twork-based proxy mobile IP. IP Security (IPsec) IPsec refers to IPv6 protocol features providing authentication, integrity protection, anti-replay protection, access control, and encryption. These are provided with AH and ESP headers. The IPsec does not refer to the general security of the IPv6 protocol. IPv6 transition The IPv6 should one day replace IPv4 in all Internet communications. The path from IPv4 Internet to IPv6 Internet is a rocky and very complex path requiring standards, implementation, verification, policies, education, governance, deployment, willingness, money, and effort. This path from IPv4 to IPv6 is generally referred as IPv6 transition. IPv6 transition tools The protocols and practices that help nodes with IPv4-only, IPv6- only, and dual-stack access to communicate with each other by using tunneling, protocol translation, and proxying technologies. Link layer Layer two in the OSI model. Responsible for transporting data over the phys- ical layer, detecting errors, and providing physical layer addressing (such as MAC addresses on WLAN). Ethernet and PPP are examples of link layer protocols. LTE See 4G and LTE. M2M See IoT, MTC, M2M. Mobile Management Entity (MME) Responsible for mobility management, authentica- tion, and authorization of the UE in 4G networks. The MME is, in practice, a very similar element to the SGSN in UMTS. The difference between the 3G-SGSN and the xxxviii Glossary MME is that the MME is only a control plane element, and it does not perform any user-plane functions. Mobile Switching Center (MSC) The local exchange responsible a set of Base Station Controllers (BSC), and Mobile Stations (MS) under those base stations in a geo- graphical area. Performs authentication and mobility management, and exchanges the subscribers' calls. MSC is a Circuit Switched network entity. MTC See IoT, MTC, M2M. Multicast address An address that identifies multitude of interfaces on, usually, a multi- tude of nodes. An IPv6 packet sent to a multicast address is delivered to all receivers of 