XRA-31 5.1 Changelog
Posted by Dieter Dobbelaere, Last modified by Dieter Dobbelaere on 08 November 2021 01:23 PM


We are very excited to announce this release of the XRA-31 system!

To ease analysis, this version performs real-time resequencing of captured packets (obviating the need for post-reordering steps). In addition, all core software components (Debian GNU/Linux, Wireshark) are upgraded to their latest stable upstream versions.

This release also brings several improvements and bug fixes.

New since 5.1!

Captured packets are now ordered by timestamp.

Changelog 5.1-1652 (2021-02-15) 


  • [System] Upgraded operating system to Debian 10 (buster).
  • [System] More helpful welcome message of SSH console and login shell.
  • [System] Increased overall system robustness by throttling internal logging.
  • [System] Clarified software licenses and added XRA-31 EULA.
  • [GUI] Added licensing information to help page.
  • [GUI] Improved accessibility for visually impaired users.
  • [Wireshark] Upgraded on-system Wireshark version to v3.4.2.
  • [Firmware] Improved OFDM channel recovery after loss of PLC lock.


  • [System] Fixed rare bug in timestamp calculation due to imprecise conversions.
  • [System] Fixed bogus downstream SC-QAM packet timestamps if reference channel is not locked yet (or is not primary capable).
  • [System] Fixed missing codeword info metadata for large US DOCSIS (annex B) downstream SC-QAM MAC frames (up to 2030 bytes).
  • [System] Fixed issue where highly-loaded upstream channels fail to relock after a reference SC-QAM loss-of-lock event.
  • [System] Fixed possible memory corruption during A-TDMA locking.
  • [Wireshark] The absolute timestamp of an upstream MAC frame for segment-header-on service flows is now defined as the timestamp of the last upstream segment needed for reassembly (inverse concatenation and fragmentation).
  • [Wireshark] Removed redundant "Reed-Solomon decoding successful" and "LDPC decoding successful" XRA header metadata for SC-QAM packets and OFDMA initial fine/ranging bursts, as uncorrectable packets are never captured to disk anyway.



  • Real-time demodulation and decoding 
  • Full line rate
  • All FFT sizes, cyclic prefixes and roll-off periods defined by [CM-SP-PHYv3.1] 
  • Data demodulation and decoding 
    • All interleaver settings defined by [CM-SP-PHYv3.1] 
    • All modulations from zero-bit-loading up to 4096-QAM defined by [CM-SP-PHYv3.1] 
    • All possible configurations of exclusion bands defined by [CM-SP-PHYv3.1] 
    • Multiple concurrent data profiles (from A up to P) 
    • Mixed-modulation profiles 
    • Dynamic data profile changes 
    • Timestamp precision of DOCSIS frames is equal to one OFDM symbol (between 21 and 45 microseconds depending on FFT size and cyclic prefix) 
  • PLC and NCP demodulation and decoding 
    • Including MER statistics 
    • Timestamp precision is on the order of a few nanoseconds 


  • Real-time demodulation and decoding 
  • Full line rate
  • All FFT sizes, cyclic prefixes and roll-off periods defined by [CM-SP-PHYv3.1] 
  • Dynamic UCD changes (including data profile IUC changes) 
  • Data demodulation and decoding 
    • All interleaver settings defined by [CM-SP-PHYv3.1] 
    • All modulations from zero-valued up to 4096-QAM defined by [CM-SP-PHYv3.1] 
    • All possible configurations of exclusion bands and unused sub-carriers defined by [CM-SP-PHYv3.1] 
    • All data profile IUCs defined by [CM-SP-MULPIv3.1] concurrently 
    • Supported pilot patterns: 1-4, 8-11 
    • Timestamp precision of DOCSIS frames is equal to one OFDMA frame (between 126 and 1665 microseconds depending on OFDMA frame size, cyclic prefix and FFT size) 
  • Real-time full line rate bandwidth request (REQ) message demodulation and decoding 
    • Timestamp precision is on the order of a few nanoseconds 
  • Initial Ranging and Fine Ranging demodulation and decoding 
    • Including MER statistics and time offset estimations 
    • Timestamp precision is on the order of a few nanoseconds

Downstream SC-QAM 

  • Real-time demodulation and decoding 
  • Full line rate
  • Hardware timestamping of packets using reference channel clock (nanosecond resolution) 
  • 64/256-QAM, independently configurable per channel 
  • Dynamically configurable annex 
    • Annex A (EuroDOCSIS)  
    • Annex B (US DOCSIS)  
      • All interleaving parameters (control words) defined in [ITU-T Rec. J.83] supported 
      • Viterbi decoding for increased reliability. 
  • Extended downstream frequency range support 
    • Channel frequencies can be any multiple of 62.5 kHz between 108 and 1006 MHz, complying with all CM requirements in [CM-SP-PHYv3.1]. 
  • Two independent 248 MHz wide receive modules 
    • All channel frequency configurations that can be grouped evenly into the two receive module bands are valid, e.g. a channel configuration consisting of three channels at 200 MHz, 440 MHz and 1000 MHz is valid, but a configuration with frequencies 200 MHz, 600 MHz and 1000 MHz is not. 
  • Data MER and Reed-Solomon decoder statistics 
  • Timestamp precision of DOCSIS frames is equal to one MPEG frame (between 29 and 56 microseconds depending on annex and modulation)


  • Real-time demodulation and decoding 
  • Full line rate
  • Full A-TDMA UCD type 29 and 35 support (with the sole exceptions of differential encoding, zero-length preambles and IUC 2 Request_2 demodulation). 
    • All channel bandwidths (from 200 kHz to 6.4 MHz) defined in [CM-SP-PHYv3.0] 
    • All upstream center frequencies allowed by [CM-SP-PHYv3.0] 
    • All modulation types (from QPSK to 64-QAM) defined in [CM-SP-PHYv3.0] 
    • All preamble patterns, types (QPSK0/QSPK1) and lengths from 2 to 1536 bits defined in [CM-SP-PHYv3.0] (Hence, the minimum allowed preamble length is one QPSK symbol) 
    • Scrambler on/off 
    • Fixed/shortened last codeword 
    • All interleaving parameters allowed by [CM-SP-PHYv3.0] 
    • All Reed-Solomon FEC parameters allowed by [CM-SP-PHYv3.0] 
    • Supported IUCs: 1 (Request), 3 (Initial Maintenance), 4 (Station Maintenance), 5 (Short Data Grant), 6 (Long Data Grant), 9 (Advanced PHY Short Data Grant), 10 (Long PHY Short Data Grant), 11 (Advanced PHY Unsollicited Grant) 
    • Dynamic UCD changes 
  • Detailed statistics per demodulated burst 
    • Data MER 
    • Time offset 
    • Reed-Solomon decoder statistics 
    • Start minislot ID


  • [CM-SP-PHYv3.0] DOCSIS® 3.0 Physical Layer Specification (December 2017, http://www.cablelabs.com/specs/) 
  • [CM-SP-PHYv3.1] DOCSIS® 3.1 Physical Layer Specification (September 2019, http://www.cablelabs.com/specs/) 
  • [CM-SP-MULPIv3.1] DOCSIS® 3.1 MAC and Upper Layer Protocols Interface Specification (September 2019, http://www.cablelabs.com/specs/) 
  • [ITU-T Rec J.83] ITU-T J.83: Digital multi-programme systems for television, sound and data services for cable distribution  (December 2007, Telecommunication Standardization Sector of ITU)

Known limitations


  • OFDM

    • Possible temporary data loss during dynamic NCP updates
    • Zero-bit-loading of NCP subcarriers not supported
    • No data MER statistics

    • Unsupported pilot patterns: 5-7, 12-14
    • No probing sequences
    • No data MER statistics
  • A-TDMA

    • UCD type 2 (DOCSIS 1.x PHY channel and mixed DOCSIS 1.x/2.0 TDMA PHY channel) channels not supported
    • Differential encoding not supported
    • Zero preamble length not supported
    • IUC 2 (Request_2) not supported

Environment and system tools

  • xra31-admin: It is not possible to follow the system/service logs

Known Issues


  • The first channel locking attempt of an OFDM or downstream SC-QAM channel after a system reset or a CMTS change can take considerably longer than subsequent locking attempts. This is because internal frequency offset has to be reliably estimated (after which it is cached).

System and services

  • The reported upstream channel MER is the average over all fine ranging requests (for OFDMA) or all data bursts excluding initial ranging requests and bandwidth requests (for A-TDMA) over an elapsed interval of at most 30s. As such, it is possible that N/A (not available) is shown on low-load channels with T4 timeout multiplier higher than 1.
  • Captured Wireshark traces might contain invalid (malformed) packets corresponding to collisions (or possible RF interference) on A-TDMA IUC 1 (bandwidth request) grants. In a future release we plan to filter out these spurious bursts.
  • Inverse upstream Concatenation and Fragmentation (ICCF) of "segment header on" service flows is now performed for each channel independently. Hence, for CMs in MTCM (multi transmit channel mode), MAC frames that are fragmented over multiple upstream channels are not detected and consequently absent in the Wireshark trace. A future release will support ICCF over multiple channels.
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