In their place new, high speed, point-to-point, component interconnection standards have been developed. System Packet Interface (SPI) is one of the more popular interfaces used in the packet processing portion of the line card, while standards such as the Common Switch Interface (CSIX) and the Network Processing Forum Streaming Interface (NPSI) are used for the Switch Fabric interface portion of the line card. The SPI-3 specification is designed to operate at up to OC-48 (2.5 Gbps). The SPI-4 specification is designed to operate at up to OC-192 (10 Gbps). Both of these specifications include backpressure signaling and control, and the implementation of up to 256 logical ports. Since these are point-to-point protocols some kind of interface device must be used if more than two devices need to be interconnected on the line card. The IDT Packet Exchange devices provide a single-chip solution for this interconnect problem. In this example, the line card is handling an OC-48 line. The line card design requires that a PHY device, NPU, Security Processor and Fabric Interface chip must be interconnected. The IDT SPI Exchange Device provides data switching between all four devices as well as aggregating the three SPI-3 ports to the NPU’s SPI-4 interface. This switching is implemented at the logical port level allowing packets with different logical port tags coming in on the same physical port to be routed to different physical ports. Unlike the SPI-4 specification, the SPI-3 specification is not symmetric. The link layer side is not the same as the PHY layer side. The SPI-3 ports on the IDT Packet Exchange Devices can be configured as a link layer device or a PHY device allowing it to be connected to either type of device externally.