Abstract:
The disclosed invention relates to a method and system to transmit data packets through a switched network system that is composed of a plurality of routing entities. The method determines whether or not the output port assigned to the data packet and the associated input port are local to the routing entity by referencing an index pointer to a routing table.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to the transmission of data packets in a networking environment, and relates in particular to a system and method for transmitting data packets in an Infiniband network.  
       BACKGROUND OF THE INVENTION  
       [0002]     A central processor unit of a computer may communicate with peripheral devices, such as network adapters through an Input/Output (I/O) network. One type of I/O network is known and referred to as the InfiniBand (IB) network. InfiniBand which is a trademark of the InfiniBand Trade Association is a recent industry architecture (IBA) for I/O communications. IBA enables servers, remote storage and other networking devices, also called endnodes, to communicate concurrently through IBA fabrics or subnets made of switches and routers that convey data packets to their destination, either within single or multiple subnets. A Subnet Manager Agent (SMA) of the IB switch allows data packets received from one source endnode to be passed to a destination endnode within the same subnet. The Subnet Manager Agent configures the switches at the initialization of the network by sending commands to the Subnet Manager Agent. The configuration process includes implementing a routing table within each switch, referenced as the Forwarding Table or Forwarding Database (FDB).  
         [0003]     Each destination endnode contains one or more channel adapters having one or more output ports. A unique address is assigned to each output port, known as the port&#39;s Local Identifier (LID). The LID address is related to the source endnode using a route field header of a data packet, namely the Local Route Header (LRH), to define its destination address. Each data packet has a unique Destination Local Identifier (DLID) assigned by the (SM) and corresponding to a 16-bit address of a switch output port through which the data packet is conveyed. A Forwarding Table located in a switch maps the DLIDs to the output ports. The Forwarding Database is arranged as a list of port blocks, each port block containing a list of destination output ports.  
         [0004]     A complete description of the FDB and all previously defined elements of an IB network may be found in the InfiniBand Architecture Specification Volume 1, Release 1.0.a available at www.infiniband.org which is incorporated herein by reference.  
         [0005]     To support high capacity switching, a switch may be implemented with several interconnected chips. A data packet arriving at an external input-port of such a switch may be routed internally through several levels of chips before arriving at its destination external output-port. These chips can either be separate switches from the point of view of the Subnet Manager, each with separate Subnet Manager Agent, or a combined switch with only one Subnet Manager Agent, greatly simplifying the management of such a switching fabric.  
         [0006]     A multi-chip switch architecture implementation requires the maintenance of the complete routing path of each data packet regardless of the internal routing paths inside one or more switches.  
         [0007]     Moreover, all the different constraints of priority, load balancing or Quality of Services (QoS) must be guaranteed as defined by the subnet manager.  
         [0008]     The present invention offers a system and method to achieve these requirements.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, the main object of the invention is to provide a switch fabric decomposed in a plurality of sub-switches or routing entities, which appears as a single InfiniBand compliant switch entity.  
         [0010]     In a preferred embodiment, the method is implemented for a switching system with at least a SL-to-VL mapping table and includes a plurality of input ports coupled to a plurality of output ports by multiple routing entities. The method enables transmission of a data packet received at a first routing entity to an output port by: 
        a) assigning an output port to the data packet from a switch routing table associated with the switching system;     b) proceeding to step d if the output port is coupled to the first routing entity, or proceeding to step c if the output port is not coupled to the first routing entity;     c) assigning a local output port to the data packet from a local routing table associated with the first routing entity if the output port previously obtained is not coupled to the first routing entity;     d) proceeding to step f if the input port is coupled to the first routing entity or proceeding to step e if the input port is not coupled to the first routing entry;     e) associating a VL with the data packet from the SL-to-VL mapping table; and     f) placing the data packet in a VL queue.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The above and other objects, features and advantages of the invention will be better understood by reading the following more particular description of the invention in conjunction with the accompanying drawings wherein:  
         [0018]      FIG. 1  is a schematic block diagram of a networking environment in which the invention preferably applies;  
         [0019]      FIG. 2  is a schematic block diagram of a 8-port switch built out of four interconnected 4-port switches;  
         [0020]      FIG. 3  is a flow chart of the steps for routing unicast data packets according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     The invention is preferably implemented in a networking environment as illustrated on  FIG. 1  which shows at a high level an example of an IBA subnet  100 . For sake of simplicity, one IBA subnet is shown but it is to be appreciated that an IB network may include several IBA subnets interconnected by routers  102 . Router  102  may also be a bridge between an IBA subnet and other types of networks such as WANs or LANs. IBA subnet  100  comprises a plurality of switches  104  to allow a plurality of endnodes  106  to communicate through data packets transmission links.  
         [0022]     A Subnet Manager  108  (SM) controls the configuration of the subnet in terms of initialization and maintenance of the routing tables included within the switches. The Subnet Manager is also responsible for initialization and configuration of the SL-to-VL mapping tables (SL 2 VL), which contain the correspondence between the Service Level (SL) of an incoming packet to its output Virtual Lane (VL). The SL value is placed in the Local Route Header of each data packet and defines the operational Service Level for each data packet.  
         [0023]     The VL creates multiple virtual links within a single physical link. Virtual Lanes are configured by the Subnet Manager and are based on the Service Level value of a data packet. As a data packet traverses the switch fabric, its associated SL determines which VL is selected on each link by pointing to a SL-to-VL mapping table configured by the Subnet Manager in the switch.  
         [0024]     Once again, a complete description of SL and VL and all previously defined elements of an IB network may be found in the InfiniBand Architecture Specification Volume 1, Release 1.0.a referenced above.  
         [0025]     Referring to  FIG. 2 , a switching system  104  as used in a preferred embodiment of the invention is detailed.  FIG. 2  shows an 8-port global switch implemented with four interconnected 4-port switches ( 202 - 1 , 202 - 2 , 202 - 3 , 202 - 4 ). It is understood that the present example is intended for ease of description while the invention is operable with any configuration of combined chips, such as, for example, a 32-port switch implemented with twelve 8-port switches or a 64-port switch implemented with twenty-four or thirty-two switches depending on the amount of redundant paths required for load balancing. The naming convention of input-port and output-port used in the description is adopted for clarity purposes and is not to be considered as a limitation since a single port may be both an input-port and an output-port.  
         [0026]     As shown in  FIG. 2 , the 8-port global switch has four external input-ports or switch input-ports  212 - 1  to  212 - 4  coupled to two 4-port switches  202 - 1 , 202 - 2  and four external output-ports or switch output-ports  214 - 1  to  214 - 4  coupled to two 4-port switches  202 - 3 , 202 - 4 . In the exemplified two-stage configuration, switches  202 - 1  to  202 - 4  each have two internal ports or switch ports  208 - 1  to  208 - 4  and  210 - 1  to  210 - 4 . The internal ports ( 208 - 1 , 208 - 2 , 208 - 3 , 208 - 4 ) are coupled respectively to internal ports  210 - 1 , 210 - 3 , 210 - 2  and  210 - 4 .  
         [0027]     A configuration register that is managed by the Subnet Manager Agent classifies each port as external or internal. For each switch port there is also a mapping rule corresponding to one of the switch output-ports.  
         [0028]     When an incoming data packet arrives at an external input-port  212 - i ( 1 - 4 ) of the switch, it has to be routed to the assigned external output-port  214 - i ( 1 - 4 ) as defined by its corresponding Destination Local Identifier (DLID). The internal routing path is determined by the algorithm now described with reference to  FIG. 3 .  
         [0029]      FIG. 3  shows a flow chart detailing the steps for routing data packets within a switch. At step  302 , a data packet arriving on an external link of the switch is received at an external input-port  212 - i ( 1 - 4 ). The DLID of the incoming data packet is extracted from the data packet header and used at step  304  to obtain an external output-port number  214 - i ( 1 - 4 ) assigned to this data packet. The output-port number is obtained by using the extracted DLID as an index to point to a mapping table (Forwarding Table FWD) that is associated with the switch  104 .  
         [0030]     Step  306  checks whether the external output-port number obtained from the Forwarding Table is local to the chip the data packet is passing through. If the external output-port is local to the chip (branch YES), then step  308  checks the input port to determine whether it is an internal port or an external port.  
         [0031]     If the input-port is an internal port (branch YES), then step  310  sets output VL equal to the packet VL and the data packet is placed in a corresponding VL queue for step  310 . The process ends on step  312  by forwarding the data packet out of the switch.  
         [0032]     If the input-port is an external port (branch NO), then the process continues to step  316 .  
         [0033]     Step  316  performs a SL to VL mapping. The incoming SL, the input-port number and the external output-port derived in previous steps are used to address a SL 2 VL table to obtain the VL that is going to be sent with the data packet. The process then continues with steps  310  and  312  as previously described.  
         [0034]     Going back to step  306 , If the external output-port number obtained from the Forwarding Table is not local to the chip (branch NO) then the process continues to step  314 .  
         [0035]     Step  314  uses the external output-port number obtained on the previous step as an index to point to a second mapping table (Internal Forwarding Table IFWD) associated with the current chip to assign a local output-port number to the data packet.  
         [0036]     In alternate embodiments where load balancing is required, one or several ‘Isb’ bits of the DLID may be combined with the external output-port number for indexing the IFWD table.  
         [0037]     Then, the process continues with step  308  as previously described.  
         [0038]     It is to be appreciated that the description has been made for unicast network traffic of data packets but may be applied with minor adaptations to multicast network communications. In particular, the external input-port is encoded with a number of bits based on the number of multicast addresses used in the subnet, the number of ports in the switch and other implementation tradeoffs.  
         [0039]     While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous other modifications and variations can be devised without departing from the scope of the invention.