Multiplex communications – Channel assignment techniques – Combining or distributing information via time channels...
Reexamination Certificate
1999-04-29
2001-06-26
Vu, Huy D. (Department: 2664)
Multiplex communications
Channel assignment techniques
Combining or distributing information via time channels...
C370S447000, C370S457000
Reexamination Certificate
active
06252885
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to data communication by a CATV communication system, and more particularly to a CATV communication system including a center device and terminal devices, and a method of performing data communication by means of the CATV communication system.
2. Description of the Prior Art
There are conceivable some methods of the data communication by using a duplex or bi-directional CATV communication system. One of them is the packet communication method with collision detection function, which is generally employed in a LAN or the like. Now, it is assumed that a user A sends data to another user B via the CATV wired line. According to this method, the user A sends data via the upstream transmission line to the center device, which returns data thus received to send it to all the terminal devices, including the terminal device of the user B, via the downstream transmission line. If no collision takes place, the user A, the sender, refers to data returned via the downstream transmission line and determines the coincidence of returned data with data that he has sent, thereby confirming the correct data transmission being executed. On the other hand, if plural users send data, respectively, almost simultaneously, data collision likely takes place.
FIG. 7
schematically illustrates the manner of the data collision, wherein the user A sent data Da via the upstream transmission line, but the user B also sent data Db almost at the same time. Data Da and data Db collide with each other to be broken, and consequently data Dx different from original data Da and Db is generated. Data Dx is received by the center device, which returns it to the downstream transmission line. The users A and B detect discordance between data that they have sent, respectively, and data returned, and recognize the collision has taken place.
An alternative way for the data communication via the CATV communication system is to use the timeslot system which is generally illustrated in FIG.
8
. This system divides the upstream transmission line and the downstream transmission line into a plurality of unit time (generally called “timeslot”) each having a predetermined time width, and a timeslot is assigned to a user. For example, assuming now that the eighth timeslot (oblique portion in
FIG. 8
) is assigned to the user A, he uses the eighth timeslot thus assigned for the data communication thereafter. Large capacity data may be transmitted by repeatedly sending the divided portions of data at the successive cycles of the eighth timeslot each having a limited data capacity.
However, the packet communication method with collision detection function described above has the following drawbacks. First, the collision occurrence is not found until broken data is received in the downstream transmission line by the sender, and hence the collision detection generally delays. Second, the users send data of random data length, respectively, and hence, when a user sends a large data, other users have to wait for a long time until his data transmission ends. Third, since downstream data cannot be transmitted while the upstream data is returned by the center device for the purpose of the collision detection, a complete duplex communication cannot be achieved.
On the other hand, the timeslot communication system has the following disadvantages. First, since the limited number of timeslots are assigned to the users for the exclusive use, only a limited number of users can make the data transmission simultaneously. Second, generally, the user does not actually send or receive data for a continuous long time period. Even when two users are communicating with each other by sending and receiving data, data is not actually running through the transmission line for a long time period, and the users are not sending or receiving data but referring to the received data or preparing the response in the major time period. But even in such a period in which data is not actually running through the transmission line, the transmission line is still kept connected, and hence the transmission line is not very efficiently used.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of data communication by using a CATV communication system, by which efficient data transmission can be achieved.
It is another object of the present invention to provide a CATV communication system by which data communication can be efficiently achieved.
It is still another object of the present invention to provide a center device and terminal devices employed in the CATV communication system.
According to one aspect of the present invention, there is provided a communication method for a CATV communication system which includes a center device and a plurality of terminal devices connected by CATV wired lines, the method including the steps of: (a) transmitting, from the center device to the terminal devices, cyclically a group of downstream timeslots each of which is distinctive from each other, each of the downstream timeslots including upstream timeslot occupancy information indicating whether or not an upstream timeslot corresponding to the downstream timeslot is vacant, collision information indicating whether or not a collision has occurred, and downstream data; (b) checking, at the terminal device, the upstream timeslot occupancy information in the downstream timeslots to detect a downstream timeslot including the upstream timeslot occupancy information of the vacant state; (c) sending upstream data, from the terminal device to the center device, by the upstream timeslot specified by the upstream occupancy information of the vacant state at a timing corresponding to the downstream timeslot detected in the step (b); (d) receiving, at the center device, the upstream timeslot sent in the step (c), detecting a collision of the upstream timeslot, and sending a downstream timeslot, in response to the upstream timeslot sent in the step (c), which includes the collision information set in accordance with the result of the collision detection; (e) detecting, at the terminal device, the collision information of the downstream timeslot sent in the step (d), and sending to the center device upstream data by the upstream timeslot corresponding to the downstream timeslot sent in the step (d), if the collision is not detected; and (f) detecting, at the center device, a carrier signal to be modulated by the upstream data in the upstream timeslots, and setting the upstream timeslot occupancy information of the downstream timeslot, corresponding to the upstream timeslot which includes no carrier signal, to the vacant state.
In accordance with the method, a group of downstream timeslots are transmitted from the center device to the terminal devices. Each downstream timeslot includes upstream timeslot occupancy information and collision information as well as downstream data. Then, the upstream timeslot occupancy information is checked at the terminal device to detect a downstream timeslot including the upstream timeslot occupancy information of the vacant state. Then, upstream data is sent from the terminal device to the center device via the upstream timeslot of the vacant state thus detected. Then, the center device receives the upstream timeslot thus sent and detects the collision to send the collision information of the timeslot to the terminal device. The terminal device checks the collision information thus sent, and continues transmission of the upstream data by the upstream timeslot if no collision is detected.
In this way, the center device detects the collision and informs the terminal devices of the collision occurred by means of the collision information, and hence the portion of the downstream timeslot other than the collision information can be used for the downstream data transmission, even if the collision occurred, thereby the data transmission loss resulted by the collision is diminished. Namely, since data capacity of merely the single upstream timeslot co
Sasada Tetsuichiro
Yashiro Kenji
Harper Kevin C.
Pioneer Electronic Corporation
Vu Huy D.
Young & Thompson
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