Multiplex communications – Fault recovery – Bypass an inoperative channel
Reexamination Certificate
1998-06-09
2001-06-12
Marcelo, Melvin (Department: 2733)
Multiplex communications
Fault recovery
Bypass an inoperative channel
C370S248000
Reexamination Certificate
active
06246668
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to a hitless manual path switching method and apparatus, and more particularly, to a method and apparatus for hitless manual path switching using linked pointer processors.
BACKGROUND ART
Hitless (error-free) switching is required mainly in the case of fiber-maintenance/construction. When telecommunication cables are relocated in an existing digital network, the information that was transported on these cables must be redirected on an alternative path to avoid interruption of services. In such cases, the network operator must redirect manually the traffic on the affected path over an alternative path, that most probably has a different length and a different number of network elements (NEs).
In case of protected networks, it is possible to use the protection fiber to accommodate the traffic affected by the relocation/maintenance operation.
However, in general, hitless manual switching operation requires reconfiguring the network for locating an alternative path to accommodate the disrupted traffic, which is not an easy task.
As there is a difference in the length of the permanent and alternative paths and in the number of NEs in each of these paths, the signals travelling along these two paths generally experience a differential delay, which must be aligned at the receiver site in order to obtain hitless switching.
There is a need to achieve cross-connection of the paths without disrupting the services, whereby eliminating the need for network operations associated with switching traffic from one path to another.
There is also a need to provide a communication network with hitless switching capabilities for traffic at small physical granularity, for flexibility and cost purposes.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a communication system with a method and apparatus for hitless switching between a cable-to-be-relocated and a cable for normal operation.
It is another object of the invention to provide a method and apparatus for implementing hitless switching at the path level in a synchronous communication system operating according to the SDH/SONET standard.
Therefore in accordance with a first aspect of the present invention there is provided a hitless path switching method for re-establishing synchronous traffic along a primary path from an alternate path, comprising the steps of at an originating path terminal, generating a trace message, inserting the trace message in an information signal and transmitting the information signal along the primary path as a first information signal and along the alternate path as a second information signal, at a receiving path terminal, recovering a first variant of the trace message from the first information signal and recovering a second variant of the trace message from the second information signal, each the first and second variants being a respective delayed variant of the trace message; aligning the first and the second information signals based on the phase difference between the first and the second variants generating a signal when alignment is completed, and at the originating path terminal, discontinuing transmission of the information signal along the alternate path upon generation of the signal.
In accordance with a second aspect of the present invention there is provided a hitless path switching apparatus for re-establishing synchronous traffic along a primary path from an alternate path, comprising, a first align block for receiving an information signal over a primary path and providing a first outgoing information signal of a controlled phase difference with the information signal, a link for providing to the first align block, time information from a second align block, and a first buffer for storing a first variant of a received trace message extracted from a known timeslot of L successive frames of the information signal.
Advantageously, the method and apparatus according to the present invention provide a delay adjustment function which equalizes the phases of the signal travelling along the cable-to-be-relocated and the cable for the normal operation, so that the path switching occurs with practically no errors.
The method and apparatus according to the present invention advantageously use linked point processors, which eliminate the need for a master-slave relationship. A master-slave relationship is generally more difficult to control.
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K. Nishihata, et al., “SDH 52/156 Mb/s (VC-3/4) Digital Cross-Connect Systems with Hit-Less Switching Function”, NTT Review, vol. 5, No. 5, Sep. 1993, pp. 64-71.
Y. Sato et al., “Economical and Reliable SDH Optical Transmission System”, NTT Review, vol. 7, No. 6, Nov. 1995, pp. 80-84.
Diaconescu Aprilia U.
Marcelo Melvin
Nortel Networks Limited
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