s space in needed block sizes throughout the whole address space. This change prolonged IPv4's lifetime adequately for the community to start redesigning the Internet Protocol, and specifying a new IP protocol version that would have ade- quate address space for the growth of the Internet. CIDR addressed the efficiency of IPv4 address allocation well enough to accommodate the growth of the Internet throughout the 1990s and the beginning of 2000s. Deploying IPv6 in 3GPP Networks The growth of broadband networking, and the proliferation of networked computers and other network devices, fueled the Internet's growth. Networks in enterprises, and even in homes grew. This introduced the need to have multiple addresses per subscriber both for enterprise connections, and for private subscribers. However, operators were conserving IP addresses allocated to the subscriber lines. Most operators gave just one address per subscriber, hence allowing just one computer to be connected to the network at a time. There was a need to multiplex multiple computers to a single public IP address. The introduction of private address space [12] and Network Address Translation (NAT) [38] made this possible. NAT is a technique that allows multiplexing of multiple private IP addresses to a single public IP address. The multiplexing is done by using upper layer protocol identifiers - for example the TCP and UDP port numbers. Figure 1.6 describes the NAT principle. Practically, the NAT follows the traffic coming from the inside the network (from the left in the picture) going to the Internet. The NAT rewrites the outgoing packet by replacing the source IP address with its external IP address, and the source port in the transport protocol with one of its available ports. When a downlink packet comes destined to the NAT's address, and the port, it knows to rewrite the packet to go to the host inside the private network. Hence, a NAT extends the IP address range using port numbers. As the IPv4 address space approaches exhaustion, many operators d