 Deploying IPv6 in 3GPP Networks Application and service layer Traffic flow aggregates Traffic flow aggregates DownLink Packet UpLink Packet Filters Filters DL-PF S1-TEID UL-PF RAB-ID DL-PF -> DSCP RAB-ID <-> S1-TEID eNodeB S1-TEID -> DSCP Radio bearer S1 bearer IP transport leg EPS bearer Legend: UL-PF - Uplink Packet Filter DL-PF - Downlink Packet Filter RAB-ID - Radio Access Bearer Identifier TEID - Tunnel Endpoint Identifier DSCP - Differentiated Servies Code Point Figure 4.2 Simplified unicast EPS Bearer concept for Proxy Mobile IP (PMIP)-based S5/S8- interface. A default bearer (and also a dedicated bearer) activation and removal has a cost. Both involve a significant amount of e.g. Non-Access Stratum (NAS) [12, 13] signaling over the radio link between the UE and the network (Mobile Management Entity (MME) or SGSN elements), a number of bearer management signaling messages, and policy and subscription data related signaling within the packet core. If bearer activations and removals are frequent, it may lead to unwanted signaling load. Additionally, each new bearer always consumes an additional Radio Access Bearer (RAB), which impacts scarce radio access resources. Finally, it is common for equipment vendors to build licensing schemes around the number of concurrent bearers, which means that operators have an incentive to optimize the number of used bearers per UE. 4.1.2 PDP and PDN Types As discussed in Section 4.1, each PDN Connection is associated with an IPv4 address and/or IPv6 prefix. A PDN Connection can only carry the protocol type(s) that got IPv6 in 3GPP Networks negotiated during the default bearer establishment. (Historically, a PDP Context could also carry Point to Point Protocol (PPP) [14] frames. However, PPP has been deprecated since the introduction of EPS in 3GPP Release-8.) There are three different PDP Types (in GPRS) and PDN Types (in EPS). For simplicity we use the term PDN Type for both PDP Type and PDN Type, unless noted otherwise: PDN Type IPv4 - the PDN Connection is associated wit