Interactive video distribution systems – Video distribution system components – Receiver
Reexamination Certificate
1998-10-30
2003-02-18
Faile, Andrew (Department: 2611)
Interactive video distribution systems
Video distribution system components
Receiver
C725S131000, C725S139000, C370S395100, C370S469000, C714S004110, C714S025000, C375S240250, C348S737000
Reexamination Certificate
active
06523178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video transmission system, and in particular to a video transmission system which transmits video data through an ATM network.
As a recent communication is carried out in the form of multimedia, the transmission of multimedia information including dynamic video information has become more and more important. For the transmission of the multimedia information, the ATM network is suitable which has a high-speed transmission rate, a variable transmission rate function, and a multi-connection function.
Particularly in a video monitoring apparatus, a receiver is required with a function for receiving dynamic videos of a plurality of cameras and to display them on one screen switched over one after another.
2. Description of the Related Art
FIG. 10
shows an arrangement (
1
) of a prior art video transmission system, in which video data generators
1
a
-
1
n
are connected to transmitters (CODEC)
2
a
-
2
n
respectively, which are connected to receivers (CODEC)
4
a
-
4
n
through an ATM switch
31
which forms an ATM network
3
with virtual channels VCIa-VCIn as fixed virtual connections, PVC's (Permanent Virtual Connections (Circuits)). The receivers
4
a
-
4
n
n are commonly connected to a selector
8
, which is connected to a display unit
9
.
In operation, the transmitters
2
a
-
2
n
encode and cellulate video data received from the video data generators
1
a
-
1
n
respectively and send the cellulated video information to the receivers
4
a
-
4
n
respectively through the virtual channels VCIa-VCIn. The receivers
4
a
-
4
n
decellulate and decode the received video information and send the decoded video data to the selector
8
. The selector
8
selects one of the video data to be sent to the display unit
9
, which displays the video data.
This video transmission system is defective in that the introduction cost rises high because the same number of receivers as the transmitters are required.
FIG. 11
shows an arrangement (
2
) of the prior art video transmission system, in which the same number of receivers as the transmitters are not required, and compared with the arrangement (
1
) shown in
FIG. 10
where the receivers
4
a
-
4
n
are provided, only one receiver
4
is provided and the selector
8
is not provided to reduce cost. Also, between one of the transmitters
2
a
-
2
n
and the receiver
4
, virtual channels VCIa-VCIn as switched virtual connections (SVC) corresponding to the transmitters
2
a
-
2
n
are set up.
In operation, different from the arrangement (
1
), when the video information of the transmitter
2
a
is displayed on the display unit
9
, the virtual channel VCIa is set up between the transmitter
2
a
and the receiver
4
, and through the virtual channel VCIa the transmitter
2
a
sends the video information to the receiver
4
. When the video information of the transmitter
2
b
is displayed, the virtual channel VCIb is newly set up between the transmitter
2
b
and the receiver
4
, and through the virtual channel VCIb the transmitter
2
b
sends the video information to the receiver
4
.
FIG. 12A
specifically shows a system clock of the transmitters and the receiver in the arrangement (
2
) shown in FIG.
11
.
The transmitters (CODEC)
2
a
-
2
n
holds the system clock
21
respectively, and the receiver (CODEC)
4
holds a PLL circuit
51
which includes the system clock.
In operation, for example, when the transmitter
2
a
and the receiver
4
are mutually connected with the virtual channel VCIa, system clock standard information PCR (Program Clock Reference) which is included in the video data out of the transmitter
2
a
is sent to the receiver
4
through the virtual channel VCIa. In the receiver
4
, the PLL circuit
51
leads in the frequency of the system clock (not shown) of its own with reference to the system clock standard information PCR so that the frequency may become the same as that of the system clock
21
of the transmitter
2
a.
FIG. 12B
shows an example of the video data received by the receiver
4
.
By the channel switchover operation of the ATM switch
31
the receiver
4
receives the system clock information and the video data synchronized therewith from the transmitters
2
a
-
2
e
in order.
Since the system clocks of the receiver
4
and transmitters
2
a
-
2
n
are asynchronous with each other, the PLL circuit
51
in the receiver
4
has to execute a lead-in operation of the clock at the time when the video data are switched over. Normally, since additional (average) processes are executed for the lead-in operation more than several tens of times for the measure of clock jitter, the lead-in time is elongated.
There are some defects in the video transmission system in the arrangement (
2
) as follows;
{circle around (1)} Since the video data are not sent to the receiver while the ATM switch
31
switches over the connection (the virtual channel), phenomena such as a temporary freeze or blackout in the worst case, of the display video arise;
{circle around (2)} Since more switchover time is required when the video data is sent through a plurality of ATM switches, the above phenomena arise remarkably and so are not suitable for the monitoring operation in a wide area;
{circle around (3)} The lead-in time is so long that it takes long until the system clock becomes stable.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a video transmission system comprising; transmitters in which video data from video data generators are encoded, cellulated and outputted, an ATM network which transmits the cellulated video data, a receiver in which the cellulated video data received through the ATM network are decellulated, decoded and outputted, and a display unit which displays the video data wherein at a switchover of the video data, a temporary freeze or blackout of a display screen is removed, the switchover is executed at a high-speed, and a lead-in operation time for a system clock is shortened.
[1] In order to achieve the above-mentioned object in a video transmission system according to the present invention, the ATM network provides fixed virtual connections between the transmitters and the receiver, and the receiver includes a connection control portion for designating a desired one of the virtual connections, and a header controller only extracts cells of the designated virtual connection.
FIG. 1
shows a schematic arrangement of a video transmission system according to the present invention, in which the video data generators
1
a
-
1
n
which generate the video data are connected respectively to the transmitters
2
a
-
2
n
, which are connected to the receiver
4
through an ATM switch
31
which forms the ATM network
3
. It is assumed that between the transmitters
2
a
-
2
n
and the receiver
4
fixed virtual connections PVCa, PVCb, . . . , PVCn are preliminarily set up. The receiver
4
includes the connection control portion and the header controller (both are not shown).
The connection control portion designates the virtual connection e.g. PVCa which includes the video data to be displayed from among the fixedly provided virtual connections PVCa, PVCb, . . . , PVCn. The header controller only extracts a cell VCIa of the virtual connection PVCa which is designated by the connection control portion and abandons other cells.
Namely, the video data of the video data generators
1
a
-
1
n
are multi-connected by the ATM switch
31
and are inputted commonly to the receiver
4
. In the receiver
4
, the header controller only selects the video data of the virtual connection designated by the connection control portion.
As a result, without the switchover operation of the ATM switch
31
it becomes possible for the receiver
4
to display exclusively the video of the video data generator as designated, to avoid a temporary freeze or blackout of the display screen due to the switchover operation of the ATM switch, and to execute the switchover at a high-speed.
[2]
Fujiyama Takehiko
Todogawa Norifumi
Yamamoto Masaharu
Yoshiyuki Wada
Faile Andrew
Fujitsu Limited
Huynh Son P.
Katten Muchin Zavis & Rosenman
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