 single network interface. A packet sent to a unicast address is delivered to a single recipient. Universal Mobile Telecommunications System (UMTS) The UMTS Terrestrial Radio Access Network (UTRAN) is a communications network, commonly referred to as 3G, and consists of NodeBs (3G base stations) and Radio Network Controllers (RNCs), which make up the UMTS radio access network. The UTRAN allows connectivity between the UE and the core network. The UTRAN is composed of WCDMA, HSPA, and HSPA+ radio technologies. User Datagram Protocol (UDP) Simple transport layer protocol capable of transporting datagrams that provides ports for multiplexing different flows and checksum for error detection. UDP does not guarantee packet delivery or that packets are delivered order. User Equipment (UE) or Mobile Station (MS) Everything that is on the user side of the cellular network connection. Traditionally refers to a mobile handset, but nowadays also covers dongles providing cellular access to computers (e.g., via USB or WLAN), fixed home gateways using cellular access as uplink, or even a set of devices behind the single cellular connection. User layer In the 3GPP domain this refers to the layer that consists of users' packets, including IP packets and all payload. The addressing, IP version, and the traffic on the user layer are completely separate from the 3GPP network's transport layer. User plane Takes care of the end user packet transmissions through the network. Voice over LTE (VoLTE) VoLTE is an IMS-based solution for providing IP-based voice and short message services over LTE access technology. It is also the solution from 3GPP for replacing circuit switched voice services in LTE networks. Wireless Local Area Network (WLAN) Wireless short-range radio standard defined in the IEEE 802.11 standard suite. Very commonly used for Internet access in homes, enterprises, cities and such. Supported by all smart phones, and nowadays also by many feature phones. Introduction Recently, Internet access has been revolutionized by mobi