and a connection for a case of handling a data flow without need for retransmission.  
         [0006]     Where a mobile station performs a communication consisting of one data flow, it can select an RLC connection mode suitable for QoS (Quality of Service) requirements for the data flow. In a scheme in which a number of communication terminals perform mobile communication through one mobile station, however, there are two conceivable forms of utilization of the RLC connection. One is a form in which all data flows are transferred by one RLC connection, and the other a form in which an RLC connection is established for each data flow. The former has a problem that all the data flows with various QoS requirements must have the same QoS condition on the RLC connection. The correction for data error in a radio section with a high error rate by automatic retransmission control is an essential technology for improvement in throughput in the case of the data communication that is required to make no error. However, for example, if the same retransmission is carried out in the case of voice communication, a communication delay due to retransmission will raise a problem of failure in meeting required QoS. Therefore, the retransmission control in the radio protocol should be carried out according to QoS. The latter has a problem that one mobile station must perform management of many RLC connections. This requires that the apparatus have the performance of managing the RLC connections for respective data flows. In addition, a transport connection for transfer of RLC frames is simultaneously switched for an entire data flow every handover of a mobile station, which imparts loads on the mobile station and network and which degrades the performance thereof. There is another problem that when a mobile station adds a data flow, a connection delay occurs for establishment of an RLC connection.  
         [0007]     Non-patent Document 1: 3GPP, TS23.107, “Radio Link Control (RLC) protocol specification,” December 2002.  
       SUMMARY OF THE INVENTION  
       [0008]     Where one mobile station transfers data flows with a plurality of QoS requirements as described above, the same retransmission condition is applied to the transfer of the data flows by a single radio protocol connection. It was thus difficult to transfer data flows so as to satisfy both an application requiring real-timeness and an application not requiring real-timeness. By setting different radio protocol connections according to respective QoS conditions, it becomes feasible to satisfy each of the QoS conditions. However, the establishment of many radio protocol connections results in producing a delay due to establishment of a radio protocol connection at every addition of a new data flow. The change of a path of a radio protocol connection at the same time as a handover of each mobile station will increase control loads on a radio access network and, in turn, degrade the network performance.  
         [0009]     An object of the present invention is therefore to provide a frame transmission/reception system, a frame transmitting apparatus, a frame receiving apparatus, and a frame transmission/reception method capable of reducing the establishment of radio protocol connections, while improving the communication quality and the performance of mobile equipment and network.  
         [0010]     A frame transmission/reception system according to the present invention is a frame transmission/reception system for transferring a data packet on a connection established prior to communication, the system comprising: identifier providing means for building frames for transmission of the data packet and for providing each of the built frames with a QoS identifier for identifying whether the frame is an acknowledgement type frame or an unacknowledgement type frame; retransmission requesting means for identifying whether a frame is an acknowledgement type frame or an unacknowledgement type frame, based on the QoS identifier provided therefor, and for determining whether a frame is lost, only for each acknowledgement type frame, and requesting retransmission of the lost acknowledgement type frame; and retransmitting means for retransmitting the acknowledgement type frame under the request for the retransmission.  
         [0011]     Since the frame transmission/reception system of the present invention is configured to determine whether each frame is an acknowledgement type frame, based on the QoS identifier, and to determine whether a frame is lost, only for each acknowledgement type frame, and request transmission of a lost frame, it is able to perform the retransmission control for the acknowledgement type frames only.  
         [0012]     A frame transmitting apparatus according to the present invention is a frame transmitting apparatus used in a frame transmission/reception system for transferring a data packet on a connection established prior to communication, the frame transmitting apparatus comprising: identifier providing means for building frames for transmission of the data packet and for providing each of the built frames with a QoS identifier for identifying whether the frame is an acknowledgement type frame or an unacknowledgement type frame.  
         [0013]     Since the frame transmitting apparatus of the present invention is configured to provide each of the built frames with a QoS identifier, it is able to provide each frame with information for determining whether the frame is an acknowledgement type frame.  
         [0014]     In the frame transmitting apparatus of the present invention, preferably, the data packet is comprised of a plurality of data flows, and the identifier providing means provides each of the frames with a data flow identifier for identifying one of the data flows. Since each frame is provided with a data flow identifier for identification of the data flow, it is feasible to provide each frame with information for identifying to which data flow the frame belongs.  
         [0015]     Preferably, the frame transmitting apparatus of the present invention comprises number providing means for providing each acknowledgement type frame with a sequence number for each established connection. Since acknowledgement type frames are provided with their respective sequence numbers, for example, a frame receiving apparatus is able to acknowledge a loss of an acknowledgement type frame from discontinuity of the sequence numbers.  
         [0016]     Preferably, the frame transmitting apparatus of the present invention comprises number providing means for providing each acknowledgement type frame with a sequence number for each established connection and for each data flow identifier. Since sequence numbers are provided for each data flow identifier, for example, a frame receiving apparatus is able to acknowledge a loss of an acknowledgement type frame from discontinuity of the sequence numbers in each data flow.  
         [0017]     A frame receiving apparatus according to the present invention is a frame receiving apparatus used in a frame transmission/reception system for transferring a data packet on a connection established prior to connection, the frame receiving apparatus comprising: retransmission requesting means for identifying whether a frame is an acknowledgement type frame or an unacknowledgement type frame, based on a QoS identifier provided therefor, and for determining whether a frame is lost, only for each acknowledgement type frame, and requesting retransmission of the lost acknowledgement type frame.  
         [0018]     Since the frame receiving apparatus of the present invention is configured to determine whether a frame is an acknowledgement type frame, based on its QoS identifier, and to determine whether a frame is lost, only for each acknowledgement type frame, and request retransmission of a lost frame, it is able to perform the retransmission control for the acknowledgement type frames only.  
         [0019]     Preferably, the frame receiving apparatus of the present invention comprises holding means for, when the retransmission requesting means requests retransmission of the acknowledgement type frame, temporarily holding a previously received acknowledgement type frame until reception of the acknowledgement type frame retransmitted according to the request for the retransmission. Since a previously received acknowledgement type frame is temporarily held, it is feasible to reconfigure a data packet by combining it with the retransmitted acknowledgement type frame.  
         [0020]     In the frame receiving apparatus of the present invention, preferably, the data packet is comprised of a plurality of data flows, and, where each of the frames is provided with a data flow identifier for identifying each of the data flows, the holding means temporarily holds an acknowledgement type frame with the same data flow identifier as that of the lost acknowledgement type frame. Since a previously received acknowledgement type frame is temporarily held for each data flow, it is feasible to reconfigure a data packet by combining it with the retransmitted acknowledgement type frame in each data flow.  
         [0021]     A frame transmission/reception method of the present invention is a frame transmission/reception method of transferring a data packet on a connection established prior to communication, the frame transmission/reception method comprising: a step wherein identifier providing means builds frames for transmission of the data packet and provides each of the built frames with a QoS identifier for identifying whether the frame is an acknowledgement type frame or an unacknowledgement type frame; a step wherein retransmission requesting means identifies whether a frame is an acknowledgement type frame or an unacknowledgement type frame, based on the QoS identifier provided therefor, and the retransmission requesting means determines whether a frame is lost, only for each acknowledgement type frame, and requests retransmission of the lost acknowledgement type frame; and a step wherein retransmitting means retransmits the acknowledgement type frame under the request for the retransmission.  
         [0022]     In the frame transmission/reception method of the present invention, whether a frame is an acknowledgement type frame is determined based on its QoS identifier, whether a frame is lost is determined for each acknowledgement type frame only, and retransmission of a lost frame is requested based on the determination; therefore, it is feasible to perform the retransmission control for the acknowledgement type frames only. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     The present invention may be more readily described with reference to the accompanying drawings, in which:  
         [0024]      FIG. 1  is an illustration showing a configuration of a network for describing an embodiment of the present invention;  
         [0025]      FIG. 2  is an illustration showing a configuration of a frame transmitting apparatus as an embodiment of the present invention;  
         [0026]      FIG. 3  is an illustration showing a configuration of a frame receiving apparatus as an embodiment of the present invention;  
         [0027]      FIG. 4  is an illustration for explaining identifiers used in an embodiment of the present invention;  
         [0028]      FIG. 5  is an illustration for explaining an operation of the frame transmitting apparatus and frame receiving apparatus as an embodiment of the present invention;  
         [0029]      FIG. 6  is an illustration for explaining another operation of the frame transmitting apparatus and frame receiving apparatus as an embodiment of the present invention; and  
         [0030]      FIG. 7  is a flowchart of an operation of the frame transmitting apparatus and frame receiving apparatus as an embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     The essence of the present invention can be readily understood in view of the following detailed description with reference to the accompanying drawings presented for illustrative purposes only. Subsequently, embodiments of the present invention will be described with reference to the accompanying drawings. The same portions will be denoted by the same reference symbols as much as possible, without redundant description.  
         [0032]     As a premise for the description of the present embodiment a network  1   a  (frame transmission/reception system) will be described using  FIG. 1 . This network  1   a  is comprised of a mobile communication network  10 , a mobile station  20 , and a mobile network  30 . The mobile communication network  10  includes a base station  101 , a radio link control station  102 , and a core network  103 . The mobile station  20  has a radio interface to access the mobile communication network  10  and is linked to the mobile network  30  consisting of at least one communication terminal. The base station  101  has a radio interface to the mobile station  20 , and an interface to the radio link control station  102 . The radio link control station  102  is able to communicate with the exterior of the mobile communication network  10  through the core network  103 . In the network  1   a  of  FIG. 1 , the base station  101  and the radio link control station  102  are described as separate nodes, but they can also be configured as a single node. The mobile station  20  transfers data flows from many communication terminals of the mobile network  30  through one radio interface to the mobile communication network  10 .  
         [0033]     When the mobile station  20  requests the mobile communication network  10  to perform communication for transfer of packet, a radio protocol connection is established between the mobile station  20  and the radio link control station  102 . The radio protocol has the functions of generating radio frames and performing the retransmission control. The radio frames can be of either fixed length or a variable length. The radio protocol has a function of, when a length of an upper-layer data packet is longer than a maximum load length of radio frame, dividing the upper-layer data into pieces, loading them on radio frames, and transferring them to a lower layer, and a function of, when receiving a data packet divided into a plurality of radio frames, building them into original data and transferring it to an upper layer.  
         [0034]     Subsequently, a frame transmitting apparatus  40  and a frame receiving apparatus  50  of the present embodiment will be described. The frame transmitting apparatus  40  and the frame receiving apparatus  50  of the present embodiment are installed in each of the mobile station  20  and the radio link control station  102  so as to terminate a radio protocol. A configuration of the frame transmitting apparatus  40  of the present embodiment is shown in  FIG. 2 , and a configuration of the frame receiving apparatus  50  in  FIG. 3 . In the description of the frame transmitting apparatus  40  and frame receiving apparatus  50  below, it is assumed that the frame transmitting apparatus  40  is placed in the mobile station  20  and the frame receiving apparatus  50  in the radio link control station  102 .  
         [0035]     First, the frame transmitting apparatus  40  will be described with reference to  FIG. 2 . The frame transmitting apparatus  40  includes a QoS identifying part  401 , a frame building part  402  (identifier providing means and number providing means), a retransmission management part  403  (retransmitting means), and an error detection code providing part  404 . When the mobile station  20  with the frame transmitting apparatus  40  therein receives a data packet from the mobile network  30 , it loads the data packet on a radio frame in accordance with a radio frame format. When this radio frame has the length shorter than that of the data packet, the data packet is divided into pieces and these pieces are loaded on radio frames.  
         [0036]     The QoS identifying part  401  of the frame transmitting apparatus  40  is a part that identifies QoS information described in a data packet or QoS information of a connection forming a data flow. Conceivable examples of the QoS information described in a data packet include Differentiated Services Code Point (DSCP) in Internet Protocol (IP) packet and others, and conceivable examples of the QoS information of connection include service categories set for respective Virtual Channel Connections (VCCs) in Asynchronous Transfer Mode (ATM) and others.  
         [0037]     The frame building part  402  of the frame transmitting apparatus  40  is a part that divides a data packet, if necessary, to generate radio frames. The frame building part  402  divides a data packet to generate radio frames if the length of the data packet is longer than the maximum load length of radio frame. The frame building part  402  provides a header of each generated radio frame with a QoS identifier according to the QoS information described in the data packet or the QoS information of the connection forming the data flow. In general communication with a QoS level of tolerating some error but being strict on delay like voice communication or the like is handled so as not to perform retransmission. On the other hand, communication with a QoS level of tolerating some delay but not tolerating error like data communication is subjected to error correction by retransmission control. In the description hereinafter, a frame to request retransmission in conjunction with data error or frame loss will be referred to as an acknowledgement type frame, and a frame without retransmission as an unacknowledgement type frame. The frame building part  402  sequentially provides acknowledgement type frames of one radio protocol connection with sequence numbers. The frame building part  402  outputs acknowledgement type frames to the retransmission management part  403  and outputs unacknowledgement type frames to the error detection code providing part  404 .  
         [0038]     Examples of QoS identifiers will be described with reference to  FIGS. 4 . The example of  FIG. 4  ( a ) is an example in which whether it is necessary to perform retransmission is determined from the QoS information of each data packet and in which an identifier is provided based on the determination. In the example of  FIG. 4  ( a ), the QoS identifier of “0” indicates an unacknowledgement type frame, and the QoS identifier of “1” an acknowledgement type frame. The example of  FIG. 4  ( b ) is an example in which the QoS information of each data packet is mapped as it is. In the example of  FIG. 4  ( b ), it is necessary to preliminarily determine which type of retransmission control should be performed for each QoS class of data packet, between the frame transmitting apparatus  40  and the frame receiving apparatus  50 .  
         [0039]     Referring back to  FIG. 2 , the retransmission management part  403  is a part that buffers an acknowledgement type frame for retransmission and, when receiving a request from the frame receiving apparatus  50 , outputs a corresponding acknowledgement type frame to the error detection code providing part  404 . The retransmission management part  403  starts a retransmission timer at the same time as transmission of a frame, and buffers the frame for retransmission before receiving an acknowledgement response (ACK) from the frame receiving apparatus. When receiving an ACK, the retransmission management part  403  discards the buffered frame. When detecting a timeout of the retransmission timer or detecting a frame loss from a sequence number of an ACK, the retransmission management part  403  outputs the buffered frame to the error detection code providing part  404 .  
         [0040]     The error detection code providing part  404  is a part that provides error detection codes for radio frames (acknowledgement type frames and unacknowledgement type frames) outputted from the frame building part  402  and from the retransmission management part  403  and that outputs the radio frames to a lower layer for transmitting them to the frame receiving apparatus  50 .  
         [0041]     Subsequently, the frame receiving apparatus  50  will be described with reference to  FIG. 3 . The frame receiving apparatus  50  includes an error detection part  501 , a QoS reference part  502  (retransmission requesting means), a sequence number reference part  503  (retransmission requesting means), a buffer part  504  (holding means), and a packet reconfiguration part  505 . When the radio link control station  102  with the frame receiving apparatus  50  therein receives a radio frame, the radio frame is fed from a lower layer to the error detection part  501  of the frame receiving apparatus  50 .  
         [0042]     The error detection part  501  is a part that performs error detection of each radio frame, that discards a frame with error, and that outputs a frame without error to the QoS reference part  502 .  
         [0043]     The QoS reference part  502  is a part that refers to a QoS identifier of each frame outputted from the error detection part  501 , that outputs an acknowledgement type frame to the sequence number reference part  503 , and that outputs an unacknowledgement type frame to the packet reconfiguration part  505 .  
         [0044]     The sequence number reference part  503  is a part that refers to a sequence number of each acknowledgement type frame and that transmits an ACK with the sequence number to the frame transmitting apparatus  40 . The sequence number reference part  503  also outputs an acknowledgement type frame outputted from the QoS reference part  502 , to the buffer part  504 . Furthermore, the sequence number reference part  503  refers to a sequence number of each acknowledgement type frame and, when detecting a frame loss with a sequence number drop, instructs the buffer part  504  to buffer an acknowledgement type frame received thereafter.  
         [0045]     The buffer part  504  is a part that outputs an acknowledgement type frame outputted from the sequence number reference part  503 , to the packet reconfiguration part  505 . When receiving an instruction to buffer an acknowledgement type frame, from the sequence number reference part, the buffer part  504  buffers an acknowledgement type frame received thereafter. Furthermore, when receiving an acknowledgement type frame retransmitted from the frame transmitting apparatus  40 , the buffer part  504  performs ordering control of frames including every buffered acknowledgement type frame and outputs the frames in order to the packet reconfiguration part  505 .  
         [0046]     The packet reconfiguration part  505  is a part that removes a radio protocol header from each of radio frames (acknowledgement type frame and unacknowledgement type frame) outputted from the QoS reference part  502  and from the buffer part  504  and that reconfigures a data packet and transfers it to an upper layer.  
         [0047]     In order to describe a method of transmission/reception of frames in the network  1  a of the present embodiment, the operation of the aforementioned frame transmitting apparatus  40  and frame receiving apparatus  50  will be described in detail with reference to  FIG. 5 . Each “U” in  FIG. 5  indicates an unacknowledgement type frame. In the example of  FIG. 5 , the sequence number reference part  503  of the frame receiving apparatus  50  detects a loss of frame  3 . The sequence number reference part  503  instructs the buffer part  504  to buffer a subsequent acknowledgement type frame, and then the buffer part  504  buffers frame  4 . When receiving the frame  3  retransmitted thereafter, the buffer part  504  performs the ordering control and the packet reconfiguration part  505  reconfigures a packet. Since an unacknowledgement type frame is directly outputted from the QoS reference part  502  to the packet reconfiguration part  505 , it is not subjected to the buffer process in the buffer part  504 .  
         [0048]     The above described the example in which the sequence number management was carried out for a radio protocol connection, and subsequently, an example in which the sequence number management is carried out for each data flow identifier will be described.  
         [0049]     The QoS identifying part  401  identifies the QoS information described in each data packet or the QoS information of a connection forming data flows, and identifies a data flow. This data flow is identified based on IP address of IP packet and a port number of the transport layer protocol, a VCI (Virtual Channel Identifier) of ATM connection, or the like.  
         [0050]     The frame building part  402  divides a data packet, if necessary, to generate radio frames. When the length of the data packet is longer than the maximum load length of radio frame, the frame building part  402  divides the data packet to generate radio frames. The frame building part  402  sequentially provides generated acknowledgement type frames with their respective sequence numbers for each data flow identifier. The retransmission management part  403  starts the retransmission timer at the same time as transmission of a frame, and buffers the frame for retransmission before receiving an acknowledgement response (ACK) from the frame receiving apparatus. When receiving an ACK, the retransmission management part  403  discards the buffered frame. When detecting a timeout of the retransmission timer or a frame loss from the sequence number of the ACK, the retransmission management part  403  outputs the buffered frame to the error detection code providing part  404 .  
         [0051]     The sequence number reference part  503  refers to a sequence number of each acknowledgement type frame and, when detecting a frame loss with a sequence number drop, instructs the buffer part  504  to buffer an acknowledgement type frame of the same data flow received thereafter.  
         [0052]     When receiving an instruction to buffer an acknowledgement type frame, from the sequence number reference part, the buffer part  504  buffers an acknowledgement type frame of the same data flow received thereafter. Furthermore, when receiving an acknowledgement type frame retransmitted from the frame transmitting apparatus  40 , the buffer part  504  performs the ordering control of frames with every acknowledgement type frame of the same data flow buffered and outputs the frames in order to the packet reconfiguration part  505 .  
         [0053]     The example in which the sequence number management is carried out for each data flow identifier will be described in detail with reference to  FIG. 6 . Each “U” in  FIG. 6  indicates an unacknowledgement type frame. A numeral before a hyphen in each frame indicates a data flow identifier, and a numeral after a hyphen a sequence number in each data flow. In the example of  FIG. 6 , the sequence number reference part  503  of the frame receiving apparatus  50  detects a loss of frame  1 - 2 . When the sequence number reference part  503  instructs the buffer part  504  to buffer a subsequent acknowledgement type frame of the same data flow, the buffer port  504  buffers frame  1 - 3 . When receiving the frame  1 - 2  retransmitted thereafter, the buffer part  504  performs the ordering control of frames and the packet reconfiguration part  505  reconfigures a packet. Frames  2 - 1  to  2 - 2  of a different data flow are directly outputted without being buffered, to the packet reconfiguration part  505 .  
         [0054]     The operation of the present embodiment will be described with reference to the flowchart shown in  FIG. 7 . The frame building part  402  of the frame transmitting apparatus  40  builds frames for transmission of a data packet and provides each of the built frames with a QoS identifier (step SO  1 ).  
         [0055]     The frames with the respective QoS identifiers are transmitted to the frame receiving apparatus  50  (step S 02 ).  
         [0056]     The QoS reference part  502  of the frame receiving apparatus  50  identifies whether each frame is an acknowledgement type frame or an unacknowledgement type frame, based on its QoS identifier (step S 03 ).  
         [0057]     The QoS reference part  502  outputs an acknowledgement type frame to the sequence number reference part  503  and outputs an unacknowledgement type frame to the packet reconfiguration part  505  (step S 04 ).  
         [0058]     The sequence number reference part  503  determines whether a frame is lost, for each acknowledgement type frame, and requests retransmission of a lost acknowledgement type frame (step S 05 ).  
         [0059]     In response to the request, the retransmission management part  403  outputs a corresponding acknowledgement type frame to the error detection code providing part  404 . The error detection code providing part  404  provides an error detection code for the acknowledgement type frame outputted from the retransmission management part  403 , and transmits the radio frame to the frame receiving apparatus  50  (step S 06 ).