sired PDN is realized using an APN, which essentially refers to a gateway in the packet core that has connectivity to the PDN. The gateway in a 3GPP packet core is the Gateway GPRS Support Node (GGSN) or the Packet Data Network Gateway (PGW). For readability we will mostly use the term PGW as a synonym for a GGSN when there is no real functional difference between the two. Specific release, functional, or interface-related differences are separately noted. Deploying IPv6 in 3GPP Networks: Evolving Mobile Broadband from 2G to LTE and Beyond, First Edition. Jouni Korhonen, Teemu Savolainen and Jonne Soininen. © 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd. Deploying IPv6 in 3GPP Networks Once a PDN Connection has been created, the required PDN Connection state is established in various packet core nodes, such as Serving Gateway Support Node (SGSN), Serving Gateway (SGW), Home Location Register (HLR), and SO on. The PDN Con- nection state information contains addresses of peering gateway nodes, various GPRS Tunneling Protocol (GTP) related identifiers, Quality of Service (QoS) related parameter, but most importantly the IPv4 address and/or IPv6 prefix associated with the PDN Con- nection. Each PDN connection has its own IPv4 address and/or IPv6 prefix assigned to it by the PDN and topologically anchored in the corresponding gateway (GGSN or PGW) to the PDN. The PDN is responsible for the IPv4 address and/or IPv6 prefix allocation to the UE. On the UE, a PDN Connection is equivalent to a network interface. We will further discuss different types of PDN Connections in Section 4.1.2. 4.1.1 Bearer Concept An important part of the PDN Connectivity service is the bearer concept. An EPS Bearer uniquely identifies traffic flows that receive a common QoS treatment between a UE and a PGW for GTP-based S5/S8-interfaces [3, 4], and between a UE and an SGW PMIP-based S5/S8-interfaces [5-7]. A bearer can be further divided into radio bearers between the UE and the base station, S1-bearers between the base