Abstract:
A digital cross-connect switching system that has a single-stage architecture, a scalable bandwidth, and reduced connection memory storage requirements. The scalable bandwidth digital cross-connect switching system includes a plurality of digital cross-connect building blocks. Each digital cross-connect building block includes at least one cross-connect having a plurality of input ports and a plurality of output ports, at least one connection memory communicatively coupled to the cross-connect, and at least one OR gate. Bandwidth is scaled in the digital cross-connect switching system by interconnecting predetermined numbers of the digital cross-connect building blocks. In general, the size of the digital cross-connect switching system increases as the square of the bandwidth requirement.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    N/A  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    N/A  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention relates generally to digital communications systems, and more specifically to an architecture of a scalable bandwidth single-stage digital cross-connect switching system.  
           [0004]    Digital communications systems are known that employ digital cross-connect switching systems for cross-connection of high speed optical or electrical signals in broadband communications networks. An architecture of a conventional digital cross-connect switching system includes a plurality of input ports, a plurality of output ports, a cross-connect such as a Time Division Multiplex (TDM) cross-connect, and at least one connection memory. The TDM cross-connect is typically configured to connect any input port with any one or more of the output ports based on connection information stored in the connection memory. For example, high speed optical or electrical signals received by the TDM cross-connect may comprise a plurality of data frames contained in a number of respective time slots. Further, the TDM cross-connect may temporarily store the data received at one of the input ports during a first time slot, and may subsequently retransmit that data during a second time slot, which is assigned to at least one of the output ports. The TDM cross-connect accesses the connection information pertaining to the respective time slot/output port assignments from the connection memory.  
           [0005]    Various techniques are known for increasing the bandwidth of conventional digital cross-connect switching systems. For example, the TDM cross-connect may be employed in a Synchronous Optical NETwork (SONET) multiplexed communications system. According to the SONET standard, high speed optical or electrical signals are generally formatted in Synchronous Transport Signal (STS) frames. A basic STS- 1  frame comprises nine rows of data bytes by ninety columns of data bytes, in which the first three columns contain Transport OverHead (TOH) bytes and the remaining eighty-seven columns contain Synchronous Payload Envelope (SPE) bytes. In order to increase the bandwidth of the TDM cross-connect in the SONET communication system, M (M&gt;1) STS- 1  tributaries may be multiplexed together to form a single STS-M frame by interleaving the STS- 1  tributaries one byte at a time (“byte interleaving”). Alternatively, the bandwidth of the TDM cross-connect may be increased by interleaving the STS- 1  tributaries one bit at a time (“bit interleaving”) or one column at a time (“column interleaving”).  
           [0006]    However, such conventional techniques for increasing the bandwidth of digital cross-connect switching systems have drawbacks. For example, the first row of a typical STS- 1  frame includes TOH bytes A 1  and A 2 , which form a framing pattern of bits indicative of the start of the frame. When performing byte, bit, or column interleaving on STS- 1  tributaries, these framing bits are frequently lost, thereby requiring the cross-connect switching system to generate new framing bits for the interleaved data. Further, the bit interleaving technique normally cannot increase the bandwidth of the TDM cross-connect by more than a factor of 8. Moreover, an increased amount of connection information is typically needed for properly routing the interleaved bits/bytes/columns of data to the desired output port(s), thereby requiring use of a significantly larger connection memory.  
           [0007]    It would therefore be desirable to have an architecture of a digital cross-connect switching system that has a scalable bandwidth. Such a cross-connect switching system would employ a connection memory that is smaller than that used in conventional high bandwidth cross-connect switching systems. It would also be desirable to have a scalable bandwidth digital cross-connect switching system that has a single-stage architecture.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    In accordance with the present invention, a digital cross-connect switching system is provided that has a single-stage architecture, a scalable bandwidth, and reduced connection memory storage requirements. Benefits of the presently disclosed digital cross-connect switching system are achieved by providing a Time Division Multiplexing (TDM) cross-connect building block, a plurality of which may be connected together to form the scalable bandwidth digital cross-connect switching system.  
           [0009]    In one embodiment, the scalable bandwidth digital cross-connect switching system includes a plurality of TDM cross-connect building blocks. Each TDM cross-connect building block includes at least one TDM cross-connect having a plurality of input ports and a plurality of output ports, at least one connection memory communicatively coupled to the TDM cross-connect, and at least one OR gate. The TDM cross-connect building block is configured to receive first input data at a first data rate, and switched input data at a second data rate. The TDM cross-connect building block is further configured to provide first output data at the first data rate, and second switched output data at the second data rate. In the preferred embodiment, the second data rate is equal to the first data rate. Further, the data contained in the first output data matches the data contained in the first input data. The TDM cross-connect is configured to receive the first input data at one or more of the input ports, and to provide first switched output data at one or more of the output ports based on connection information stored in the connection memory. The OR gate is configured to receive the switched input data and the first switched output data generated by the TDM cross-connect, and to generate the second switched output data.  
           [0010]    In another embodiment, the TDM cross-connect building block is configured to receive first input data at a first data rate, second input data at the first data rate, first switched input data at a second data rate, and second switched input data at the second data rate. The TDM cross-connect building block is further configured to provide first output data at the first data rate, second output data at the first data rate, third switched output data at the second data rate, and fourth switched output data at the second data rate. In the preferred embodiment, the second data rate is equal to the first data rate. Further, the data contained in the first output data matches the data contained in the first input data, and the data contained in the second output data matches the data contained in the second input data. The TDM cross-connect is configured to receive the first input data and the second input data at one or more of the input ports, and to provide first switched output data and second switched output data at one or more of the output ports based on connection information stored in the connection memory. A first OR gate is configured to receive the first switched input data and the first switched output data generated by the TDM cross-connect, and to generate the third switched output data. A second OR gate is configured to receive the second switched input data and the second switched output data generated by the TDM cross-connect, and to generate the fourth switched output data.  
           [0011]    In the presently disclosed embodiment, bandwidth is scaled in the TDM cross-connect switching system by interconnecting predetermined numbers of the TDM cross-connect building blocks. Four TDM cross-connect building blocks are operatively interconnected to double the bandwidth of the TDM cross-connect switching system. Nine TDM cross-connect building blocks are operatively interconnected to triple the bandwidth of the TDM cross-connect switching system. In general, the size of the TDM cross-connect switching system increases as the square of the bandwidth requirement.  
           [0012]    By providing a TDM cross-connect building block, and operatively interconnecting predetermined numbers of the TDM cross-connect building blocks, a TDM cross-connect switching system can be formed that has a single-stage architecture, a scalable bandwidth, and reduced connection memory storage requirements.  
           [0013]    Other features, functions, and aspects of the invention will be evident from the Detailed Description of the Invention that follows.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0014]    The invention will be more fully understood with reference to the following Detailed Description of the Invention in conjunction with the drawings of which:  
         [0015]    [0015]FIG. 1 is a block diagram of a conventional digital cross-connect switching system;  
         [0016]    [0016]FIG. 2 is a block diagram of a first embodiment of a TDM cross-connect building block for a digital cross-connect switching system according to the present invention;  
         [0017]    [0017]FIG. 3 is a block diagram depicting four of the TDM cross-connect building blocks of FIG. 2 operatively interconnected to double the bandwidth of the digital cross-connect switching system;  
         [0018]    [0018]FIG. 4 is a block diagram depicting nine of the TDM cross-connect building blocks of FIG. 2 operatively interconnected to triple the bandwidth of the digital cross-connect switching system;  
         [0019]    [0019]FIG. 5 is a block diagram of a second embodiment of a TDM cross-connect building block for a digital cross-connect switching system according to the present invention;  
         [0020]    [0020]FIG. 6 is a block diagram depicting four of the TDM cross-connect building blocks of FIG. 5 operatively interconnected to double the bandwidth of the digital cross-connect switching system;  
         [0021]    [0021]FIG. 7 is a block diagram depicting four of the conventional digital cross-connects of FIG. 1 operatively interconnected to double the bandwidth of a digital cross-connect switching system; and  
         [0022]    [0022]FIG. 8 is a flow diagram depicting a method of operating the TDM cross-connect building block of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    An architecture of a digital cross-connect switching system is disclosed that has a single-stage architecture, a scalable bandwidth, and reduced connection memory storage requirements. The presently disclosed digital cross-connect switching system achieves such benefits by providing a Time Division Multiplexing (TDM) cross-connect building block, a plurality of which can be operatively interconnected to suit the cross-connection requirements of the overall communications system.  
         [0024]    [0024]FIG. 1 depicts an illustrative embodiment of a conventional TDM cross-connect switching system  100 . In the illustrated embodiment, the cross-connect switching system  100  includes an input bus  108 , an output bus  110 , a cross-connect  104  such as a TDM cross-connect, and a connection memory  102 . The TDM cross-connect  104  is configured to receive optical and/or electrical input signals, e.g., data frames, from the input bus  108  at one or more of a plurality of input ports (not shown), and to provide the data to one or more of a plurality of output ports (not shown) based on connection information stored in the connection memory  102 . The TDM cross-connect  104  provides the data at the output ports to the output bus  110  as switched output data for subsequent transmission through the digital communications system.  
         [0025]    [0025]FIG. 2 depicts a first illustrative embodiment of a TDM cross-connect switching system  200 , in accordance with the present invention. In the illustrated embodiment, the cross-connect switching system  200  includes a first input bus  208 , a second input bus  218 , a first output bus  210 , and a second output bus  220 . The cross-connect switching system  200  further includes a cross-connect  204  such as a TDM cross-connect including a plurality of input ports  203  and a plurality of output ports  205 , a connection memory  202 , and an OR gate  206 . The TDM cross-connect  204  is configured to receive first optical and/or electrical input signals, e.g., DS- 3 , OC- 3 , OC- 12 , STS- 1 , STS- 3 , STS-NC, STS-M, and/or STM- 1  data frames, from the input bus  208  at one or more of the respective input ports  203 , and to provide the data to one or more of the respective output ports  205  based on connection information stored in the connection memory  202 . The TDM cross-connect  204  provides the data at the output ports  205  to the OR gate  206  as first switched output data. The cross-connect switching system  200  further provides the first input data carried by the input bus  208  to the output bus  210  as first output data for subsequent transmission through the digital communications system.  
         [0026]    As shown in FIG. 2, the OR gate  206  is configured to receive second optical and/or electrical input signals, e.g., data frames, as second switched input data from the input bus  218 , and to provide the logical OR of the first switched output data (generated by the TDM cross-connect  204 ) and the second switched input data to the output bus  220  as second switched output data for subsequent transmission through the digital communications system. It is noted that the digital communications system comprising the cross-connect switching system  200  may include one or more broadband digital communications networks such as a Local Area Network (LAN), a Wide Area Network (WAN), the Internet, or any other suitable network.  
         [0027]    In order to provide a scalable bandwidth digital cross-connect switching system, the cross-connect switching system  200  may be employed as a TDM cross-connect building block, and a plurality of such building blocks  200  may be operatively interconnected to meet the bandwidth requirements of the system.  
         [0028]    The presently disclosed scalable bandwidth digital cross-connect switching system will be better understood with reference to the following first and second illustrative examples and FIGS. 3-4. As shown in FIG. 3, four of the TDM cross-connect building blocks  200  are operatively interconnected to double the bandwidth of the digital cross-connect switching system. Specifically, a TDM cross-connect switching system  300  having double the bandwidth capacity of the TDM cross-connect switching system  200  (see FIG. 2) includes four TDM cross-connect building blocks  200 . 1 - 200 . 4  (see FIG. 3). Each of the TDM cross-connect building blocks  200 . 1 - 200 . 4  is like the TDM cross-connect switching system  200  of FIG. 2. For example, the TDM cross-connect building block  200 . 3  is coupled to an input bus  308  (see FIG. 3) that corresponds to the input bus  208  (see FIG. 2), an input bus  318  (see FIG. 3) that corresponds to the input bus  218  (see FIG. 2), an output bus  310  (see FIG. 3) that corresponds to the output bus  210  (see FIG. 2), and an output bus  320  (see FIG. 3) that corresponds to the output bus  220  (see FIG. 2). It is noted that in this first example, the Switched Data In (“SwD In ”) inputs of the TDM cross-connect building blocks  200 . 1 - 200 . 2  are tied to ground potential.  
         [0029]    Accordingly, the TDM cross-connect building block  200 . 1  receives input data from an input bus  302  at a Data In (“D In ”) input, provides output data to the D In  input of the TDM cross-connect building block  200 . 2  via a Data Out (“D out ”) output and an output bus  304 , and provides switched output data to the SwD In  input of the TDM cross-connect building block  200 . 3  via a Switched Data Out (“SwD out ”) output and an output bus  318 . The TDM cross-connect building block  200 . 2  provides switched output data to the SwD In  input of the TDM cross-connect building block  200 . 4  via a SwD out  output and an output bus  306 . The TDM cross-connect building block  200 . 3  receives input data from the input bus  308  at a D In  input, provides output data to the D In  input of the TDM cross-connect building block  200 . 4  via a D out  output and the output bus  310 , and provides switched output data to the output bus  320 . Similarly, the TDM cross-connect building block  200 . 4  provides switched output data to an output bus  322 .  
         [0030]    As shown in FIG. 4, nine of the TDM cross-connect building blocks  200  are operatively interconnected to triple the bandwidth of the digital cross-connect switching system. Specifically, a TDM cross-connect switching system  400  having triple the bandwidth capacity of the TDM cross-connect switching system  200  (see FIG. 2) includes nine TDM cross-connect building blocks  200 . 1 - 200 . 9  (see FIG. 4). Each of the TDM cross-connect building blocks  200 . 1 - 200 . 9  is like the TDM cross-connect switching system  200  of FIG. 2. It is noted that the SwD In  inputs of the TDM cross-connect building blocks  200 . 1 - 200 . 3  are tied to ground potential.  
         [0031]    Accordingly, the TDM cross-connect building block  200 . 1  receives input data from an input bus  402  at a D In  input, provides output data to the D In  input of the TDM cross-connect building block  200 . 2  via a D out  output and an output bus  404 , and provides switched output data to the SwD In  input of the TDM cross-connect building block  200 . 4  via a SwD out  output and an output bus  407 . The TDM cross-connect building block  200 . 2  provides output data to the D In  input of the TDM cross-connect building block  200 . 3  via a D out  output and an output bus  406 , and switched output data to the SwD In  input of the TDM cross-connect building block  200 . 5  via a SwD out  output and an output bus  409 . The TDM cross-connect building block  200 . 3  provides switched output data to the SwD In  input of the TDM cross-connect building block  200 . 6  via a SwD out  output and an output bus  411 .  
         [0032]    The TDM cross-connect building block  200 . 4  receives input data from an input bus  408  at a D In  input, provides output data to the D In  input of the TDM cross-connect building block  200 . 5  via a D out  output and an output bus  410 , and provides switched output data to the SwD In  input of the TDM cross-connect building block  200 . 7  via a SwD out  output and an output bus  413 . The TDM cross-connect building block  200 . 5  provides output data to the D In  input of the TDM cross-connect building block  200 . 6  via a D out  output and an output bus  412 , and switched output data to the SwD In  input of the TDM cross-connect building block  200 . 8  via a SwD out  output and an output bus  415 . The TDM cross-connect building block  200 . 6  provides switched output data to the SwD In  input of the TDM cross-connect building block  200 . 9  via a SwD out  output and an output bus  417 .  
         [0033]    The TDM cross-connect building block  200 . 7  receives input data from an input bus  414  at a D In  input, provides output data to the D In  input of the TDM cross-connect building block  200 . 8  via a D out  output and an output bus  416 , and provides switched output data to an output bus  420 . Similarly, the TDM cross-connect building block  200 . 8  provides output data to the D In  input of the TDM cross-connect building block  200 . 9  via a D out  output and an output bus  418 , and switched output data to output bus  422 . Further, the TDM cross-connect building block  200 . 9  provides switched output data to an output bus  424 .  
         [0034]    [0034]FIG. 5 depicts a second illustrative embodiment of a TDM cross-connect building block  500 , in accordance with the present invention. In the illustrated embodiment, the cross-connect building block  500  includes a first input bus  508 , a second input bus  509 , a third input bus  518 , a fourth input bus  519 , a first output bus  510 , a second output bus  511 , a third output bus  520 , and a fourth output bus  521 . The cross-connect building block  500  further includes a cross-connect  504  such as a TDM cross-connect including a plurality of input ports  503  and a plurality of output ports  505 , a connection memory  502 , a first OR gate  506 , and a second OR gate  508 .  
         [0035]    The TDM cross-connect  504  is configured to receive first input data (“Data In 1”) from the input bus  508  at one or more of the respective input ports  503 , and to provide the first data to one or more of the respective output ports  505  based on connection information stored in the connection memory  502 . Similarly, the TDM cross-connect  504  is configured to receive second input data (“Data In 2”) from the input bus  509  at one or more of the respective input ports  503 , and to provide the second data to one or more of the respective output ports  505  based on connection information stored in the connection memory  502 . The TDM cross-connect  504  provides the first data at the output ports  505  to the OR gate  506  as switched output data on a bus  534 , and similarly provides the second data at the output ports  505  to the OR gate  508  as switched output data on a bus  532 . The cross-connect switching system  500  further provides the first input data carried by the input bus  508  to the output bus  510  as first output data (“Data Out 1”), and provides the second input data carried by the input bus  509  to the output bus  511  as second output data (“Data Out 2”), for subsequent transmission through the digital communications system.  
         [0036]    As shown in FIG. 5, the OR gate  506  is configured to receive first switched input data (“Switched Data In 1”) from the input bus  518 , and to provide the logical OR of the switched output data on the bus  534  and the Switched Data In  1  to the output bus  520  as first switched output data (“Switched Data Out 1”). Similarly, the OR gate  508  is configured to receive second switched input data (“Switched Data In 2”) from the input bus  519 , and to provide the logical OR of the switched output data on the bus  532  and the Switched Data In  2  to the output bus  521  as second switched output data (“Switched Data Out 2”) for subsequent transmission through the digital communications system.  
         [0037]    The presently disclosed scalable bandwidth digital cross-connect switching system will be better understood with reference to the following third illustrative example and FIG. 6. As shown in FIG. 6, four of the TDM cross-connect building blocks  500  are operatively interconnected to double the bandwidth of the digital cross-connect switching system. Specifically, a TDM cross-connect switching system  600  having double the bandwidth capacity of the TDM cross-connect switching system  500  (see FIG. 5) includes four TDM cross-connect building blocks  500 . 1 - 500 . 4  (see FIG. 6). Each of the TDM cross-connect building blocks  500 . 1 - 500 . 4  is like the TDM cross-connect switching system  500  of FIG. 5. It is noted that in this third example, the SwD In1  inputs of the TDM cross-connect building blocks  500 . 1 - 500 . 2 , the D In2  inputs of the TDM cross-connect building blocks  500 . 2  and  500 . 4 , and the SwD In2  inputs of the TDM cross-connect building blocks  500 . 3  and  500 . 4  are tied to ground potential.  
         [0038]    Accordingly, the TDM cross-connect building block  500 . 1  receives input data from an input bus  602  at the D In1  input, receives input data from an input bus  606  at the D In2  input, receives input data from an input bus  605  at the SwD In2  input, provides output data to the D In1  input of the TDM cross-connect building block  500 . 2  via the D out1  output and an output bus  604 , and provides switched output data to the SwD In1  input of the TDM cross-connect building block  500 . 3  via the SwD out  output and an output bus  603 . The TDM cross-connect building block  500 . 2  receives input data from an input bus  608  at the D In2  input, receives input data from an input bus  609  at the SwD In2  input, and provides switched output data to the SwD In1  input of the TDM cross-connect building block  500 . 4  via the SwD out1  output and an output bus  607 . The TDM cross-connect building block  500 . 3  receives input data from an input bus  610  at the D In1  input, receives input data from an input bus  614  at the D In2  input, provides output data to the D In1  input of the TDM cross-connect building block  500 . 4  via the D out1  output and an output bus  612 , and provides switched output data to an output bus  618 . Similarly, the TDM cross-connect building block  500 . 4  receives input data from an input bus  616  at the D In2  input, and provides switched output data to an output bus  620 .  
         [0039]    It is understood that the conventional TDM cross-connect switching system  100  (see FIG. 1) may be employed as a TDM cross-connect building block, and a plurality of such building blocks may be operatively interconnected to meet the bandwidth requirements of the system. For example, a TDM cross-connect switching system  700  having double the bandwidth capacity of the conventional TDM cross-connect switching system  100  (see FIG. 1) includes four TDM cross-connect building blocks  100 . 1 - 100 . 4  (see FIG. 7). Each of the TDM cross-connect building blocks  100 . 1 - 100 . 4  is like the TDM cross-connect switching system  100  of FIG. 1.  
         [0040]    Accordingly, the TDM cross-connect building block  100 . 1  receives input data from an input bus  702  at the D In  input, and provides switched output data to an OR gate  722  via the SwD out  output and an output bus  704 . The TDM cross-connect building block  100 . 2  receives input data from an input bus  710  at the D In  input, and provides switched output data to the OR gate  722  via the SwD out  output and an output bus  708 . The TDM cross-connect building block  100 . 3  receives input data from an input bus  706  (which is coupled to the input bus  702 ) at the D In  input, and provides switched output data to an OR gate  724  via the SwD out  output and an output bus  714 . The TDM cross-connect building block  100 . 4  receives input data from an input bus  712  (which is coupled to the input bus  710 ) at the D In  input, and provides switched output data to the OR gate  724  via the SwD out  output and an output bus  716 . The OR gates  722  and  724  provide switched output data to respective output buses  718  and  720 .  
         [0041]    A method of operating the presently disclosed TDM cross-connect switching system is illustrated by reference to FIG. 8. As depicted in step  802 , first input data having a first data rate is received at one or more input ports of a TDM cross-connect from an input bus. Next, the first input data is provided, as depicted in step  804 , as first switched output data to one or more output ports of the TDM cross-connect based on connection information accessed from a connection memory. The first switched output data is then provided, as depicted in step  806 , to an OR gate. Next, second switched input data having a second data rate is received, as depicted in step  808 , at the OR gate. The OR gate then performs, as depicted in step  810 , a logical OR operation on the first switched output data and the second switched input data, and provides, as depicted in step  812 , the logical OR&#39;d data as second switched output data to an output bus for subsequent transmission through the digital communications system.  
         [0042]    It will further be appreciated by those of ordinary skill in the art that modifications to and variations of the above-described technique for building a large single-stage cross-connect using multiple devices without interleaving may be made without departing from the inventive concepts disclosed herein. Accordingly, the invention should not be viewed as limited except as by the scope and spirit of the appended claims.