Method and apparatus for providing network protection at input/output interfaces of a cross-connect switch

A telecommunications system (10) includes a first cross-connect switch (12) and a second cross-connect switch (14). The first cross-connect switch (12) includes a switching matrix that provides information from a matrix connection to a selector (28) of an output interface (18). The selector (28) places the information from the switching matrix onto one or both of a working channel (24) and a protection channel (26). The second cross-connect switch (14) receives the working channel (24) and the protection channel (26) at an input interface (20). The input interface (20) includes a selector (30) that checks a signal quality of the working channel (24) and the protection channel (26). When necessary, the selector (30) sends a request to the selector (28) to bridge the working channel (24) onto the protection channel (26). According to the signal quality, the selector (30) selects one of the working channel (24) and the protection channel (26) for transfer to a switching matrix (22) of the second cross-connect switch (14). The selector (30) avoids creating and deleting matrix connections in the switching matrix (22) in performing protection switches between the working channel (24) and the protection channel (26).

TECHNICAL FIELD OF THE INVENTION

The present invention is related in general to telecommunications signal transport and more particularly to a method and apparatus for providing network protection at input/output interfaces of a cross-connect switch.

BACKGROUND OF THE INVENTION

When network protection is implemented in a cross-connect switch, there are stringent requirements concerning the amount of time needed to perform the protection switch once a problem has been detected. Typically, the protection switch is performed by cutting another connection through the matrix of the cross-connect switch. However, cutting another connection through the matrix has various disadvantages. Cross-connection algorithms generally take more time to complete than is allowed by the protection switching requirements. For example, the protection switching requirements specify tens of milliseconds rather than the hundreds of milliseconds it takes to cut a new connection. Creating and deleting cross-connections may not meet the desired switching times. If center stage rearrangements are required in a standard three stage non-blocking matrix, then the time needed to adjust matrix connections for a protection switch may take even longer. Therefore, it is desirable to avoid the slower than required changes in matrix connections to perform a protection switch in a cross-connect switch.

SUMMARY OF THE INVENTION

From the foregoing, it may be appreciated by those skilled in the art that a need has arisen for a technique to perform protection switching that does not require changing connections in the matrix of a cross-connect switch. In accordance with the present invention, a method and apparatus for providing network protection at input/output interfaces of a cross-connect switch are provided that substantially eliminate or reduce disadvantages and problems associated with conventional protection switching techniques.

According to an embodiment of the present invention, there is provided a method for providing network protection at input/output interfaces of a cross-connect switch that includes receiving an inbound working channel and an inbound protection channel at an input interface. A signal quality of the inbound working and protection channels is determined. One of the inbound working and protection channels is selected in response to the signal quality of the inbound working and protection channels. The selected one of the inbound working and protection channels is provided to a switching matrix. Thus, protection switching is performed at the interfaces to the cross-connect switch and not in the switching matrix. Pre-determined connections in the switching matrix may be maintained regardless of which one of the inbound working and protection channels are selected to be provided to the switching matrix.

The present invention provides various technical advantages over conventional protection switch techniques. For example, one technical advantage is to avoid adjusting connections in a matrix of a cross-connect switch to effect a protection switch. Another technical advantage is to provide a capability to effect protection switches in a cross-connect switch at its input/output interfaces rather than its matrix. Yet another technical advantage is to provide a simpler protection switch technique for any protection scheme implementation. Other technical advantages may be readily apparent to those skilled in the art from the following figures, description, and claims.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a portion of two cross-connect switches in a telecommunications system10.FIG. 1illustrates an example of a 1+1 linear automatic protection switching protection scheme. Telecommunications system10includes a first cross-connect switch12at a node A and a second cross-connect switch14at a node B. First cross-connect switch12includes a switching matrix16, an output interface18, and an input interface (not shown). Second cross-connect switch14includes an input interface20, a switching matrix22, and an output interface (not shown). The input interface for first cross-connect switch12may be similar to input interface20of second cross-connect switch14. Also, the output interface of second cross-connect switch14may be similar to output interface18of first cross-connect matrix12. Information is carried between nodes A and B over one or both of a working channel24and a protection channel26.

In operation, information is transferred over a matrix connection in switching matrix16to output interface18. Switching matrix16may implement any type of switching scheme including a three stage non-blocking switching technique. Output interface18receives the information from switching matrix16at a bridge selector28. Bridge selector28places the information onto both working channel24and protection channel26. Second cross-connect switch14receives working channel24and protection channel26at input interface20. Input interface20includes a selector30that determines a signal quality of both working channel24and protection channel26. Based on the signal qualities, selector30selects one of working channel24and protection channel26. The selected one of working channel24and protection channel26is provided to switching matrix22. Switching matrix22can maintain its pre-determined matrix connections regardless of which one of working channel24and protection channel26is selected. Thus, time consuming creation and deletion of matrix connections to accommodate a protection switch is avoided.

FIG. 2shows an example of a linear 1:n automatic protection switching protection scheme. In this example, n is 2 but may include any integer number. Switching matrix16of node A provides two information lines32to output interface18. Selector28receives the two information lines and broadcasts the information over protection channel26and a plurality of working channels24aand24bin order to transfer the information. Selector28may also broadcast the information over protection channel26upon detecting a failure in any of working channels24. At input interface20of node B, selector30receives protection channel26and the plurality of working channels24aand24b. Selector30determines a signal quality of each of the plurality of working channels24aand24b. If a working channel fails, selector30signals28to place the failed channel on protection channel26. Selector30selects the data of the failed channel from protection channel26and the plurality of the unfailed working channels, either24aor24b, onto information lines34for transport to switching matrix22.

FIGS. 3A and 3Bshow an example of a bidirectional line switched ring protection scheme.FIG. 3Ashows a normal operation of the bidirectional line switched ring protection scheme where selector28provides information received from switching matrix16to working channel24and selector30switches the information on working channel24for transfer to switching matrix22. Selector30checks the signal quality of working channel24and protection channel26.FIG. 3Bshows operation during a span switch. For a span switch, selector28places information from switching matrix16onto protection channel26in response to a request from selector30. Selector30provides information from protection channel26to switching matrix22. A span switch may occur whenever working channel24has poor or no signal quality.

FIGS. 4A and 4Bshow a ring switch in a bidirectional line switched ring protection scheme.FIG. 4Ashows a normal operation where selector28provides information to working channel24and protection channel26inbound to input interface20at node B. Input interface20also provides an outbound working channel25and an outbound protection channel27.FIG. 4Bshows the events involved in a ring switch. Upon detection of a failure in the channels between node B and another node, selector30routes information on inbound working channel24to outbound protection channel27. Selector30also routes information on inbound protection channel26to outbound working channel25. The routing performed by selector30effects the ring switch without disrupting matrix connections within either switching matrix22or switching matrix16.

FIG. 5shows a fast facility protection (FFP) scheme. The FFP scheme may occur within cross-connect switch14. Cross-connect switch14receives working channel24and protection channel26at input interface20. Selector30aprovides working channel24to switching matrix22and selector30bprovides protection channel26to switching matrix22. Switching matrix22provides working channel24and protection channel26to an output interface35. Output interface35includes a selector37that receives working channel24and protection channel26from switching matrix22. Selector37checks a signal quality of both working channel24and protection channel26and accordingly selects on of working channel24and protection channel26for output.

All of the protection schemes discussed above provide for the occurrence of protection switching in the input and output interfaces of a cross-connect switch to avoid disruption of matrix connections in the switching matrix of the cross-connect switch. Thus, protection switching time requirements may be efficiently met without expending various resources necessary to perform a conventional protection switching operation. Though certain protection schemes are described, other protection schemes may implement this protection switching technique, including unidirectional path switched ring protection schemes.

Thus, it is apparent that there has been provided, in accordance with the present invention, a method and apparatus for providing network protection at input/output interfaces of a cross-connect switch that satisfy the advantages set forth above. Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations may be readily ascertainable by those skilled in the art and may be made herein without departing from the spirit and scope of the present invention as defined by the following claims.