Enabling Forward Error Correction

The Forward Error Correction (FEC) functionality reduces the loss of traffic packets in links, especially for UDP applications, and the number of retransmissions, which lead to delays, and also recovers received data on the CPE device. Data recovery is provided by redundant encoding of the data stream on the device on the source CPE device.

If FEC is enabled on a link, the source CPE device encodes the traffic packet stream transmitted through the link and adds redundant traffic packets. Encoding on CPE devices may cause delays due to extra data processing.

The destination CPE device buffers traffic packets received through the link and decodes them, recovering lost traffic packets, if possible. We recommend using FEC on noisy links to reduce the packet loss and increase the speed of TCP connections. The general diagram of FEC is shown in the figure below.

The diagram shows the data stream on a sender CPE device to which extra packets with redundant code are added. This code is used to recover lost data on the receiving CPE device.

FEC diagram

To enable FEC:

  1. Enable FEC in one of the following ways:
    • If you want to enable FEC for a link that was established from a CPE device, go to the SD-WAN → CPE section, click the CPE device, select the Links tab, and click Management → FEC/reordering next to the link.
    • If you want to enable FEC for one of the links in the table of all links, go to the Infrastructure section, click Management → Configuration menu next to the controller, go to the Links section, and click Management → FEC/reordering next to the link.
    • If you want to enable FEC for one of the links in the graphic topology with all links, go to the Infrastructure section, click Management → Configuration menu next to the controller, go to the Topology section, click the link, and click FEC/reordering.
  2. This opens a window; in that window, select the Override check box to enable FEC on the link. This check box is cleared by default.
  3. In the Redundancy ratio (original/redundant packet) drop-down list, select the ratio of original traffic packets to extra traffic packets with redundant code. Default value: 0:0 (FEC off) means FEC is not used. You can also specify the ratio of original traffic packets to redundant traffic packets by using the topology.link.fec.ratio controller property.
  4. In the Timeout field, enter the time, in milliseconds, during which a traffic packet can stay in the queue for FEC to apply. Range of values: 1 to 1000.
  5. Click Save.

    FEC is enabled.

  6. If you enabled FEC for a link established from the CPE device, click Save in the upper part of the settings area to save the CPE device settings.
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