Extra Service Data Unit Delivery Probability

Description

Extra SDU delivery probability is a quality of service (QoS) parameter that measures the proportion of service data units (SDUs) that are delivered to a destination user but were not requested. It is defined as the ratio of total (unrequested) extra SDUs to total SDUs received by a destination user in a specified sample, as per ITU-T Recommendation X.140. This metric is used to assess the accuracy and reliability of data delivery in packet-switched networks, particularly in the context of 3GPP specifications such as 3GPP TS 21.905 and TS 22.060.

In packet-switched networks, SDUs are the units of data exchanged between the network and the user. Ideally, the network should deliver exactly the SDUs that were requested, no more and no less. However, due to errors, duplication, or other anomalies, extra SDUs may be delivered. These extra SDUs can cause confusion, waste resources, and potentially lead to security issues. The Extra SDU delivery probability quantifies this phenomenon. A lower value indicates better performance, as it means fewer unrequested SDUs are delivered.

The metric is calculated over a specified sample, which could be a period of time or a number of SDUs. The ratio is expressed as a probability or percentage. For example, if 1000 SDUs are received and 10 of them are extra, the Extra SDU delivery probability is 1%. This metric is typically used in conjunction with other QoS parameters such as SDU error ratio, SDU loss ratio, and SDU duplication rate to provide a comprehensive view of network performance.

In 3GPP, this term is part of the vocabulary defined in TS 21.905, which provides abbreviations and definitions for 3GPP specifications. It is also referenced in TS 22.060, which specifies the QoS requirements for the General Packet Radio Service (GPRS). The term has been present since Release 4 and has been carried forward through subsequent releases without change. It is based on ITU-T X.140, which defines general quality of service parameters for digital networks.

The Extra SDU delivery probability is important for network operators and equipment vendors to ensure that their networks meet the required QoS levels. It helps in troubleshooting, performance monitoring, and optimization. By measuring this metric, operators can identify issues such as duplicate packet delivery, which may be caused by network misconfiguration or faulty equipment. It also helps in verifying that the network adheres to service level agreements (SLAs) and regulatory requirements.

Purpose & Motivation

The Extra SDU delivery probability exists to provide a standardized way to measure and quantify the occurrence of unrequested data units in packet-switched networks. Before its definition, there was no common metric to assess this aspect of QoS, leading to inconsistent evaluations and difficulty in comparing network performance. The term was derived from ITU-T X.140, which aimed to standardize QoS parameters for digital networks, including packet-switched services. 3GPP adopted this metric to ensure that its networks could be evaluated against internationally recognized standards.

It solves the problem of detecting and quantifying duplicate or unsolicited data delivery, which can degrade user experience and waste network resources. In applications such as voice over IP or video streaming, extra SDUs can cause glitches, increase latency, and consume bandwidth. By defining a clear metric, operators can set thresholds and take corrective actions. It also enables vendors to design equipment that minimizes extra SDU delivery, improving overall network efficiency.

Furthermore, the metric supports interoperability and benchmarking across different networks and vendors. It allows operators to compare performance and ensure that they meet the QoS expectations of their customers. As networks evolve towards 5G and beyond, the need for accurate QoS metrics remains, and the Extra SDU delivery probability continues to be a relevant parameter in the 3GPP vocabulary.