Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
2000-12-28
2004-10-26
Vincent, David (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S474000
Reexamination Certificate
active
06810046
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of communicating data in communication systems, in particular but not exclusively in optical communication systems. The invention also relates to a communication system operating according to the method.
In conventional optical communication systems comprising arrays of interconnected nodes, information is conveyed from a first node to a second node by modulating optical radiation generated in the first node and guiding the radiation, for example along optical fibre waveguides, to the second node whereat the radiation is detected and demodulated to yield the information thereat. The modulation can be either of digital or analogue form.
When digital modulation is employed, it is conventional practice to modulate a radiation source such as a laser between two states corresponding to two mutually different laser radiation output levels. Conversely, when analogue modulation is employed, for example to convey time division multiplexed analogue speech information, the laser is modulated in a continuous manner over a range of optical radiation intensities.
When assessing the quality of optical communication in the conventional systems employing analogue modulation, it is relatively straightforward to measure signal-to-noise ratio performance at the second node. However, if the analogue modulating signal is modulated with digital data, it is extremely difficult to determine a corresponding bit error rate performance at the second node; the bit error rate does not correlate in a simple manner with signal-to-noise ratio performance. Moreover, it is also problematical to include digital overhead control information when analogue modulation is employed.
In the conventional communication systems employing digital modulation, additional digital information can be added to sending client payload data for determining bit error rate and for control purposes. Such conventional systems are operable to receive sending client payload data at the first node and arrange it into fixed length blocks of data to which overhead control data is added to provide aggregate data for transmission. Examples of such conventional systems will now be described with reference to published patent applications and granted patents.
In a published European patent application no. EP 0 663 776, there is described a method of communicating block coded digital data with associated synchronization and control data. In the method, block coded digital data is communicated with associated overhead data in a data stream having a succession of coded blocks. Each block contains N symbols wherein M of the symbols comprise information to be transmitted and the remaining N-M of the symbols comprise error correcting data. The ratio M/N comprises a first information rate. The coded blocks in the data stream are divided into a succession of frames, each frame comprising F of the coded clocks. A frame overhead symbol is added for each of the frames to provide data necessary for a receiver function such as synchronization. The addition of the frame overhead symbols effectively lowers the first information rate to a second information rate M′/N′ as provided in Equation 1 (Eq. 1):
M
N
=
(
M
′
+
b
)
(
N
′
+
b
)
Eq
.
1
where
b=an integer chosen to provide the second information rate at a desired value.
N is less than 2
n
+1, where n is the number of bits in each of the symbols. The number of coded blocks F in each frame is determined from Equation 2 (Eq. 2):
F
=
M
′
P
(
N
-
M
)
b
Eq
.
2
where
P=a smallest value integer that will render F an integer, P being equal to the number of overhead symbols added per frame.
A plurality of X of the frames are formed into a multiframe containing FX coded blocks and PX frame overhead symbols. X is chosen to provide enough n-bit frame overhead symbols to implement the desired receiver function.
In another published European patent application no. EP 0 540 007, there is described a method and apparatus for transmitting an information-bearing signal by:
(a) generating a plurality of block signals on the basis of the information-bearing signal;
(b) generating a plurality of parity block signals on the basis of the plural data block signals;
(c) generating a frame signal containing the plural data block signals and the parity block signals; and
(d) sending out the frame signal.
In the method, each of the data block signals includes a first block synchronizing signal indicating the start of the data block signal, a data signal containing the information signal and a first parity signal derived by encoding the data signal. Each of the parity lock signals includes a second block synchronizing signal indicating the start of the parity block signal, a second parity signal and a third parity signal. Bit signals located at same bit positions in the respective second parity signals are derived by encoding bit signals located at the same positions in the respective data signals. Bit signals located at the same bit positions in the respective third parity signals are derived by encoding the bit signals located at the same bit positions in the respective first parity signals; alternatively, the third parity signal in each parity block signal is derived by encoding the second parity signal in each parity block signal.
In an international application no. PCT/FI99/00477, there are described data transmission methods in a telecommunication system. The methods are concerned with employing “payload numbering” instead of or in addition to conventional frame numbering. Data in the system is split into fixed-length data blocks or payload units. The size of a block is preferably equal to or smaller than the shortest information field in frames of the protocols used. Each protocol frame carries one or more payload units. In an optimum situation, the length of the information field in a protocol frame equals n times the length of the payload unit where n in an integer. Alternatively or additionally, the protocol frame carries payload numbers both for indicating the payload units conveyed in the protocol frame and for acknowledging the received blocks.
In a United States granted patent no. U.S. Pat. No. 5,490,142, there is described a VT group optical extension interface and VT group optical extension format method. In the method, a VT group extension format defines a transport frame for the transfer of 135 bytes, each byte comprising 8 bits, the format providing a line rate of 8 640 Mbit/s. Each frame comprises a transport overhead portion and a payload portion. The transport portion comprises 27 bytes and defines various operations, administration and maintenance functions. Moreover, the payload portion comprises 108 bytes which directly correspond to one VT group of an STS-N frame. The VT group optical extension format line rate is determined an as integer multiple m of an STS-N network element clock where m is 6 if N is 1 and m is 18 if N is 3. An optical extension interface is provided between a VTG bus and an optical extension, the interface being responsive to the provision of a multiplexed VT group payload provided on the VTG bus for providing a corresponding VT group optical extension transport frame on the optical extension, the interface being further responsive to the provision of a VT group optical extension transport frame on the optical extension for providing a multiplexed VT group payload and associated path overhead to the VTG bus.
It is conventional practice in contemporary optical communication systems where sending client data does not precisely partition into the blocks to partially fill the blocks with sending client data and then to add additional justification code after the sending client data to ensure that the blocks are completely filled. This practice is known as justification and assists to ensure, for example, satisfactory radiation spectra within the conventional systems.
The amount of justification employed is a function of the payload data that
Abbas Ghani A. M
Arnold Philip A
Goatly Bernard J
Livermore Peter J
Kirschstein et al.
Marconi UK Intellectual Property Ltd.
Vincent David
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