Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-02-19
2004-03-30
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S465000, C370S470000, C375S370000
Reexamination Certificate
active
06714540
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data communication method, a communication frame generating method, and a medium on which a program for executing the methods are recorded, and more particularly to a data communication method which prevents delay in data transmission in half duplex communication in a communication device having a utilization portion for executing application processings and a control portion for executing communication protocol processings, a communication frame generating method which prevents deterioration of data transmission (transfer) efficiency in asynchronous communications by radio and wire, and a medium on which program for carrying out the data communication method and the communication frame generating method are recorded.
2. Description of the Background Art
In a communication device having a utilization portion for executing application processings and a control portion for executing communication protocol processings, the utilization portion and the control portion exchange data in data transmission/reception. In data transmission, the utilization portion sends a data transmission request to the control portion. The control portion receives the data transmission request and then performs the processing of transmitting the data. In data reception, the control portion receives data and transfers the received data to the utilization portion. The utilization portion receives and processes the transferred data from the control portion.
Known data communication systems that perform between the communication devices generally include the full duplex communication system and half duplex communication system.
In the full duplex communication system, lines for transmission and reception are individually provided between communication devices, so that each communication device can freely transmit data without being affected by other communication devices. On the other hand, in the half duplex communication system, only a single line is provided between communication devices, so that a communication device cannot transmit data while the other communication device is transmitting data (therefore it receives the data).
Hence, in the half duplex communication system, a “transmission right” indicating which of the communication devices is the subject of the data transmission is generally transmitted/received together with the data. The half duplex communication system thus defines that only a communication device having the transmission right can perform data transmission.
Next,
FIG. 8
shows an example of conventional data communication by half duplex performed between communication devices having utilization portions and control portions as described above.
FIG. 8
is a diagram showing an example of a conventional communication sequence performed between communication devices A and B using the conventional data communication method. In
FIG. 8
, the utilization portion in the communication device A is represented as “utilization portion A” and its control portion as “control portion A,” and the utilization portion in the communication device B is represented as “utilization portion B” and its control portion as “control portion B.”
In the initial state, suppose that the transmission right resides in the communication device A and that a request for transmitting data B is occurring in the communication device B. First, the control portion A transmits only the transmission right to the control portion B, for it does not have a data transmission request at this time. The control portion B receives the transmission right sent from the control portion A, obtains the transmission-requested data B from the utilization portion B, and then transmits the data together with the transmission right to the control portion A. The control portion A then receives the data B and transmission right sent from the control portion B. Suppose that a request for transmitting data A is now occurring in the communication device A. In this case, the control portion A transfers the data B to the utilization portion A to preferentially process the data B transmitted from the control portion B. When receiving the data B, the utilization portion A processes the data B and then transfers the transmission-requested data A to the control portion A. Then, at last, the control portion A transmits the data A to the control portion B together with the transmission right.
In this conventional communication device, as stated above, application processing to received data (the data B) has priority over its own data transmission request processing (the data A). Accordingly its data transmission is delayed by the time the utilization portion (the utilization portion A) takes to process the received data (shown by the thick arrow in FIG.
8
). In the case of systems for communications of audio data, moving picture data, etc. which seriously require the real-time property, such data transmission delay causes serious problems such as discontinuity of sound, blanks of image, etc.
Conventionally, there have been two kinds of systems for connecting a plurality of communication devices: synchronous communication system and asynchronous communication system. In these communication systems, communication devices generally transmit/receive information etc. by using communication frames. In the asynchronous communication system, communication timing of communication frames transmitted/received between communication devices is not synchronized. Therefore the communication devices use communication frames including start and end flags at the beginning and end so that they can recognize the beginning and end of each communication frame.
FIG. 9
shows an example of structure of a communication frame used in the asynchronous communication. Referring to
FIG. 9
, the communication frame used in the asynchronous communication includes address for identification of the destination communication device, data representing the transmitted information, etc., as well as the above-described start and end flags.
When receiving the start flag, the communication device checks the following address and then processes the information to the end flag. The communication device thus recognizes the beginning and the end of the communication frame in accordance with the start and end flags. If any address code or data code identical to the start or end flag exists, the communication device may erroneously recognize the beginning or end of the communication frame. To avoid this problem, the communication device applies transparency control to codes representing the same codes as the start and end flags.
In short, this transparency control means conversion of one value to another value. For example, if a code A identical to the start flag code is included in data, the code A is replaced by another code B (needless to say, the code B differs from the end flag code). The code after converted is generally provided with an extra identifier code so that the recipient can correctly recognize the data transparency-controlled on the sender. That is to say, the transparency-controlled code B is preceded by an identifier code to allow the recipient to determine whether the code B after transparency control is a transparency-controlled code B or the code B not transparency-controlled.
The following is a specific example of the transparency control method, in which address, data, etc. which are identical to the start flag code “C0h” and the end flag code “C1h” are converted. The letter “h” represents hexadecimal.
C0h→7Dh E0h
C1h→7Dh E1h
7Dh→7Dh 5Dh
In the example above, the one-byte code “C0h” is converted into the two-byte code “7Dh E0h,” and the one-byte code “C1h” is converted into the two-byte code “7Dh E1h.” The part “7Dh” corresponds to the identifier code. Note that the code “7Dh” used as the identifier code is converted into the two-byte code “7Dh 5Dh.” If the code “7Dh” is left unchanged, then data not subjected to transparency control (e.g., “E0h”) will be erroneously
Ogawa Noriyuki
Saeki Yuko
Sugimoto Kuniaki
Hsu Alpus H.
Wenderoth , Lind & Ponack, L.L.P.
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