Survival Time

Description

Survival time is a Quality of Service (QoS) parameter defined by 3GPP as the time that an application consuming a communication service may continue without an anticipated message. It is a critical concept for time-sensitive networking (TSN) and industrial automation applications, where the loss of a single message can disrupt a production process. Survival time specifies the maximum duration for which the application can tolerate the absence of an expected message before it considers the communication service to have failed.

In 3GPP systems, survival time is used in conjunction with other QoS parameters such as latency, reliability, and jitter to characterize the performance requirements of a communication service. It is particularly relevant for periodic traffic patterns, where messages are expected at regular intervals. If a message does not arrive within the expected time window plus the survival time, the application may take corrective action, such as stopping a production line or triggering a fail-safe mechanism. The survival time thus defines the grace period for recovering from a transient communication failure.

The concept was introduced in Release 15 as part of the 5G QoS framework, which was designed to support ultra-reliable low-latency communication (URLLC) and industrial IoT use cases. Survival time is specified in 3GPP specifications such as 22.104 (Service requirements for cyber-physical control applications in vertical domains), 22.261 (Service requirements for the 5G system), and 23.501 (System architecture for the 5G system). These specifications define how survival time is used in QoS profiles and how the network should ensure that the required survival time is met.

From an implementation perspective, the network must ensure that the communication service meets the survival time requirement. This involves monitoring the packet delay and packet loss and taking actions such as packet duplication, retransmission, or path redundancy to maintain the service. The survival time is typically expressed in milliseconds or seconds and is part of the QoS characteristics associated with a 5G QoS Identifier (5QI). The network uses this parameter to allocate resources and prioritize traffic accordingly.

Survival time is closely related to the concept of "time-to-failure" in industrial systems. It allows the network to provide deterministic communication with bounded latency and reliability, which is essential for applications like motion control, discrete manufacturing, and smart grid. By defining survival time, 3GPP enables the integration of 5G with TSN and other industrial Ethernet standards, facilitating the convergence of IT and OT networks.

Purpose & Motivation

Survival time was introduced to address the needs of time-sensitive applications in industrial and cyber-physical systems. Traditional mobile networks were designed for best-effort or enhanced mobile broadband services, where occasional packet loss or delay is acceptable. However, industrial applications such as factory automation, power distribution, and motion control require deterministic communication with very low latency and high reliability. In these scenarios, the loss of a single message can cause a production stoppage or safety hazard. Survival time provides a quantitative measure of how long an application can tolerate the absence of a message, enabling the network to prioritize and protect critical traffic.

The concept solves the problem of transient communication failures in wireless networks. Unlike wired networks, wireless links are subject to interference, fading, and handover interruptions. Survival time allows the application to continue operating during short disruptions, as long as the network can recover within the specified time. This is achieved through mechanisms such as redundant transmission, multi-connectivity, and QoS flow management. By defining survival time, 3GPP provides a framework for ensuring that 5G networks can meet the stringent requirements of industrial use cases.

Historically, survival time emerged in Release 15 as part of the 5G QoS model, which was designed to support diverse services with different performance requirements. It was motivated by the need to integrate 5G with TSN and other industrial networks, where similar concepts like "max allowable interruption" exist. The term has evolved across releases, with refinements in specifications and additional use cases, but the core definition has remained consistent.