s based on Diameter. Serving Gateway (SGW, S-GW) Mobility anchor in 4G networks for inter-eNodeB mobility. It routes the user traffic between the radio network and the Packet Data Network Gateway (PGW). Serving Gateway Support Node (SGSN) Responsible for authentication, authorization, and mobility management in GPRS. In addition, SGSN gathers charging information and terminates the radio protocols between UE and SGSN. SGi interface Interface connecting the EPS to the external IP networks, such as the Internet. Signaling Connection Control Part (SCCP) Protocol used in the SS7 protocol suite. Split-UE A UE that is either split into completely separate MT and TE devices, such as a modem and a computer, or a single device that is internally architectured to separate the MT and TE components from each other. Subnetwork Dependent Convergence Protocol (SNDCP) Protocol that transports IP packets over the 2G GSM radio network. The SNDCP is responsible for multiplexing multiple PDP Contexts between the UE and the SGSN, perform header compression, packet segmentation and reassembly, and content compression. Tethering A process where a mobile station shares the cellular uplink Internet connec- tivity to devices in a local area network, typically using WLAN or USB technologies. Transit network The part of the Internet that connects different Internet service operators together. Transport Control Protocol (TCP) Transport layer protocol that transmits a stream of data in reliable and in-order form. TCP implements error detection, retransmission, flow control, and congestion control. Glossary Transport layer Layer four in the OSI model. Responsible for transporting data over the network, providing, if needed: in-order delivery, flow control, retransmissions, and multiplexing (e.g., via port concept). TCP and UDP are the most common transport layer protocols. In the context of 3GPP the transport layer also refers to protocols used to transport both control and user-plane protocols. Unicast address An address that is assigned to a