f a larger data set. The main task of the IP layer is addressing, which requires global Inter- net addresses, and routing of the IP packets from the source computer to their destination via a number of interconnected networks. The basic net- work elements in the IP network are routers and permanently connected computers (hosts) with different application protocols that provide services for Internet users. Each such element has at least one Internet address. They are different from the addresses used in the PSTN. The Internet addresses are global and their usage is internationally controlled by the NIC. 6.6.4.1 IP Addresses Every host and router in the Internet has a unique fixed-length IP address, that defines the network and the host. No two machines connected to the global Internet have the same IP address. All IP addresses are 32 bits long and are used in source and destination address fields of IP packets. Figure 6.38 shows the format of an IP address. Data Communications 32 bits, 4 bytes Address Range of host class addresses 1.0.0.0 to Network 127.255.255.255 128.0.0.0 to Network 191.255.255.255 192.0.0.0 to Network 233.255.255.255 234.0.0.0 to Multicast address 239.255.255.255 240.0.0.0 to 11110 Reserved for future use 247.255.255.255 Figure 6.38 IP address format (IPv4). Machines connected to multiple networks have different addresses on each network [3]. NIC assigns the network part, and the administrator of each network assigns the host part of addresses. IP addresses, which are 32- bit numbers, are usually written in dotted decimal notation as shown in Figure 6.38. For example, class C binary address 11000000 00101001 00000111 00110100, which is in hexadecimal form C0290734, is written as 192.41.7.52. Some addresses, such as lowest 0.0.0.0 and highest 255.255.255.255, have special uses, as shown in Figure 6.39 [3, 4]. Because 32 bits, 4 bytes This host 00000000000000000000000000000000 0.0.0.0 A host in this network Broadcast on the local network, limited 111111111111111111111111111111 broadcast 255.255.