tract their configurations from a server (the 'DHCP server') or servers. The overall purpose of this is to reduce the work necessary to administer a large IP network. The most significant piece of information distributed in this manner is the IP address. Mobile IP Mobile IP refers to the access method that is based on the Internet standard specified in RFC 2002. Here the user can use either a static or dynamic IP address belonging to its home network. The mobility options permit users to maintain their IP address no matter whether moving throughout their own or other networks. A goal is to have the same IP address in the mobile network and WLAN network ('all-IP approach'). Simple IP Simple IP refers to the access method in which the user is assigned a dynamic IP address from a service access provider. The user can keep the IP address within a certain network dependent area. This method permits a restricted mobility. 8.9.4 CONVERGENCE LEADS TO INTERWORKING Numbering Interworking There will be interworking of E.164 to/from IPv4, E.164 to/from IPv6 and finally IPv6 to/from IPv4. Figures 8.37-8.39 illustrate the situation. 8.9.5 UMTS NUMBERING When the WCDMA/UMTS terminal is used for access to IP networks, it must be inte- grated in the IP numbering. Addresses can be dynamically assigned (fetched from an external server or a pool of own addresses) or statically assigned (fetched from the HLR). Address allocation is the responsibility of GGSN (gateway GPRS support node). It is Service Implementation Internet Transparent GW number + PSTN number PSTN number Gateway Gateway IP operator Figure 8.37 The PSTN number is sent through the IP network 64 bits V4 Addr Interface ID Public topology topology Interface identifier 6 to 4 relay router IPv6 domain IPv6 domain 6 to 4 relay V6 edge router router V4 backbone Figure 8.38 Tunnelling IPv4 through IPv6 V6 UE End to end V4 host IPv6 domain IPv4 domain Edge router V4 edge router/ translator V4 backbone Figure 8.39 IPv4 and IPv6 domain interconnect requires translation. Tunnellin