Description
Printable character Error Rate (PER) is a key performance indicator (KPI) defined in 3GPP specifications to quantify the reliability of character-oriented telecommunication services. It measures the accuracy of information transfer for services where the payload consists of printable characters from defined alphabets (e.g., GSM 7-bit default alphabet, UCS2). PER is defined as the ratio between the number of printable characters that are delivered erroneously to the destination and the total number of printable characters sent by the source, over a given observation period. An erroneous delivery includes characters that are substituted, deleted, or inserted compared to the original message.
The architecture for measuring PER involves the end-to-end service layer. The source application (e.g., an SMS Center) and the destination application (e.g., a receiving UE) are the logical points of measurement. The calculation considers the entire path, including core network transport, any interworking functions, and the radio access. Key components in the evaluation are the defined character sets and the rules for character mapping and counting. For instance, in SMS, a message containing national language shift tables or locking shift characters requires careful interpretation to count printable characters correctly. The measurement is typically conducted in a test environment or via network probes that can compare sent and received payloads.
How PER works as a metric is tied to service testing and benchmarking. Test equipment generates messages with known sequences of printable characters and sends them through the network under test. The receiving equipment compares the delivered characters to the original. Discrepancies are logged, and the PER is calculated. This process tests the robustness of the underlying transport protocols (e.g., MAP for SMS), encoding/decoding algorithms, and any transcoding that may occur between different network domains. A low PER indicates high fidelity in the text service, which is paramount for services where data integrity is critical, such as authentication codes (e.g., one-time passwords), financial alerts, or emergency notifications. PER is often measured under various network conditions, including marginal radio coverage, to ensure service robustness.
Purpose & Motivation
The Printable character Error Rate metric exists to provide a standardized, quantifiable measure of quality for non-voice, character-based services. As mobile networks evolved beyond voice to offer messaging services like SMS, it became necessary to move beyond simple success/failure metrics (like delivery reports) to understand the quality of the delivered content. A message could be delivered but corrupted, which is unacceptable for many applications.
PER solves the problem of undefined service quality for text. Prior to its standardization, operators and vendors lacked a common way to benchmark and compare the performance of messaging platforms. It was motivated by the need to ensure user trust in messaging services, especially as they began to be used for critical communications. A high PER would mean users receive garbled messages, leading to confusion, failed transactions, and poor customer satisfaction.
Its creation addresses the limitations of simpler metrics like Frame Error Rate (FER) or Bit Error Rate (BER), which measure lower-layer performance but do not directly translate to user-perceived quality at the application layer. PER is service-specific, focusing on the information meaningful to the end-user: the characters. It is particularly important for the evolution of messaging towards rich communication services (RCS), machine-to-machine (M2M) communication where commands must be exact, and interoperability between different networks and character sets. By defining PER, 3GPP provided a tool for network engineers to objectively assess, troubleshoot, and improve the reliability of a fundamental class of mobile services.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (46 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-2, normative work from Rel-15.
In Release 15, the PER (Printable character Error Rate) function was addressed as part of 5G QoS fixes for URLLC services alongside attributes like PDB and 5QI. The release formalized specific performance requirements for text conversation, mandating that the printable character error rate must be less than 1% for both stationary and mobile calls under nominal radio conditions. This ensured that real-time, character-by-character text transmission for services like Text Telephony (TTY) could meet the stringent reliability targets required for URLLC.
- Clean-up of Characteristics signalling TS 23.501CR0054
- Correcting the support of charging Characteristics TS 23.501CR0075
- 5G QoS fixes for URLLC services related attributes - PDB, PER, MDB, 5QI TS 23.501CR0087
- Emergency Services Support indication per RAT TS 23.501CR0170
- Handling of maximum supported data rate per UE for integrity protection TS 23.501CR0334
- Clarifications for signalled QoS characteristics TS 23.501CR0606
+ 1 more changes
In Release 16, the specification for the Printable character Error Rate (PER) function was formally defined with a quantitative performance target, stating it shall be less than 1% for both stationary calls and calls with pedestrian or typical vehicle speed under nominal radio conditions. This introduced a clear, measurable requirement for real-time text conversation quality in line with ITU-T T.140, complementing the existing throughput requirement of at least 10 characters per second.
- QoS parameters mapping between TSN characters and 5G QoS TS 23.501CR1003
- Extension of standardized 5QI to QoS characteristics mapping table to accommodate enhanced V2X requirements TS 23.501CR1735
- Corrections and alignments for the 5QI characteristics table TS 23.501CR1408
- Applying Per-Stream Filtering and Policing TS 23.501CR1981
- Correct errors in Port Management information table TS 23.501CR2009
- CN component of the PDB is configured per UL and DL TS 23.501CR2015
+ 5 more changes
In Release 17, the specific new feature for the Printable character Error Rate (PER) function was the introduction of support for per-slice QoE measurement. This enhancement allows the monitoring and reporting of the PER, a key performance metric for real-time text conversation requiring less than 1% error under nominal conditions, to be conducted on a per-network-slice basis. This provides more granular visibility into the text transmission quality experienced by users of specific network slices.
- PMF enhancements to support per QoS Flow measurements TS 23.501CR2583
- Decision to apply measurements per QoS Flow TS 23.501CR2720
- QoS Flow recognition for per QoS Flow measurements TS 23.501CR2746
- Introduction of support of GSMA NG.116 attributes Maximum DL/UL throughput per slice/UE TS 23.501CR2822
- Completion of NSAC per access type TS 23.501CR3201
- Handling of Session Management Policy Data per PLMN TS 29.513CR0294
+ 5 more changes
In Release 18, the key update for the Printable Character Error Rate (PER) function was its replacement by more granular, direction-specific metrics. Specifically, the PSER (Printable character Sequence Error Ratio) and PSDB (Printable character Sequence Delay Budget) superseded the PER and PDB (Packet Delay Budget) on a per-direction basis. This change allowed for more precise monitoring and provisioning of performance characteristics for real-time text conversation services.
- KI#3: provisioning of traffic characteristics and monitoring of performance characteristics TS 23.501CR4087
- Support of extra traffic characteristics for alternative QoS profile TS 23.501CR4183
- [FS_XRTraffic] Application Layer FEC Traffic characteristics TS 26.926CR0001
- PCF mapping of PER received in altSerReqsData TS 29.513CR0534
- Corrections to handling of LADN area per DNN and S-NSSAI TS 23.501CR4211
- Updates of functional description for LADN per DNN and S-NSSAI TS 23.501CR4970
+ 4 more changes
In Release 19, the changes to the Printable Character Error Rate (PER) function were not detailed in the provided CR titles or grounding context. The grounding context only reiterates the existing performance requirements, such as maintaining a PER of less than 1% under nominal conditions. Therefore, based solely on the given materials, no specific new feature or modification for PER in Release 19 can be described.
In Release 20, no changes to the Printable character Error Rate (PER) function are indicated by the provided Change Requests or the grounding specification text. The CRs focus on new exposure capabilities for energy consumption and application ranking, and subscriber MAC address management, which are unrelated to the PER performance requirements. The PER function itself, as described, maintains its existing performance objectives, such as being less than 1% under nominal conditions, as defined in prior releases.
Explore further
Broader topics and technologies where PER plays a role.
Defining Specifications
3GPP specifications that define or reference PER, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 22.226 vj00 | Global Text Telephony (GTT) Stage 1 | Rel-19 |
| TR 22.804 vg30 | 5G Automation in Vertical Domains Study | Rel-16 |
| 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 25.469 vj00 | HNBAP Specification for HNB to HNB-GW Interface | Rel-19 |
| TS 26.233 vf00 | 3GPP Packet-Switched Streaming Service (PSS) | Rel-15 |
| TS 26.247 vj00 | 3GPP Progressive Download & DASH over HTTP | Rel-19 |
| TS 26.881 vf00 | MBMS FEC for Mission Critical Services Study | Rel-15 |
| 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 |
| TR 26.957 vj00 | Evaluation of MPEG DASH SAND for 3GPP | Rel-19 |
| TS 28.403 vj00 | WLAN Performance Measurements | Rel-19 |
| TS 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 32.298 vj30 | Charging Data Record (CDR) Parameter Specification | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TR 38.835 vi01 | Technical Report on XR Enhancements for NR | Rel-18 |