rk radio interface ciphering to protect the confidentiality and authenticity of future exchanges over the radio interface. Some networks may also perform a check of the device identity by comparing the International Mobile Equipment Identity (IMEI) to the Equipment Identity Register (EIR) to see if the used device has been stolen, or for some other reason blacklisted from attaching to the network. After the subscriber has been authenticated, and the radio communication has been secured, the location of the subscriber is updated to the HLR. In 2G/3G networks the UE is informed when the attach has been successful, after which the UE has finished the network attach procedure. The UE is attached to the network, Basics of the 3GPP Technologies 1. Activate PDP Context 2. Create PDP Context 2. Create PDP Context A. Update PDP Context 3. Activate PDP Context 4. IP Traffic Figure 2.13 2G and 3G GPRS PDP Context activation. but it does not yet have a connection to the Internet. The connection has to be separately activated with the Packet Data Protocol (PDP) Context Activation procedure. In 2G and 3G-GPRS the establishment of the IP layer connectivity is not part of the network attach procedure, but has to be explicitly performed. This procedure is called PDP Context Activation. The PDP Context is the name of the connection, or session, which actually connects the UE to the external Packet Data Network (PDN) - such as the Internet. GPRS supports different types of PDP Contexts - hence, different PDP Types. The different PDP Types currently supported are IPv4, IPv6, Dual-Stack (IPv4v6), and Point to Point Protocol (PPP) [31]. However, practically speaking, PPP is not used any- more. Thus, we ignore the PDP Type PPP in this book. Figure 2.13 shows PDP Context activation procedure, and the explanation can be found below: 1. Activate PDP Context request message is sent by the UE to the SGSN to indicate that the UE wishes to open a packet data connection, such as a connection to the Internet. The message indicates if the UE wou