e and the user's fee is typically fixed or based on the time they are connected to the network of their ISP. However, because of the variable delay of packets, the quality of speech is not as good as in PSTN. The Internet has turned into the major information network in the world, but problems that restrict its usage remain with this technology. The major problems are the inability to charge for services, lack of security, qual- ity of the interactive real-time information, such as voice, capacity of the net- work when usage increases, and shortage of Internet addresses. However, the technical solutions to these problems are under development or implementa- tion and the rapid growth of the Internet is expected to continue as more and more commercial applications become available. The Internet is expected to take a growing share of the telecommunications for which we presently use PSTN or ISDN. 6.6.2 Protocols Used in the Internet Protocols used in the Internet are usually referred to as the TCP/IP protocol suite, which was introduced in Section 6.3 and is shown in Figure 6.11. As we saw, TCP/IP does not follow the OSI model exactly but it does follow a Data Communications layered structure. It was developed in the 1970s for fault-tolerant data com- munications, while the OSI model was designed to serve as a reference model for future protocol development. TCP/IP is a collective term including all protocols in Figure 6.36, not only IP and TCP. The corresponding names of the OSI layers are given in Figure 6.36 although protocols in the figure do not exactly follow OSI speci- fications. Protocols in Figure 6.36 are, from the bottom up, as follows: Serial Line Internet Protocol (SLIP); Point-to-Point Protocol (PPP); Address Resolution Protocol (ARP); Reverse Address Resolution Protocol (RARP); Internet Protocol (IP); Open Shortest Path First (OSPF) Protocol; Routing Information Protocol (RIP) Border Gateway Protocol (BGP) Internet Control Message Protocol (ICMP); Transmission Control Protocol (TCP); User Datagram Pro