Multiplex communications – Fault recovery – Bypass an inoperative station
Reexamination Certificate
1998-06-30
2003-09-02
Nguyen, Chau (Department: 2663)
Multiplex communications
Fault recovery
Bypass an inoperative station
C370S228000, C370S539000
Reexamination Certificate
active
06614753
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system with a 1+1 switching function, applied to a synchronous communication network.
2. Description of the Related Art
A 1+1 switching function (1+1 MSP) based on ITU standards performs switching by transmitting and receiving K1 and K2 bytes provided in the overhead of the data frame in an SDH (Synchronous Digital Hierarchy) or SONET (Synchronous Optical NETwork) network as bytes for monitoring and controlling between an opposite apparatus and an own apparatus. In this case, the settings of the own apparatus are known, but the settings of the opposite apparatus are unknown, since in the K1 and K2 bytes there are no Revertive/Non-Revertive mode settings (in order to simplify, hereinafter revertive and non-revertive are called “rev” and “non-rev”, respectively) and uni-directional/bi-directional mode settings (in order to simplify, hereinafter uni-directional and bi-directional are called “uni” and “bi”, respectively) in the conventional North American SONET specifications. As a result, some failure occurs when the apparatuses are connected. (For details of K1 and K2 bytes, see ITU Recommendations G783.)
FIG. 1
explains the concept of a 1+1 MSP.
In a communication network where station A and station B being terminal stations are opposed, stations A and B comprise multiplexers
600
and
602
for multiplexing and demultiplexing received signals and transferring to signal processing units located at a latter stage (not shown in the diagram), and optical transmitter-receiver units
604
and
605
connected to optical transmission lines, for transmitting and receiving light beams. A running (work) line and a stand-by (protection) line each consist of a pair of an upward line and a downward line between the optical transmitter-receiver units
604
and
605
of stations A and B. Switches
601
and
602
are provided on the receiving side of the optical transmitter-receiver units
605
and
605
, respectively, in stations A and B, and the switches
601
and
602
are to switch (bridge) the work and protection lines when a failure occurs. A switch for automatically preforming this bridging using the above-mentioned K1 and K2 bytes is called an “APS (Automatic Protection Switch)”.
The configuration in
FIG. 1
shows a 1+1 bridging function, and one protection line is provided for one work line. In a 1+1 MPS the transmitting side always continues to transmit the same signal in both the work line and the protection line, and the receiving side can receive the same signal by bridging the lines when a failure occurs. On the other hand, a bridging method in which the transmitting side does not always transmit the same signal to both lines, and starts transmitting a signal when the receiving side bridges the lines, is called a 1:1 MSP. Although in a 1:1 MSP one protection line is provided for one work line, a bridging method in which one protection line is provided for a plurality (N pieces) of work lines is called a 1:N MSP.
The above-mentioned rev mode and non-rev mode differ in whether or not a bridged protection line is bridged back the original work line when the failure is repaired. That is, in the case of a rev mode, the bridged protection line and the original work line are bridged back when the failure is repaired, and in the case of a non-rev mode the bridged protection line and the original work line are not bridged back. In the case of a uni mode, for example, when a failure is detected in station B, only on the receiving side of station B are the work line and a protection line bridged, and station A does nothing. On the other hand, in the case of a bi mode, when a failure is detected in station B and the work line and a protection line are bridged, this information is also transmitted to station A, and in station A too, the work line and a protection line are bridged.
FIGS. 2 through 9
explain the problems caused by K1 and K2 bytes without the settings of a rev or non-rev mode, and a uni or bi mode.
FIGS. 2 through 5
show the case where a terminal station with a rev mode and a terminal station with a non-rev mode are opposed, and
FIGS. 6 through 9
show the case where a terminal station with a uni mode and a terminal station with a bi mode are opposed. In these diagrams a 1+1 MSP is presumed, and the diagrams are indicated in a 1:N compatible mode. Although an optimized 1+1 MSP based on the above-mentioned ITU Recommendations differs from a 1:N MSP in the way of using the K1 and K2 bytes set in the overhead of a data frame in an SDH or SONET network, the 1:N compatible mode of a 1+1 MSP means that in a 1+1 MSP K1 and K2 bytes are used in the same way as in a 1:N MSP.
FIG. 2
explains the case where the own station is in a uni and rev mode, and the opposite station is in a uni and non-rev mode.
When there is no failure, a signal in which an NR (No Request) and “0s” are respectively assigned to K1 and K2 bytes, is transmitted from each terminal station. That is, there is no request for an APS. In the same way, an NR is transmitted from the opposite station too. In this way, when there is no failure, the NR continues to be exchanged between the own station and the opposite station. When a failure is detected in the work line of the own station, an SF (Signal Failure) is set in the K1 byte and is transmitted to the opposite station. This indicates that a failure has occurred in a work line for transmitting signals from the opposite station to the own station. Therefore, when receiving an SF from the own station, the opposite station sets in the K2 byte a line number for commanding which protection line to use in order to bridge the work line, and transmits the line number to the own station. When receiving this line number, the own station bridges the work line and a protection line of the line number designated in the K2 byte which is transmitted from the opposite station, sets information that the work line is in a status of failure in the K1 byte as an SF, and transmits the information to the opposite station. At this time, although the work line for transmitting signals from the opposite station is out of order, the protection line also transmits the same information, and both the own and opposite stations always use the protection line to receive the K1 and K2 bytes. Accordingly, even if there is any failure in the work line, the K1 and K2 bytes are normally received. It is because bridging is meaningless if there is also a failure in the protection line when there is a failure in a work line, and the protection line is presumed to be normal when the bridging is performed so that a protection line is used to transmit and receive K1 and K2 bytes in this way. While the protection line is used, from the own station an SF continues to be transmitted, and the line signal of the protection line continues to be transmitted from the opposite station. When it is detected on the own station side that the failure of the work line is repaired, the protection line is bridged back over to the work line, and an NR is transmitted to the opposite station. When the opposite station has received the NR, the opposite station judges that the work line is restored, and also transmits an NR to the own station. In this way, when bridging and bridging-back due to a failure are performed on the own station side with a uni and rev mode, there is no problem.
FIG. 3
explains the case where the own station is in a uni and non-rev mode, and the opposite station is in a uni and rev mode.
In this drawing too, when there is no failure in both the own and opposite stations, a K1 byte is transmitted as an NR consisting of “0s”. When there is a failure in the own station, an SF is set in the K1 byte in the own station, and the K1 byte is transmitted to the opposite station in the same way as described in FIG.
2
. When receiving the K1 byte, the opposite station sets a line number for a protection line in the K2 byte, and transmits the K2 byte to the own station. The own
Hyun Soon-Dong
Katten Muchin Zavis & Rosenman
Nguyen Chau
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