Chapter 1. A Short History of Computer Networking

Today, computer networks are taken for granted much as the telephone network is. The telephone network was, until the explosive growth of the Internet, the largest network in the world. It just wasn't a computer network. You could use modems to connect computers to each other on a one-by-one basis, but this wasn't networking in the sense we think of it today. And those early modems300 bps or lessdidn't make the transfer of data an inexpensive matter, especially when long-distance calls were required. In a funny twist of fate, voice communications are becoming very popular in the networking world. Both corporate and home network users can now use Voice over IP (VoIP) to make telephone calls via the Internet, making the telephone network itself less important. No wonder that many telephone companies have expanded into the data networking field so that they can offer data, voice, video, and other services. Many have also developed cellular or other alternatives to the traditional telephone network.

Computer networking has been evolving since the late 1960s. Early work on the ARPANET began in the 1960s, and in 1969 a four-node network using primitive packet switching was created. The growth of this predecessor of today's Internet wasn't quite the phenomenon you see today.

As discussed in Chapter 13, "Ethernet: The Universal Standard," the ALOHAnet was created to establish connections between several computers in Hawaii. Robert Metcalf was later to use the basic principles from ALOHAnet to create what eventually became the Ethernet local area networking protocol still used today. Ethernet was simply a means to get a signal from one place to anotherit was another thing to decide what kind of signaling to use. On the ARPANET, TCP was being created, and refined. If you examine the OSI Seven-Layer Networking Reference Model (see Appendix A, "Overview of the OSI Seven-Layer Networking Reference Model"), you can see that Ethernet works at a low level in the model, and is used to transmit packets of information from higher-level protocols. TCP was the first major higher-level protocol created. One of the first refinements of TCP was to break it into several parts (or layers), which is why the protocol "suite" is known today as TCP/IP.

TCP (the Transmission Control Protocol) and IP (the Internet Protocol) are the basis of the Internet. Another break-out from TCP was the User Datagram Protocol (UDP). Both TCP and UDP provide different types of service, yet both use IP as the workhorse protocol that is used to route packets (or datagrams) on the Internet, as well as any intranet. And what does IP use to send data across the wire (or the air, in case of a wireless network)? Ethernet in most cases. Learn more about how wireless networks work with Ethernet in Part V of this book, "Wireless Networking Protocols."

It is important to keep in mind that Ethernet and other wire-level protocols simply provide the means to frame datacreate discrete units of data for transmissionand then use a specified method to send data across the network media. For example, simply varying the voltage on a wire can be used to send data from one point to another. An early transmission method, called non-return to zero (NRZ) encoding, used just this method. A high value was used to specify the bit value of one, and a low value was used for zero. A drawback to this encoding scheme is that a long stream of either ones or zeros can be difficult to decipher at the receiving end. The term "clock" is used to mean that each end of the transmission understands where a bit starts and where it ends during the transmission. Because it would be very expensive to have a physical clock at each end that could precisely time each bit transmission, this encoding method does not scale well.

Early Ethernet networks used a technique called Manchester encoding. This method does provide a clocking mechanism that is built into the coding scheme itself. Instead of using a high- or low-voltage state to indicate a specific bit, Manchester encoding uses the change from one state to another, during a specific interval.

While TCP/IP continued its development on the ARPANET, computer vendors began to recognize the importance of networking, and many proprietary protocols were developed. Digital Equipment Corporation (DEC) created DECnet (and numerous other protocols), which was used to connect its PDP computers and, later, VAX and AlphaServer computers. Today DECnet is still used, although TCP/IP has pretty much replaced it for most installations. For a short time in the 1980s, however, DEC operated the largest computer network in the world, short of the Internet. What protocol was used? DECnet, of course. During that same period, the OSI model was created, and Digital incorporated the concepts of that model, as well as the protocols that were developed by ISO based on the OSI model, into DECnet. Because the VMS (Virtual Memory System) operating system used on DEC's VAX computers was adopting these open standards, the name of the operating system was changed to OpenVMS. However, few other vendors chose to incorporate the high-overhead concepts of these open protocols, and this first attempt to standardize networking protocols between different computers failed to come about.

Other computer manufacturers also produced their own proprietary network protocols. For example, IBM's work in this direction resulted in SNA, which combined networking protocols from the high end (application) down to the low end (wire protocols). As networking began to become an important part of the computing world, other vendors, such as Xerox (XNS), also came up with their own protocols.

The result was that if you wanted to create a network of computers for your business, you had to stick with a single vendor. Proprietary protocols, then, were not a good solution to the problem of exchanging data between computers.

During the early days of PCs, the same sort of situation occurred. Although PCs were basically the same when it came to the operating system (DOS at the start), you could buy a network setup from many different vendors. One that comes to mind is NetWare (which is still around today, although in recent years TCP/IP has replaced the proprietary IPX/SPX NetWare protocols). LAN Manager was Microsoft's entry into the field, with a legacy of NetBEUI and NetBIOS still lurking around on many Windows computers prior to Windows 2000. When DEC started to build its own PCs, it licensed LAN Manager technology and created Pathworks. You might still find Pathworks in some networks, although, like LAN Manager, it is considered history today.

Other pioneering networking packages included Banyan Vines and Artisoft LANtastic, neither of which is still on the market. However, Banyan Vines helped establish the idea of a nameservice, StreetTalk, which helped pioneer the idea of a distributed database for tracking network resources. LANtastic was an early advocate of peer-to-peer networking, which has led to the current popularity of SOHO wired and wireless networks.

The Internet changed the entire landscape. As TCP/IP continued to mature into the stable protocol suite that it is today, the PC landscape, as well as mainframe and minicomputers, began to adopt TCP/IP. Although the ISO first attempted to define open protocols so that computers from different vendors could interact to exchange data, it turns out that TCP/IP is the winner in the end. And when IPv6 (IP version 6) finally reaches from the inner core of the Internet to the edge, you will find that TCP/IP continues to add new features, enhance security, and provide more robust features.

Other protocols, such as ATM and Frame Relay, are used for long-distance transfer of data, and can encapsulate other protocols such as TCP/IP. Fibre Channel is a wire protocol that is the most widely used protocol in Storage Area Networks today (see Chapter 11, "Network Attached Storage (NAS) and Storage Area Networks (SAN)").

The old standard Ethernet has itself continued to be enhanced to keep up with the need for speed. Early versions operated at 25Mbps, and most desktops today use 100BASE-T, or 100Mbps Ethernet. Gigabit and 10Gigabit Ethernet are now on the market, although these newer versions do not use the same signaling techniques as earlier versions. The capability to provide backward compatibility with earlier versions, however, is another important factor for the continued use of Ethernet.

Today you will find that most desktop computers in a company's LAN use TCP/IP. Although other protocols may encapsulate TCP/IP for transmission over a long distance, the TCP/IP protocol is still the de facto standard for computer-to-computer communications. TCP/IP is also supported by networked printers and wireless communications.

Because of this standardization, prices for equipment that support Ethernet and TCP/IP are dramatically less than a decade ago. Network adapters themselves may become history because many computer motherboard manufacturers are starting to incorporate that functionality for both wired and wireless connections directly onto the motherboard.

So what does this all mean? It means that whether you operate a business or a home network, or if you just connect to the Internet from home, it has been a long process to get to where we are today. In this book you will find topics that cover many of the important protocols in use today, as well as topics on newer developments.