with, including addresses to application servers. 'Address management' is a huge task. DNS translates only from text address to numerical IP address, which is not sufficient. You also need a directory service such as LDAP, similar to properties/characteristics in computer applications (Outlook is an example). If informed through log-on processes, LDAP can also, together with the SIP protocol, act as a translator between a universal identity (John@company.com) and a geographical terminal location with a fixed IP address to route to or an address in the mobile network or an DHCP originated address (similar to call forwarding or the number portability feature). The new IPv6 standard (Figure 8.35) uses 128 bits for addressing compared to the IPv4 standard with 32 bits. APN Address APN stands for access point name and consists of network ID + operator ID. There are two types of network ID: Regional APN network ID: ends with an area identifier. National APN network ID: ends with no area identifier. The operator ID denotes the type of network, e.g. GPRS. Long haul Long haul provider provider Service Service Service provider provider provider Top level aggregator 13 bits Next level aggregator 24 bits Site level aggregator 16 bits Interface ID Locator (routing part) 8 bytes Interface identifier 8 bytes Figure 8.35 IPv6 number structure. Observe the hierarchical organization of the number with some similarity with E.164 numbers Service Implementation 8.9.3 SERVERS WITH NUMBERING AND ADDRESS SUPPORT Among the servers involved in numbering are DNS, LDAP, RADIUS (optional), NAT and DHCP. Domain Name Server (DNS) DNS handles mapping between host names, which we find convenient, and Internet addresses, which computers deal with. It also provides several additional functions such as reverse mapping and secure querying. DNS is used by virtually all internetworking soft- ware, including e-mail, remote terminal programs like telnet, and file transfer programs like ftp (file transfer protocol). See Figure 8.36. Lightweight Directory