operators have more of fixed infrastructure like optical or copper cabling and related sites, while mobile-only operators have far less or none 9 Transport of such infrastructure and have relied on leased lines and possibly on self-built and self-operated microwave radio links. In practice, mobile transport networks often partly use their own infrastructure, and partly leased services. One technical impact is that with leased services monitoring of the SLA (service level agreement), any violation of it is of special importance, as is fault localization: it is required to be able to detect which side of the UNI (user to network interface) the fault is on. In mobile networks, the transport network may be shared along with the shared radio network infrastructure with two or more mobile operators. Sharing the infrastructure in some way is expected to grow. Furthermore, many networks are operated as a service. All this blurs the otherwise clear distinction own and leased transport. 9.1.4 Common Transport Common transport here refers to the fact that often multiple radio technologies like 2G, 3G, 4G, and 5G are supported partly or (almost) completely by the same transport network. On the base station site, several base stations may be deployed and combined by a transport device to a common uplink, or alternatively, a single multi-radio capable base station supports many radio standards with a common transport link. In these cases, transport links and nodes are shared for all technologies. The common links will fulfill the needs for all of the radio technologies, meeting the specific demands for capacity, quality of service (QoS), availability, and security. With 5G, typically the existing network links need to be upgraded at least for capacity, and also assessed for other 5G demands like latency, connectivity, security, and availability. When the access link or node is shared, failure on this common facility impacts all radio technologies. This needs to be considered in the availability analysis and design and addresse