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Internet Routing Architectures Second Edition - Cisco press.pdf
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Internet Routing Architectures, Second Edition

provided in this chapter to set the stage for understanding the challenges of interfacing the Internet and the steps involved in building scalable internetworks.

Origins and Recent History of the Internet

The Internet started as an experiment in the late 1960s by the Advanced Research Projects Agency (ARPA, now called DARPA) of the U.S. Department of Defense[]. DARPA experimented with the connection of computer networks by giving grants to multiple universities and private companies to get them involved in the research.

In December 1969, an experimental network went online with the connection of a four-node network connected via 56 kbps circuits. The new technology proved to be highly successful and led to the creation of two similar military networks—MILNET in the U.S. and MINET in Europe. Thousands of hosts and users subsequently connected their private networks (universities and government) to the ARPANET, thus creating the initial "ARPA Internet." Figures 1-1 and 1-2 illustrate the ARPANET in the early days, from its inception in 1969 to its growing number of connectors in 1976.

Figure 1-1. ARPANET Architecture, December 1969

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Internet Routing Architectures, Second Edition

Figure 1-2. ARPANET Architecture, July 1976

The conglomeration of research, academic, and government networks, combined with the ARPANET core network, was the beginning of what came to be known as the Internet. However, ARPANET had an Acceptable Usage Policy (AUP) that prohibited the use of the Internet for commercial purposes. Nonetheless, the usefulness of the ARPANET to its connectors resulted in scalability problems, the most apparent of which was link congestion. As a result, the National Science Foundation (NSF) began development of the NSFNET[].

The ARPANET was decommissioned in 1989.


By 1985, the ARPANET was heavily utilized and burdened with congestion. In response, the National Science Foundation initiated phase 1 development of the NSFNET. The NSFNET was composed of multiple regional networks and peer networks (such as the NASA Science Network) connected to a major backbone that constituted the core of the overall NSFNET.

In its earliest form, in 1986, the NSFNET created a more distributed, three-tiered network architecture. This architecture connected campuses and research organizations to regional networks, which in turn connected to a main backbone network linking six nationally funded supercomputer centers. The original links of 56 kbps were upgraded in 1988 to faster T1 (1.544 Mbps) links. This was a result of the 1987 NSF competitive solicitation for faster network service, awarded to Merit Network, Inc. and its partners MCI, IBM, and the state of Michigan. The NSFNET T1 backbone connected a total of 13 sites, including Merit,

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BARRNET, MidNet, Westnet, NorthWestNet, SESQUINET, SURAnet, NCAR (National Center for Atmospheric Research), and five NSF supercomputer centers.

In 1990, Merit[], IBM, and MCI started a new organization known as Advanced Network and Services (ANS). Merit's Internet engineering group provided a policy routing database and routing consultation and management services for the NSFNET, whereas ANS operated the backbone routers and a Network Operation Center (NOC).

By 1991, data traffic had increased tremendously, which necessitated upgrading the NSFNET's backbone network service to T3 (45 Mbps) links. Figure 1-3 illustrates the original NSFNET with respect to the location of its core and regional backbones.

Figure 1-3. The NSFNET-Based Internet Environment

As late as the early 1990s, the NSFNET was still reserved for research and education applications, and government agency backbones were reserved for mission-oriented purposes. These and other emerging networks were feeling new pressures as different agencies needed to interconnect with one another. Commercial and general-purpose interests were clamoring for network access, and Internet service providers (ISPs) were emerging to accommodate those interests, defining an entirely new industry in the process. Networks in places other than the U.S. had developed, along with international connections. As the various new and existing entities pursued their goals, the complexity of connections and infrastructure grew.

In the United States, government agency networks interconnected at Federal Internet eXchange (FIX) points on both the east and west coasts. Commercial network organizations had formed the Commercial Internet eXchange (CIX) association, which built an interconnect point on the west coast. At the same time, ISPs around the world, particularly in Europe and Asia, had developed substantial infrastructures and connectivity.

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To begin sorting out the growing complexity, Sprint was appointed by the NSFNET to be the International Connections Manager (ICM), responsible for providing connectivity between the U.S., European, and Asian networks. NSFNET was decommissioned in April 1995.

The Internet Today

The decommissioning of the NSFNET had to be done in specific stages to ensure continuous connectivity to institutions and government agencies that used to be connected to the regional networks. Today's Internet infrastructure is a move from a core network (NSFNET) to a more distributed architecture operated by commercial providers such as UUNET, Qwest, Sprint, and thousands of others, connected via major network exchange points, as well as direct network interconnections. Figure 1-4 illustrates the general form of the Internet today.

Figure 1-4. The General Structure of Today's Internet

The contemporary backbone of the Internet is a collection of service providers that have connection points called POPs (points of presence) over multiple regions. Its collection of POPs and the infrastructure that interconnects them form a provider's network. Customers are connected to providers via access or hosting facilities in a service provider's POP. These customers can be service providers themselves. The prevalent service models employed by ISPs today are discussed in more detail in Chapter 2, "ISP Services and Characteristics."

Providers that have POPs throughout the U.S. are commonly referred to as national providers. Providers that cover specific regions, or regional providers, connect themselves to other providers at one or more points. To enable customers of one provider to reach customers connected to another provider, traffic is exchanged at public Network Access Points (NAPs) or via direct interconnections. The term ISP (Internet service provider) is commonly used to refer to anyone who provides Internet connectivity service, whether directly to the end user, or to other service providers. The term NSP (Network Service Provider) was traditionally

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