Answer. TCP/IP in fact consists of dozens of different protocols, but only a few are the "main" protocols that define the core operation of the suite. Of these key protocols, two are usually considered the most important. The Internet Protocol (IP) is the primary OSI network layer (layer three) protocol that provides addressing, datagram routing and other functions in an internetwork. The Transmission Control Protocol (TCP) is the primary transport layer (layer four) protocol, and is responsible for connection establishment and management and reliable data transport between software processes on devices.

Due to the importance of these two protocols, their abbreviations have come to represent the entire suite: "TCP/IP". IP and TCP are important because many of TCP/IP's most critical functions are implemented at layers three and four. However, there is much more to TCP/IP than just TCP and IP. The protocol suite as a whole requires the work of many different protocols and technologies to make a functional network that can properly provide users with the applications they need.

TCP/IP uses its own four-layer architecture that corresponds roughly to the OSI Reference Model and provides a framework for the various protocols that comprise the suite. It also includes numerous high-level applications, some of which are well-known by Internet users who may not realise they are part of TCP/IP, such as HTTP (which runs the World Wide Web) and FTP. In the topics on TCP/IP architecture and protocols I provide an overview of most of the important TCP/IP protocols and how they fit together.

The Internet is a primary reason why TCP/IP is what it is today. In fact, the Internet and TCP/IP are so closely related in their history that it is difficult to discuss one without also talking about the other. They were developed together, with TCP/IP providing the mechanism for implementing the Internet. TCP/IP has over the years continued to evolve to meet the needs of the Internet and also smaller, private networks that use the technology.

The TCP/IP protocols were initially developed as part of the research network developed by the United States Defense Advanced Research Projects Agency (DARPA or ARPA). Initially, this fledgling network, called the ARPAnet, was designed to use a number of protocols that had been adapted from existing technologies. However, they all had flaws or limitations, either in concept or in practical matters such as capacity, when used on the ARPAnet. The developers of the new network recognized that trying to use these existing protocols might eventually lead to problems as the ARPAnet scaled to a larger size and was adapted for newer uses and applications.

In 1973, development of a full-fledged system of internetworking protocols for the ARPAnet began. What many people don't realize is that in early versions of this technology, there was only one core protocol: TCP. And in fact, these letters didn't even stand for what they do today; they were for the Transmission Control Program. The first version of this predecessor of modern TCP was written in 1973, then revised and formally documented in RFC 675.

Testing and development of TCP continued for several years. In March 1977, version 2 of TCP was documented. In August 1977, a significant turning point came in TCP/IP’s development. Jon Postel, one of the most important pioneers of the Internet and TCP/IP, published a set of comments on the state of TCP.

Postel's observation led to the creation of TCP/IP architecture, and the splitting of TCP into TCP at the transport layer and IP at the network layer; thus the name "TCP/IP". The process of dividing TCP into two portions began in version 3 of TCP, written in 1978. The first formal standard for the versions of IP and TCP used in modern networks (version 4) were created in 1980. This is why the first "real" version of IP is version 4 and not version 1. TCP/IP quickly became the standard protocol set for running the ARPAnet. In the 1980s, more and more machines and networks were connected to the evolving ARPAnet using TCP/IP protocols, and the TCP/IP Internet was born.

Each TCP/IP network interface requires a unique IP address, which IP routers use to forward packets, as needed, across the various network cables, which connect communicating systems. An IPv4 address, 32 bits long, is capable of accommodating several million such interconnections, more than enough to handle the needs of the TCP/IP community through the future, at least, as far ahead as anyone could have foreseen twenty years ago. Yesterday's anticipated networks of tens of thousands of computers, however, have since blossomed into today's potential for hundreds of millions of connections. The internet is fast becoming the whole world's backbone network, and as the world scrambles to connect to it, the IPv4 addressing scheme is gradually running out of gas.

Within its 32-bit address field, IPv4 organises the networked world into a simple two-level hierarchy: network numbers, and host numbers within network numbers. To guarantee globally unique addresses, a central authority (The Internet Assigned Numbers Authority, IANA, which has now largely delegated this job to Internet Service Providers) assigns unique network numbers to requesting organisations, where local authorities (corporate network administrators) then assign unique host numbers to its attached devices. Apart from addresses, other limitations affecting IPv4 are the lack of prioritisation and security issues preventing it from expanding further. The limitations of IPV4 needed to be addressed, and this has been done with the birth of IPv6.

IPv6 is short for 'Internet Protocol Version 6'. IPv6 is the 'next generation' protocol designed by the IETF to replace the current version Internet Protocol, IP Version 4 ('IPv4').

Most of today's internet uses IPv4, and despite its age, it has been remarkably resilient, but it is beginning to face problems as mentioned above. Most importantly, is the growing shortage of IPv4 addresses, which are needed by all new machines added to the Internet.

IPv6 fixes a number of problems in IPv4, such as the limited number of available IPv4 addresses. It also adds many improvements to IPv4 in areas such as routing and network autoconfiguration. IPv6 is expected to gradually replace IPv4, with the two coexisting for a number of years during a transition period.

Many of the discussions about a new internet protocol focus on the fact that we will sooner or later run out of Network Layer addresses, due to IPv4's outdated 32-bit address space. The Internet Network Information Center (InterNIC) is the authority that assigns blocks of IP addresses to large network service providers and network operators.

Since 1991, InterNIC has been increasingly stingy about the way these addresses are handed out, though most predictions for IPv4 address exhaustion target a time frame that starts well into the next decade.

With the long-haul in mind, IPv6 has been outfitted with an enormous 128-bit address space that should guarantee globally unique addresses for every conceivable variety of network device for the foreseeable future (i.e., decades). IPv6 has 16 bytes of addressing, or 340, 282, 366, 920, 938, 463, 463, 374, 607, 431, 768, 211, 456?addresses, according to one IPv6 maven. The addressing gets a lot of attention but it is only one of many important issues that IPv6 designers have tackled.

Other IPv6 capabilities have been developed in direct response to currently critical business requirements for more scalable network architectures, improved security and data integrity, integrated quality-of-service (QoS), autoconfiguration, mobile computing, data multicasting, and more efficient network route aggregation at the global backbone level. IPv6 is a big package, and addressing is only the most visible component of the work. By conservative estimates, IPv6 will support thousands of addresses for each square meter of the Earth's surface.

With these significant enhancements it seems that IPv6 could be the answer. The migration from IPv4 to IPv6 still remains a challenge and huge amounts of work will be necessary over many years, but with the major issues that held back IPv4 seemingly dealt with and answered the future looks rosy with IPv6.