range IPsec Security Parameters Index (SPI) [52] Type of Service (TOS) (IPv4) / Traffic class (IPv6) Flow Label (IPv6). The local address and port refer to the UE's address and port. Consequently, the remote address and port refer to the address of the remote host and its ports. Basics of the 3GPP Technologies 2.5.4 3GPP Link Model Principles We have now described how 3GPP networks open, modify, and close sessions, the principles of mobility management, and how user-plane packets are mapped to the open sessions. However, we have not yet touched on how the IP stack sees the 3GPP access. We will next concentrate on the IP stack's view of the 3GPP networks. This section concentrates on the principles on which the 3GPP link model relies. We will look at the details in Section 4.1. Compatibility with IP and the Internet The 2G-GPRS was being specified during the 1990s, 3G-GPRS in the early 2000s, and EPS in the later part of the first decade of the 2nd century. However, mobile broadband only really started growing during the specification of the EPS architecture. Hence, it is obvious that during the design and specification time the equipment which is now used on these networks, was not available. Especially, while specifying GPRS, the capabilities of handsets and even computers were much more restricted than the smartphones of today. The phones were special devices with very restricted computing capabilities. In addition, the networks themselves were much more restricted in the terms of bandwidth and latency. Still, at the beginning of the 2000s, the norm for mobile data was circuit switched data with bandwidth between 9.6 kbps and 14.4kbps. In addition, in the early stages of 3G standardization even WLAN was not widely used, and the mobile phones were strictly supporting only cellular access. Therefore, people who standardized the 3GPP system could not even envision what the future mobile phones would be, and for what the networks would in the end be used. In the early days of GPRS standardization, IP stack was cons