CAPÍTULO IV: Análisis e interpretación de resultados
4.3 Verificación de las Hipótesis
While ARPA was working on the Internet research project, the UNIX operating system was also taking the computing world by storm. A group of computer researchers developed UNIX in the early 1970s at the Bell Labs. Bell Labs allowed universities to have copies of UNIX for teaching and research purposes. To encourage its portability, Bell Labs provided the source code of the UNIX operating system to the students. This meant that the students could try it out in a variety of ways to see if it worked and could also modify it to make it better. A group of students at the University of California at Berkeley wrote application programs and modified the UNIX operating system to have network capabilities (e.g., sending a message to another computer, accessing a file stored on a remote computer, etc.). This version of UNIX, later called as BSD UNIX (Berkeley Software Distribution) became very popular.
ARPA noticed that BSD was now a well-known entity. They signed a deal with Berkeley researchers under which the BSD UNIX now incorporated TCP/IP protocol in the operating system itself. Thus, with the next
41 version of BSD UNIX, people got TCP/IP software almost free. Although few universities who bought BSD UNIX had connection to the Internet, they usually had their own Local Area Networks (LANs). They now started using TCP/IP for LANs. Later on, the same concept was applied to the Internet. Thus, TCP/IP first entered the LANs at the universities, and from there, to other networks.
By early 1980s, the Internet had become reliable. The main interconnection at this stage was between academic and research sites. The Internet had demonstrated that the basic internetworking principles were quite sound. This convinced the US military. They now
connected their computers to the Internet using TCP/IP software. In 1982, the US military decided to use the Internet as its primary computer communication medium. At the start of 1983, ARPANET and the concerned military networks stopped running old communication software and made TCP/
IP the de facto standard.
Before the US military started switching its computers to use TCP/IP, there were about 200 computers connected to the Internet. In 1984, this number almost doubled. Other US government agencies, such as Department of Defense (DOD) and National Aeronautics and Space Administration (NASA), also got themselves connected to the Internet. Meanwhile, the Cold War suddenly ended. The Internet came out of the secret world of the military and became open to the general public and businesses. Since then, the number of computers connected to the Internet kept almost doubling every year. In 1990, there were approximately 290,000 computers connected to the Internet. At the time of going to the press, it is estimated
that every three seconds a new computer connects to the Internet. Table 2.4 shows the number of computers connected to the Internet from 1995 to 2007. It is indeed quite an explosive growth!
This is shown graphically in Fig. 2.16.
Fig. 2.16 The growth of the Internet
Table 2.4 The growth of the Internet
Year Number of Users (in Millions)
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SUMMARY
l When multiple computers are connected to each other, a computer network is formed. When multiple computer networks are connected to each other, it becomes an internetwork, or an internet.
l A router is a special-purpose computer that can connect multiple computer networks. For this, a router has an interface (NIC) to each of the networks that it connects to.
l The Internet is a virtual network of computer networks. The term virtual arises because it is actually a network of a number of networks, which differ in their hardware and software characteristics, and yet work seamlessly with each other.
l Networking and internetworking devices are used respectively for connecting computers and networks together.
l Networking devices include repeaters and bridges. Internetworking devices can be classified into routers and gateways.
l A repeater is an electronic device, which simply regenerates a bit stream. It works at the physical layer of the OSI protocol.
l A bridge is a computer that has its own processor, memory and two NIC cards to connect to two portions of a network. A bridge does not run application programs, and instead, facilitates host-to-host communication within a network.
l A router is an intelligent device. Its capabilities are much more than those of a repeater or a bridge. A router is useful for interconnecting two or more networks.
l The most powerful device is a gateway. A gateway can forward packets across different networks that may also use different protocols.
l The Internet is one of the most significant developments of the 20th century.
REVIEW QUESTIONS
Multiple-choice Questions
1. In internetworking, the two or more networks that connect with each other incompatible with one another.
(a) have to be (b) may be (c) must not be (d) None of the above 2. Usually, a is used for internetworking purposes.
(a) host (b) wire (c) router (d) joiner
3. A router must have at least NICs.
(a) 2 (b) 3 (c) 4 (d) 5
4. There are incompatibility issues when forming an internet out of networks.
(a) both hardware and software (b) only hardware
(c) only software (d) software but not hardware
5. A bridge is a device.
(a) networking (b) connecting (c) internetworking (d) routing
43 6. A is the simplest of all networking/internetworking devices.
(a) repeater (b) bridge (c) router (d) gateway
7. Generally, a is used to divide a network into segments.
(a) repeater (b) bridge (c) router (d) gateway
8. A builds its mapping table as and when it gets more information about the network.
(a) simple bridge (b) repeater (c) adaptive bridge (d) regenerator 9. A logical address is the physical address.
(a) the same as (b) tightly coupled with
(c) sometimes related to (d) completely unrelated to 10. A can understand multiple networking protocols.
(a) repeater (b) bridge (c) router (d) gateway
Detailed Questions
1. Discuss the motives for internetworking.
2. What is universal service?
3. What are the various broad-level issues in internetworking?
4. How does a router facilitate interconnection between two or more networks?
5. Explain the role played by the repeater at the physical layer.
6. What is a bridge? Explain its functions.
7. What are the types of bridges? Explain the simple bridge.
8. What is a router? How does it work?
9. How does a gateway work?
10. Discuss in brief the history of the Internet.
Exercises
1. Find out more about the history of the Internet.
2. Investigate what is required to become an ISP.
3. If your background is not in data communications, learn more about the various data communications and networking technologies, such as LAN (Ethernet, Token Ring, FDDI), MAN (SMDS, DQDB) and WAN (X.25, Frame Relay).
4. Assume that you have to build a router on your own. What would be the hardware/software requirements for the same?
5. Find out what sort of router or bridge is being used by your organization, college or university.
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