The FPX: Field-programmable Port Extender

Block diagram of WUGS with FPX modules

As shown in the diagram, the queuing modules are distributed across the inputs of the switch. Each queue maintains linked-list pointers in memory to track individual traffic flows. Pointers to each flow are then maintained both in a circuit table and in a service queue. The service queue tracks flows on a per-destination basis, allowing an input scheduler to achieve optimal throughput. The circuit index tracks cells on a flow basis, enabling flows to be served in response to an output port request.

• The project has begun!
  July 1999 Workshop Talk

• A first prototype of this system has been created.
  Details of this hardware are described in:
  FPX Implementation Results

• The initial description of this project, which summarized
  plans integrate the WUGS and iiQueue is still on-line as:
  Initial WUGS-iiQueue Project Description

  The new FPX Module

  For this project, we will create a new single circuit board that contains all of the features of the iiQueue plus the proper interface connectors to the WUGS. This allows configuration of a switch with multiple distributed input queue modules and it enables the FPX hardware to be shared with other institutions. A diagram of this new board is shown below.

  
  PCB Layout of the new FPX Module

  By using a high-density Ball Grid Array (BGA) package,the new FPX consolidates the functions of the iiQueue's Ingress and Egress units into one FPGA. Two banks of 64-bit, Synchronous Dynamic Random Access Memory (SDRAM) provide pipelined cell storage. Two banks of 32-bit wide SRAM maintain pointers and data structures in the low-latency control memory. The circuit uses FIFO devices to separate the clock domain of the line card from that of the FPX.

  
  Physical configuration of FPX in WUGS module

  Physically, this new FPX fits into the WUGS cabinet as shown above. The FPX (middle) attaches to the WUGS switch (bottom), as if it were a line card. The line card (top) then attaches to the FPX as if it were a switch. The height of the combined queue and line card easily fit within the cabinet. Because the new FPX is physically same size as a line card, every port of a WUGS could be equipped with a FPX module.

  Reprogrammable Design Flow

  
  Design flow to reprogram the FPX Module

  All memory signals attach to the FPGA. Because the function of the FPGA device is reprogrammable, the FPX can be implement arbitrary queue strategies. Further, the reprogrammable hardware allows rapid experimentation and testing of new designs. The design flow used to reprogram the FPGA is shown above. From our experience with the iiQueue, we expect the total time from a hardware modification to experimentation on the actual switch to be approximately fifteen minutes.

  Applications for the FPX

  As a reprogrammable logic device with memory, the FPX can perform arbitrary transformations on the data that it processes. Using the FPX hardware, it is possible to research distributed input fair queuing systems. One such systems provides enhanced functionality of the constant-time 3DQ operations, while another provides Core edge and router functionality at the perimeter of the WUGS switch. A table that summarizes the queuing features of the FPX are shown below:

  Line Type	Line Rate	Memory operations per cell period (SRAM+SDRAM)	Queuing Algorithms
  OC3	155 Mbps	888 Operations	WF2Q, SCFQ, LFVC, 3DQ, CORE
  OC12	622 Mbps	222 Operations	SCFQ, LFVC, 3DQ, CORE
  OC48	2.4 Gbps	56 Operations	3DQ, CORE

  FPX performance for implementation of per-flow, fair-queue algorithms

  As a reprogrammable logic device with cell storage, there are several applications that can be implemented using a FPX. A few applicatons that have been already been proposed by other groups requesting FPX modules are:
  • Traffic Shaping
  • QoS for IP Traffic
  • Active network congestion control
  • Many-to-many multicast
  • Video Queuing for Distance Learning
  • Wireless LAN to WUGS interconnect

  If you or your group is interested in receiving FPX modules for your research, please take a minute to complete the survey form below:

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  • FPX Interest Survey
    If you are interested in obtaiing FPX modules for your own research, please complete the survery below.

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  John W. Lockwood
  iPOINT Research Group