The key performance requirements for cyber-physical control applications in vertical domains are specified in TS 22.104, including the new KPIs in addition to the usual KPIs (i.e., end-to-end latency, message size, service bit rate, and transfer interval): Survival time - The maximum survival time indicates the time period the communication service may not meet the application's message delay requirement before there is an application layer failure such that the communication service is deemed to be in an unavailable state. Communication service availability - This KPI indicates if the communication system works as contracted ("available"/"unavailable" state). The communication service is in the "available" state as long as the availability criteria for transmitted messages are met. The communication service is unavailable if the messages received at the target are impaired and/or untimely (e.g. update time > stipulated maximum), resulting in survival time being exceeded. Communication service reliability - Mean time between failures is one of the typical indicators for communication service reliability. This KPI states the mean value of how long the communication service is available before it becomes unavailable.

Meanwhile the 5G QoS characteristics are specified in TS 23.501 to describe the packet forwarding treatment that a QoS Flow receives edge-to-edge between the UE and the UPF. The most relevant performance characteristics to the identified key performance requirements are: Packet Delay Budget - The Packet Delay Budget (PDB) defines an upper bound for the time that a packet may be delayed between the UE and the UPF that terminates the N6 interface. For a certain 5QI the value of the PDB is the same in UL and DL. In the case of 3GPP access, the PDB is used to support the configuration of scheduling and link layer functions (e.g. the setting of scheduling priority weights and HARQ target operating points). Packet Error Rate - The Packet Error Rate (PER) defines an upper bound for the rate of PDUs (e.g. IP packets) that have been processed by the sender of a link layer protocol (e.g. RLC in RAN of a 3GPP access) but that are not successfully delivered by the corresponding receiver to the upper layer (e.g. PDCP in RAN of a 3GPP access) within the packet delay budget. Thus, the PER defines an upper bound for a rate of packet losses. The purpose of the PER is to allow for appropriate link layer protocol configurations (e.g. RLC and HARQ in RAN of a 3GPP access). For every 5QI the value of the PER is the same in UL and DL.

The communication service reliability and communication service availability are complementary to packet error rate (PER). PER can be used to indicate the significance of individual packet losses which for many of the industrial applications differs from the significance of losing several consecutive packets (packet is 'lost' if it is not delivered intact within PDB). For example, loss of a single packet may only slightly reduce the quality of experience of an industrial application (e.g.. precision of a motion control application), while loss of several consecutive packets is considered as communication service unavailability potentially resulting in an emergency stop in the application. Packet error rate (PER) is directly related to communication service reliability and communication service availability only in the special case where 'failure' of the communication system is specified to be loss of a single packet ( e.g., survival time is zero and 1 message is contained in 1 packet) for periodic deterministic traffic. Communication service availability and communication service reliability indicate the significance of how packet losses are distributed in time domain. For example, if 5G system design considers avoidance of multiple consecutive packet losses with higher priority than individual packet losses, this may result in a system design that improves the quality of experience of the industrial applications. Both communication service availability and communication service reliability are meaningful only when specified in context with survival time. Communication service reliability can be quantified as the mean time between failures. Failure refers to the event when the communication service becomes 'unavailable' considering the application specific requirements. For many of the industrial applications, the communication service is considered unavailable if survival time is exceeded. For applications that have survival time equal to zero, any loss of packet triggers this unavailability, while for applications with non-zero survival time only two or more consecutive packet losses will trigger unavailability (depending on the agreed traffic periodicity and length of the survival time). The communication service is considered available again when it successfully delivers a packet, or the full set of packets constituting a message when message segmentation is utilized, within the delay constraints. The communication service reliability and communication service availability can be considered in 5G system design e.g., by developing solutions that reduce the probability of exceeding the survival time. Communication service availability can also be estimated from the mean time between failures (MTBF) and the mean time to repair (MTTR) of the communication service; In this context, MTBF excludes downtime, as illustrated in Figure 4.2-1, while MTTR refers to the mean time until the communication service is available after a failure, i.e., until the next valid packet has been received .

Survival time is another indicator that may be considered for 3GPP 5G system design to allow the performance requirements of cyber-physical control applications to be met. If survival time is assumed to be zero, the 5G system may over-provision the PER targets which may lead to significant reduction is system capacity and/or reduce the communication service reliability and communication service availability (e.g., in the case when there is resource conflict between two URLLC service flows) When message segmentation is utilized in the 5G system, survival time relates to the successful delivery of all packets comprising an application layer message rather than a single packet. For many IIoT applications individual packet errors can be tolerated but exceeding survival time cannot. This allows that One potential use of survival time could be to adjust PER if survival time is in jeopardy. For example, if packet errors are detected but survival time has not yet expired, steps could be taken to ensure delivery of subsequent packets within survival time. The dependencies between communication service availability, communication service reliability and survival time might be considered in the 5G system to see if more efficient optimization can be achieved. One dependency to be considered is the number of packets lost during the survival time interval.