Loopback Mode

 

The Loopback application in the main menu allows the user to establish a manual loopback on the test set. The loopback function is used when an end-to-end test needs to be performed with one of the test partners in software loopback mode. The loopback function will loopback the incoming traffic to the test set back into the network under test.

 

The type of traffic that the loopback function loops back will depend on the type of test layer configured (Layer 1, 2, 3, or 4). Additional criteria can be set to allow only messages with specific criteria to be looped back.

 

  • Layer 1: All incoming traffic to the Rx loopback interface will be sent out unaltered to the Tx loopback interface.

  • Layer 2, 3, & 4: In a Layer 2 or 3 loopback, all incoming test traffic will be looped back.

    • The loopback function will swap the MAC destination and MAC Source addresses (for Layer 2) or MAC and IP destination and source addresses (for Layer 3 and Layer 4).

    • All incoming frames with CRC errors will be dropped, similar to what an Ethernet switch does.

    • All broadcast and multicast frames will be dropped including any incoming unicast frames that have the MAC Source address equal to the MAC Destination address.

    • Loopback Parameters: The following parameters are available on Layer 2, 3 and 4. For more information on the parameters, please see BERT Header Settings in the BERT section. It is possible to enable any of these parameters to create a customer loopback filter. For example, enabling a filter with VLAN 64, Priority 7, will only loop back traffic corresponding to these values.

      • VLAN ID

      • VLAN Priority

      • MAC Source

      • MAC Destination

      • IP Source Address (Layer 3 & 4 only)

      • IP Destination (Layer 3 & 4 only)

      • Precedence (Layer 3 & 4 only)

      • TOS Value (Layer 3 & 4 only)

      • UDP SPort (Layer 4 only)

      • UDP DPort (Layer 4 only)

 

To enable/disable specific filter criteria, tap on Filter Settings under the General tab. Use the drop-down menus to make desired selections and tap Filter OK to enable/disable any filter changes.

 

Available loopback modes include the following:

  • Simple Loopback: Displays single stream loopback results. Configure the parameters under general to filter the stream for specific parameters.

  • Multi-stream Loopback: Displays loopback results for up to 8 streams. S1-S8 tabs represent individual streams. Tap on an S tab to filter the stream for specific parameters.

After setting up loopback criteria, tap Apply to apply settings.

 

Press Start to begin loopback. indicates that loopback is in progress. The Results tab displays current test results. Per Stream results are available for Multi-stream setup. Results for each stream can be viewed by selecting the stream from the Stream # drop-down. Please see BERT Results for information on the Results tabs.

 

Loopback Setup

 

Loopback Filter

 

Loopback Per Stream Summary Results