Description
The Packet Delay Budget (PDB) is a fundamental Quality of Service (QoS) parameter in the 5G System (5GS), defined in 3GPP TS 23.501. It specifies the maximum allowable end-to-end packet delay for a QoS Flow, measured from the UE to the User Plane Function (UPF) that terminates the N6 interface (towards the Data Network), or vice-versa. The PDB is not a guaranteed delay but a target used by the network's packet scheduling and resource management functions. It is intrinsically linked to a standardized 5G QoS Identifier (5QI), where each 5QI value has a default PDB (and Packet Error Rate) assigned, as per Annex A of TS 23.501.
Operationally, the PDB influences decisions across the RAN and core network. In the Radio Access Network (RAN), the gNB uses the PDB for uplink and downlink scheduling. For example, packets belonging to a QoS Flow with a tight PDB (e.g., 10 ms for URLLC) are prioritized over those with a lax PDB (e.g., 300 ms for buffered streaming). The PDB helps determine scheduling priorities, Hybrid ARQ (HARQ) configurations, and potentially the selection of numerology and slot format. In the core network, the Session Management Function (SMF) may use the PDB during QoS Flow establishment and for policy control interactions with the PCF.
The parameter works in conjunction with other QoS attributes like Guaranteed Flow Bit Rate (GFBR), Maximum Flow Bit Rate (MFBR), and Averaging Window. The network aims to ensure that the 95th percentile of the packet delay distribution does not exceed the PDB for the QoS Flow. For Non-GBR QoS Flows, the PDB indicates a packet delay tolerance used for scheduling. The PDB is a critical enabler for service differentiation, allowing the network to simultaneously support diverse applications from massive IoT to ultra-reliable low-latency communications (URLLC) on a common infrastructure.
Purpose & Motivation
The PDB was introduced to provide a standardized, quantifiable latency target for QoS management in 5G, addressing the need for predictable performance for latency-critical applications. Previous generations (4G LTE) had QoS Class Identifiers (QCIs) with implied performance targets, but 5G's expanded use cases—particularly Industrial IoT, autonomous vehicles, and real-time gaming—required more explicit and stringent delay parameters for reliable network behavior.
It solves the problem of inefficient or unpredictable latency handling for mixed traffic types. By assigning a concrete PDB value to each standardized 5QI, network equipment from different vendors can implement consistent scheduling and admission control algorithms. This ensures interoperability and allows application developers and vertical industries to rely on specific network performance levels. The PDB is a cornerstone of 5G's network slicing capability, as different slices can be configured with different latency budgets to serve distinct service level agreements (SLAs).
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (101 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-14, normative work from Rel-15.
In Release 15, the PDB (Packet Delay Budget) function was clarified for dynamically assigned 5QIs and its role in supporting URLLC services was enhanced alongside related attributes like PER. The specifications were refined to define PDB as an upper bound for packet delay between the UE and the UPF, used to configure scheduling and link layer functions in 3GPP access. Additionally, clarifications were provided for the support of the Delay Critical resource type and the handling of traffic mapping for URLLC.
- Delay budget report and MAC CE adaptation for NR for TS 38.300 TS 38.300CR0042
- 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
+ 7 more changes
In Release 16, the PDB (Packet Delay Budget) function was enhanced to support URLLC services through the introduction of End-to-End PDB division and QoS monitoring. This allowed for accumulated packet delay estimation to optimize reliability and manage the division of the PDB budget between network components. Furthermore, clarifications were added regarding the configuration of the CN (Core Network) PDB per UL and DL direction and its association with redundant PDU sessions for URLLC traffic.
- New clause for URLLC supporting TS 23.501CR0810
- Introduction of E2E PDB Division TS 23.501CR0989
- Introduction of QoS Monitoring to assist URLLC Service TS 23.501CR0990
- New Solution for Key Issue #7-URLLC Always on Control for the GBR QoS Flow TS 23.725CR0015
- Accumulated packet delay estimation for QoS monitoring and division of PDB TS 23.725CR0028
- Update description for E2E PDB division TS 23.501CR1142
+ 30 more changes
In Release 17, enhancements for the Packet Delay Budget (PDB) function included the introduction of a specific PDB value for the standardized 5QI 10 and clarifications for the Supported Analytics Delay mechanism. The release also provided corrections and clarifications for procedures related to PDB, such as residence time calculation for delay measurements and bridge delay calculation for integration with Time-Sensitive Networking (TSN). Furthermore, it defined the usage of packet size for PDB and incorporated redundant transmission experience analytics to support Ultra-Reliable Low-Latency Communication (URLLC) services.
- Enchantments for supporting Supported Analytics Delay mechanism TS 23.501CR2530
- Adding the usage of Redundant Transmission Experience analytics for URLLC service TS 23.501CR2581
- Packet Loss Rate measurements TS 23.501CR2587
- Introduction of Rel-17 IIoT/URLLC to TS 38.300 TS 38.300CR0416
- Introduction of enhanced IIoT&URLLC support for NR TS 38.321CR1200
- PDB value for 5QI 10 TS 23.501CR3029
+ 14 more changes
In Release 18, enhancements to the Packet Delay Budget (PDB) function included clarifying its handling for Non-3GPP access and PIN scenarios, and introducing the relaxation of 5QI delay requirements for first packets in RRC-INACTIVE mode. The release also formally introduced Packet Delay Variation (PDV) as a QoS monitoring parameter alongside the PDB. Furthermore, the concept of "Timing Resiliency" was introduced as part of broader URLLC enhancements related to delay budget management.
- PCF support of 5GS Packet Delay Variation monitoring based on QoS monitoring mechanism and exposed to AF TS 23.501CR3792
- Non-3GPP QoS and delay budget - 23.501 TS 23.501CR3912
- Update about the Packet Delay Variation description and add PDV in QoS monitoring parameters TS 23.501CR4506
- Packet delay variation monitoring enhancement TS 29.513CR0476
- Handling of Packet Delay Budget for PIN scenarios TS 29.513CR0490
- Introduction of Timing Resiliency and URLLC enhancements TS 38.300CR0730
+ 17 more changes
In Release 19, enhancements to the Packet Delay Budget (PDB) function focused on enabling N6 delay measurement and consideration, with new support for the SMF to trigger N6 delay measurements and for UPF selection to consider N6 delay. These improvements, along with clarifications on measurement protocols and security parameters, allow the system to more accurately account for the delay between the UE and the UPF terminating the N6 interface within the edge-to-edge PDB.
- Adding the NAT information exposure and Packet Inspection functionality in the UPF NF profile TS 23.501CR5420
- Support of L-PSA UPF Selection Considering N6 Delay TS 23.501CR5437
- AF request and functionalities enhancement to support N6 delay measurement TS 23.501CR5443
- KI#4: Correct the RTCP 'MID' for IP packet filter set TS 23.501CR5958
- N6 delay measurement triggered by SMF TS 23.501CR6024
- N6 delay measurement for I-SMF case TS 23.501CR6025
+ 3 more changes
Explore further
Broader topics and technologies where PDB plays a role.
Defining Specifications
3GPP specifications that define or reference PDB, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 22.832 vh40 | Study on cyber-physical control in vertical domains | Rel-17 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.725 vg20 | Study on URLLC Architecture Enhancements | Rel-16 |
| TR 23.737 vh20 | Satellite Access in 5G Architecture Study | Rel-17 |
| TR 23.780 ve00 | MBMS for Mission Critical Communication Services | Rel-14 |
| TS 24.385 vj00 | V2X Communication Provisioning Management Object | Rel-19 |
| TS 24.386 vj00 | V2X Communication Protocols and Procedures | Rel-19 |
| TR 26.926 vj00 | Traffic Models & Quality Evaluation for Media/XR in 5G | Rel-19 |
| TR 26.928 vj00 | Study on eXtended Reality (XR) in 5G | Rel-19 |
| TS 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |
| TR 38.835 vi01 | Technical Report on XR Enhancements for NR | Rel-18 |
| TR 38.838 vh00 | Study on XR Evaluations for NR | Rel-17 |