easured latency was 29 ms because the signal travels to the gateway in Helsinki, back to the server in Oulu, again to Helsinki, and back to the UE in Oulu. There is no gateway in Oulu. It is typically the case in mobile networks today that the core network architecture is centralized. These simple measurements illustrate that millisecond-level latency requires changes in the network architecture, and more gateways are required. Two example solutions for low latency are Multi-Access Edge Computing (MEC) and the Distributed Core network. MEC brings the content close to the subscribers. Dis- tributed Core allows access to the local Internet and intranet. Figure 10.17 illustrates the architecture evolution from a centralized core network to the distributed approach. 10.4 Latency Centralized core Centralized gateway Distributed core with mobile edge computing Local cloud Local cloud Figure 10.17 Distributed architecture with mobile edge computing. The traditional network architecture includes only a small number of centralized core network gateways, which can cause long propagation delays. 10.4.3 Control Plane Latency Another part of latency optimization is the control plane setup time. A low latency con- trol plane enables low latency also for the transmission of the first packets. If the control plane latency is high, then the first packets have high latency due to the setup times. The following control plane protocols increase the latency in LTE networks: Transition from idle to Radio Resource Control (RRC) connected takes 50-100 ms. The delay is because approximately 10 signaling messages are required between the UE and the network for the connection setup. The typical inactivity timer in LTE networks is 5-10s, after which the UE is moved to idle. Therefore, RRC connection setup occurs quite frequently for the first packet in LTE networks. Resource allocation takes 10-20 ms if there are no PUSCH resources available. The UE needs to send capacity requests and get the capacity allocation on the PDCCH. The inactivity