nalities of the radio resource controller (BSC in 2G, and RNC in 3G). Fall back Reverting to using something as an alternative to a preferred choice. In this book fall back refers to using one address family instead of an other (e.g., use of IPv4 if IPv6 has failed), or using less preferred bearers if more preferred ones have failed to work (e.g., using parallel IPv4 and IPv6 PDP Contexts if IPv4v6 PDP Context did not open). Fragmentation and reassembly Fragmentation is a process for slicing outgoing large protocol data units into chunks that can be sent in IPv6 packets that fit into the MTU of the path. Reassembly is the process of combining chunks of data received in multiple IPv6 packets into the original protocol data unit. Gateway GPRS Support Node (GGSN) The topological anchor point of the mobility management in the GPRS network. It is the gateway between the GPRS network and external networks, such as the Internet. From UE's IP stack point of view GGSN is the first-hop router. Gb-interface The interface between the BSS and the core network - hence, between the BSC and the SGSN. This interface comprises both of the control and user plane parts. General Packet Radio Service (GPRS) Packet data service for GSM network. 3G uses the same architecture, and hence both 2G and 3G are often referred to as GPRS. Gi-interface The interface that connects the GPRS network to the external IP networks. GSM radio protocols GSM Radio Frequency (RF), Media Access Control (MAC), Radio Link Control (RLC), and Logical Link Control (LLC) provide the GSM radio functionality including ciphering, reliability, and other radio procedures. Gn/Gp-interface The interface between the SGSN and the GGSN. The Gn-interface is used when the Mobile Station (MS) is in the home network, whereas the Gp-interface is used when the subscriber is roaming in another network. Thus, the Gp-interface is the interface between two network operators. The Gn-interface is also used between SGSNs during a handover to exchange MS related information, and for for