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XRA-31 3.1 Changelog
Posted by Dieter Dobbelaere, Last modified by Dieter Dobbelaere on 10 February 2021 10:05 AM

Welcome 

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

The system now supports the use of a downstream SC-QAM channel as reference.
This makes it possible to capture upstream traffic (both A-TDMA and OFDMA) in absence of an OFDM channel, extending the debugging capabilities of  the XRA-31 to an even wider range of DOCSIS 3.0/3.1 setups. 

Moreover, the new "rolling file capture" functionality allows you to capture continuously to a ring buffer of files (without being limited by disk capacity).
This makes it possible to analyze rare events effectively. 

Furthermore this release has several new improvements and bug fixes. 

Check out the details below. 

Features 

  • New since 3.1! 

    • Reference Downstream SC-QAM 

      • Select a downstream SC-QAM channel as timing reference and source for upstream demodulation 
      • Fully flexible 
        • Choose any configured SC-QAM channel as reference 
        • Both OFDMA/A-TDMA supported 
        • Can be combined with other OFDM channels 

    • Rolling File Capture 

      • Capture to a ring buffer of files 
      • File stop criterion based on duration or size 

  • OFDM

    • Real-time demodulation and decoding 
    • Full line rate (up to approx. 2 Gbps per channel)
    • 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 

  • OFDMA

    • Real-time demodulation and decoding 
    • Full line rate (up to approx. 1 Gbps per channel)
    • 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 (up to approx. 1.2 Gbps combined) 
    • 24 independent channels supported 
    • 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 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)

  • A-TDMA 

    • Real-time demodulation and decoding 
    • Full line rate (up to approx. 240 Mbps combined) 
    • 8 independent channels supported 
    • 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

References 

  • [CM-SP-PHYv3.0]      DOCSIS 3.0 Physical Layer Specification (version I13 or later; http://www.cablelabs.com/specs/) 
  • [CM-SP-PHYv3.1]      DOCSIS 3.1 Physical Layer Specification (version I13 or later; http://www.cablelabs.com/specs/) 
  • [CM-SP-MULPIv3.1]   DOCSIS 3.1 MAC and Upper Layer Protocols Interface Specification (version I14 or later; 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

Firmware

  • OFDM

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

  • OFDMA

    • Limited to one supported channel receiver
    • Unsupported pilot patterns: 5-7, 12-14
    • No probing sequences
    • No data MER statistics

  • SC-QAM

    • Limited to 24 supported channel receivers

  • A-TDMA

    • Limited to 8 supported channel receivers
    • 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

Analysis

  • Captured packets are not ordered by timestamp

Changelog 3.1-1600 (2019-11-05) 

Improvements  

  • WebAdmin (GUI)

    • Improved capture and channel status reporting in status panel.
    • The configure page now stays in edit mode after an authentication failure. 
    • The capture page is now also continuously updated in read-only mode. 
    • Consistently use 1024 (instead of 1000) for all byte-related calculations and reported file sizes and capture rates, in line with the convention used in most operating systems.

Bugfixes 

  • Firmware

    • Fixed critical bug in embedded software that prevented downstream SC-QAM annex B channels from locking under certain circumstances.

  • Systems and services 

    • Fixed critical bug in OFDM codeword stream processor that resulted in daemon crash. 
    • Reject full access mode request if firmware feature level is unsupported. 
    • Fixed several race conditions. 

  • WebAdmin (GUI) 

    • Copy-down modulation button for downstream SC-QAM configuration now properly copies the value to the rows below (and not to all rows). 
    • Fixed incorrect display of capture start/stop button in some conditions.

Known Issues

  • Firmware

    • General
      • After a system (re)boot, e.g. as part of a system update, it's possible that the inter-FPGA serial links are stuck in a non-operational state. This is signaled in the GUI by error messages on connector US-1. We have taken several measures to improve resilience against this behavior, but are still working on a more pertinent solution. In the meantime, please reset the system via the GUI system page until the serial links are fully operational.
    • OFDM
      • The first channel locking step after a system reset or a CMTS change can take considerably longer than subsequent locking steps. This is because internal frequency offset has to be reliably estimated (after which it is cached).

        This effect is considerable on small-bandwidth OFDM channels. Depending on PLC frequency and FFT size, initial locking of a 24 MHz channel (the minimum allowed per [CM-SP-PHYv3.1]) can take up to 10 minutes. Subsequent re-locking steps, even on different channels, should be on the order of seconds. A workaround is to first 'pre-lock' the XRA-31 on a dummy 192 MHz channel (which should take no longer than 1 minute), remove this channel and re-add the 24 MHz channel.

  • System and services

    • The system accepts file names longer than 255 characters and starts capturing, but storing the file fails in this case.
    • 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.

  • WebAdmin (GUI)

    • Once a support archive is created, the UI framework sometimes start creating multiple archives in a loop. Other system tasks (for example system reset) might take a long time until they are performed.
      As a workaround the user can use the power button on the system to restart the system. Press once shortly to start shutting down the system properly. Once shut down, press the power button again to start the system again.
    • Layout on small displays can be improved.
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