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Networking: Tracing WANs From ARPANET to Internet
By Jim Metzler

June 1, 2008 —

I mentioned in my last column that I wanted to use my first two columns to create a level setting in terms of networking. With that goal in mind, my last column presented an overview of how local area networks have evolved, and this one will present an overview of how wide area networks (WAN) have evolved.

Wide area computer networks got their start in 1969 with the deployment of ARPANET, the precursor to today’s Internet. Of course, in 1969 ARPANET was used exclusively to connect research institutions, and any commercial use of the network was strictly not allowed. The technology began to be commercialized in 1973 with the development of X.25. The purpose of the X.25 standard was to allow IT organizations to acquire the hardware that they deployed in branch offices from a wide variety of vendors and feel comfortable that they could use that equipment to connect with any service provider that supported X.25.

In 1974 IBM introduced to the market a proprietary network architecture called System Network Architecture (SNA). In the 1970s, the wide area links that were a key part of SNA were typically 9600-baud multipoint private lines. A single multipoint private line could connect offices in different cities. For example, a multipoint private line might link offices in Washington, Philadelphia, New York and Boston. A 9600-baud private line ran at 9,600 bits/second. The term baud implied that the private line was analog—a statement that applied to virtually all private lines used by enterprises in the 1970s.

In the late 1970s and early 1980s SNA was typically deployed only by relatively large companies, most notably in the financial services industry. In addition, these companies often had what was referred to as an electronic tandem network to connect their PBXs and provide simple voice services. While it is still possible to find SNA running today, IBM no longer sells it. In fact, if you Google the term SNA, System Network Architecture is the sixth listing.

A common building block of many enterprise WANs today is a T1 link running at 1.544 Mbits/second. It is used extensively in North America, Japan and Korea. The rest of the world uses an E1 link—a digital circuit that runs at 2.048Mbps. T1s were in use in AT&T’s network since the early 1960s. However, they were only made generally available to enterprise IT organizations in 1984. At that time, it was common for a 500-mile T1 link to cost several thousand dollars a month and have an installation lead time of several months.

Up until 1984, when T1 facilities were made available, the only digital private lines that IT organizations could use were referred to as Dataphone Digital Service (DDS). DDS facilities typically include rates of 2.4, 4.8, 9.6 and 56Kbps. These circuits were exceptionally expensive. As a result, it was common that if you needed three 56Kbps DDS circuits between two locations, you could justify the cost of acquiring a T1 circuit by using the extra bandwidth for voice.

In the late 1980s, it became common for enterprise IT organizations to deploy integrated WANs to carry both voice and data traffic. These WANs were usually built using T1 links and T1 multiplexors. The way this worked is that IT organizations would configure the T1 multiplexor to assign a given amount of bandwidth for data communications and the rest was available for voice calls—each of which consumed 64Kbps of bandwidth. So, for example, if a T1 link was configured to support 256Kbps of data traffic, it could also support up to 20 simultaneous voice calls.

In the early 1990s, IT organizations began to deploy WANs based on a technology called Frame Relay. Frame relay is very similar to X.25, with two key differences. One difference is that since frame relay typically runs over high-quality digital circuits (as opposed to the lower-quality analog circuits that X.25 usually ran over) frame relay does not do as much error checking as X.25 does. Partially as a result of not having to do that extra checking, frame relay runs at speeds significantly higher than X.25 does. In particular, it is rare to find an X.25 link running at a speed greater than 56Kbps. Frame relay, however, runs on a variety of types of links. This includes a T3 link—which runs at 44.736Mbps.

In the mid 1990s, many IT organizations deployed WANs based on ATM (Asynchronous Transfer Mode). Whereas frame relay allowed for variable-sized frames, ATM was based on a 53-byte cell. ATM is a connection-oriented technology, in which a logical connection is established between the two endpoints before the actual data exchange begins. ATM was designed to be a single networking technology that could transport real-time video and audio as well as image files, text and e-mail.

Both frame relay and ATM enjoyed some success in the market. However, the use of both of these technologies is declining. Today the most common WAN technologies are the Internet and a technology referred to as Multi-Protocol Label Switching (MPLS). In areas such as cost, complexity, lead time and support for nomadic workers, Internet based services are superior to MPLS. One area where MPLS services are superior to Internet based services is that MPLS promises low predictable delay.

Today, many of the key questions associated with wide area networking have nothing to do with what technology will come along and replace the Internet and MPLS. Rather, the key questions have to do with how to make the existing WAN services perform better. That will be the topic of future columns.

Jim Metzler has worked in just about every aspect of the networking industry in more than 30 years of professional experience. He can be reached at jim@ashtonmetzler.com.

Related Search Term(s): Networking

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