Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-10-02
2001-07-03
Ngo, Ricky (Department: 2731)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S514000
Reexamination Certificate
active
06256326
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a pseudo-synchronization prevention method in an SDH transmission mode, a pseudo-synchronization preventing SDH transmission system, and a transmitter-receiver in the pseudo-synchronization preventing SDH transmission system, all of which are suitable for use in a transmission unit to which the SDH transmission mode is applied.
(2) Description of the Related Art
According to an SDH (Synchronous Digital Hierarchy) transmission mode defined in ITU-T, at a time of data transmission from one terminal apparatus to another terminal apparatus, data link is enabled between the terminal apparatus by using a container [minimum unit of transmission information such as F2 byte (UserCH)] in a VC (Virtual Container) path, that is, a clear channel provided to a user.
In the SDH transmission mode, data to be transmitted is inserted in a predetermined frame called STM (Synchronous Transport Module) frame, and is transmitted and received with synchronization established by using the STM frame. The STM frame includes a payload showing the data to be transmitted itself, and an overhead for a control of the data. The data to be transmitted is asynchronously inserted in the payload.
For this purpose, when transmission/reception of signal is made by using the asynchronously inserted data, a predetermined frame pattern (hereinafter often referred to as synchronization pattern) is allocated to a data row thereof to form a periodical frame bit.
For example, a frame format for the F2 byte has a simple frame structure having a small number of bits, in which a bit rate of the data row is 8 k b/s×8. Hence, in order to allocate the predetermined synchronization pattern in the frame format for the F2 byte, it is required to use the minimum number of bits.
However, data having the same synchronization pattern as the predetermined synchronization pattern used for the allocation may exist in a signal with an interval identical with that of the predetermined synchronization pattern. In such a case, a receiving side for receiving the above data may erroneously recognize a position of a header of the frame, resulting in possibility of pseudo-synchronization.
Thus, in order to prevent the pseudo-synchronization, there is a possible method including the steps of mounting two frame synchronization counters in the terminal apparatus, defining one counter as a counter for true synchronization and bringing the one counter into synchronization with a predetermined frame, and defining the other counter as a counter for pseudo-synchronization and bringing the other counter into synchronization with a frame other than the predetermined frame.
That is, in the system including the two counters as described above, when a certain error signal [such as CRC (Cyclic Redundancy Check) code] is outputted from a signal which has been brought into synchronization, the output signal triggers a discrimination between the true synchronization and the pseudo-synchronization.
However, in the above method, it is necessary to provide a special bit as error monitoring information in addition to the synchronization pattern allocated in the frame format for the F2 byte, resulting in a problem of an increase in number of bits other than those of the information to be transmitted (main information). That is, since the F2 byte has the frame structure with the small number of bits, the increase in number of bits used for information other than the main information reduces an amount of main information, thereby causing a reduction in transmission efficiency.
SUMMARY OF THE INVENTION
In view of the foregoing problem, it is an object of the present invention to provide a pseudo-synchronization prevention method in an SDH transmission mode, a pseudo-synchronization preventing SDH transmission system, and a transmitter-receiver in a pseudo-synchronization preventing SDH transmission system in which pseudo-synchronization can easily be prevented by posting a message to the effect that a pseudo-synchronization state is established to an opposite terminal apparatus by using an overhead of an STM frame, and changing a synchronization pattern in byte information in the opposite terminal apparatus.
Further, according to the present invention, for achieving the above-mentioned object, there is provided a pseudo-synchronization prevention method in an SDH transmission mode. The method includes, when a data transmission is made in the SDH transmission mode between a first transmitter-receiver and a second transmitter-receiver opposed to each other by using predetermined byte information in a VC path in an STM frame, a pseudo-synchronization detecting step of detecting, by a receiver in one transmitter-receiver of the first transmitter-receiver and the second transmitter-receiver, that a pseudo-synchronization state is established by finding the same pattern as a synchronization pattern in the byte information, a pseudo-synchronization posting step of, when establishment of the pseudo-synchronization state is detected in the pseudo-synchronization detecting step, causing a transmitter in the one transmitter-receiver to insert information to the effect that the pseudo-synchronization state is established in an overhead of the STM frame, and posting the information to a receiver in the other transmitter-receiver of the first transmitter-receiver and the second transmitter-receiver, and a changed synchronization pattern transmitting step of, when the establishment of the pseudo-synchronization state is posted to the receiver in the other transmitter-receiver in the pseudo-synchronization posting step, changing a synchronization pattern into an additional synchronization pattern different from the synchronization pattern in the byte information, and transmitting the synchronization pattern obtained by the change from a transmitter in the other transmitter-receiver to the receiver in the one transmitter-receiver.
Further, according to the present invention, a pseudo-synchronization prevention method in an SDH transmission mode may include an alarm generating step of giving an alarm when a pseudo-synchronization state is still detected in the pseudo-synchronization detecting step though a synchronization pattern is changed and transmitted a predetermined number of times in the changed synchronization pattern transmitting step.
On the other hand, there is provided a pseudo-synchronization preventing SDH transmission system including a first transmitter-receiver and a second transmitter-receiver opposed to each other for a data transmission made by using predetermined byte information in a VC path in an STM frame. In the pseudo-synchronization preventing SDH transmission system, a byte information receiving apparatus in one transmitter-receiver of the first transmitter-receiver and the second transmitter-receiver is provided with a pseudo-synchronization detecting unit to detect that a pseudo-synchronization state is established by finding the same pattern as a synchronization pattern in the byte information, and an STM frame transmitting apparatus in the one transmitter-receiver is provided with a pseudo-synchronization posting unit to, when the pseudo-synchronization detecting unit detects that the pseudo-synchronization state is established, insert information to the effect that the pseudo-synchronization state is established in an overhead of the STM frame, and post the information to an STM frame receiving apparatus in the other transmitter-receiver of the first transmitter-receiver and the second transmitter-receiver.
In addition, the STM frame receiving apparatus in the other transmitter-receiver is provided with a pseudo-synchronization posting information receiving unit to receive the information to the effect that the pseudo-synchronization state is established, posted from the pseudo-synchronization posting unit, and a byte information transmitting apparatus in the other transmitter-receiver is provided with a synchronization pattern changing unit
Fujitsu Limited
Helfgott & Karas P.C.
Ngo Ricky
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