Electrical computers and digital processing systems: support – Clock control of data processing system – component – or data...
Reexamination Certificate
2000-11-01
2004-01-06
Butler, Dennis M. (Department: 2185)
Electrical computers and digital processing systems: support
Clock control of data processing system, component, or data...
C713S400000, C713S503000
Reexamination Certificate
active
06675314
ABSTRACT:
TECHNICAL FIELD
This invention relates to a data receiving apparatus that regenerates at a receiver side a source clock frequency of a transmitter side particularly when the network clock and the source clock supplied to the transmitter side are mutually asynchronous or when the network clocks supplied to the transmitter side and the receiver side are mutually asynchronous in the communications via an ATM (Asynchronous Transfer Mode) network, a method of regenerating a source clock to be used for this, and, a computer-readable recording medium recorded with a program for making the computer execute the method according to this invention.
BACKGROUND ART
The ATM system collecting attention as the communication system for the multi-media era. This ATM system is characterized in that circuits between terminals are set as logical virtual circuits regardless of each medium while an STM (Synchronous Transfer Mode) system occupies a physical circuit of an STM network at each medium between terminals. Thus, the ATM system can realize an efficient multi-media communication system.
A communication system that employs the STM system will be now explained.
FIG. 15
is a diagram that shows a configuration of the communication system realizing a telephone service in the STM network. A transmitter-side device group
45
transmits sound data (data string) to an STM network
47
at a constant speed. A receiver-side device group
46
receives the sound data transmitted from the STM network
47
at a constant speed. The STM network
47
communicates in a synchronous transfer mode, and outputs a network clock
42
.
Telephones
40
a
and
40
b
are telephones corresponding to ISDN (Integrated Services Digital Network), and these telephones
40
a
and
40
b
are connected to PBX (Private Branch Exchanges)
41
a
and
41
b
respectively. The PBX
41
a
operates with a source clock
43
, and the PBX
41
b
operates with a local clock
44
. Sound information that has been input to the telephone
40
a
of the transmitter-side device group
45
is transmitted as sound data to the STM network
47
at a constant speed via the PBX
41
a
, and is then received by the telephone
10
b
via the PBX
41
b
within the receiver-side device group
46
.
In the communication system of the STM system shown in
FIG. 15
, basically all the devices connected to the STM network
47
operate in synchronism with a sole clock frequency. In FIG.
15
, a network clock
42
within the STM network
47
becomes a master clock, and the source clock
43
within the PBX
11
a
and the local clock
44
within the PBX
11
b
follow this master clock in synchronism.
Further, the sound data (data string) output from the PBX
41
a
is transmitted to the STM network
47
at a constant speed, for example, at 1.544 Mb/s, by using the source clock
43
within the PBX
41
a
as a reference. A data type transmitted at this constant speed is called CBR (Constant Bit Rate), and the sound data or the like corresponds to this CBR data, which is the data required to have real time nature.
The PBX
41
b
within the receiver-side device group
46
receives the sound data transmitted at a constant speed from the STM network
47
, using the local clock
44
as a reference. As described above, as the source clock
43
and the local clock
44
are both slave synchronous with the network clock
42
, the clock frequencies of the source clock
43
and the local clock
44
are the same as a result. Therefore, the PBX
41
b
can normally receive the CBR data transmitted from the PBX
41
a
within the transmitter-side device group
45
without over-flowing or under-flowing an inside receiving buffer not shown.
A communication system that employs the ATM system will be explained.
FIG. 16
is the same as
FIG. 15
but shows the configuration of a communication system realizing a telephone service in the ATM network. First, in order to realize the STM network
47
in the ATM system, that is, in order to realize by the ATM system the telephone services that are realized in a circuit switching network and a personal circuit, a service for making the ATM network appear as if it is the STM network to the transmitting and receiving devices (terminals) is necessary. That is, what is called a circuit emulation service is necessary.
In this ATM communication system, an ATM network
50
exists as a network in place of the STM network
47
. A transmission CLAD (Cell Assembly and Disassembly)
51
is provided between this ATM network
50
and the transmitter-side device group
45
, and a reception CLAD
52
is provided between the ATM
50
and the PBX
41
b
within the receiver-side device group
46
. Other components are the same as those in FIG.
15
. Those components that are the same as the components shown in
FIG. 15
have been provided with identical legends. The above-described circuit emulation service is carried out by using the transmission CLAD
51
and the reception CLAD
52
.
The ATM network
50
shown in
FIG. 16
carries out communications in the asynchronous transfer mode, and transmits in an ATM cell unit that is divided into 53-byte fixed-length packets. The transmitter-side device group
45
transmits sound data to the ATM network
50
in a cell format (ATM cell) at a constant speed. The receiver-side device group
46
receives the ATM cell transmitted from the ATM network
50
at a constant speed. The ATM network
50
has network clocks
42
a
and
42
b
. The telephones
40
a
and
40
b
are ISDN telephones. The PBX's
41
a
and
41
b
operate with the source clock
43
and the local clock
44
respectively. The transmission CLAD
51
converts a series of data string into an ATM cell, and the reception CLAD
52
converts the received ATM cell into a series of data string.
The sound information that has been input through the telephone
40
a
within the transmitter-side device group
45
is input as sound data (data string) to the transmission CLAD
51
via the PBX
41
a
, and is changed into an ATM cell in this transmission CLAD
51
. Thereafter, this ATM cell is transmitted to the ATM network
50
at a constant speed. After that, the ATM cell is received by the reception CLAD
52
within the receiver-side device group
46
, and this ATM cell is returned to the original data string in this reception CLAD
52
, and then the data string is received by the telephone
40
b
via the PBX
41
b.
In this ATM communication system, devices within the ATM network
50
, for example, all the devices including the ATM switching unit do not necessarily operate in synchronism with a sole frequency clock, unlike in the STM communication system. In other words, a sole frequency clock that can be commonly used is not necessarily supplied to all the devices connected to the ATM network
50
. In this sense, two network clocks
42
a
and
42
b
exist within the ATM network
50
shown in
FIG. 16
, and the frequencies of these two network clocks
42
a
and
42
b
are not necessarily synchronous with each other.
In the mean time, in order to carry out a normal communication between the two PBX's
41
a
and
41
b
, it is necessary to transmit and receive data at a constant speed based on the same frequency clock as a reference. For this purpose, it is necessary to post the frequency of the source clock
43
within the PBX
41
a
to the PBX
41
b
and to match the frequency of the local clock
44
within the PBX
41
b
with the source clock
43
by some means.
At ITU advice I.363.1 B-ISDN ATM Adaptation Layer specification: Type 1 AAL, ITU-T (Telecommunication Standardization Sector of International Telecommunication Union) defines a function that matches the frequency of the local clock with the source clock as a source clock frequency regeneration function. In other words, this is a function of regenerating at a receiver user side the source clock frequency of a transmitter user side between the transmitter user and the receiver user who are connected to each other via the ATM network.
Further, as one of the source clock frequency generation methods, the adaptive
Nakashima Koichi
Tanaka Kentaro
Yamada Hirotoshi
Birch Stewart Kolasch & Birch, LLP.
Butler Dennis M.
Mitsubishi Denki & Kabushiki Kaisha
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