JP2000059460A - Data communication method and data communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data communication method and the data communication device for which transmission errors are suitably corrected through selective retransmission. SOLUTION: A transmitter side decides a packet to be sent next to a transmission packet and adds the decided contents to protocol control information as succeeding packet notice information. A receiver side makes reference to the succeeding packet notice information in the protocol control information of a received packet for predicting a packet that is expected to be sent next and decides its received position. When the succeeding packet is receiver, whether or not division data in the received packet are received at a correct position is discriminated, by comparing the identification result with the expected result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data communication method and a data communication apparatus for transmitting data between a plurality of data terminal apparatuses, and more particularly to transmitting data by dividing the data into packets of a predetermined length. The present invention relates to a data communication method and a data communication device. More specifically, the present invention relates to a data communication method and a data communication device for correctly assembling original terminal data from a received packet in a data terminal device on the receiving side, and more particularly, to a data communication device for sequentially assembling an original terminal data from a packet received sequentially. Simplify data assembly process to assemble data,
The present invention relates to a data communication method and a data communication device for speeding up.

[0002]

2. Description of the Related Art Two or more data terminal devices (DTE: Da)
Research and development relating to “data communication” for exchanging data between the terminals (Ta Terminal Equipment) have been actively conducted.

Here, the data terminal device may be a general-purpose computer system in which communication software is introduced, in addition to a dedicated communication terminal. Each data terminal device is a line termination device (DCE: Data Circuit Terrier).
connected to a transmission medium via a “minal equipment”.

As a transmission medium for connecting data terminals, a LAN (Local Area) is used.
Network), dedicated line, general public line (PST)
N).

[0005] If the transmission medium is an analog line such as PSTN, DCE is a modem / Modulator / Decoder.
modulator). Also, ISDN (Int
Egrated Services Digital
Network), the DCE is a TA (Terminal Adapter) and a DSU (Digital Service).
ce Unit). In the case of a LAN, DCE is a LAN adapter (for example, Ethernet
Cards and token ring cards).

[0006] When a specific data terminal device exchanges data with each other, if a specific transmission path is occupied by another data terminal device, the other data terminal device (for example, while data or a message is interrupted) is not used. The terminal device cannot perform communication. Therefore, packet communication has been devised as a communication method for realizing a plurality of communications by a plurality of data terminal devices. In packet communication, data on a transmission line is handled in a predetermined length called a “packet”. That is,
Since the data to be transmitted is intermittent, the transmission medium can be shared, and the transmission line is not occupied for a long time by the communication between the specific data terminal devices.

FIG. 9 schematically shows packet communication performed between data terminal devices. In packet communication,
The data terminal device on the transmission side performs data division processing. That is, a series of data to be transmitted is divided into appropriate lengths, and protocol control information called a header or a trailer is added to each divided data before transmission. The divided data with a header is called a “packet”. The protocol control information includes information (that is, an address) indicating the destination data terminal device. On the other hand, the data terminal device on the receiving side performs data assembling processing. That is, the protocol control information is removed from the received packet to restore the original series of data.

[0008] Note that data communication is enabled by data terminals communicating with each other in accordance with a predetermined communication protocol. The standard model of the communication protocol is OSI (O
pen Systems Interconnection
on: open system interconnection) reference model.
The OSI reference model includes seven layers: a physical layer, a data link layer, a network layer, a transport layer, a session layer, a presentation layer, and an application layer (well-known).

On the transmission line, transmission errors such as destruction or partial loss of data in a packet, loss of the entire packet, rearrangement of the order, and duplication may occur (see FIG. 10). Further, it is undefined for the data terminal device on the receiving side which packet is to be received and at what timing. One of the transmitted packets
If one of them is lost, the receiving data terminal device cannot correctly assemble the original data, and as a result,
Information will not be correctly transmitted to the other party. Therefore,
A function or protocol is required, such as checking whether a packet is missing or not, and if so, requesting transmission again (ie, retransmission control).

[0010] The transmitting-side data terminal device adds the protocol control information necessary for retransmission control to the packet as a part of the header, and then transmits the packet. For example, a serial number for specifying the order of transmission packets, information (check sum) for detecting partial loss or destruction of data in the packet, and the like are added. On the other hand, the data terminal device on the receiving side inspects the data in the packet for destruction or partial loss based on the protocol control information, and assembles the data in the packet received without error, thereby obtaining the original terminal data. Restore data. Further, the data terminal device on the receiving side requests the transmitting side to retransmit the lost or destroyed packet, and the data terminal device on the transmitting side retransmits the packet according to the retransmission request.

A protocol for controlling retransmission of lost packets is generally defined in the transport layer or data link layer (described above) of the OSI reference model. TCP (Transmission Cont)
(Protocol) protocol is an industry standard communication protocol positioned at the transport layer. The TCP software adds a TCP header as protocol control information to the top of data when passing through the transport layer.

FIG. 11 illustrates the format of a TCP header. As shown in the figure, the TCP header includes data required for retransmission control, such as a serial number indicating a positional relationship between packets, a checksum for detecting the presence or absence of a data error occurring during transmission. .

FIG. 12 illustrates, in the form of a block diagram, one of the conventional data assembling processes performed in the data terminal device on the receiving side. In the figure, a packet receiving unit captures a transmission packet in synchronization with a signal on a transmission line and writes the packet on a reception packet memory. Further, the packet identification unit reads out the protocol control information in the packet stored on the received packet memory,
The position of the divided data in the packet in the original terminal data is specified. The data memory is a storage device for sequentially storing only the divided data portion in each packet in accordance with the positional relationship in the original terminal data. The data copy unit separates only the divided data in the packet from the received packet memory, and sequentially copies the divided data to a corresponding position on the data memory based on the position information determined by the packet identification unit. According to such a procedure, the original terminal data is assembled and restored from the sequentially received packets.

However, since the reception order and the reception timing of the packets are generally indefinite, it is not possible to specify the location in the data memory where the divided data in the packet is to be written before receiving the packet. Further, it is necessary to separate a packet into divided data and protocol control information. For this reason, in the conventional example shown in FIG. 12, a step of once writing a received packet into the received packet memory, separating only the divided data from the received packet, and then copying the divided data back to the data memory is performed. Such a step causes an increase in overhead in the data assembly processing throughput.

As a technique for eliminating the overhead associated with data copying as described above, there is a data assembling processing system disclosed in Japanese Patent Application No. 10-18827 by the present applicant. In this data assembly processing method,
The receiving data terminal device directly receives the packet on the data memory without temporarily storing the received packet in the received packet memory. Then, the reception position of each packet is determined so that the data assembling process is completed as a result when all the packets have been received.

In order to assemble the original terminal data without rearranging the data, it is necessary to correctly receive the divided data in each packet at the corresponding position on the data memory. In the data assembling method disclosed in the above-mentioned Japanese Patent Application No. 10-218827, means for predicting the position of data contained in a packet received next based on protocol control information in a packet received earlier. Is provided, and the packet receiving position is determined based on the expected result. That is, since the data copy operation is unnecessary by expecting the next received packet, the throughput is improved.

FIG. 13 illustrates a data assembling process disclosed in Japanese Patent Application No. 10-218827 in the form of a block diagram. In the figure, a packet receiving unit writes a received packet on a data memory in synchronization with a signal on a transmission line. Further, the packet identification unit reads the protocol control information in the received packet taken into the data memory and specifies the position information of the received packet. The packet expecting unit expects a subsequent packet based on the identification result of the previously received packet. The position where the packet receiving unit writes the packet on the data memory follows the expected result by the packet expecting unit. Therefore, the original terminal data can be correctly assembled on the data memory from the divided data in each received packet.

The protocol control information in the received packet does not originally constitute terminal data.
If the packet is received as it is in the memory, the already received data may be overwritten and destroyed. Therefore, the data saving unit is provided to temporarily save data at a position where the data is overwritten and destroyed by the protocol control information in the received packet when writing the received packet to the data memory. The position of the data to be saved is determined based on the expected result of the packet expectation unit. Before the packet is received, the data is saved, then the packet is received, and after the protocol control information in the received packet is read by the packet identification unit, the saved data returns to the original position.

For example, by deciding a communication protocol between transmission and reception so that the order of packet transmission in the data terminal device on the transmitting side is deterministic even in the terminal device on the receiving side, anticipated data communication is suitably realized. can do. That is, the terminal device on the receiving side can correctly expect the subsequent packet based on the serial number of the previously received packet. When a packet is lost due to a transmission error, the lost packet can be recovered according to the “GO-BACK-N retransmission procedure”.

FIG. 14 schematically shows how a lost packet is recovered by the GO-BACK-N retransmission procedure. The data terminal device on the transmission side divides the terminal data into predetermined lengths to form packets, and sequentially transmits the packets so that the serial numbers are in ascending order. If a packet loss is detected in the data terminal device on the receiving side, the transmitting side sequentially retransmits all packets after the lost packet.

According to such a retransmission control method, if a data terminal device on the receiving side receives a packet as expected, it may further expect a packet immediately after the received packet (that is, if the received packet is What is necessary is just to expect the arrival of the packet including the divided data immediately after the included divided data.) Also, when receiving a different packet than expected, keep discarding the packet,
What is necessary is just to wait until the expected packet is received by the retransmission request. As a result, each packet can always be received at the correct position in the data memory.

According to the data assembling method disclosed in Japanese Patent Application No. 10-218927, the overhead problem associated with data copying in the conventional example shown in FIG. 12 can be solved. In order to adopt this method, it is necessary to determine a communication protocol so that the order of packet transmission on the transmitting side is deterministic also on the receiving side. To recover lost packets, GO-
It depends on the BACK-N procedure.

However, the GO-BACK-N procedure must retransmit all transmitted packets after the lost packet. For this reason, there is a problem that the data transfer efficiency is significantly reduced in a transmission path having a large band delay product.

One of the retransmission procedures for maintaining high data transfer efficiency even on a transmission path having a large band delay table is a "selective retransmission procedure". The selective retransmission procedure is
As the name implies, only packets lost due to transmission errors are retransmitted. However, applying this selective retransmission procedure to the terminal data assembling method disclosed in the above-mentioned Japanese Patent Application No. 10-218827 involves the following two problems. (1) Even if a packet is transmitted without error on the transmission path, if the receiving side fails to predict the packet, that is, if the packet is received at an incorrect position on the data memory, the correct It is necessary to repeat retransmission until it is received at the location. This causes a reduction in transfer efficiency. (2) In the GO-BACK-N retransmission procedure, the transmission order of packets on the transmission side is deterministic even on the reception side, and it is relatively easy to expect received packets. However, in the selective retransmission procedure, the order in which packets are received on the receiving side is not unique to the order in which packets are transmitted on the transmitting side.

The former problem can be solved by adding a means for moving data in the data memory in addition to the configuration shown in FIG. That is, the divided data received at the wrong position on the data memory may be moved to the correct position.

There are two types of selective retransmission procedures: "batch retransmission" and "sequential retransmission". Batch retransmission is a process in which a terminal device on the receiving side waits for the end of a series of packet transmissions while detecting a loss of a packet due to a transmission error while dividing certain terminal data and transferring it as a series of packets.
Thereafter, a packet retransmission request is collectively transmitted to the terminal device on the transmission side (see FIG. 15). The transmitting side sequentially retransmits the requested packets in response to the retransmission request.
Thereafter, until all the packets constituting the terminal data are correctly received, the operation of detecting the loss of the packet, requesting a retransmission after the end of a series of packet transmission, and retransmitting the requested packet is repeatedly performed. .

In the case of batch retransmission, if the data terminal device on the transmitting side retransmits a packet in accordance with the order of the retransmission request, the transmitting order of the retransmitted packet is univocal to the receiving order on the receiving side. Expecting packets is easy. That is, the data terminal device on the receiving side stores the order of the packet requested to be retransmitted by itself, and every time a retransmitted packet is received, by comparing the identification result of the received packet with the stored content of the retransmission order, It is possible to expect a received packet. However, if the retransmission packet is lost again due to a transmission error, it is necessary to search for the identification result of the received packet in the storage of the retransmission order, which complicates the processing.

The sequential retransmission is a method in which, when a packet loss due to a transmission error is detected, a terminal device on the receiving side issues a request for retransmission of a sequential packet without waiting for the end of a series of packet transmissions ( See FIG. 16). Upon receiving a retransmission request even during a series of packet transmissions, the data terminal device on the transmitting side retransmits the requested packets sequentially.

In the case of sequential retransmission, the timing at which a retransmission request from the receiving side is reflected on packet transmission on the transmitting side is undefined. That is, the order in which packets are transmitted on the transmitting side is not unique to the order in which packets are received on the receiving side. It is unknown to the receiving data terminal apparatus at what point in time the requested packet will be retransmitted, and the next packet to be received cannot be expected.

To summarize the above, when correcting a packet transmission error by selective retransmission, the order in which packets are transmitted on the transmitting side and the order in which packets are received on the receiving side are not unambiguous. The next received packet cannot be expected simply by referring to the protocol control information of the preceding received packet.

[0031]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an excellent data communication system capable of performing data communication in a packet communication system and correctly assembling original terminal data from a received packet in a receiving data terminal device. It is to provide a method and a data communication device.

A further object of the present invention is to provide an excellent data communication method and apparatus which can simplify and speed up data assembling processing for assembling original terminal data from sequentially received packets. It is in.

A further object of the present invention is to perform an assembling process from a received packet to original terminal data, thereby causing an overhead problem associated with data copying and a reduction in data transfer efficiency due to a GO-BACK-N retransmission procedure. An object of the present invention is to provide an excellent data communication method and an excellent data communication device, which are free from the problem described above.

It is a further object of the present invention to provide a data terminal device on the receiving side that accurately predicts the next received packet based on the protocol control information of the previously received packet, thereby selectively retransmitting. An object of the present invention is to provide an excellent data communication method and an excellent data communication apparatus, which can preferably correct a transmission error by using the method.

[0035]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and a first aspect of the present invention is to provide a packet format including divided data obtained by dividing terminal data and its protocol control information. A data communication method for exchanging data between data terminal devices connected via a transmission line, wherein a data terminal device on the transmitting side transmits a packet to be transmitted next when transmitting a certain packet. Deciding, adding the decision contents to the protocol control information as subsequent packet notification information, and transmitting the result. In the data terminal device on the receiving side, the next reception is performed by referring to the subsequent packet notification information in the received packet. Expecting expected packets.

According to a second aspect of the present invention, there is provided a method for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information between data terminal devices connected via a transmission line. A data communication method comprising: (a) when transmitting a certain packet in a data terminal device on the transmitting side, a packet to be transmitted next is determined, and the determined content is used as subsequent packet notification information as protocol information; (B) receiving, on a data memory, a packet transmitted via a transmission line in a receiving data terminal device; and (c) receiving a data terminal device on the receiving side. At the step of referring to the subsequent packet notification information in the received packet to predict the next packet expected to be received,
(D) determining, in the receiving data terminal device, a position in the data memory where the next received packet is to be written based on the expected result of the step (c);
(E) at the receiving data terminal device, when writing the next received packet, temporarily save the data at the location overwritten and destroyed by the protocol control information of the received packet before receiving the next packet; (F) writing the next received packet to the data memory location determined based on the expected result in the receiving data terminal device; and (g) writing the next received packet in the received data terminal device in the receiving data terminal device. Reading the protocol information to identify the received packet; and (h) in the receiving data terminal device, after the protocol information is read,
Restoring the saved data to its original location,
(I) In the data terminal device on the receiving side, the expected result of the step (c) is compared with the identification result of the step (g). If the result is different, the data memory determined based on the expected result Moving the divided data of the received packet from the upper position to a position on the data memory calculated based on the identification result.

According to a third aspect of the present invention, there is provided a method for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information between data terminal devices connected via a transmission line. (B) receiving, on a data memory, a packet containing subsequent packet notification information for identifying at least one subsequent transmission packet as part of protocol control information; A) expecting a packet expected to be received next by referring to subsequent packet notification information in the received packet; and (c) data to be written with the next received packet based on the expected result of the step (b). Determining a location on the memory, and (d) when the next received packet is written, is overwritten and destroyed by the protocol control information of the received packet. (E) temporarily saving data at a location prior to receiving the next packet, (e) writing the next received packet at a location on the data memory determined based on the expected result, and (f) receiving the next packet. Reading the protocol information therein to identify the received packet;
(G) restoring the saved data to its original location after the protocol information is read, and (h) comparing the expected result of step (b) with the identification result of step (f) And when the result is different, moving the divided data of the received packet from the position on the data memory determined based on the expected result to the position on the data memory calculated based on the identification result; A data communication method comprising:

According to a fourth aspect of the present invention, there is provided a method for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information between data terminal devices connected via a transmission line. In the data communication method, the protocol control information includes divided data identification information indicating a position of the divided data in the packet in the entire terminal data, and subsequent packet notification information for identifying at least one subsequent transmission packet. A data communication method comprising:

Here, the divided data identification information may be a divided serial number sequentially assigned to each divided data from the beginning of the terminal data. Alternatively, the divided data identification information may be an offset (the number of bytes) from the head of the terminal data to each divided data divided.

According to a fifth aspect of the present invention, divided data obtained by dividing terminal data and data in a packet format including its protocol control information are exchanged between another data terminal apparatus connected via a transmission line. A data communication device for exchange, and when transmitting a certain packet,
A data communication apparatus, which determines a packet to be transmitted next, adds the determined content to protocol control information as subsequent packet notification information, and transmits the packet control information.

According to a sixth aspect of the present invention, packet data including protocol control information and data obtained by dividing terminal data are exchanged between another data terminal device connected via a transmission line. A data communication device for exchanging, comprising: means for generating a packet to be transmitted, means for determining a packet to be transmitted next, and means for adding the determined content to the protocol control information as subsequent packet notification information. Means for transmitting a packet having subsequent packet notification information on a transmission line. According to a seventh aspect of the present invention, there is provided a method for exchanging data in a packet format including divided data obtained by dividing terminal data and protocol control information thereof with another terminal device connected via a transmission line. Means for generating a packet to be transmitted, the data communication device comprising:
Means for determining a packet to be transmitted next, means for adding the determined content to the protocol control information as subsequent packet notification information, means for transmitting a packet having the subsequent packet notification information on the transmission line, Means for receiving a packet on a data memory via a network, means for referring to subsequent packet notification information in the received packet to predict a packet expected to be received next, and divided data of the received packet based on the expected result And a means for determining a position in a data memory to which the data is to be written.

According to an eighth aspect of the present invention, there is provided a method for exchanging data in a packet format including divisional data obtained by dividing terminal data and its protocol control information with another terminal connected via a transmission line. A data communication device for: (a) generating a packet to be transmitted;
(B) means for determining a packet to be transmitted next;
(C) means for adding the decision made by the means (b) to the protocol control information as subsequent packet notification information;
Means for transmitting a packet having the subsequent packet notification information on the transmission line, (e) a data memory in which the packet transmitted via the transmission line is written, and (f) reference to the subsequent packet notification information in the received packet Packet expectation means for expecting the next expected packet to be received,
(G) packet receiving means for writing the next received packet at a position on the data memory determined based on the expected result of said means (f); and (h) said received packet when writing the next received packet. Data saving means for temporarily saving data at a location overwritten and destroyed by the above protocol control information before receiving the next packet, and for restoring the original location after reading the written protocol control information; (i) Means for reading the protocol information in the received packet to identify the received packet; and (j) comparing the expected result by means (f) with the identification result by means (i). From the position in the data memory determined based on the result, the divided data of the received packet is stored in the position in the data memory calculated based on the identification result. A data position correcting means for moving the,
A data communication device comprising:

According to a ninth aspect of the present invention, data obtained by dividing terminal data and data in a packet format including its protocol control information are transmitted to and from another data terminal device connected via a transmission line. A data communication device for exchanging, comprising: (a) a data memory into which a packet including subsequent packet notification information for identifying at least one subsequent transmission packet as part of protocol control information is written; b) packet predicting means for predicting a packet expected to be received next by referring to subsequent packet notification information in the received packet; and (c) data memory determined based on the expected result of said means (b). Packet receiving means for writing the next received packet in the upper position,
(D) The data at the location overwritten and destroyed by the protocol control information of the received packet when the next received packet is written is temporarily saved prior to receiving the next packet, and the written protocol control information is read. Data saving means for later restoring to the original location; (e) means for reading out protocol information in the received packet to identify the received packet; (f) expected result of said means (b) and said means (e) If the result is different, the divided data of the received packet is transferred from the position on the data memory determined based on the expected result to the position on the data memory calculated based on the identification result. A moving data position correcting unit.

According to a tenth aspect of the present invention, a packet which is connectable to a transmission line and which divides terminal data, and which includes protocol control information, is transmitted between another data terminal device via the transmission line. A computer-readable storage medium tangibly storing a computer program that runs on a computer system that can be replaced by a computer program, the computer program comprising: (a) transmitting one packet when transmitting one packet; A routine for determining a packet to be transmitted next, adding the determined content to the protocol information as subsequent packet notification information and transmitting the packet, and (b) determining a packet transmitted via the transmission line at the time of reception. A routine for receiving data in a data memory; A routine for referring to the information to predict a packet expected to be received next, and (d) a position in the data memory where a next received packet is to be written at the time of reception based on the expected result of the routine (c). And (e) a routine for temporarily saving, at the time of reception, data at a location where the next received packet is written and destroyed by the protocol control information of the received packet prior to receiving the next packet When,
(F) a routine for writing the next received packet at a position on the data memory determined based on the expected result at the time of reception; and (g) reading protocol information in the received packet at the time of reception and (H) a routine for restoring the saved data to its original location after the protocol information is read at the time of reception, and (i) the routine (c) at the time of reception. Is compared with the identification result of the routine (g). If the result is different, the data on the data memory calculated based on the identification result from the position on the data memory determined based on the expected result is compared. And a routine for moving the fragmented data of the received packet to the position of (1).

According to an eleventh aspect of the present invention, a packet which can be connected to a transmission line and divides terminal data and includes protocol control information thereof is transmitted between the transmission line and another data terminal device. A computer-readable storage medium tangibly storing a computer program running on a computer system replaceable with: (a) a computer-readable storage medium for identifying at least one subsequent transmission packet; A routine for receiving a packet containing packet notification information as part of the protocol control information on the data memory; and (b) predicting a packet expected to be received next by referring to subsequent packet notification information in the received packet And (c)
A routine for determining a position in the data memory where the next received packet is to be written based on the expected result of the routine (b); and (d) using a protocol control information of the received packet when the next received packet is written. A routine for temporarily saving data at a location where overwriting is to be destroyed before receiving the next packet; (e) a routine for writing the next received packet at a position on the data memory determined based on the expected result; f) a routine for reading out the protocol information in the received packet to identify the received packet; and (g) a routine for restoring the saved data to the original location after the protocol information is read out;
(H) comparing the expected result of the routine (b) with the identification result of the routine (f), and when the result is different, based on the identification result from the position on the data memory determined based on the expected result; A routine for moving the divided data of the received packet to a position on the data memory calculated by
A computer-readable storage medium characterized by including:

[0046]

The present invention is applied to packet format data exchange. In packet communication, terminal data is divided into data of a predetermined length and further transmitted in the form of a packet to which protocol control information necessary for transmission control is added (described above). The protocol control information includes divided data identification information indicating a position occupied by the divided data in the packet in the entire terminal data, a checksum for detecting destruction of data in the packet, and the like. The protocol control information is generally added as a header at the beginning of the divided data or as a trailer at the end of the divided data.

The present invention has been made in view of the fact that it is easy to determine at least a packet to be transmitted immediately after a packet is transmitted at a data terminal device on the transmission side. It is.

The data communication apparatus according to the present invention determines the next packet to be transmitted when transmitting a certain packet, and adds the determined content to the protocol control information as subsequent packet notification information. To send from.

On the other hand, when a packet is received, the next packet expected to be received is expected by referring to the subsequent packet notification information included as protocol control information of the received packet, and the receiving position on the data memory is determined. can do. The received packet is received once at the determined position.

The protocol control information of the received packet includes:
Also includes divided data identification information for identifying the position occupied by the divided data in the packet. Therefore, by identifying the received packet with reference to the protocol control information and comparing the identification result with the previous expected result, it can be determined whether or not the divided data in the received packet has been received at a correct position. If the comparison results are different,
The divided data of the received packet is moved from the position on the data memory determined based on the expected result to the position on the data memory calculated based on the identification result.

The data memory sequentially receives the divided data in the packet, and finally restores the original terminal data. Protocol control information added as a header or trailer does not originally constitute terminal data, and must be discarded after use. When the received packet is written as it is at the expected receiving position on the data memory, there is data that is overwritten and destroyed by the protocol control information. For this reason, data that is overwritten and destroyed is temporarily saved before receiving the next packet. Then, after the protocol information is read, the saved data is restored to the original location.

According to the present invention, the data communication apparatus can appropriately predict the next packet to be received based on the subsequent packet notification information included in the received packet. Therefore, even when performing selective retransmission (described above), the data terminal device on the transmission side can appropriately predict a packet to be transmitted next, and transmission error correction can be performed with high transfer efficiency and high throughput. Can do

The computer-readable storage medium according to the tenth and eleventh aspects of the present invention may be a computer-readable storage medium for realizing the functions of a computer program on a computer system. It defines functional cooperative relationships. In other words, by attaching the computer storage medium to a computer system (or installing a computer program in the computer system), a cooperative action is exerted on the computer system, and the second and the third aspects of the present invention are achieved. The same operation and effect as those of the third aspect can be obtained.

Still other objects, features and advantages of the present invention are:
It will become apparent from the following more detailed description based on the embodiments of the present invention and the accompanying drawings.

[0055]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 schematically shows a data communication system 100 provided for implementing the present invention. The data communication system 100 includes a network 10 as a data transmission medium and two or more terminal devices (DTEs) 50A, B ... connected to the network. One
One terminal device can transmit data to another specific terminal device.

The network 10 is a LAN (Local Area Network) laid in a specific premises.
k) Other than leased line, general public line (PSTN), IS
DN (Integrated Service Dig)
ital network or the Internet.

On the network 10, each data terminal device 50a can communicate with each other in accordance with a predetermined communication protocol. The standard model of the communication protocol is OSI (Open Systems Interc).
connection: Open system interconnection) reference model. The OSI reference model includes seven layers: a physical layer, a data link layer, a network layer, a transport layer, a session layer, a presentation layer, and an application layer.

Each of the data terminal devices 50A, 50B,... Is generally provided with a line termination device (DCE: Data Circuit).
Terminal Equipment) 51A, B
Are connected to the network 10 via. If the network 10 is an analog line such as PSTN, DC
E is a modem (Modulator / Demodulator)
or). For ISDN, DCE is T
A (Terminal Adapter) and DSU (Digital
Service Unit). Also, L
In the case of an AN, the DCE is a LAN adapter (for example, an Ethernet card or a token ring card). Although the DCE is illustrated separately from the data terminal device in FIG. 1, the DCE may be built in the data terminal device.

The data terminal devices 50a, 50b, ... may be general-purpose computer systems in which communication software is installed, in addition to dedicated communication terminals. Data terminal device 50
Is a CPU (Central Processing)
Unit 61, a memory 62, a display 63a as a user interface, and a keyboard 63b.
And a mouse 63c, a hard disk drive (HDD) 64a as an external storage device, a floppy disk drive (FDD) 64b, a CD-ROM drive 64c, and the like.

The CPU 61 normally operates
The program code loaded into the memory 62 is executed under the control of the system (OS). The execution program code is supplied in the form of a storage medium such as a floppy disk or a CD, and is installed in the HDD 64a. Recently, the execution program code may be installed in the device 50 via the network 10.

To configure the data terminal device 50, many electric circuits and the like other than those shown in FIG. 1 are required. However, since these are well known to those skilled in the art and do not constitute the gist of the present invention, they are omitted in this specification. Also, it should be noted that only a part of the connections between the respective hardware blocks in the drawings is illustrated in order to avoid complicating the drawings (for example, the CPU 61
Normally, peripheral devices are connected by bus instead of local connection).

FIG. 2 illustrates, in the form of a block diagram, data division and packet generation processing realized by the data terminal device 50 on the transmitting side according to the present invention. As shown in the figure, the data division and packet generation processing includes a terminal data memory 301, a divided data copy unit 302,
This is realized by the cooperative operation of the packet transmission order determination unit 303, the protocol control information addition unit 304, the transmission packet memory 305, and the packet transmission unit 306.

The terminal data memory 301 is a storage device for temporarily storing terminal data to be transmitted from the data terminal device 50 on the transmitting side.

The packet transmission order determining unit 303 is a device that determines a packet transmission order according to a communication protocol defined between the transmitting and receiving terminals. For example, during normal transmission, the transmission order is determined according to the order in which the divided data is cut out from the terminal data. When a retransmission request is received from the receiving side due to packet loss, the packet transmission order is determined according to a retransmission control protocol determined between transmission and reception. The retransmission control protocol is GO-BA
In addition to CK-N retransmission, selective retransmission (described above) such as batch retransmission or sequential retransmission may be used. The packet transmission order determining unit 303 outputs divided data identification information for identifying the divided data included in the transmission packet, and subsequent packet notification information indicating the divided data included in the packet to be transmitted next. .

The divided data copy unit 302 is a device for sequentially extracting divided data from the terminal data memory 301. That is, the packet transmission order determination unit 303
According to the divided data identification information output from the terminal, the corresponding divided data is cut out from a predetermined position on the terminal data memory 301 and passed to the transmission packet memory 305.

The transmission packet memory 305 is a storage device for temporarily holding packet data to be transmitted.

The protocol control information adding unit 304 writes the values of the divided data identification information and the subsequent packet notification information output from the packet transmission order determining unit 303 into a predetermined field of the protocol control information (see below and FIG. 3). In addition, the values of the error correction code field and the packet length field are also set. The protocol control information generated here is added to the divided data held in the transmission packet memory 305, and as a result, a transmission packet is formed.

The packet transmission unit 306 transmits
The packet held in the memory 305 is transmitted in synchronization with a signal on a transmission line.

Each module in the block diagram shown in FIG. 2 can be implemented as dedicated hardware incorporated in the terminal device 50 or as a program code executed by the CPU 61. For example, functions equivalent to those shown in the block diagram of FIG. 2 constitute a communication protocol negotiated between the transmitting and receiving terminals, and can be implemented as a part of the transport layer or the data link layer in the OSI reference model. .

FIG. 3 schematically shows a format of protocol control information added to a packet generated in data terminal device 50 on the transmitting side. The protocol control information is added in the form of, for example, a header or a trailer.

As shown in the figure, the protocol information is
It has divided data identification information for identifying the divided data in the packet, an error detection code for detecting an error in the data in the packet, fields for writing the packet length, and a notification of the next packet to be transmitted. A subsequent packet notification information field for writing information for performing

The protocol control information shown in FIG. 3 may be a part of a packet header or a trailer. For example, the TCP header shown in FIG.
May be incorporated as part of

On the other hand, FIG. 4 shows a data assembling process realized by the data terminal device 50 on the receiving side according to the present invention.
Illustrated in block diagram form. As shown in the figure,
The data assembling process is realized by the cooperative operation of the packet receiving unit 201, the packet identifying unit 202, the packet expecting unit 203, the terminal data memory 204, the data saving unit 205, and the divided data position correcting unit 206. You.

The packet receiving unit 201 is a device for taking in a packet transmitted from the data terminal device on the transmitting side in synchronization with a signal on the transmission line, and writes the received packet on the data memory 204. ing. The terminal data memory 204 is secured as a predetermined area in the memory 62, for example.

The packet identification section 202 reads out the protocol control information in the received packet taken into the terminal data memory 204, and identifies the received packet. The packet identification unit 202 outputs, as a result of the identification, information on a position occupied by the divided data in the received packet with respect to the entire terminal data (ie, “divided data position information”).

The packet expecting unit 203 expects the next packet to be received based on the subsequent packet notification information included in the protocol control information of the packet. The position where the packet receiving unit 201 writes the next received packet on the data memory 204 is determined according to the result of the prediction by the packet expecting unit 203.

The data saving unit 205 is provided for temporarily saving data at a position where the data is overwritten and destroyed by the protocol control information in the received packet when writing the received packet to the terminal data memory 204. The position of the data to be saved is determined based on the prediction result of the packet prediction unit 203. Before the packet is received, the data is saved, then the packet is received, and after the protocol identification information in the packet is read out by the packet identification unit, the saved data returns to the original position.

The divided data position correcting section 206 is a device for correcting the position where the received packet is fetched into the terminal data memory 204 when the position is incorrect. More specifically, the expected result of the packet expectation unit 203 for a certain received packet is compared with the identification result of the packet identification unit 202. If the two are different, it is determined that the position where the received packet is captured is incorrect. Modify the position. At this time, the divided data of the received packet is copied from a position determined based on the expected result of the packet to a correct position determined based on the identification result.

Each module in the block diagram shown in FIG. 4 can be implemented as dedicated hardware incorporated in the terminal device 50 or as a program code executed by the CPU 61. For example, functions equivalent to those shown in the block diagram of FIG. 4 constitute a communication protocol negotiated between transmitting and receiving terminals, and can be implemented as a part of the transport layer or the data link layer in the OSI reference model. .

Here, the data length of the entire terminal data is represented by Lt.
[Byte], and the data length of the divided data included in each packet (that is, the size for dividing the terminal data) is Ld.
If it is [byte], the number Nd of packets for constituting terminal data is represented by the following equation. That is,

[0082]

Nd = (Lt + Ld-1) / Ld

A packet (more specifically, protocol control information added to a packet) usually includes divided data identification information for identifying the divided data contained in the packet. The protocol information of the present embodiment further includes subsequent packet notification information for specifying a packet to be transmitted next. The former divided data identification information (ID) has a property indicating a position occupied by the divided data in the packet with respect to the entire terminal data. In the communication protocol determined between the transmitting and receiving terminal devices according to the present embodiment, a division serial number given in ascending order to each divided data obtained by dividing the terminal data is used as divided data identification information (however, The first ID is 0, and 1
Increment by 1). In addition, as the division data identification information, the number of bytes from the head of the terminal data can be used in addition to the division serial number.

The place where the protocol control information is added to the packet complies with the communication protocol determined between the transmission and reception. For example, a packet can be formed by adding a trailer to the end of the divided data, adding a header to the beginning, or adding both a header and a trailer.

When the packet includes a header, the terminal data memory 204 that receives the packet stores at least one header (that is, protocol control information) further ahead of where the first divided data that constitutes the terminal data is received. It must have a free area corresponding to the length Lh. FIG. 5 schematically shows the memory space of the data memory 204 in this case. In the figure, A
t indicates a head position (address) for receiving terminal data.

When the packet includes a trailer, the terminal data memory 204 receiving the packet stores
Behind the place where the last divided data constituting the terminal data is received, there must be an empty area corresponding to the length Lt of at least one trailer (that is, protocol control information). FIG. 6 schematically shows the memory space of the data memory 204 in this case.

When the packet includes both the header and the trailer, the terminal data memory 204 that receives the packet stores at least one header ahead of the location where the first divided data that constitutes the terminal data is received. Must have an empty area corresponding to the length Lt of the trailer and at least one trailer behind the place where the last divided data is received. FIG. 7 schematically shows the memory space of the data memory 204 in this case.

In the communication protocol between transmission and reception applied to this embodiment, a packet is configured by adding protocol control information as a header.

FIG. 8 shows a flow of a data assembling process according to the present embodiment. The flow can be implemented, for example, in the form of a program code executed by the CPU 61 of the data terminal device 50. Hereinafter, this will be described in detail.

The header (ie, protocol control information) of the received packet includes divided data identification information for identifying the position of the divided data in the packet with respect to the entire terminal data, and specifies the next packet to be transmitted. And subsequent packet notification information for performing the operation (described above).

The packet expectation unit 203 outputs the divided data identification information of the next received packet as an expected result based on the subsequent packet notification information. However, at the start of reception, the divided data identification information IDexp is set to an initial value 0 as an expected result of the first received packet (step S).
501).

Prior to receiving a packet, the packet expectation unit 203 outputs and holds the divided data identification information IDexp of the packet to be received next as an expected result.

The position Aexp at which the next packet to be received is written on the terminal data memory 205 is obtained by the following formula based on the expected result IDexp of the packet expectation unit 203.

[0094]

## EQU2 ## Aexp = At-Lh + IDexp × Ld

Since the header in the received packet does not constitute terminal data, the entire packet is
When the data is received on the memory 204, the already received data may be overwritten and destroyed by the header. Therefore, the data saving unit 205 saves the data at the location where the header of the received packet is to be written in advance. After saving the data, when the packet receiving unit 201 receives the packet, the packet receiving unit 201 transmits the packet to the position Ae on the terminal data memory 205.
xp (step S502).

The packet identification unit 202 reads the protocol control information from the reception packet writing position Aexp on the terminal data memory 205 and identifies the reception packet (step S503). More specifically, packet identification section 202 outputs divided data identification information IDrcv included in the protocol control information as an identification result. After the protocol control information is read, the data saving unit 204 writes the saved data back to the original location.

After receiving the packet, the divided data position correction unit 206 compares the expected result output by the packet expectation unit 203 with respect to the received packet and the identification result output by the packet identification unit 202 (step S504). .

When the two match, that is, when the succeeding packet as notified by the previous received packet is received, the divided data in the packet is taken in the correct position on the terminal data memory 204 as it is.

On the other hand, if they do not match, it means that the divided data in the subsequent packet has been fetched at an incorrect position on the terminal data memory 205 according to an incorrect expectation. Therefore, the divided data position correction unit 206 determines the position Asr at which the divided data is scratched at this time.
Data is copied from c = At + IDexp × Ld to a correct write position Adst = At + IDrcv × Ld (step S510).

Next, based on the subsequent packet notification information included in the protocol control information of the received packet, the packet expectation unit 203 expects the next packet expected to be received and replaces the divided data identification information IDnxt with the expected result ID.
Output as exp (step S505).

Next, the flow returns to step S502, and the above processing is repeatedly executed until the reception of all the divided data constituting the terminal data is completed and the end of the data assembling processing is determined (step S506).

Although the present embodiment makes it possible to recover a packet lost due to a transmission error in accordance with a selective retransmission procedure, the present embodiment is applicable to either the above-described batch retransmission or sequential retransmission. Can be. However, specific communication protocol operations and means for realizing these selective retransmission procedures are not directly related to the gist of the present invention, and will not be further described in this specification.

[Supplement] The present invention has been described in detail with reference to the specific embodiments. However, it is obvious that those skilled in the art can modify or substitute the embodiment without departing from the spirit of the present invention. That is, the present invention has been disclosed by way of example, and should not be construed as limiting. In order to determine the gist of the present invention, the claims described at the beginning should be considered.

[0104]

As described above in detail, according to the present invention,
It is possible to provide an excellent data communication method and an excellent data communication device that can perform data communication by a packet communication method and can correctly assemble original terminal data from a received packet in a receiving-side data terminal device.

Further, according to the present invention, there is provided an excellent data communication method and apparatus which can simplify and speed up data assembling processing for assembling original terminal data from sequentially received packets. Can be.

Also, according to the present invention, when assembling a received packet into original terminal data, there is an overhead problem associated with data copying and a reduction in data transfer efficiency due to a GO-BACK-N retransmission procedure. It is possible to provide an excellent data communication method and an excellent data communication device which are free from the problem described above.

Further, according to the present invention, the data terminal device on the receiving side accurately predicts the next received packet based on the protocol control information of the previously received packet, and thus selectively retransmits the packet. It is possible to provide an excellent data communication method and an excellent data communication device, which can appropriately correct a transmission error by using the method.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a data communication system 100 provided for implementing the present invention.

FIG. 2 is a block diagram showing data division and packet generation processing realized by a data terminal device 50 on the transmission side according to the present invention.

FIG. 3 is a diagram schematically illustrating a format of protocol control information added to a packet generated in a data terminal device 50 on the transmission side.

FIG. 4 is a block diagram schematically showing a data assembling process realized by the data terminal device 50 on the receiving side according to the present invention.

FIG. 5 is a diagram schematically showing a memory space of a terminal data memory 204 when a packet includes protocol control information in the form of a header.

FIG. 6 is a diagram schematically showing a memory space of a terminal data memory 204 when a packet includes protocol control information in the form of a trailer.

FIG. 7 is a diagram schematically showing a memory space of the terminal data memory 204 when a packet includes protocol control information in the form of a header and a trailer.

FIG. 8 is a diagram illustrating a flow of a data assembling process according to the embodiment;

FIG. 9 is a diagram schematically illustrating packet communication performed between data terminal devices;

FIG. 10 is a schematic diagram illustrating an example of transmission errors that may occur on a transmission line, such as destruction or partial loss of data in a packet, loss of the entire packet, rearrangement of the order, and duplication. FIG.

FIG. 11 is a diagram schematically showing a format of a TCP header.

FIG. 12 is a diagram showing, in the form of a block diagram, one conventional example of a data assembling process performed in a data terminal device on the receiving side.

FIG. 13 is a block diagram showing a data assembling process disclosed in Japanese Patent Application No. 10-218827.

FIG. 14 is a diagram schematically showing how a lost packet is recovered by a GO-BACK-N retransmission procedure.

FIG. 15 is a diagram schematically showing how a lost packet is recovered by a selective retransmission procedure of a batch retransmission method.

FIG. 16 is a diagram schematically showing how a lost packet is recovered by a selective retransmission procedure of a sequential retransmission method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Network 50 ... Terminal device 51 ... Line terminator 61 ... CPU 62 ... Memory 63 ... User interface 64 ... External storage device 100 ... Data communication system 201 ... Packet receiving unit 202 ... Packet identification unit 203 ... Packet prediction unit 204 ... Terminal data memory 205: Data saving unit 206: Divided data position correcting unit 301: Terminal data memory 302: Divided data copying unit 303: Packet transmission order determining unit 304: Protocol control information adding unit 305: Transmission packet memory 306 … Packet transmitter

Claims (16)

[Claims] 1. A data communication method for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information between data terminal devices connected via a transmission line, comprising: In the data terminal device, when transmitting a certain packet, a next packet to be transmitted is determined, and the determined content is added to the protocol control information as subsequent packet notification information, and then transmitted. A step of, in the data terminal device on the side, referring to subsequent packet notification information in the received packet to expect a packet expected to be received next. 2. A data communication method for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information between data terminal devices connected via a transmission line, comprising: ) When transmitting a certain packet in the data terminal device on the transmission side,
Next, a packet to be transmitted is determined, the content of the determination is added to the protocol information as subsequent packet notification information, and the packet is transmitted. (B) The data terminal device on the receiving side is transmitted via the transmission line. Receiving the received packet on the data memory; and (c) in the receiving data terminal device, referring to the subsequent packet notification information in the received packet and expecting the next expected packet to be received; (D) determining, in the receiving data terminal device, a location in the data memory where the next received packet is to be written based on the expected result of the step (c); and (e) receiving data terminal device. In the above, when the next received packet is written, the data at the location overwritten and destroyed by the protocol control information of the received packet is received by the next packet reception. A step of temporarily saved in advance,
(F) writing the next received packet to the data memory location determined based on the expected result in the receiving data terminal device; and (g) writing the next received packet in the received data terminal device in the receiving data terminal device. Reading the protocol information to identify the received packet; and (h) restoring the saved data to its original location after the protocol information is read in the receiving data terminal device; (I) In the data terminal device on the receiving side, the expected result of the step (c) is compared with the identification result of the step (g). If the result is different, the data memory determined based on the expected result Moving the divided data of the received packet from the upper position to the position on the data memory calculated based on the identification result. 3. A data communication method for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information between data terminal devices connected via a transmission line, comprising: Receiving a packet containing, as part of the protocol control information, subsequent packet notification information for identifying at least one subsequent transmission packet on the data memory; and (b) subsequent packet notification information in the received packet. (C) determining a position in the data memory where the next received packet is to be written based on the expected result of the step (b). ,
(D) temporarily saving, prior to receiving the next packet, data at a location overwritten and destroyed by the protocol control information of the next received packet when the next received packet is written; and (e) based on an expected result. Data determined
Writing the next received packet to a location in memory;
(F) reading the protocol information in the received packet,
Identifying the received packet; (g) restoring the saved data to its original location after the protocol information has been read; (h) expecting the result of step (b) and the step (F) comparing the identification results, and if the results are different, the received packet of the received packet is shifted from the position on the data memory determined based on the expected result to the position on the data memory calculated based on the identification result. Moving the divided data. 4. A data communication method for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information between data terminal devices connected via a transmission line, comprising: Data communication characterized in that the information includes divided data identification information indicating a position of the divided data in the packet in the entire terminal data, and subsequent packet notification information for identifying at least one subsequent transmission packet. Method. 5. The data communication method according to claim 4, wherein said divided data identification information is a divided serial number sequentially allocated to each divided data from the beginning of terminal data. 6. The data communication method according to claim 4, wherein the divided data identification information is an offset (the number of bytes) from the head of the terminal data to each divided data. 7. A data communication apparatus for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information with another data terminal apparatus connected via a transmission line. When transmitting one packet, the data communication apparatus determines a packet to be transmitted next, and transmits the packet after adding the determined content to subsequent protocol control information as subsequent packet notification information. 8. A data communication device for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information thereof with another data terminal device connected via a transmission line. Means for generating a packet to be transmitted; means for determining a packet to be transmitted next; means for adding the determined content to the protocol control information as subsequent packet notification information; Means for transmitting on a transmission line. 9. A data communication device for exchanging divided data obtained by dividing terminal data and packet data including protocol control information thereof with another data terminal device connected via a transmission line. Means for generating a packet to be transmitted; means for determining a packet to be transmitted next; means for adding the determined content to the protocol control information as subsequent packet notification information; Means for transmitting on a transmission line, means for receiving a packet on a data memory via the transmission line, and means for predicting the next packet expected to be received by referring to subsequent packet notification information in the received packet Means for determining a position in the data memory where the divided data of the received packet is to be written based on an expected result. Data communication device. 10. A data communication device for exchanging divided data obtained by dividing terminal data and data in a packet format including protocol control information thereof with another data terminal device connected via a transmission line. (A) means for generating a packet to be transmitted, (b) means for determining a packet to be transmitted next, and (c) protocol control information using the contents determined by the means (b) as subsequent packet notification information. (D) means for transmitting a packet having subsequent packet notification information on a transmission line, (e) a data memory in which the packet transmitted via the transmission line is written, and (f) reception. Packet predicting means for predicting a packet expected to be received next by referring to subsequent packet notification information in the packet; and (g) determining based on an expected result of the means (f). Packet receiving means for writing the next received packet at a location on the data memory to be written; and (h) writing the data at the location overwritten and destroyed by the protocol control information of the next received packet when the next received packet is written. Data saving means for temporarily saving prior to packet reception and restoring the original location after reading the written protocol control information; and (i) a packet for reading the protocol information in the received packet and identifying the received packet Comparing the identification means with (j) the expected result of the means (f) and the identification result of the means (i), and when the results are different, from the position on the data memory determined based on the expected result Data position correcting means for moving the divided data of the received packet to a position on the data memory calculated based on the identification result; Data communication apparatus which comprises a. 11. A data communication device for exchanging divided data obtained by dividing terminal data and data in a packet format including its protocol control information with another data terminal device connected via a transmission line. (A) a data memory in which a packet including, as part of the protocol control information, subsequent packet notification information for identifying at least one subsequent transmission packet is written; and (b) a subsequent packet notification in the received packet. Packet prediction means for referring to the information to predict the next expected packet;
(C) packet receiving means for writing the next received packet at a position on the data memory determined based on the expected result of said means (b); and (d) said received packet when the next received packet is written. (E) data saving means for temporarily saving data at a location overwritten and destroyed by the above protocol control information before receiving the next packet, and restoring the original location after reading the written protocol control information; Reading the protocol information in the received packet and identifying the received packet; and (f) comparing the expected result by the means (b) with the identification result by the means (e). From the position in the data memory determined based on the result, the divided data of the received packet is stored in the position in the data memory calculated based on the identification result. A data position correcting means for moving the,
A data communication device comprising: 12. A packet of a type in which protocol control information is added as a trailer of a packet, wherein the data memory is added as a trailer further behind a location where the last divided data constituting terminal data is held. 12. The data communication apparatus according to claim 10, wherein the data communication apparatus has a free area equal to or larger than the size of the protocol control information. 13. A packet of a type in which protocol control information is added as a header of a packet is exchanged, wherein the data memory is added as a header further ahead of a location where a leading divided data constituting terminal data is held. 12. The data communication device according to claim 10, wherein the data communication device has a free area equal to or larger than the size of the protocol control information. 14. A packet of a type in which protocol control information is added as a header and a trailer of a packet is exchanged, and the data memory further includes a header as a header further ahead of a place for holding a leading divided data constituting terminal data. Having a free space equal to or larger than the size of the added protocol control information, and further behind a place where the last divided data constituting the terminal data is held, a free space equal to or larger than the size of the protocol control information added as a trailer is set. The data communication device according to claim 10, further comprising: 15. A computer system connectable to a transmission line and capable of exchanging divided data obtained by dividing terminal data and a packet containing protocol control information with another data terminal device via the transmission line. A computer-readable storage medium tangibly storing an operating computer program, the computer program comprising: (a) at the time of transmission, when transmitting a certain packet, determining a packet to be transmitted next; A routine for adding the determined content to the protocol information as subsequent packet notification information and transmitting the packet; and (b) a routine for receiving a packet transmitted via a transmission line on a data memory at the time of reception. , (C) at the time of reception, the next packet reception information A routine for determining a position in a data memory where a next received packet is to be written based on an expected result of the routine (c) at the time of reception; and (e) receiving A routine for temporarily saving data at a location overwritten and destroyed by the protocol control information of the next received packet when the next received packet is written before receiving the next packet; A routine for writing the next received packet at a position on the data memory determined based on the result, (g) a routine for reading out the protocol information in the received packet at the time of reception and identifying the received packet, At the time of reception, after the protocol information is read, a routine for restoring the saved data to the original location (I) comparing the expected result of the routine (c) with the identification result of the routine (g) at the time of reception, and if the result is different, the position on the data memory determined based on the expected result A routine for moving the divided data of the received packet to a position on the data memory calculated based on the identification result from the received data. 16. A computer system connectable to a transmission line and capable of exchanging divided data obtained by dividing terminal data and a packet containing protocol control information with another data terminal device via the transmission line. A computer-readable storage medium tangibly storing an operating computer program, the computer program comprising: (a) transmitting subsequent packet notification information for identifying at least one subsequent transmission packet to one of protocol control information; A routine for receiving a packet included as a part on a data memory; (b) a routine for referring to subsequent packet notification information in a received packet to predict a packet expected to be received next; and (c) the routine Data to be written with the next received packet based on the expected result of (b)
A routine for determining a position on the memory; and (d) a routine for temporarily saving data at a location where the next received packet is overwritten and destroyed by the protocol control information of the received packet prior to receiving the next packet. When,
(E) a routine for writing the next received packet to a location on the data memory determined based on the expected result;
(F) reading the protocol information in the received packet,
A routine for identifying a received packet; (g) a routine for restoring saved data to its original location after the protocol information is read; and (h) the routine (b).
Is compared with the identification result of the routine (f),
If the result is different, a routine for moving the divided data of the received packet from the position on the data memory determined based on the expected result to the position on the data memory calculated based on the identification result. A computer-readable storage medium characterized by the above-mentioned.