Multiple access communication system and data transceiver

A multiple access communications system achieving an improvement in transmission efficiency is disclosed. A slave station receives data from variable speed data terminals and generates a plurality of data packets. The slave station then transmits a transmission request packet containing a total amount of data packets to be concatenated to a master station. The master station transmits a transmission permission packet containing a total amount of data packets permitted to be concatenated through a broadcast line to the slave station. The slave station concatenates a plurality of uplink transmission data packets within a predetermined range, and transmits a concatenated uplink transmission data packet to the master station through the multiple access line network.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a multiple access communication system and a data transceiver used in a broadband access network or the like.

2. Related Art

Broadband access networks such as cable modems using cable television lines or Fixed Wireless Access (FWA) using fixed radio channels have been provided even in ordinary households to implement high speed internet access. Cable modems and FWA are described in detail in, for example, Nikkei Communication, No. 316, April 2000. Those broadband access networks nearly all use multiple access lines where a number of users share the same frequency band as an uplink, in order to reduce costs. With multiple access type lines, each slave station is connected to a master station through shared media for sharing the same frequency band with other slave stations and a transmission order between slave stations is controlled by master station multiple access control.

In order to synchronize time between the master station and all of the slave stations, the master station distributes a time synchronization packet via a broadcast channel. In this type of multiple access communication system, in order to use the uplink efficiently, each slave station concatenates a plurality of uplink transmission data packets to transmit them. Also, the slave stations separately manage transmission data itself and state information representing the state of the transmission data. When a slave station sets a control flag within the state information to unchangeable, a MAC (media access control) controller automatically transmits a corresponding transmission data body to the uplink. When concatenating and transmitting, the slave station sets a concatenated transmission flag in the state information, and the MAC controller consecutively concatenates all transmission data bodies having a concatenated transmission flag set and automatically transmits them to the uplink.

When transmitting communication data, a conventional multiple access communications system adds additional information to the communication data to be transmitted. In the case of concatenating a plurality of transmission data, additional information for indicating that there is concatenated data is further added for transmission. By doing this, if the size of the additional information becomes large compared to the size of the transmission data, the concatenating of a plurality of transmission data for transmission suffers from a first problem that conversely the utilization rate of the multiple access lines is degraded.

Also, when a slave station concatenates and transmits a plurality of transmission data, the uplink is occupied for a long period of time so there is a second problem that the length of time that other slave stations must wait until transmitting transmission data is increased.

According to a conventional multiple access communication system, generation of transmission data and transmission to the multiple access line is asynchronous. Accordingly, there is developed a third problem that a delay in transmission data, which is required in real time, is increased.

Since transmit packets in a transmission buffer are transmitted automatically one by one in order to concatenate and transmit transmission data there is a fourth problem that it is necessary to have completed concatenating processing by the time transmission data is put into the transmission buffer.

The uplink control information and uplink user data make shared use of the same transmission buffer, and a slave station sequentially performs transmission from header transmission data in the transmission buffer. Accordingly, there is a fifth problem that the uplink control information is not given priority over the uplink user data when performing transmission.

In the case of concatenating a plurality of packets having a fixed information length, Japanese Patent Application Unexamined Publication No. 61-33054 discloses a packet transmitting/receiving system where a start block is added to the leading end of the concatenated packets and an end block is added to the trailing end thereof. However, this prior art is applicable to a fixed-length packet transmitting/receiving system.

SUMMARY OF THE INVENTION

The present invention has been conceived in view of the above described situation and a first object of the present invention is to provide a multiple access communication system and a data transceiver allowing always highly efficient utilization rates for multiple access lines.

A second object of the present invention is to provide a multiple access communication system and a data transceiver avoiding an uplink to be occupied by a single slave station for a long period of time.

A third object of the present invention is to provide a multiple access communication system and a data transceiver allowing reduced delay of transmission data that is required in real time.

A fourth object of the invention is to provide a multiple access communication system and a data transceiver allowing all transmission data satisfying concatenated transmission conditions to be concatenated and transmitted.

A fifth object of the present invention is to provide a multiple access communication system and a data transceiver allowing uplink control information to be transmitted with priority over uplink user data.

In order to achieve the above described objects, a first aspect of the present invention is a multiple access communications system including: a master station; and a plurality of slave stations, each of which is connected to the master station using an uplink and a downlink and is connected to at least one terminal. Each of the slave stations includes: a transmission buffer for storing data received from a terminal as uplink transmission packets; a condition memory storing a transmission condition for packet concatenation; a packet concatenation section for concatenating a plurality of uplink transmission packets stored in the transmission buffer within a range satisfying the transmission condition, to produce a concatenated uplink transmission packet; and a transmitter for transmitting the concatenated uplink transmission packet to the master station.

The packet concatenation section may concatenate a plurality of uplink transmission packets within an upper limit to number of uplink transmission packets determined by the transmission condition. The packet assembler may concatenate a plurality of uplink transmission packets within an upper limit to a total amount of uplink transmission packets determined by the transmission condition.

The transmission condition may be previously set such that concatenating of the plurality, of uplink transmission packets is performed only when a total amount of first additional information that would be added if the uplink transmission packets are individually transmitted is not smaller than an amount of second additional information that would be added if the concatenated uplink transmission packet is transmitted, wherein the packet concatenation section concatenates the plurality of uplink transmission packets when the transmission condition is satisfied.

The slave station may further include a table memory storing a table containing correspondence between a packet data size and an amount of additional information to be added when individually transmitted, wherein the table is used to determine whether the total amount of first additional information is not smaller than the amount of second additional information.

The slave station may further include a table memory storing a table containing correspondence between a packet data size, a number of packets to be concatenated, an amount of additional information to be added when concatenated, and wherein the table is used to determine whether the total amount of first additional information is not smaller than the amount of second additional information.

According to another aspect of the present invention, a multiple access communications system includes: a master station; and a plurality of slave stations, each of which is connected to the master station using an uplink and a downlink and is connected to at least one fixed speed data terminal. The master station includes a time synchronization packet transmitter for transmitting a time synchronization packet to the slave stations to obtain time synchronization with the slave stations, and each of the slave stations includes: a converter for converting all fixed speed data received from the at least one fixed speed data terminal to uplink transmission data packets in synchronization with the time synchronization packet, and a transmitter for starting transmission processing of the uplink transmission data packets when the fixed speed data from all of the at least one fixed speed data terminal have been stored.

Each of the slave stations may further include: a detector for detecting at least one fixed speed data terminal that is in an active state, wherein the transmitter starts the transmission processing or the uplink transmission data packets when the fixed speed data from all of the at least one fixed speed data terminal that is in the active state has been stored.

The master station may periodically transmit a transmission permission packet to the slave stations, wherein the converter converts the fixed speed data to uplink transmission data packets in synchronism with the transmission permission packet, and the transmitter performs transmission of the uplink transmission data packets according to timing designated by the transmission permission packet.

According to further another aspect of the present invention, a multiple access communications system includes: a master station; and a plurality of slave stations, each of which is connected to the master station using an uplink and a downlink and is connected to at least one terminal, wherein each of the slave stations transmits an uplink data packet and an uplink control information packet to the master station as an uplink transmission data packet. Each of the slave station includes a first buffer for storing uplink transmission data packets; a second buffer for storing uplink transmission data packet status information indicating a status of each of the uplink transmission data packets; and a buffer controller controlling such that, when an uplink transmission data packet is stored in the first buffer, a control flag is set to not-changeable and is added to uplink transmission data packet status information corresponding to the uplink transmission data packet, and the uplink transmission data packet status information with the control flag set to not-changeable is stored in the second buffer.

The buffer controller may previously set an upper limit to a number of uplink transmission data packets to be set to not-changeable, wherein, when a number of uplink transmission data packets exceeds the upper limit, the buffer controller sets the control flag to changeable and adds it to uplink transmission data packet status information corresponding to uplink transmission data packets exceeding the upper limit, to store the uplink transmission data packet status information with the control flag set to changeable in the second buffer.

Each of the slave stations may further include a condition memory storing a transmission condition, wherein, when a number of uplink transmission data packets set to not-changeable falls below the upper limit, the buffer controller determines whether the uplink transmission data packets set to changeable stored in the first buffer satisfy the transmission condition, and when the uplink transmission data packets set to changeable satisfy the transmission condition, the buffer controller sets a control flag of uplink transmission data packet status information corresponding to each of the uplink transmission data packets set to changeable to not-changeable, and concatenates the uplink transmission data packets set to changeable in sequence to produce a concatenated uplink transmission packet for transmission to the master station.

The buffer controller may controls such that, when the uplink control information packet is stored in the first buffer, the uplink control information packet is stored at a location of the first buffer immediately before the uplink transmission data packets set to not-changeable stored in the first buffer.

According to the present invention, a data transceiver connected between a master station and at least one terminal to transfer data between the master station and the at least one terminal, includes: a transmission buffer for storing data received from a terminal as uplink transmission packets; a condition memory storing a transmission condition; a packet concatenation section for concatenating a plurality of uplink transmission packets stored in the transmission buffer within a range satisfying the transmission condition, to produce a concatenated uplink transmission packet; and a transmitter for transmitting the concatenated uplink transmission packet to the master station.

According to the present invention, a data transceiver connected between a master station and at least one fixed speed data terminal to transfer data between the master station and the at least one terminal, includes: a packet data generator for generating uplink transmission data packets from fixed speed data received from the at least one fixed speed data terminal, in synchronization with a time synchronization packet received from the master station to; and a data packet transmitter for performing transmission processing of the uplink transmission data packets when the fixed speed data from all of the at least one fixed speed data terminal have been received.

According to the present invention, a data transceiver connected between a master station and at least one terminal to transfer data between the master station and the at least one terminal, includes: a first buffer for storing uplink transmission data packets; a second buffer for storing uplink transmission data packet status information indicating a status of each of the uplink transmission data packets and a buffer controller controlling such that, when an uplink transmission data packet is stored in the first buffer, a control flag is set to not-changeable and is added to uplink transmission data packet status information corresponding to the uplink transmission data packet, and the uplink transmission data packet status information with the control flag set to not-changeable is stored in the second buffer.

According to the present invention, a multiple access communication method between a master station and a plurality of slave stations, each of which is connected to the master station using an uplink and a downlink and is connected to at least one terminal, includes the steps of: at a slave stations, generating a plurality of data packets from data received from the at least one terminal; transmitting a transmission request packet containing a total amount of data packets to be concatenated to the master station; at the master station, in response to the transmission request packet, transmitting a transmission permission packet containing a total amount of data packets permitted to be concatenated to the slave station; at the slave station, concatenating a plurality of uplink transmission data packets within a predetermined range to produce a concatenated uplink transmission data packet; and transmitting the concatenated uplink transmission data packet to the master station.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A first embodiment of the present invention will be described in the following with reference to the drawings.

FIG. 1is a block diagram showing a multiple access communication system of this embodiment. In this drawing, a plurality of slave stations20,21and23receive data and control information from a master station10through a broadcast line50. The master station10receives data packets and control information packets from the plurality of slave stations through a multiple access line60. Also, the slave station20is connected to a variable speed data terminals30and31through variable speed communication lines80and81respectively.

FIG. 2is a block diagram showing the above-described slave station in detail. A broadcast line termination circuit200receives data from the master station, while a multiple access line termination circuit210transmits data to the master station. A variable speed communication line termination circuit220transmits and receives data to and from the variable speed communication terminal, and a variable speed data transmission buffer240holds uplink transmission data from the variable speed communication terminals. A broadcast line network interface260receives downlink transmission data packets from the master station10, and a multiple access line network interface270receives uplink transmission data packets from the slave station20. Variable speed communication network interfaces280and281perform data communication with the variable speed communication terminals.

Next, an operation of the first embodiment will be described. InFIG. 1andFIG. 2, when the variable speed communications terminals30and31transmit data, the variable speed communication network interfaces280and281receive this data, and this data is held in the variable speed data transmission buffer240through the variable speed communication line termination circuit220. At this time, the multiple access line termination circuit210references a transmission condition for packet concatenation being held internally. Only when this transmission condition is satisfied, the slave station20produces a transmission request packet360having its own station number and a total data size included therein, and transmits it to the master station10through the multiple access line network60. When having received the transmission request packet360from the slave station20, the master station10produces a transmission permission packet300having the number of the slave station20and a data size approved for transmission included therein and transmits this signal to the slave station20via the broadcast line50. The slave station20receives the transmission permission packet300at the broadcast line termination circuit200through the broadcast line network interface260. Then, the broadcast line termination circuit200sends a transmission instruction signal370containing data size information approved for transmission to the multiple access line termination circuit210The multiple access line termination circuit210, when having received the transmission instruction signal370, extracts a plurality of transmission data appropriate for the designated data size from the variable speed data transmission buffer240, concatenates the plurality of data within a predetermined range and adds an overhead such as concatenated header information containing information used for separation at the receive side and physical layer header information such as Forward Error Correction (FEC). After that, the data is sent via the multiple access line network interface270and the multiple access line60to the master station10as an uplink transmission data signal310.

FIG. 3is an example of the format of the uplink transmission data packet signal310. When transmission data packets400,401,402and403of P1, P2, . . . Pn−1, Pn are held in the variable speed data transmission buffer240of the slave station20, the multiple access line termination circuit210reads out an internally held transmission condition. When the transmission condition sets an upper limit to the number of concatenated transmission packets, the multiple access line termination circuit210performs concatenating for a number of concatenated data packets440that is only a number of data packets that does not exceed the upper limit set by the transmission condition. The multiple access line termination circuit210adds a concatenated transmission overhead530to the concatenated transmission data packets510and then transmits a resultant signal to the master station10via the multiple access line network60.

Here, assuming that the upper limit to the number of concatenated data packets is twenty and twenty-five transmission data packets are held in the variable speed data transmission buffer240, twenty ones of the twenty-five transmission data packets are concatenated, a concatenated transmission data packet510is generated, a concatenated transmission overhead530is added and transmission is performed.

Second Embodiment

Next, a second embodiment of the present invention will be described with reference toFIG. 1,FIG. 2andFIG. 4.

FIG. 4is an example of the format of an uplink transmission data packet according to the second embodiment. When uplink transmission data packets P1, P2, . . . Pn−1, Pn are held in the variable speed data transmission buffer240, the multiple access line termination circuit210reads out an internally held transmission condition. When an upper limit value for a concatenated data packet size has been set in the transmission condition, the multiple access line termination circuit210performs concatenating for only a concatenated data packet size430that does not exceed the upper limit value, adds a concatenated transmission overhead530to the concatenated transmission data packet510and transmits a resultant packet to the master station10through the multiple access line network60.

For example, assuming that the upper limit to the concatenated data packet size is 1100 bytes and the variable speed data transmission buffer240holds a total of five uplink transmission data packets: P1=100 bytes, P2=200 bytes, P3=300 bytes, P4=400 bytes and P5=500 bytes, uplink transmission data packets P1to P4are concatenated, and the multiple access line termination circuit210generates a 1000-byte concatenated transmission data packet510.

Third Embodiment

Next, a third embodiment of the present invention will be described with reference toFIG. 1,FIG. 2andFIG. 5.

FIG. 5is an example of the format of an uplink transmission data packet of this third embodiment. When uplink transmission data packets400,401,402and403shown as P1, P2, . . . Pn−1, Pn are held in the variable speed data transmission buffer240, the multiple access line termination circuit210reads out a transmission condition for packet concatenation. Processing is set for the case where a concatenated transmission overhead size meeting the transmission condition is smaller than the total size of individual transmission overheads.

In the case of individual transmission, transmission overheads520,521,522and523shown as II1, II2. . . IIn are individually added to uplink transmission data packets400,401,402and403and are transmitted. Also, in the case of concatenated transmission, the uplink transmission data packets400,401,402and403are transmitted as a concatenated transmission data packet510having a concatenated transmission overhead530added thereto. Here, a sum Hsum of the sizes of the overheads H1, H2. . . Hn at the time of each individual transmission is compared with the size of the concatenated transmission overhead530. The concatenated transmission is only carried out when the size of the concatenated transmission time overhead530is smaller than the sum Hsum of the sizes of the individual transmission overheads.

For example, it is assumed that a 10-byte overhead is added if uplink data packets are sent individually using the multiple access line network60and that a 15-byte overhead is added if transmitting a concatenated data packet. With this embodiment when a 500-byte uplink data packet A and a 100-byte uplink data packet B are held in the variable speed data transmission buffer240, with individual transmission an uplink data packet of a total of 620 bytes, that of two uplink data packets of 510 bytes and 110 bytes, each having a 10-byte overhead added, is generated. On the other hand, with concatenated transmission, a data packet having a total of 615 byes, that of the 600-byte concatenated transmission data packet with a 15-byte overhead added, is generated. Accordingly, since the method of concatenated transmission has a smaller overhead size compared to the individual transmission, transmission data A and B are concatenated and transmitted.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be described with reference toFIG. 1,FIG. 6andFIG. 7.

FIG. 6shows the structure of a slave station20according to the fourth embodiment. In this embodiment, a memory circuit380holds an overhead size correspondence table. Here, a transmission condition for packet concatenation is set such that, when an overhead size for concatenated transmission is smaller than the total size of overheads for individual transmission, the multiple access line termination circuit210concatenates transmission data packets.

FIG. 7shows an example of the overhead size correspondence table being stored in the memory circuit380of the slave station20as shown inFIG. 6. The multiple access line termination circuit210inside the slave station20notifies a data packet size to the memory circuit380using the control signal390when transmitting a plurality of uplink transmission data packets being held in the variable speed data transmission buffer240. In response to the data packet size, the memory circuit380searches the individual transmission overhead size correspondence table600FIG. 7) for a corresponding overhead size and outputs the found overhead size back to the multiple access line termination circuit210via the control signal390. The multiple access line termination circuit210compares the total overhead size calculated from the overhead sizes found in the table600with a concatenated transmission overhead that is calculated separately, and performs concatenated transmission only if the overhead size is smaller for the concatenated transmission than for the individual transmission.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described with reference toFIG. 1,FIG. 6andFIG. 8.

FIG. 8shows an example of an overhead size correspondence table held in the memory circuit380of the slave station20as shown inFIG. 7. The multiple access line termination circuit210inside the slave station20notifies the number of data packets and the size of the data packets to the memory circuit390using the control signal390when transmitting a plurality of uplink transmission data packets being held in the variable speed data transmission buffer240. In response to the number or data packets and the data packet size, the memory circuit380searches the concatenated transmission overhead size correspondence table700(FIG. 8) for a corresponding overhead size and outputs the found overhead size back to the multiple access line termination circuit210via the control signal390. The multiple access line termination circuit210compares the concatenated transmission overhead size received from the memory circuit380with the total overhead size that is separately calculated, and performs concatenated transmission only if the overhead size is smaller for the concatenated transmission than for the individual transmission.

Sixth Embodiment

Next, a sixth embodiment of the present invention will be described with reference toFIG. 9,FIG. 10andFIG. 11.

FIG. 9shows a multiple access communication system of the sixth embodiment. A master station10and a plurality of slave stations20,21and22are connected through distributors70and71. Data and control information are sent from the master station10to the plurality of slave stations21,21and22using a broadcast line50. Data packets and control information are sent from the plurality of slave stations20,21and22to the master station10using the multiple access line60. Also, the slave station20is connected to respective fixed speed data terminals40,41and42via fixed speed communication lines90,91and92.

FIG. 10shows the structure of the slave station20according to the sixth embodiment. When all of the fixed speed data terminals40,41and42are in an active state, first of all if three fixed speed data signals330,331and332are received, sampling is carried in the fixed speed communication line termination circuit230of the slave station20, using a signal obtained by dividing a time synchronization packet393that is provided through the broadcast line50in order to obtain time synchronization of the master station10with the slave stations20,21and22. Then, all of the input fixed speed data signals330,331and332are transferred to the fixed speed data transmission buffer250inside the multiple access line termination circuit210as fixed speed data packets800,801and802(seeFIG. 11). When all of the fixed speed data packets800,801and802are accumulated in the fixed speed data transmission buffer250, the multiple access line termination circuit210produces a transmission request packet360having its own station number and a total data size included therein, and transmits it to the master station10through the multiple access line network60. The master station10that has received the transmission request packet360produces a transmission permission packet300having the slave station number and a data size permitted to be transmitted included therein and transmits it to the slave station20via the broadcast line50. When receiving the transmission permission packet300at the broadcast line termination circuit200, a transmission instruction signal370containing information for data permitted for transmission is transferred to the multiple access line termination circuit210.

The multiple access line termination circuit210that has received the transmission instruction signal370extracts a plurality of transmission data packets corresponding to the designated data size from the fixed speed data transmission buffer250, concatenates the extracted data packets and attaches an overhead such as FEC thereto. After that, the concatenated data is transmitted to the master station10as a transmission data signal310through the multiple access line60.

FIG. 11shows processing of a signal at each section of the above described embodiment. After carrying out sampling of the fixed speed data signals330,331and332in the fixed speed communication line termination circuit230of the slave station20using a signal divided from a time synchronization packet, respective fixed speed data packets800,801and802are generated. The fixed speed data packets800,801and802are sent to the fixed speed data transmission buffer250. Upon completion of receipt of all fixed speed data packets, the multiple access line termination circuit210requests concatenated transmission to the master station10using the transmission request packet360. The master station10gives permission for this concatenated transmission and notifies the slave station20using the transmission permission packet300. In the event that performing concatenated transmission satisfies the transmission conditions, the multiple access line termination circuit210of the slave station20concatenates all of the fixed speed data packets800,801and802to create a concatenated transmission data packet510, adds to this a concatenated transmission overhead530and transmits a resultant packet as a transmission data signal310to the master station10through the multiple access line network60.

Seventh Embodiment

Next, a seventh embodiment of the present invention will be described With reference toFIG. 9,FIG. 12andFIG. 13.

FIG. 12shows a slave station of this embodiment. InFIG. 12, an active station detection circuit391detects whether or not the fixed speed data terminal is in an active state.FIG. 13shows processing of a signal at each section of this seventh embodiment.

InFIG. 9,FIG. 12andFIG. 13, the fixed speed communication line termination circuit230of the slave station20has the active state detection circuit391inside, and in the active state detection circuit391it is detected whether or not all fixed speed data terminals40,41and42connected to the slave station20are in an active state. In the example shown inFIG. 13, two fixed speed data terminals40and41are in an active state. The number of fixed speed data terminals that are in the active state is notified to the multiple access line termination circuit210using an active state notification signal392. The multiple access line termination circuit210receiving this notification receives the fixed speed data packets800and801from the two fixed speed data terminals40and41. When concatenating and transmitting satisfies the transmission condition, concatenating and transmitting of these two data packets is requested to the master station10using a transmission request packet360. When the master station10permits this action and notifies the slave station20of transmission permission using the transmission permission packet300, the broadcast line termination circuit200of the slave station20receives the transmission permission packet300and transfers a transmission instruction signal to the multiple access line termination circuit210. The two fixed speed data packets800and801are then concatenated in the multiple access line termination circuit210, a concatenated transmission data packet510is made, and a concatenated transmission overhead530is added thereto, and then transmitted to the master station10as a transmission data signal310via the multiple access line network60.

Eighth Embodiment

Next, an eighth embodiment of the present invention will be described with reference toFIG. 9,FIG. 14andFIG. 15.

FIG. 14shows a slave station20of this eighth embodiment, whileFIG. 15is a drawing showing processing of a signal at each section of this embodiment.

InFIG. 9,FIG. 14andFIG. 15, in the event that only the fixed speed data terminal40connected to the slave station20is in an active state, the master station10periodically transmits the transmission permission packet to the slave station20. When the broadcast line termination circuit200receives the transmission permission packet300from the master station10, a synchronization pulse900is sent to the fixed speed data communication line termination circuit230as a transmission synchronization signal394in compliance with transmission timing of the multiple access line termination circuit210, and the fixed speed data communication line termination circuit230produces a fixed speed data packet800synchronized to the synchronization pulse signal900and sends it to the fixed speed data transmission buffer250within the multiple access line termination circuit210. The multiple access line termination circuit210produces a transmission request packet having its own station number and a total data size included therein and transmits this transmission request packet to the master station10through the multiple access line60. The master station10that has received the transmission request packet360produces a transmission permission packet300having the number of the slave station20and a data size permitted to be transmitted included therein and sends it to the slave station20via the broadcast circuit50. When the broadcast line termination circuit200of the slave station20has received the transmission permission packet300, it is transferred to the multiple access line termination circuit210as a transmission instruction containing data information for permitting transmission. The multiple access line termination circuit210adds an individual transmission overhead520to the fixed speed data packet800produced in synchronism with the aforementioned master station, and transmits a resultant packet to the master station10as a transmission data signal310via the multiple access line60.

Ninth Embodiment

Next, a ninth embodiment of the present invention will be described with reference toFIG. 1,FIG. 16andFIG. 17.

FIG. 16shows a slave station of this ninth embodiment. The slave station20has a control circuit1000, while the multiple access line termination circuit210has an uplink status information buffer1100and an uplink data transmission buffer1110.

When the multiple access line termination circuit210has received a variable speed data packet signal340from the variable speed communication line termination circuit220, this signal is stored in the uplink data transmission buffer1110as uplink transmission data packet1030. When the multiple access line termination circuit210has received an uplink control information packet signal1010from the control circuit1000, this signal is stored as an uplink control information packet1020in the uplink transmission buffer1110. In this way, when the uplink transmission data packet1030is stored in the uplink transmission buffer1110, the multiple access line termination circuit210produces uplink transmission data packet status information1050. Also, when an uplink control information packet1020is stored in the uplink data transmission buffer1110, the multiple access line termination circuit210produces uplink control information packet status information1040. The uplink transmission data packet status information1050and uplink control information packet status information1040are held in the uplink status information buffer1100. The respective uplink transmission data packet status information1050and uplink control information packet status information1040have control flags therein. Either not-changeable or changeable is set in each control flag, and the number of uplink transmission data packets that can be set to not-changeable has an upper limit value.

FIG. 17shows the detailed structure of the uplink status information buffer1100and the uplink data transmission buffer1110.

It is assumed that the upper limit value for the number of data packets that can be stored in each of the uplink status information buffer1100and the uplink data transmission buffer1110is made to be 2. InFIG. 17, reference numerals1140,1141, and1150to1155, denote uplink transmission data packets. Reference numerals1120,1121and1130to1135denote uplink transmission data packet status information corresponding to the uplink transmission data packets1140,1141and1150to1155. Control flags of the uplink transmission data packet status information1120and1121are not changeable. Control flags of the uplink transmission data packet status information1130and1135are changeable.

It is assumed that the uplink data transmission buffer1110is empty. The two uplink transmission data packets1140and1141are respectively held at A1and B1in the uplink data transmission buffer1110. At this time, the multiple access line termination circuit210produces two uplink transmission data packet status information1120and1121corresponding respectively to the uplink transmission data packets1140and1141. Control flags of the uplink transmission data status information1120and1121are set to be not-changeable. At this time, the multiple access line termination circuit210respectively holds the uplink transmission data packet status information1120and1121at A2and B2in the uplink status information buffer1100. In the case where the slave station20has received more uplink transmission data packets, the multiple access line termination circuit210holds uplink transmission data packets1150to1155at C1to H1in the uplink transmission data buffer1110. At this time, the multiple access line termination circuit210produces uplink transmission data packet status information1130to1135respectively corresponding to the uplink transmission data packets1150to1155. Control flags of the uplink transmission data packet status information1130to1135are set to be changeable. These uplink transmission data packet status information1130to1135are respectively held at C2to H2in the uplink status information buffer1100.

In the above described status denoted by “S”, the slave station20transmits the transmission request packet360to the master station10. The master station10receives this transmission request packet360and transmits a transmission permission packet300to the slave station. When the slave station20receives permission for transmission, the multiple access line termination circuit210extracts the uplink transmission data packet1140from A1in the uplink transmission data packet buffer1110. The multiple access line termination circuit210adds a transmission request packet for transmitting the next uplink transmission data packet1141to the uplink transmission data packet1140, and transmits it to the master station. At this time, the multiple access line termination circuit210deletes the uplink transmission data packet status information A2from the uplink status information buffer1110. This causes the number of not-changeable uplink transmission data status information to be lower than the upper limit value to the number of data packets that can be stored in each of the uplink status information buffer1100and the uplink data transmission buffer1110.

Subsequently, the transmission condition stored in the multiple access line termination circuit210are referenced. If concatenating and transmitting of all uplink transmission data packets1150to1155having a changeable control flag satisfies the transmission condition, then the multiple access line termination circuit210performs concatenating processing, and changes control flags of all uplink transmission data packet status information1130to1135having changeable control flags corresponding to these uplink transmission data packets1150to1155to not-changeable.

Tenth Embodiment

Next, a tenth embodiment of the present invention will be described with reference toFIG. 1,FIG. 16andFIG. 18.

FIG. 18shows the detailed structure of the uplink status information buffer1100and the uplink data transmission buffer1110. Similarly to the ninth embodiment, an upper limit to the number of data packets that can be stored in the uplink status information buffer1100and the uplink transmission data packet buffer1110is made 2. Reference numeral1190indicates an uplink control information packet, and reference numeral1180indicates uplink control information packet status information corresponding to uplink control information packet Z2.

At the time of the previously described status S, the multiple access line termination circuit210inserts the uplink control information packet1190into Z1immediately before C1to II1. Next, the multiple access line termination circuit210produces uplink control information packet status information1180from the uplink control information packet1190. The multiple access line termination circuit210then inserts the uplink control information packet status information1180into Z2immediately before C2to H2. In this manner, the uplink control information packet1190can be transmitted with taking precedence over user data packets.

The ten embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications are possible within the scope of the present invention. For example, in all of these embodiments, the master station and the slave stations are connected by a wired network, but it is also possible to apply the present invention to the case where they are connected using a wireless network.

As has been described above, according to the present invention, the size of overheads to be added is compared between concatenated transmission and individual transmission, and concatenated transmission is performed only if the size of the overhead for the concatenated transmission case is smaller than for the individual transmission case. This has the effect of always being able to achieve improvement in the transmission efficiency of a multiple access line network

Also, when concatenating a plurality of packets for transmission, a transmission condition for packet concatenation is referred to and a plurality of packets is concatenated and transmitted only when a transmission condition for packet concatenation is satisfied. Accordingly, it is possible to prevent a slave station from transmitting a large amount of concatenated packet data over a long period of time, which means that in a multiple access line network, the effect is obtained of preventing a single base station being active over a prolonged period of time and occupying the uplink.

Further, it is possible for a slave station to periodically transmit data packets due to the master station periodically sending a transmission permission packet and the slave station produces fixed speed data packets in synchronism with timing at which data packet transmission is permitted. Accordingly, it is possible to shorten the waiting time for a transmission buffer within the slave station, and thus obtain the effect of making it possible to reduce a delay time for fixed speed data required in real time, such as a telephone.

Further, in a state where a control flag in uplink transmission data packet status information produced when storing uplink transmission data packets in the transmission buffer is set to changeable, the uplink transmission data packet status information is held in the uplink status information buffer. Accordingly, the effect is obtained of enabling concatenating of a plurality of uplink transmission data packets even in the case where uplink transmission data packets in the transmission buffer are automatically transmitted.

Also, since an uplink control information is inserted into immediately before all uplink user data having the control flag set to changeable in the transmission buffer, the effect is obtained of making it possible to prioritize transmission of uplink control information compared to the uplink user data.