Description
Packet Loss Ratio (PLR) is a quantitative metric defined as (Number of Packets Lost) / (Number of Packets Sent), often expressed as a percentage or a value between 0 and 1. In 3GPP specifications, PLR is used both as a Key Performance Indicator (KPI) for network monitoring and as a parameter for defining Quality of Service (QoS) requirements. It is measured at various layers and interfaces: end-to-end for a service, over a specific bearer (e.g., an EPS bearer or QoS Flow), or across a particular network link (e.g., N3 interface in 5G). The loss can occur due to congestion, radio link errors, buffer overflows in network nodes, or handover failures.
From a technical measurement perspective, PLR is often calculated using sequence numbers in protocol headers. For example, in the RTP protocol used for voice and video, the receiver can analyze the sequence numbers of arriving packets to detect gaps and compute loss. In the 3GPP radio access network, lower layers like the Packet Data Convergence Protocol (PDCP) and Radio Link Control (RLC) have their own mechanisms to detect and report packet loss. The PDCP layer, responsible for header compression and integrity protection, maintains sequence numbering for user plane data. Counters for PDCP packet losses are defined for performance measurement (PM) in specifications like TS 38.314 (NR) and are reported to the management system. These measurements help isolate whether loss is occurring in the radio link versus the core network.
PLR is intrinsically linked to QoS management. In the 5G QoS model defined in TS 23.501, certain QoS Flow characteristics reference packet loss rate. For instance, a Guaranteed Flow Bit Rate (GFBR) QoS Flow for a Ultra-Reliable Low Latency Communication (URLLC) service will have a very stringent maximum allowed packet loss rate (e.g., 10^-5 or 10^-6). The network uses admission control and resource scheduling to try to meet this target. For multimedia services, 3GPP TS 26.114 defines performance objectives for IMS-based services, where PLR is a critical parameter for voice (VoLTE/VoNR) and video telephony. The network's transport layer, in conjunction with application-layer techniques like forward error correction (FEC) and retransmissions (e.g., RLC Acknowledged Mode for non-real-time data), works to keep the PLR within acceptable bounds for each service type.
Purpose & Motivation
PLR exists as a fundamental metric because packet loss directly and severely degrades the quality of experience (QoE) for digital services, especially real-time interactive ones. For voice over IP, even a small packet loss ratio (e.g., 1%) can cause audible clicks and gaps, while for video streaming, it leads to frozen frames or blocky artifacts. Quantifying this loss is the first step towards managing and mitigating it. Before standardized QoS metrics, network performance was assessed with vague terms; PLR provided an objective, measurable target for service level agreements (SLAs) and network optimization.
The motivation for its precise definition in 3GPP stems from the transition to all-IP networks in Release 5 and beyond, where traditional circuit-switched voice with its guaranteed delivery was replaced by packet-switched Voice over IP (VoIP). In packet networks, loss is inherent due to statistical multiplexing and best-effort routing. 3GPP needed to define acceptable loss thresholds for conversational services to ensure they remained viable over wireless IP networks. This led to the inclusion of PLR in QoS Class Identifier (QCI) characteristics in EPS and 5QI characteristics in 5G, allowing the network to treat traffic differently based on its loss sensitivity.
Historically, PLR addressed the limitation of not having a standardized way to correlate network performance with user-perceived quality. It enables several key network functions: 1) Performance Monitoring: Operators measure PLR to identify congested links or faulty equipment. 2) QoS Enforcement: The policy framework (PCRF/PCF) can use PLR measurements to trigger corrective actions. 3) Service Development: Application designers (e.g., for video conferencing) know the network's guaranteed PLR and can design appropriate error resilience (like FEC) around it. Thus, PLR is not just a measurement but a cornerstone for the entire QoS architecture in modern mobile networks.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (102 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, the specification introduced corrections and clarifications for the Packet Loss Ratio (PLR) function, specifically addressing the correction of packet loss measurements. This enhancement ensures that packet transport with QoS characteristics, such as bounds on loss and reliability, can be accurately measured and reported for a 5G QoS Flow.
- PS Data Off supporting non-IP data packet TS 23.501CR0680
- Corrections to RQoS logic when receiving DL packet with RQI TS 23.501CR0011
- Proposal of Specifying Packet Detection Rule TS 23.501CR0027
- Corrections and clarifications for the usage of Packet Filter Set TS 23.501CR0035
- Traffic mapping information that disallows UL packets TS 23.501CR0053
- Number of packet filters supported by UE TS 23.501CR0481
+ 8 more changes
In Release 16, the Packet Loss Rate (PLR) function was enhanced by introducing new use cases and definitions for packet loss measurement specifically over the N3 interface between the NG-RAN and the UPF. The release also updated existing Packet Loss Rate measurements and added related measurements for packet delay on the N3 and N9 interfaces, as well as for GTP packet delay within the UPF. Furthermore, it expanded the scope of performance monitoring by adding measurements for PDCP data volume in dual-connectivity scenarios and for end-user throughput.
- Add use case and definitions of PDCP data volume measurements TS 28.552CR0036
- Add measurements of PDCP data volume in DC-scenarios TS 28.552CR0046
- Add use case for PDCP end user throughput measurements TS 28.552CR0052
- Add PDCP data volume measurements for EE TS 28.552CR0055
- Add use case and definitions of packet loss measurement over N3 TS 28.552CR0074
- Add use case and definitions of packet delay measurement over N3 TS 28.552CR0075
+ 31 more changes
In Release 17, the Packet Loss Ratio (PLR) function was enhanced to include measurements for incoming and outgoing GTP data using TEID identifiers and to support PLMN granularity for packet delay measurements, including in split gNB deployment scenarios. Furthermore, the release introduced new and updated packet-based performance measurements and clarified the derivation of uplink packet filters from downlink encapsulated IPsec packets. These additions provided more granular monitoring and steering capabilities for packet flows across the 5G system.
- Packet Loss Rate measurements TS 23.501CR2587
- Add incoming and outgoing GTP data packet loss TEID TS 28.552CR0256
- Add PLMN granularity for packet delay measurements TS 28.552CR0285
- Add PLMN granularity for packet delay measurements in split gNB scenario TS 28.552CR0295
- Adding new packets based performance measurements TS 28.552CR0360
- Updating packets based performance measurements TS 28.552CR0361
+ 11 more changes
In Release 18, the Packet Loss Ratio (PLR) function was enhanced with the introduction of new measurements for the downlink packet loss rate on the Uu interface. This addition specifically targeted the monitoring of packet loss within the radio access network, complementing existing QoS monitoring parameters like packet delay budget. The release also expanded related QoS monitoring capabilities, including support for Packet Delay Variation (PDV) monitoring exposed to the Application Function (AF).
- PCF support of 5GS Packet Delay Variation monitoring based on QoS monitoring mechanism and exposed to AF TS 23.501CR3792
- Update about the Packet Delay Variation description and add PDV in QoS monitoring parameters TS 23.501CR4506
- New measurement DL PDCP buffered throughput per UE per DRB. TS 28.552CR0398
- Add measurements for DL packet loss rate on Uu TS 28.552CR0401
- Add Total number of UL PDCP SDU Packets for split gNB deployment scenario TS 28.552CR0451
- Rel-18 CR TS28.552 Add Total number of DL PDCP SDU Packets in gNB-CU-UP for split gNB deployment scenario TS 28.552CR0485
+ 15 more changes
In Release 19, the PLR (Packet Loss Ratio) function was enhanced with new measurement capabilities for the downlink packet loss on the Uu interface considering a delay threshold, as well as for network-initiated PLR specifically for ATSSS (Access Traffic Steering, Switch and Splitting). Furthermore, new filters for PDCP PDU and SDU data volume measurements were introduced to support RedCap (Reduced Capability) services.
- Adding the NAT information exposure and Packet Inspection functionality in the UPF NF profile TS 23.501CR5420
- Rel-19 CR 28.552 Add measurement for DL packet loss on Uu with delay threshold in RAN TS 28.552CR0555
- Rel-19 CR TS 28.552 Add PMF measurement of network-initiated PLR for ATSSS TS 28.552CR0605
- Rel-19 CR TS 28.552 Add new filter for PDCP PDU data volume measurements for RedCap service TS 28.552CR0709
- Rel-19 CR TS 28.552 Add new filter for PDCP SDU data volume measurements for RedCap service TS 28.552CR0724
- UPF Packet Inspection functionalities TS 29.244CR0881
+ 7 more changes
Explore further
Broader topics and technologies where PLR plays a role.
Defining Specifications
3GPP specifications that define or reference PLR, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 24.193 vj50 | ATSSS Procedures Specification | Rel-19 |
| TS 26.114 vj10 | IMS Multimedia Telephony Media Handling | Rel-19 |
| TR 26.904 vj00 | Future video capability requirements for streaming and MBMS | Rel-19 |
| TR 26.910 vj00 | MTSI enhancements for RAN delay budget reporting | Rel-19 |
| TR 26.922 vj00 | Video Telephony Robustness Improvements Study | Rel-19 |
| TR 26.926 vj00 | Traffic Models & Quality Evaluation for Media/XR in 5G | Rel-19 |
| TR 26.936 vj00 | Audio Codec Characterization Technical Report | Rel-19 |
| TR 26.959 vj00 | Enhanced VoLTE Performance Study | Rel-19 |
| TS 28.552 vk10 | 5G Performance Management Measurements | Rel-20 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | Rel-19 |