data sent/received to/from external data networks; usage of PDP addresses: how long an MS has used PDP addresses assigned to it. 4.9 IP Addressing 4.9.1 Types of Network An IP address, which is made up of 32 bits, is divided into two parts, a network address and a host address. Several machines in the same network will have the same network address prefix but a unique host address. There are three types of networks, class A, class B and class C, based on the number of bits belonging to the network or host address part. Class A Networks (/8 Prefixes) Each class A network address has an 8-bit network prefix with the highest order bit set to 0 and a 7- bit network number, followed by a 24-bit host number. Class A networks are also referred to as '/8s' (pronounced 'slash eight' or just 'eights') since they have an 8-bit network prefix. A maximum of 126 ((2 to the power of 7) - 2) number of '/8' networks can be defined. The calculation requires that 2 is subtracted because network 0.0.0.0 is reserved for use as the default route and the '/8' network 127.0.0.0 (also written 127/8 or 127.0.0.0/8) has been reserved for the 'loopback' function. Each '/8' supports a maximum of 16777214 hosts per network. The host calculation requires that 2 is subtracted from 2 to the power of 24 because all-Os ('this network') and all-1s ('broadcast') host numbers may not be assigned to individual hosts. Core Network Planning and Optimisation Class B Networks (/16 Prefixes) Each class B network address has a 16-bit network prefix with the two highest order bits set to 1-0 and a 14-bit network number, followed by a 16-bit host number. Class B networks are now referred to as '/16s'. A maximum of 16384/16 networks can be defined with up to 65 534 hosts per network. Class C Networks (/24 Prefixes) Each class C network address has a 24-bit network prefix with the three highest order bits set to 1-1-0 and a 21-bit network number, followed by an 8-bit host number. Class C networks are now referred to as '/24s' since they have a 24-bit network pr