{
  "id": 16811454,
  "title": "Two retransmissions, zero losses: RLC-NR acknowledged mode in a real 5G capture",
  "url": "https://urgent.news/2026/10/27/two-retransmissions-zero-losses-rlc-nr-acknowledged-mode-in-a-real-5g",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-10-27T22:54:08.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/eventhelix/two-retransmissions-zero-losses-rlc-nr-acknowledged-mode-in-a-real-5g-capture-4j5i"
  },
  "original_language": "en",
  "account": "A recent capture of a real 5G NR attach process reveals that the RLC (Radio Link Control) mode operated in an acknowledged manner, sending the same packet twice on two separate occasions. Remarkably, no status report in the trace identified any missing packets during this transmission. The analysis follows the RLC acknowledged mode on both bearers, the signaling bearer and the data bearer, providing a comprehensive explanation for this behavior.\n\nThe captured NEA2-ciphered link demonstrates that RLC remains readable, as ciphering is handled by the PDCP (Packet Data Convergence Protocol) function. While sequence numbers, segmentation fields, and poll bits are visible on every frame, the payload remains encrypted. Sequence numbers count data units (SDUs), not transmissions, so one segment of a capability report contains one sequence number and occupies one line in the status report.\n\nThe poll bit aligns with the buffer, not a clock, and signaling polls occur on nearly every PDU. In contrast, the data bearer polls only at the end of a burst. After processing, both retransmissions are driven by timers. Two polls were unanswered, as their connections closed, and each resend occurred 44.9 milliseconds later. This interval aligns with the default t-PollRetransmit value specified in TS 38.331, which is not adjustable within the trace.\n\nThe walkthrough covers the end-to-end process of both bearers, including segmentation, cumulative acknowledgment, and the diagnostic habit imparted by these retransmissions. For a full breakdown, please refer to the walkthrough available at https://www.eventhelix.com/5G/nr-attach-air-interface/rlc-nr-acknowledged-mode/.",
  "summary": "A real 5G NR attach capture shows the radio link sending the same RLC packet twice, on two separate occasions. Not one status report in the trace names a missing packet. The full walkthrough follows RLC acknowledged mode on both bearers, the signaling bearer and the data bearer, and explains why. What the capture shows RLC stays readable on a ciphered link. The capture is NEA2-ciphered, but…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}