r 3GPP Release-9 state that when receiving an information element that has an invalid length in a response message, the receiving node treats the signaling procedure as a failed one. This would be the case when the PDP Context information element with the Extended End User Address information element was included for dual-stack purposes in an SGSN Context Response message. Starting from 3GPP Release-9 the handling of unexpected information element lengths is more liberal. However, regarding the specific topic discussed above, there should not be any issues since the Release-9 Gn/Gp-SGSN is supposed to understand all the required dual-stack enhancements in GTPv1. 4.6 Signaling Interfaces This section takes a brief look at IPv6 as a transport protocol on various signaling interfaces with the 3GPP packet core. We are not going to discuss the IPv6 transport layer as such, which implies that RAN aspects are, for example, entirely neglected. 4.6.1 IPv6 as Transport Most of the signaling and control plane interfaces within the GPRS and EPS should be IPv6 capable by definition. GTP and Session Initiation Protocol (SIP) [122] run over UDP [66], RADIUS runs over UDP and Diameter runs over Stream Control Transmission Protocol (SCTP) [123]. They are not tied to a specific IP version. Even non-IP Signaling System No. 7 (SS7) based protocols could be transported over IP using SIGTRAN [124, 125] or SIP [126]. Whether a given signaling protocol uses IPv6 transport instead of IPv4, typically depends on two factors: Does the core network node support IPv6 on its own network interfaces? Has there been a reason to upgrade the core network to IPv6? However, within the 3GPP specifications the situation can naturally be different and not that straightforward. For instance, GTP still has an optional support for IPv6 transport (as of Release-11). Naturally, some systems and networking nodes were then implemented according to that. In practice, the majority of the 3GPP core network nodes are getting full IPv6 support independent of the ve