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A quick intro test: Configure - Ping CM - Capture - Observe ICMP in .pcap
Posted by Tom Ghyselinck, Last modified by Tom Ghyselinck on 12 June 2019 04:01 PM

Let's do a quick introduction capture to get to know the XRA-31 system.

We want to configure the XRA-31 system and lock on a network with a CM online using OFDM and OFDMA. Next we will send and capture some PING to this CM, and observe these ICMP echo frames in a .pcap.

First you will need to setup your XRA-31 and make it accessible via IP (how?). Using the XRA-31 system 'standalone' will  work as well, but then you will need to connect keyboard/mouse/VGA.

Use your favorite browser to access the XRA-31 web based GUI.

  • http://address-of-the-xra-31

The XRA-31 allows simultaneous multi-user web sessions to exist, however only one user can edit/change parameters - all the others will get a warning if they try to change operational parameters. If you are not the current owner, or if it's the first time you access the system, you will need to take ownership over the system. Taking ownership is done by clicking the pencil icon found in the lower left corner as depicted below.

Next step is to add the downstream OFDM channel.

  • Add OFDM channel
  • Configure OFDM channel
    • Which parameters should you use? 
    • If you have SNMP access on the CM, walk the docsIf31CmDsOfdmChanTable to find the PLC, RP and CP values needed.
      • Note that CM and CMTS CLI use a different reference point when it comes to the PLC frequency. In our example case, we had to substract 2.8 MHz to find the PLC frequency needed in the XRA-31 interface. The PLC reference for the XRA-31 is the start of the 6 MHz region, always on a 1 MHz grid.
  • Wait for OFDM channel to obtain lock

At this stage, your Status Bar should look like this:

Next on the agenda is to add/select the upstream OFDMA channel. Since all upstream channels are described on the (primary) downstream channel, the XRA-31 can learn the list of OFDMA channels using the locked OFDM channel.

  • Simply select and confirm your OFDMA channel form the dropdown list.
  • Wait for the channel to be locked in the Status Bar


By now your Status Bar should look something like the example below.

You can click the to find out why the power level is indicated in red.

The animation below makes a summary of the previous steps and adds a typical capture procedure.

  • Match channel parameters with CM MIB parameters
  • Switch to Capture Panel and select the streams
    • Internally the XRA-31 is demodulating in realtime, always on, always locked
    • Many internal streams are generated during the demodulation process, depending on your interest, add your stream
  • Configure the output filename and stop condition
  • Start a ping on the CM
  • Capture START
    • Observe the Status Bar to provide feedback in realtime on the capture progress
  • Capture STOP
  • Switch to Analyze Panel
  • Identify and download the .pcap file
  • Open the .pcap file using Wireshark
    • The XRA-31 stores detailed low-level RF and DOCSIS information in the Excentis defined XRA header.
    • The XRA header has been accepted for the 2.6 Wireshark release, or you can download this version.
  • Observe downstream OFDM and upstream OFDMA frames, including additional XRA header details.

Well done, you have earned your first XRA-31 badge!

In case you need additional help, do not forget to use the  buttons in the GUI, they provide access to the detailed context specific help.

Let us know if you find something is missing!

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