Abstract:
A cross-connect protection method and system having two switch fabrics each coupled to at least one SONET add/drop multiplexer. The SONET add/drop multiplexer utilizes PDI-P codes to determine which signal between a working signal received from a working fabric and protect signal received from a protect fabric to forward on to the client.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a WideBand cross-connect system method that comprises at least one SONET add/drop multiplexer, functioning as Client IO Interface, and provides protection to traffic to be cross-connected. 
     BACKGROUND OF THE INVENTION 
     Telecommunications network operators typically require that at least some minimal level of redundancy be built into equipment they use in their networks in case of equipment failure. If redundancy were not provided, and an equipment failure occurred, traffic would be lost and customers could lose service for long periods of time while a technician was called in to troubleshoot for and replace the failed equipment with functioning equipment. 
     Typically, in a cross-connect system, there are redundant switching fabrics. One of these fabric functions as a working fabric and the other as a protect fabric such that if a failure occurs in one fabric the traffic in the other fabric can be used, minimizing traffic and service loss. Communications between the cross-connect interfaces and the working and protect fabrics usually involve proprietary equipment and proprietary signaling methods. Additionally, many ADMs do not have the capability to switch traffic at the VT (VC) level as they are mostly broadband switch machines. With this view, it is decided that operating redundant WideBand switch fabrics into an ADM, a signaling method must be invented to provide the STS1 level of switching available within an ADM on even a single VT level failure. 
     The proliferation of the use of proprietary interconnections and signaling methods prevents cross-connects from using standardized interfaces with standardized signaling schemes, which are less expensive. 
     Thus, there is a need for a cross-connect system and protection method that takes advantage of standardized interfaces and signaling schemes. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a WideBand cross-connect system and protection method that takes advantage of standardized interfaces and signaling schemes. The WideBand cross-connect system utilizes two switch fabrics communicating with at least one SONET add-drop multiplexer. 
     Payload Defect Indicator-Path (PDI-P) coding from the GR-253-CORE standard is utilized in many SONET add/drop multiplexers. PDI-P coding was developed and standardized in order to provide STS-1 path-level facility protection in unidirectional, path-switched rings (UPSR). However, it has not been used for equipment protection. The present invention takes advantage of PDI-P coding to provide equipment protection for the switch fabrics. 
     The present invention has advantages over the prior art. Current solutions require custom-designed hardware and software to implement protection methods for the switching fabrics. The present invention enables the use of standard SONET add-drop multiplexers to provide this functionality. 
     An embodiment of the present invention relates to a cross-connect system and protection method utilizing PDI-P coding to select from the working and protect copies of a signal. 
     Another embodiment of the present invention provides a cross-connect system comprising two switch fabrics and at least one SONET add-drop multiplexer. 
     As such, it is an object of the present invention to provide for a method of protecting switching fabric signals in a cross-connect utilizing PDI-P coding. 
     It is another object of the present invention to provide for a cross-connect system comprising two switch fabrics and at least one SONET add-drop multiplexer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a cross-connect system according to an embodiment of the present invention. 
         FIG. 2  is a flow chart of a method for protecting traffic according an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be better understood by reference to the accompanying drawings. 
     Referring now to  FIG. 1 , a block diagram of a WideBand cross-connect system  100  according to an embodiment of the present invention is shown. Two VT switch fabric subsystems  101  and  102  are provided as well as SONET add/drop multiplexer(s)  103  and  104 . SONET add/drop multiplexer(s)  103  and  104  may be a single add/drop multiplexer or a plurality of add/drop multiplexers. Moreover, it may be contained in the same enclosure(s) as the switch fabrics or in a separate enclosure(s). SONET add/drop multiplexers and switch fabric subsystems  101  and  102  are connected through 1+1 protected connections. SONET add/drop multiplexers  103  and  104  support SONET UPSR protection with switching criteria on PDI-P values. Consistent with the standard UPSR selection criteria (defined in GR-253-CORE and GR-1400-CORE) the SONET add/drop multiplexers  103  and  104  can select between the redundant connections using section, line and path layer defects down to the STS-1 level, as will be discussed in more detail with respect to  FIG. 2 . 
     Client interfaces  105   w ,  105   p ,  106   w ,  106   p ,  107   w  and  107   p  are shown accepting working and protect signals for a plurality of clients to SONET add/drop multiplexer  103 . Although these interfaces are shown separately, some or all of these could be implemented in the form of an aggregate interface if desired, rather than separate physical interfaces. Additionally, for client signals with no protect signal, working interfaces could be solely provided. 
     Each logical connection between switch fabric  101  and an interface with a SONET add/drop multiplexer  103  or  104  has a redundant connection between switch fabric  102  and a redundant SONET interface on the same SONET add/drop multiplexer. For instance, SONET add/drop multiplexer  103  has working switch interfaces  115   w ,  116   w  and  117   w  connected to working switch fabric  101  and protect switch interfaces  115   p ,  116   p  and  117   p  connected to protect switch fabric  102 . Using a standard STS1 UPSR implementation, the traffic payload from the ADM will be broadcast to each of the working switch interfaces  115   w ,  116   w  and  117   w  and its respective protect switch interface  115   p ,  116   p  and  117   p.    
     Likewise, working switch interfaces  125   w ,  126   w  and  127   w  between working switch fabric  101  and SONET add/drop multiplexer  104  have counterpart protect switch interfaces  125   p ,  126   p  and  127   p  between protect switch fabric  102  and SONET add/drop multiplexer  104 . Ideally, each working switch interface  125   w ,  126   w  and  127   w  and each respective protect switch interface  125   p ,  126   p  and  127   p  would carry the same payload signals. However, problems could occur to a signal on one of the working or protect interfaces, on the lines connecting them with the switch fabrics, or within one of the switch fabrics that would alter the signal rendering it less desirable to pass to a client. 
     Referring now to  FIG. 2 , a method of providing equipment protection  200  according to an embodiment of the present invention is now discussed, with reference back to  FIG. 1 . 
     In step  225 , ADM  103  performs ADM functionality on the client interfaces  105 ,  106 ,  107  as provisioned to meet the network configuration (i.e. 2FBLSR, 4FBLSR, STS1 UPSR, Linear APS). 
     In step  230 , ADM  103  will configure working and protect interfaces  115 ,  116 , and  117 , as STS1 UPSR. This configuration, by requirement, will broadcast all traffic payloads to both switch fabrics  101  and  102 . 
     In step  235 , each switch fabric  101  and  102 , will provide VT level switching (also commonly referred to as connections) of the payloads independently but equally as per provisioning requirements. In addition, each switch fabric will independently monitor for equipment failures that would affect the traffic payload. In the event a failure is detected on one or more entities, the switch fabric will provide PDI-P codes to signal the presence and quantity of affected VT path failures associated with the logical connections embedded within each STS1 within each physical interface to the SONET add/drop multiplexer. 
     Step  240  indicates the receiving of traffic at ADM  104  on each pair of interfaces as  125   w  and  125   p ,  126   w  and  126   p ,  127   w  and  127   p . Each of these is configured as UPSR pairs. 
     In step  245  each working and protect pair,  125 ,  126 , and  127 , at ADM  104 , receive traffic from switch fabrics  101  and  102 . ADM  104  provides comparison and conclusion of each STS1 level PDI-P value. 
     In step  245 , analysis is performed on the value of the PDI-P codes received from each switch fabric  101  and  102 . In order to provide the best possible signal to the client, via connections  135   w  and  135   p , for example, SONET add/drop multiplexer  104  selects between signals entering interfaces  125   w  and  125   p  from switch fabrics  101  and  102 , respectively, by comparing the PDI-P codes carried in the overhead of each signal and choosing the best signal based upon the defect level to be the signal output through interfaces  135   w  and  135   p , for example, to the client in steps  245 ,  250  and  255 . For example, if the comparison shows that the defect level is better for the working signal received at switch interface  125   w , it is selected to be sent to the client from interfaces  135   w  and  135   p  in step  250 . If the defect level is better for the signal from the protect interface  125   p , it is selected to be sent to the client from interfaces  135   w  and  135   p  in step  255 . 
     The present invention allows standard SONET add/drop multiplexers to provide both standardized customer interfaces to a cross-connect system and switch fabric protection. A network operator could even utilize pre-existing SONET add/drop multiplexers in a network designed by different manufacturers to create the WideBand cross-connect system. The only requirement would be that the SONET add/drop multiplexers support SONET UPSR protection with PDI-P codes. 
     Although the preferred embodiments of the present invention have been described and illustrated in detail, it will be evident to those skilled in the art that various modifications and changes may be made thereto without departing from the spirit and scope of the invention as set forth in the appended claims and equivalents thereof.