A switch fabric is an interconnect architecture for redirecting data within a system from one of the ports in a line card to another port in a different line card. The two primary switch fabric configuration types used today are the centralized switch fabric and the distributed switch fabric. Each implementation has advantages and disadvantages, and either architecture can be implemented in Stratix™ GX devices.
Centralized Switch Fabrics
A centralized switch fabric system contains a central switch fabric card that is responsible for interconnecting all ports on all the line cards in the system. The switching function occurs on the switch fabric card in silicon and connects to the line cards using high-speed serial links across a backplane. Figure 1 shows a simplified eight-line card system in which each line card connects to the central switch fabric card.
Figure 1. Centralized Switch Fabric System
Figures 2a and 2b show more detailed versions of a 4 x 3.125 gigabit per second (Gbps) backplane interface on a line card and a switch fabric card with several sets of 4 x 3.125 Gbps links. Traffic management, buffer management, and the backplane transceiver can be implemented in a Stratix GX device on the line card (see Figure 2a). On the switch fabric card, Stratix GX devices can be used as an integrated backplane transceiver/switch fabric solution. Figure 2b shows a Stratix GX device providing a total of twenty 3.125-Gbps serial link connections to five 10-Gbps line cards. Using several Stratix GX devices supports systems with 16 or 32 line cards. The high-speed MultiTrack™ interconnect in the logic array allows for wire-speed packet transmission. With the use of TriMatrix™ memory and support for high-speed external memory interfaces in Stratix GX devices, designers can easily implement packet buffering with virtual output queuing.
Figure 2a. Backplane Interface on Line Card with Traffic Management
Figure 2b. Backplane Interface on Switch Fabric Card
Distributed Switch Fabrics
In a distributed switch fabric implementation, the switching is actually done on the line cards before data is sent out onto the backplane. As shown in Figure 3, each line card connects to every other line card in the system using high-speed serial links, creating a high-speed mesh backplane. Routing packets to the appropriate line card becomes a function that must be implemented on each line card. The high-performance logic array in Stratix GX devices provides ample programmable logic elements to help route packets on the line card. Also, traffic management, queue management, and the backplane interface can be implemented in the Stratix GX device. Stratix GX devices provide all of the functionality needed to effectively implement a distributed switch fabric solution.
Figure 3. Distributed Switch Fabric System
Figures 4 shows a more detailed version of a N x 3.125 Gbps backplane interface with an integrated distributed switch fabric module, traffic management, and buffer management. The bulk of this functionality can be implemented on a Stratix GX device as shown. The high-speed interconnect in the logic array allows for wire-speed packet transmission. With the use of TriMatrix memory in Stratix GX devices, designers can easily implement packet buffering. Also, Stratix GX devices are capable of interfacing with high-speed memory devices for external packet buffering, and these devices support interfaces such as DDR, FCRAM, SDR, ZBT, and QDR/QDRII.
Figure 4: Integrated Backplane Transceiver with Traffic & Buffer Management
