Paragon-neo: compliance with 802.3cx

Owned by Billy Marshall
Last updated: Sept 29, 2023
2 min read

Overview

IEEE 802.3cx improves the timing performance and timestamp accuracy of Ethernet interfaces, including considerations for the following aspects:

  • Data delay measurement point, DDMP (i.e. the message timestamping point)

  • Idle, Alignment Marker (AM), and Code Word Marker (CWM) insertion and removal

  • PCS lane distribution and merging

The following sections describe how Paragon-neo complies with 802.3cx and implements the above. All references to 802.3cx clauses relate to the current latest available draft, D3.2.

Data delay measurement point (message timestamp point)

802.3cx recommends that the beginning of the first symbol after the Start of Frame Delimiter (SFD) is used as the DDMP since this matches the measurement points specified in IEEE Standard 1588 and IEEE Std 802.1AS.  It also notes that using an alternative point - the beginning of the SFD – can negatively impact the accuracy that can be achieved by a time synchronisation protocol using the Time Synchronization Service Interface (TSSI).

Paragon-neo is designed to use the recommended point (i.e. the beginning of the first symbol after the SFD) as the timestamp point for PTP messages, therefore no changes were required for Paragon-neo to comply with the highest accuracy implementation recommended by 802.3cx.

Idle, Alignment Marker and Code Word Marker insertion/removal

Idles, AMs and CWMs, may be inserted or deleted by the Ethernet PHY, which affects the instantaneous data path delay.  802.3cx has recommendations for the correct operations, methods and timings for these processes.

Paragon-neo releases from 9.00.36 have been been tested against these requirements are fully compliant with no known issues. 

Neo software releases prior to the above may exhibit non-compliant intermittent AM/CWM removal timestamp compensation at the instrument receiver at the following rates: 100G FEC, 25G FEC, 50G and 40G, resulting in spurious time errors (dTE) of up to 12.8ns. Occurrences are very intermittent (intervals of up to several hours), are dependent upon PTP packet/marker coincidence - which may not happen, and are evident in measurements that the time errors cause an issue for. However, to guarantee DUT performance release 9.00.36 or greater is recommended.

PCS lane distribution/merging

802.3cx specifies using the PCS lane with the greatest delay as the egress delay and that there is no PCS lane-dependent timestamp adjustment.

Paragon-neo  is by design calibrated to use the egress delay on the lane with the greatest delay, therefore no changes were required to Paragon-neo to comply with 802.3cx.