Pulse or digital communications – Spread spectrum – Direct sequence
Patent
1990-12-20
1992-02-04
Safourek, Benedict V.
Pulse or digital communications
Spread spectrum
Direct sequence
3701054, H04L 704
Patent
active
050864386
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to signal generating and receiving apparatuses for performing quality evaluation including, e.g., measurement of an error rate in a transmission line, a multiplexer, a demultiplexer, or the like used in an SONET (Synchronous Optical Network) or an SDH (Synchronous Digital Hierarchy) as a new synchronous transfer mode as a digital communication scheme and, more particularly, to signal generating and receiving apparatuses of a synchronous transfer mode each having a timing signal generator for generating timing signals to arrange a signal string having a predetermined frame structure determined by the new synchronous transfer mode so as to obtain an array of predetermined signals at designated signal positions.
DESCRIPTION OF THE RELATED ART
A synchronous transfer mode has been used in a general digital communication line to effectively utilize a transmission line.
An example of a conventional synchronous transfer mode will be described with reference to FIG. 1. At a transmitting side, a first multiplexer (MUX) 1 multiplexes (time-divisionally multiplexes) twenty-four 64-kbits/second (64 kb/s) signals into a 1.544-Mb/s signal. A second MUX 2 multiplexes four 1.544-Mb/s signals into a 6.312-Mb/s signal. A third MUX 3 multiplexes seven 6.312-Mb/s signals into a 44.736-Mb/s signal. A fourth MUX 4 multiplexes three 44.736-Mb/s signals into a 139.264-Mb/s signal. At a receiving side, the 139.264-Mb/s signal, the 44.736-Mb/s signal, the 6.312-Mb/s signal, and the 1.544-Mb/s signal are respectively demultiplexed by first to fourth demultiplexers (DMUXs) 5 to 8 in a sequence opposite to that at the transmitting side.
A relationship between multiplexing and frame synchronization at the transmitting side of FIG. 1 will be briefly described with reference to FIGS. 2 and 3.
As shown in FIG. 2, an A-channel (Achl to AchN, which correspond to the 64-kb/s signal in FIG. 1) is time-divided by the first MUX 1, thereby multiplexing the time-divisional signals in a sequence A in FIG. 3.
This multiplexed signal is defined as one (Bchl) of B-channel (Bchl to BchM which correspond to the 1.544-Mb/s signal in FIG. 1) signals. The second MUX 2 performs time-divisional multiplexing between this B-channel signal and a signal (Bch2 to BchM) similarly input from another multiplexer (not shown) and outputs a multiplexed signal in a sequence B in FIG. 3. This multiplexed signal is defined as one of (Cchl) C-channel (Cchl to CchL which correspond to the 6.312-Mb/s signal in FIG. 1) signals. The MUX 3 performs time-divisional multiplexing between this Ch-channel signal and a signal (Cch2 to CchL) similarly input from another multiplexer (not shown) and outputs a multiplexed signal in a sequence C in FIG. 3.
Reference symbols Fa, Fb, and Fc in the sequences A, B, and C in FIG. 3 are frame signals for identifying the channel signals, respectively.
In order to extract a low-order group signal from a multiplexed high-order group signal, for example, in order to extract the C-channel signal Cchl from an output C from the third MUX 3, the output C from the third MUX 3 is frame-synchronized. However, in order to extract the B-channel signal Bchl from the output C, an output B from the second MUX 2 must be frame-synchronized after the output C is frame-synchronized. When a lower-order signal is to be extracted, these frame synchronization operations must be sequentially performed.
Since one frame can contain only signals having the same magnitude (speed), the number of frame synchronization operations is increased in correspondence with the number of orders upon an increase in order in a conventional synchronous transfer mode. Therefore, a system including various types of equipment connected to a digital communication line is complicated as a whole, resulting in inconvenience.
It is impossible to directly extract the frame signal Fa of an output A from the output C due to the following reason.
When the number of bits assigned to each input channel signal of an output signal from a given MUX
REFERENCES:
patent: 3883729 (1975-05-01), de Cremiers
patent: 4943985 (1990-07-01), Gherardi
Technical Advisory, TA-TSY-000253 (Sonet) Bellcore Issue 4, Feb. 1989.
CCITT-Recommendation, G. 707, G. 708, G. 709 (SDH) (Undated).
Fujiwara Hidefumi
Ohtake Masatoshi
Sugata Fujio
Anritsu Corporation
Safourek Benedict V.
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