McGraw-Hill©The McGraw-Hill Companies, Inc. Chapter 13 The Internet

McGraw-Hill©The McGraw-Hill Companies, Inc. Know how the Internet began. Understand the architecture of today’s Internet and its relation- ship with ISPs. Understand the importance of the TCP/IP protocol suite. After reading this chapter, the reader should be able to: O BJECTIVES Understand the role of IP, UDP, and TCP in the Internet. Understand the difference between the Internet, an intranet, and an extranet.

McGraw-Hill©The McGraw-Hill Companies, Inc. HISTORYANDADMINISTRATIONHISTORYANDADMINISTRATION 13.1

McGraw-Hill©The McGraw-Hill Companies, Inc. mid 1960s mainframe computers in research were stand alone Advanced Research Projects Agency (ARPA) in DOD got interested in connecting computers In 1967 at an ACM conference, ARPA presented ideas of the ARPANET.History The idea of Interface Message Processor was conceived, where Each host computer would be attached to this specialized computer. In 1969, the ARPANET was a reality- with four nodes, UCLA, UCSB, Stanford Research Institute, University of Utah. Software used was called Network Control Protocol (NCP).

McGraw-Hill©The McGraw-Hill Companies, Inc. 1972, Vint Cerf and Bob Khan both who were part of the ARPNET group collaborated on what was the Internetting Project. They linked different host on one network. Ran into obvious problems, e.g. packet sizes, interfaces, diverse transmission rates, unreliability etc. History In 1973 Cerf and Khan’ landmark paper outlined protocols for end-to-end delivery of packets. This was new version of the NCP. The new NCP included TCP concepts such as encapsulation, the datagram and function of the gateway.

McGraw-Hill©The McGraw-Hill Companies, Inc. The idea of Error detection and correction was conceived The ARPANET project was handed over to the Defence Communication Agency (DCA). History 1977 an internet consisting of three different network ARPANET, packet radio, and packet satellite was demonstrated. Shortly there TCP was split into two protocols, TCP and IP.

McGraw-Hill©The McGraw-Hill Companies, Inc. UNIX was modified in 1981, under DARPA contract and UC Berkeley to include TCP/IP. Working code of Berkeley UNIX was given to every manufacturer, as a base to build products upon. History 1983 all other ARPANET protocols were abolished, only TCP/IP was the official protocol of the ARPANET. Internet now is not a simple hierarchical structure, it is made up of many WAN and LANs. Internet is run by companies not the government.

McGraw-Hill©The McGraw-Hill Companies, Inc. Commonly Used Operating Systems The UNIX operating system was created at AT&T Bell Labs in the early 1970s by Ken Thompson and Dennis Ritchie The first version of the Disk Operating System (DOS) for IBM personal computers was created in about 1980 by Microsoft

McGraw-Hill©The McGraw-Hill Companies, Inc. Commonly Used Operating Systems In 1984 Apple Computer introduced the Macintosh, which integrated the operating system and the graphical interface In August 1995 Microsoft introduced the Windows 95 operating system, which integrated a copy of DOS and a copy of Windows

McGraw-Hill©The McGraw-Hill Companies, Inc. Linux Arrives In 1991 Linus Torvalds decided to create a UNIX-like operating system kernel for his IBM-compatible PC as a school project Torvalds solicited help via the Internet Hundreds of programmers around the world were working together to create a new Linux kernel

McGraw-Hill©The McGraw-Hill Companies, Inc. The Linux Software License A software license is a legal definition of who can use a piece of software and how it can be used Torvalds decided to base the software license for the Linux kernel on a model created by Richard Stallman and the Free Software Foundation

McGraw-Hill©The McGraw-Hill Companies, Inc. The Free Software Foundation and the GNU Project In 1983 Richard Stallman at the Massachusetts Institute of Technology founded an organization called the Free Software Foundation (FSF) With the GNU project, Stallman intended to create a completely free version of UNIX, written from scratch

McGraw-Hill©The McGraw-Hill Companies, Inc. The Free Software Foundation and the GNU Project Hundreds of software programs as part of the GNU project are included with the Linux kernel in each copy of a complete Linux operating system

McGraw-Hill©The McGraw-Hill Companies, Inc. The GNU General Public License (GPL) The General Public License (GPL) requires that source code be distributed with each copy of the Linux kernel –The source code is the set of human-readable programming instructions used to create the program Anyone who obtains a copy of the software can redistribute it in any form

McGraw-Hill©The McGraw-Hill Companies, Inc. The GNU General Public License (GPL) Anyone who obtains a copy of the software can redistribute it in any form Anyone can modify the software, the modifications are automatically subject to the GPL

McGraw-Hill©The McGraw-Hill Companies, Inc. How Linux Is Developed Linux kernel development follows the model of most free software projects A person identifies a need and begins writing a program The software developer announces the project on the Internet

McGraw-Hill©The McGraw-Hill Companies, Inc. How Linux Is Developed Developers who share an interest in that project respond, and soon they begin to work together on different parts of the project The project lead releases the software (including source code) on the Internet to try it and fix the bugs

McGraw-Hill©The McGraw-Hill Companies, Inc. RFCs can be found at Note:

McGraw-Hill©The McGraw-Hill Companies, Inc. Figure 13-1 Internet today

McGraw-Hill©The McGraw-Hill Companies, Inc. Technical Focus: Maturity Levels of an RFC An RFC, during its lifetime, falls into one of six maturity levels: proposed standard, draft standard, Internet standard, historic, experimental, and informational.

McGraw-Hill©The McGraw-Hill Companies, Inc. Figure 13-2 Internet administration

McGraw-Hill©The McGraw-Hill Companies, Inc. TCP/IPPROTOCOLSUITETCP/IPPROTOCOLSUITE 13.2

McGraw-Hill©The McGraw-Hill Companies, Inc. Figure 13-3 TCP/IP protocol suite

McGraw-Hill©The McGraw-Hill Companies, Inc. Figure 13-4 IP datagram

McGraw-Hill©The McGraw-Hill Companies, Inc. Technical Focus: Inside the Header of an IP Datagram An IP datagram contains several fields. The most important are the source and destination addresses of the datagram (IP addresses). The header also contains fields related to fragmentation. The size of a datagram may be too large for some LAN or WAN protocols. In this case, the datagram is divided into fragments; each fragment carries the same identification number as well as other information to help the receiver assemble the datagram. The header also has two length fields; one defines the length of the header, the other defines the length of the entire packet. One field that can decrease traffic on the Internet holds the number of routers a packet can visit before it is discarded. The header also contains a checksum field to determine the validity of the packet.

McGraw-Hill©The McGraw-Hill Companies, Inc. Figure 13-5 Internet address

McGraw-Hill©The McGraw-Hill Companies, Inc. Technical Focus: Classful versus Classless Addressing With more and more organizations wanting to use the Internet, the Internet authorities are running out of IP addresses. Internet addresses were originally designed as classful addresses. By this, we mean that the total number of 32-bit addresses was divided unevenly into five classes: A, B, C, D, and E. Class A and B contain blocks of addresses with a very large range. Each block is granted to one organization, but most of these organizations never use their allotted number of addresses. This is a tremendous waste of addresses. Recently, a new design called classless addressing has been implemented. In this design, all available addresses are put into a big pool; each organization is granted a range of addresses according to its need.

McGraw-Hill©The McGraw-Hill Companies, Inc. Figure 13-6 A part of the Internet

McGraw-Hill©The McGraw-Hill Companies, Inc. Figure 13-7 UDP user datagram

McGraw-Hill©The McGraw-Hill Companies, Inc. Technical Focus: Inside a UDP header The header of the UDP datagram is very simple: it contains only four fields. One field defines the application program that has sent the packet (the source), and another defines the application program that is to receive the packet (the destination). Another field defines the length of the entire packet. The last field carries a checksum for error detection.

McGraw-Hill©The McGraw-Hill Companies, Inc. Figure 13-8 TCP segment format

McGraw-Hill©The McGraw-Hill Companies, Inc. Technical Focus: Inside a TCP Segment Header The header of a segment is very complicated and contains optional as well as mandatory fields. We briefly discuss just the required fields. One pair of fields defines the source and destination application programs. Another pair is used for error and flow control; one holds the unique sequence number, and the other holds the acknowledgment number. One field defines the size of the sliding window in the transport layer. The sliding window in the transport layer uses the same concept as the one in the data link layer (see Chapter 5). There are also flags that define the purpose of the segment (for connection establishment, for termination, for acknowledgment, and so on). The last required field carries a checksum for error detection.

McGraw-Hill©The McGraw-Hill Companies, Inc. NEXTGENERATIONNEXTGENERATION 13.3

McGraw-Hill©The McGraw-Hill Companies, Inc. ACCESS TO THE INTERNET INTERNET 13.3

McGraw-Hill©The McGraw-Hill Companies, Inc. PRIVATE NETWORKS: INTRANET AND EXTRANET PRIVATE NETWORKS: INTRANET AND EXTRANET 13.5

McGraw-Hill©The McGraw-Hill Companies, Inc. Technical Focus: Network Address Translation (NAT) A technology that is related to private networks is network address translation (NAT). The technology allows a site to use a set of private addresses for internal communication and a set of (at least one) global Internet addresses for communication with other sites.