Multiplex communications – Channel assignment techniques – Using time slots
Reexamination Certificate
1997-04-23
2001-07-10
Patel, Ajit (Department: 2661)
Multiplex communications
Channel assignment techniques
Using time slots
C370S222000, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06259704
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a digital transmission network and in particular to a digital transmission network which is suitable for transmission of video, audio signals, etc. to monitor a plurality of monitor sites dispersed in a wide area through video and audio signals by devices in monitor centers which are provided in one or more locations, in which terminals each including a monitor device are provided in the plurality of monitor sites.
System configurations of conventional video transmission networks are shown in
FIGS. 7 and 8
.
FIG. 7
shows a system configuration in which a plurality of cameras
71
and a plurality of monitors
72
are all disposed in a star configuration and are connected to a central unit
73
so that all connection and switching between the cameras and the monitors is carried out by a matrix switch in a central unit.
FIG. 8
shows a so-called LAN (local area network) configuration in which a plurality of cameras
81
and monitors
82
are all connected through terminals
83
and a communication control unit
84
in the form of loop so that connection and switching between the cameras and monitors is carried out.
In the system of
FIG. 7
, the monitor
72
and the central unit
73
are usually disposed in the same position although the cameras
71
are dispersed. In a large scale monitor system, the distances between the cameras and between the cameras and the central unit are often several kilometers to several tens of kilometers.
For further information on the technology related with the present application, reference may be made to U.S. Pat. Nos. 4,937,823 and 5,101,405.
If the monitor area is wide and the number of monitor sites is large in the system of
FIG. 7
, the amount of the transmission line would be increased, and the matrix switch in the central unit would have an increased capacity and become complicated.
In the system of
FIG. 8
, a so-called Ethernet, token ring, or other format in which a plurality of data are randomly superposed on a looped transmission line is often adopted. Since the rate of the data of the monitor cameras is remarkably larger in comparison with that of usual personal computer and the period of its connection occupation time is extended, a waiting time for connection may occur on congestion of data and the system may often be inappropriate for emergency monitor. In particular, in case where a number of video data are concentrated on occurrence of accident, the connection will be impossible.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a simplified configured system in which the above-mentioned drawbacks are eliminated and are increase in the amount of the transmission line is prevented from occurring and no waiting time occurs.
In order to accomplish the above-mentioned object, an aspect of the present invention provides a digital transmission network in which a plurality of cameras and monitors are all connected in the form of loop through a metal cable or optical fiber cable, in which signals are transmitted in one direction by time-sharing multiplexing, an individual time slot defined by the time sharing multiplexing is allocated to each of signals transmitted from transmission terminals, and a timing device is inserted in a loop for retransmitting sequential frames so that they are continuous by correcting the transmission time for one frame and the delay time caused by the transmission line and cable and the like.
As a result, a waiting time due to conflicts of connection requests and congestion on the transmission line will not occur. Further, the delay time caused in the transmission line and each terminal can be corrected and absorbed by the timing device. The timing device may be provided at the same place as the central unit or a given monitor.
A predetermined number of the time slots are provided in the frame signal. Accordingly, a predetermined transmission capacity of the video data is always assured. Therefore, undesirable events such as occurrence of the waiting time and unable connection due to data concentration can be avoided.
The number of the video channels should not necessarily be equal to the total of all cameras and may be the total of the cameras which should be connected in emergency. Since the central unit can desiredly specify the channel of the camera to be monitored, no waiting time occurs when a necessary camera is to be connected in emergency.
A camera which always requires connection may be fixedly allocated in a given time slot.
In the usual monitor system, the number of the monitors is less than that of the cameras. Accordingly, the number of time slots (the number of channels) which are accommodated in one frame signal may be not larger than that of the cameras or may be equal to that of the monitors.
The central unit can specify the priority of connection for the transmission terminal.
REFERENCES:
patent: 3879710 (1975-04-01), Maxemchuk et al.
patent: 4713807 (1987-12-01), Caves et al.
patent: 4937823 (1990-06-01), Bekki et al.
patent: 5101405 (1992-03-01), Bekki et al.
patent: 5477542 (1995-12-01), Takahara et al.
patent: 5495285 (1996-02-01), Fujioka
Asahina Takashi
Hirono Suguru
Hisatomi Hiroyuki
Murata Nobuo
Anonelli, Terry, Stout & Kraus, LLP
Hitachi Denshi Kabushiki Kaisha
Patel Ajit
Phunkulh Bob A.
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