ic address usage, please refer to RFC 4429. Preferred address: An address that can be fully utilized for all IPv6 communications. The preferred address becomes deprecated once the preferred lifetime expires. Deprecated address: An address of which the preferred lifetime has expired. This address should not be used to initiate new outbound communications, if better alternatives are available. Existing sessions (e.g., TCP sessions) can continue to use the address, and incoming communications towards this address should be allowed. A deprecated address becomes invalid after the valid lifetime expires. Invalid address: An address of which valid lifetime has expired, and which cannot be used for any communications. Interface Identifiers Before any address autoconfiguration mechanisms are used, a node generates an IID as was discussed in Section 3.1.6 that uniquely identifies the node on a link. The method for generating the IID depends on the access technology used. For example, in Ethernet- based interfaces the identifier is often built from a 48-bit IEEE 802 hardware address. The IID may also be chosen randomly, as is done when privacy extensions are used (see Section 3.5.5). Whatever the means for selecting an IID are, a node has to ensure that it does not conflict with any of the reserved IPv6 IIDs listed in RFC 5453 [77]. Creation of Link-local Addresses A link-local address is created, initially to 'tentative' state, by combining an IID with a well-known prefix fe80 : /10 [4] SO that the 10 left most bits are the well-known prefix, the 64 right most bits are the IID, and the bits between the prefix and the IID are set to zero. The resulting tentative address is checked for uniqueness using DAD (see Section 3.4.7) before allocating the address to an interface. However, immediately before starting to perform the DAD, the node must join to the Solicited node multicast address (see Section 3.2.4) group of the tentative link-local address using MLD. Deploying IPv6 in 3GPP Networks Creation of Global Addresses A globa