Abstract:
A switching device includes multiple interfaces and a switch fabric. The switch fabric includes switch integrated circuits arranged in a number of stages. Multiple virtual switch planes may be implemented in the switch fabric. Data traffic received at the interfaces is selectively assigned to different ones of the virtual switch planes.

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 12/134,237, filed Jun. 6, 2008, now U.S. Pat. No. 8,320,369, which is a continuation of U.S. patent application Ser. No. 10/300,639, filed Nov. 21, 2002, now U.S. Pat. No. 7,397,794, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to network devices, and more particularly, to systems and methods for implementing virtual switch planes in physical switch fabrics of network devices. 
     2. Description of Related Art 
     Conventionally, high bandwidth switch fabrics have used several parallel switch “planes” that each carry a fraction of the total bandwidth.  FIG. 1  illustrates a conventional switch fabric  100  with parallel switch planes  120 ,  125 ,  130  and  135 . Each switch plane may include multiple interconnected switch integrated circuits (ICs)  110 - 1 - 110 - 12  (collectively,  110 ), with each switch IC employing one of a variety of switch architectures, such as a crossbar switch. 
     Interface cards  105  interconnect with switch ICs  110  of each of the parallel switch planes (only interconnections to switch plane  1  are shown) and divide the received bandwidth over the n planes of the switch fabric  100  (four planes shown). Each of interface cards  105  may interconnect with a number of ports on the switch ICs  110 . If switch fabric  100  must support a total bandwidth B and have P ports, then each of the parallel switch planes must also have P ports, but each switch plane only needs to support a total bandwidth of B/n, where n is the number of planes. The use of parallel switch planes thus makes it possible for switch fabric  100  to support bandwidths much larger than could be supported by a single IC switch, without introducing much complexity. 
     The number of ports on a single switch plane, however, determines the most cost-effective number of interface cards  105  in a given system. Supporting small system sizes (i.e., smaller than the natural number of ports in a fabric) generally requires wasting ports, or designing a new switch fabric. Thus, a conventional switch fabric  100  cannot be used with systems having a different number of interface cards  105  than the number of ports on switch fabric  100 . 
     Therefore, there exists a need for systems and methods that can enable a given switch fabric to support systems with fewer interface cards than the number of switch ports on the switch fabric, thus, permitting the implementation of smaller scale system sizes. 
     SUMMARY OF THE INVENTION 
     Systems and methods consistent with the principles of the invention address this and other needs by implementing multiple virtual switch planes in a physical switch plane of a network device such that the switch fabric can support systems with fewer interface cards than the number of switch ports on the switch fabric. A switch fabric with P ports may, when implemented with S virtual switch planes, connect with P/S interface cards by connecting each interface card to the switch fabric S times. Consistent with the principles of the invention, address re-mapping tables may be used within switch ICs of the switch fabric to direct incoming data units through appropriate virtual switch planes to reach destination output interfaces. The use of virtual switch planes within the switch fabric can be transparent to the interface cards, localizing changes to the switch fabric itself rather than requiring the interface cards to be configured differently depending on the switch configuration. 
     One aspect consistent with principles of the invention is directed to a method of forwarding data units through a plurality of virtual switch planes. The method includes implementing a virtual switch plane in a physical switch plane, wherein the physical switch plane includes input ports and a switch fabric. The method further includes allocating at least one of the input ports to the virtual switch plane and forwarding data units through the at least one allocated input port to the virtual switch plane. 
     A second aspect consistent with principles of the invention is directed to a method of implementing multiple virtual switch planes in a physical switch plane in which the physical switch plane includes a switch fabric and queues. The method includes segmenting the physical switch plane into the multiple virtual switch planes. The method further includes segregating the queues into groups such that each group of queues is associated with a different one of the multiple virtual switch planes. 
     Another aspect consistent with principles of the invention is directed to a method of handling data traffic at a physical switch plane of a network device, where the physical switch plane includes virtual switch planes. The method includes receiving the data traffic and selectively assigning the received traffic to different ones of the virtual switch planes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with the description, explain the invention. In the drawings, 
         FIG. 1  is a diagram of a conventional multi-plane switch fabric; 
         FIG. 2  is a diagram of an exemplary network device in which systems and methods consistent with the principles of the invention may be implemented; 
         FIG. 3  is a diagram of components of a first exemplary switch plane according to an implementation consistent with the principles of the invention; 
         FIG. 4  is a diagram of components of a second exemplary switch plane according to an implementation consistent with the principles of the invention; 
         FIG. 5  is a diagram of an exemplary switch IC consistent with the principles of the invention; 
         FIG. 6  is a diagram of exemplary next port and jump tables stored in the switch IC of  FIG. 5  consistent with the principles of the invention; 
         FIGS. 7A and 7B  are diagrams of exemplary jump tables consistent with the principles of the invention; 
         FIG. 8  is a diagram of an exemplary destination fabric output port table consistent with the principles of the invention; 
         FIG. 9  is a diagram of an exemplary source interface table consistent with the principles of the invention; and 
         FIGS. 10-11  are flowcharts of an exemplary data unit handling process according to an implementation consistent with principles of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims and equivalents. 
     Systems and methods consistent with the principles of the invention include mechanisms for implementing virtual switch planes in a physical switch plane of a network device. Through the use of virtual switch planes, the physical switch plane can support systems with fewer interface cards than the number of switch ports on the switch fabric without wasting ports, thus, enabling the implementation of cost effective smaller scale system sizes. 
     Exemplary Network Device 
       FIG. 2  is a diagram of an exemplary network device  200  in which systems and methods consistent with the principles of the invention may be implemented. Network device  200  may receive data units, such as packets, from a physical link (not shown). Network device  200  may process the data units to determine destination information and transmit the data units on one or more links in accordance with the destination information. A data unit refers to any type of data, including, for example, packets, cells, datagrams, fragments of packets, fragments of datagrams or cells, or a combination of these types of data. 
     Network device  200  may include input interfaces  205 , a switch fabric  210 , and output interfaces  215 . Input interfaces  205  may receive incoming streams of data units and send each received data unit to the switch fabric  210  for routing to an appropriate output interface of output interfaces  215 . Switch fabric  210  may include multiple physical switch planes (not shown), each of which may include a network of switch ICs that route data units from input interfaces  205  to appropriate output interfaces  215 . 
     Exemplary Switch Fabrics 
       FIGS. 3 and 4  illustrate exemplary components of a single physical switch plane, implemented with virtual switch planes, of network device  200  consistent with the principles of the invention.  FIG. 3  illustrates one exemplary embodiment in which queues associated with the different virtual switch planes are segregated.  FIG. 4  illustrates another exemplary embodiment in which the queues are shared by the different virtual switch planes implemented in the single physical switch plane. 
     As shown in  FIG. 3 , a single physical switch plane of a switch fabric  210  may include  16  switch ICs  320 - 1 - 320 - 12  (collectively,  320 ) arranged in a three stage (stage  1   305 , stage  2   310 , stage  3   315 ) Clos configuration. Input interfaces  205  may include multiple interface (I/F) cards  325 - 1 - 325 - 4  (collectively,  325 ) that interconnect with stage  1   305  switch ICs  320 . Output interfaces  215  may include multiple I/F cards  325 - 1 - 325 - 4  that interconnect with stage  3   315  switch ICs  320 . Each line shown interconnected between one of I/F cards  325  and a switch IC  320  may represent a connection, such as a copper or fiber connection, to ports on the switch ICs  320 .  FIG. 3  illustrates two virtual planes A and B implemented in physical switch fabric  210 . Each of I/F cards  325  may interconnect to a switch IC  320  via a number of connections (two shown for illustrative purposes). Some of the connections between I/F cards  325  and switch ICs  320  may be part of virtual switch plane A and others of the connections may be part of virtual switch plane B. In each stage  1   305  switch IC  320 , for example, data units received via the first connection may only be “sprayed” to the first two of stage  2   310  switch ICs  320  (designated “A”). Data units received via the second connection may only be “sprayed” to the second two of stage  2   310  switch ICs  320  (designated “B”). At stage  2   310 , two of switch ICs  320  (designated “A”) carry only data units for virtual switch plane A and the other two of switch ICs  320  (designated “B”) carry only traffic for virtual switch plane B. 
     Virtual switch planes A and B use distinct queues throughout switch fabric  100 . At stage  1   305  and stage  2   315 , each virtual switch plane uses a separate subset of the input and output ports of each switch IC. At state  2   310 , virtual switch plane A and B use separate switch ICs  320 , and virtual switch plane A and B further use distinct queues such that virtual switch plane A data units travel only through the first two input ports of each stage  3   315  switch IC  320  and virtual switch plane B data units travel only through the second two input ports of each stage  3   315  switch IC  320 . Implementing virtual switch planes in physical switch fabric  210  may, thus, require that an equal fraction of stage  1   305  switch IC  320  input ports be used for each virtual switch plane. In the exemplary embodiment of  FIG. 3 , in which two virtual switch planes (A and B) are implemented in switch fabric  210 , half of the input ports of each stage  1   305  switch IC  320  may be used for virtual switch plane A and the other half for virtual switch plane B. The ports of stage  3   315  switch ICs  320  may have similar constraints. The principles involved in dividing switch fabric  100  into two, virtual switch planes, as described above, may be generalized to divide switch fabric  100  into more than two switch planes. 
       FIG. 4  illustrates another exemplary embodiment consistent with the principles of the invention in which data units handled by both virtual switch plane A and virtual switch plane B share the same queues in stage  2   310  switch ICs  320  (designated “A+B”). In this exemplary embodiment, stage  1   305  switch ICs  320  spray data units from all input ports to all output ports. Stage  2   310  switch ICs  320  direct data units to the correct stage  3   315  switch IC  320  based on an interface card destination address and virtual switch plane number associated with each data unit. 
     Exemplary Switch IC 
       FIG. 5  illustrates an exemplary one of switch ICs  320  consistent with the principles of the invention. The switch IC  320  may include N inputs ports  505 - 1 - 505 -N (collectively,  505 ) and N output ports  515 - 1 - 515 -N (collectively  515 ) interconnected with switch logic  510 . Switch logic  510  may include, for example, crossbar switch logic. Switch logic  510  forwards each data unit received from an input port  505  to an appropriate output port  515  based on the data unit&#39;s destination I/F card  325 . Each output port  515  may further include one or more queues  520  for buffering data units received from switch logic  510  before sending the data units out of switch IC  320 . 
     Exemplary Next Port and Jump Tables 
       FIG. 6  illustrates an exemplary next port table  605  and jump table  610  consistent with the principles of the invention. A different next port table  605  and jump table  610  may be associated with each input port  505  of stage  1   305  switch ICs  320 . Next port table  605  may map an interface destination address to an output port address of a stage  1   305  switch IC  320 . Jump table  610  may map the output port address from next port table  605  to a next port value (NEXT_PORT) that may overwrite the original value in next port table  605 . Changing the value in next port table  605  as each interface destination address is mapped allows a sequence of data units, with the same interface destination address, to be load balanced (or “sprayed”) over a set of output ports. The entries in jump table  610  determine the sequence of output ports to use for spraying. 
     In a switch fabric  210  with two virtual planes, tables  605  and  610  for stage  1   305  input ports  505 , associated with virtual plane A, may be programmed to spray data units only to stage  1   305  output ports  515  for virtual plane A. This may be accomplished by storing the value ((i+1)mod p/2) in jump table  610  entry i, where p is the number of ports. Also, the initial values in next port table  605  should be less than p/2. For virtual plane B, the corresponding input ports should have jump table  610  entries set to (((i+1)mod p/2)+p/2) and the initial next port table  605  values may be greater than or equal to p/2. The pointers in jump table  610 , thus, form two disjoint circular lists, and each next port table  605  value points to a current position in one of the disjoint lists (i.e., the one corresponding to the virtual plane on which the data units were sent). A sequence of data units sent to a given destination may, therefore, cycle through only half of the output ports corresponding to the virtual plane on which the data units were sent. This algorithm may be generalized for any number of virtual planes. 
     As shown in  FIG. 6 , next port table  605  may map an interface destination address associated with a data unit to an output port  515  of stage  1   305  switch IC  320  that receives the data unit from an input interface  205 . The interface destination address may correspond to a destination I/F card  325  of output interfaces  215  and may be included in a header of a data unit. An interface destination address received at next port table  605  may be used to index the table to retrieve an output port address (OUTPUT_PORT) of stage  1   305  switch IC  320  through which the data unit should be forwarded. The entire address, part of the address, or the result of an algorithm performed on the address, such as a hash, may be used as the index value. The output port address (OUTPUT_PORT), corresponding to an output port  515 , may be passed to jump table  610 . The output port address (OUTPUT_PORT) may then index jump table  610  to retrieve a port address (NEXT_PORT) that may replace the previously retrieved entry of next port table  605 . A sequence of port addresses (NEXT_PORT) in jump table  610  determines the order in which data units are “sprayed” out the different output ports  515  of stage  1   305  switch IC  320 . 
       FIGS. 7A and 7B  further illustrate exemplary embodiments of jump table  610  consistent with the principles of the invention. The exemplary jump table  610  of  FIG. 7A  may be used in the exemplary switch fabric  210  of  FIG. 3 . The exemplary jump table  610  of  FIG. 7B  may be used in the exemplary switch fabric  210  of  FIG. 4 . 
     In the exemplary jump table  610  of  FIG. 7A , a group of port addresses may be associated with each virtual switch plane implemented in physical switch fabric  210 . For example,  FIG. 7A  illustrates port addresses NEXT_PORT_ 1 A through NEXT_PORT_NA associated with virtual plane A. Data units processed by virtual switch plane A may, thus, be “sprayed” out output ports  515  of stage  1   305  switch IC  320  according to the sequence of entries corresponding to each virtual switch plane. 
     In the exemplary jump table  610  of  FIG. 7B , the port addresses may not be associated with any virtual switch plane. Each data unit, therefore, may be “sprayed” out an output port  515  of a stage  1   305  switch IC  320  according to the sequence of entries of jump table  610  regardless of which virtual switch plane is handling the data unit. 
     Exemplary Destination Fabric Address Translation Table 
       FIG. 8  illustrates an exemplary destination fabric address translation table  800  consistent with the principles of the invention. A different table  800  may be associated with each input port  505  of stage  1   305  switch ICs  320 . Destination fabric address translation table  800  may map interface destination addresses  805  associated with each data unit to switch fabric output ports  810 . Each retrieved fabric output port  810  may correspond to an output port  515  of stage  3   315  switch ICs  320 . Each interface destination address  805  associated with a data unit may index table  800  to retrieve a fabric output port address  810  (FABRIC_OUTPUT_PORT) associated with an output port  515  of a stage  3   315  switch IC  320 . 
     In a fabric without virtual switch planes each interface card connects to a single port of each fabric plane. Therefore, each interface card has one destination address. When an interface card sends a packet into the fabric the interface card also transmits the fabric port address of the data unit&#39;s destination. In a fabric with virtual switch planes each interface card connects to more than one port of each fabric plane. In order to avoid changes to the interface card configuration depending on the presence or number of virtual planes, ideally the interface card should still have only one “logical” fabric address that is used by the other interface cards to identify a particular card. However, within a switch plane each card has multiple “physical” fabric addresses, one per virtual plane. 
     The fabric address translation table  800  re-maps the logical fabric destination address provided by the source interface card into a physical fabric address specific to a virtual plane. Because there is a different fabric address translation table  800  associated with each input port, and each input port is associated with a single virtual plane, multiple virtual planes can be supported by loading different values into each fabric address translation table. 
     Exemplary Source Fabric Address Translation Table 
       FIG. 9  illustrates an exemplary source fabric address translation table  900  consistent with the principles of the invention. A different source fabric address translation table  900  may be associated with each input port  505  of stage  3   315  switch ICs  320 . Source fabric address translation table  900  may map fabric source addresses  905  to a logical source address  910  associated with each virtual plane implemented in physical switch fabric  210 . Fabric source address  905  may be automatically constructed by recording the sequence of switch IC  320  ports along the path traveled by a data unit through the stages of switch fabric  210 . When the data unit arrives at a stage  3   315  switch IC  320  input port  505 , table  900  may be used to re-map the fabric source address  905  to a logical source address used by the I/F cards  325  of output interfaces  215 . Source fabric address translation table  900  may map physical source addresses used internally in the fabric to logical source addresses used externally by the interface cards. In a system with virtual planes, multiple physical addresses map to a single logical address so multiple entries in the table will have the same logical address. 
     Exemplary Data Unit Handling Process 
       FIGS. 10-11  are flowcharts of an exemplary process for handling data units received at network device  200  in accordance with implementations consistent with the principles of the invention. The exemplary process may begin with the receipt of a data unit at an I/F card  325  of input interfaces  205  [act  1005 ]. The receiving I/F card  325  may then determine an interface destination address, associated with a destination I/F card  325  of output interfaces  215 , and pass the received data unit to a stage  1   305  switch IC  320  [act  1010 ]. Stage  1  switch IC  320  may index next port table  605 , with the determined interface destination address, to retrieve a stage  1   305  switch IC  320  output port (OUTPUT_PORT) [act  1015 ]. Stage  1  switch IC  320  may further index jump table  610  with the retrieved stage  1   305  switch IC  320  output port (OUTPUT_PORT) to retrieve a next port value (NEXT_PORT) [act  1020 ]. Stage  1  switch. IC  320  may write the retrieved next port value (NEXT_PORT) into the same entry of next port table  605  [act  1025 ]. 
     Stage  1  switch IC  320  may then index destination fabric output port table  800  with the determined destination interface destination address to retrieve a fabric output port (FABRIC_OUTPUT_PORT) [act  1030 ]. Stage  1  switch IC  320  may then send the data unit out an output port  515  corresponding to the retrieved output port (OUTPUT_PORT) value [act  1035 ]. A stage  2   310  switch IC  320  may then receive the data unit [act  1105 ]. The stage  2   310  switch IC  320  may send the received data unit out through an output port  515  corresponding to an interface card  325  interface destination address determined by a stage  1  switch IC  320  (FABRIC_OUTPUT_PORT) [act  1110 ]. A stage  3   315  switch IC  320  on the path through switch fabric  210  may receive the data unit [act  1115 ]. The stage  3   315  switch IC  320  may index source fabric address translation table  900  with a fabric source address  905  to retrieve a logical source address [act  1120 ]. Stage  3   315  switch IC  320  may then use the interface destination address determined by a stage  1  switch IC (FABRIC_OUTPUT_PORT) to send the data unit to a corresponding I/F card  325  of output interfaces  215  [act  1125 ]. The logical source address retrieved from table  900  may be transmitted to the I/F card  325  along with the data unit. 
     CONCLUSION 
     Consistent with the principles of the present invention, multiple virtual switch planes may be implemented in a physical switch plane of a network device such that the network device switch fabric can support systems with fewer interface cards than the number of switch ports on the switch fabric. A switch fabric with P ports may, for example, when implemented with S virtual switch planes, connect with P/S interface cards by connecting each interface card to the switch fabric S times. Address re-mapping tables may, consistent with the principles of the invention, be used within switch ICs of the switch fabric to direct incoming data units through appropriate virtual switch planes to reach destination output interfaces. The use of virtual switch planes within the switch fabric can be transparent to the interface cards, localizing changes to the switch fabric itself rather than requiring the interfaces cards to be configured differently depending on the switch configuration. 
     The foregoing description of preferred embodiments of the present invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. For example, though the switch plane described above employed a three-stage Clos network, smaller switch plane implementations that have, for example, a single crossbar chip per physical fabric plane, may be used. In such an implementation, source fabric address translation table  900  and destination fabric address translation table  800  may be implemented in the same IC. 
     While series of acts have been described in  FIGS. 10-11 , the order of the acts may vary in other implementations consistent with the present invention. Also, non-dependent acts may be performed in parallel. 
     No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Where only one item is intended, the term “one” or similar language is used. 
     The scope of the invention is defined by the claims and their equivalents.