Monday, December 15, 2008

TCP/IP Overview and History Part 2

Modern TCP/IP Development and the Creation of TCP/IP Architecture
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. In that document (known as Internet Engineering Note number 2, or IEN 2), he provided what I consider superb evidence that reference models and layers aren't just for textbooks, and really are important to understand:
We are screwing up in our design of internet protocols by violating the principle of layering. Specifically we are trying to use TCP to do two things: serve as a host level end to end protocol, and to serve as an internet packaging and routing protocol. These two things should be provided in a layered and modular way. I suggest that a new distinct internetwork protocol is needed, and that TCP be used strictly as a host level end to end protocol.

-- Jon Postel, IEN 2, 1977
What Postel was essentially saying was that the version of TCP created in the mid-1970s was trying to do too much. Specifically, it was encompassing both layer three and layer four activities (in terms of OSI Reference Model layer numbers). His vision was prophetic, because we now know that having TCP handle all of these activities would have indeed led to problems down the road.
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”. (As an aside, it's interesting, given this history, that sometimes the entire TCP/IP suite is called just “IP”, even though TCP came first.) 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.

Important Factors in the Success of TCP/IP
TCP/IP was at one time just “one of many” different sets of protocols that could be used to provide network-layer and transport-layer functionality. Today there are still other options for internetworking protocol suites, but TCP/IP is the universally-accepted world-wide standard. Its growth in popularity has been due to a number of important factors. Some of these are historical, such as the fact that it is tied to the Internet as described above, while others are related to the characteristics of the protocol suite itself. Chief among these are the following:
o Integrated Addressing System: TCP/IP includes within it (as part of the Internet Protocol, primarily) a system for identifying and addressing devices on both small and large networks. The addressing system is designed to allow devices to be addressed regardless of the lower-level details of how each constituent network is constructed. Over time, the mechanisms for addressing in TCP/IP have improved, to meet the needs of growing networks, especially the Internet. The addressing system also includes a centralized administration capability for the Internet, to ensure that each device has a unique address.
o Design For Routing: Unlike some network-layer protocols, TCP/IP is specifically designed to facilitate the routing of information over a network of arbitrary complexity. In fact, TCP/IP is conceptually concerned more with the connection of networks, than with the connection of devices. TCP/IP routers enable data to be delivered between devices on different networks by moving it one step at a time from one network to the next. A number of support protocols are also included in TCP/IP to allow routers to exchange critical information and manage the efficient flow of information from one network to another.
o Underlying Network Independence: TCP/IP operates primarily at layers three and above, and includes provisions to allow it to function on almost any lower-layer technology, including LANs, wireless LANs and WANs of various sorts. This flexibility means that one can mix and match a variety of different underlying networks and connect them all using TCP/IP.
o Scalability: One of the most amazing characteristics of TCP/IP is how scalable its protocols have proven to be. Over the decades it has proven its mettle as the Internet has grown from a small network with just a few machines to a huge internetwork with millions of hosts. While some changes have been required periodically to support this growth, these changes have taken place as part of the TCP/IP development process, and the core of TCP/IP is basically the same as it was 25 years ago.
o Open Standards and Development Process: The TCP/IP standards are not proprietary, but open standards freely available to the public. Furthermore, the process used to develop TCP/IP standards is also completely open. TCP/IP standards and protocols are developed and modified using the unique, democratic “RFC” process, with all interested parties invited to participate. This ensures that anyone with an interest in the TCP/IP protocols is given a chance to provide input into their development, and also ensures the world-wide acceptance of the protocol suite.
o Universality: Everyone uses TCP/IP because everyone uses it!
This last point is, perhaps ironically, arguably the most important. Not only is TCP/IP the “underlying language of the Internet”, it is also used in most private networks today. Even former “competitors” to TCP/IP such as NetWare now use TCP/IP to carry traffic. The Internet continues to grow, and so do the capabilities and functions of TCP/IP. Preparation for the future continues, with the move to the new IP version 6 protocol in its early stages. It is likely that TCP/IP will remain a big part of internetworking for the foreseeable future.

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