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Industrial Training

Chapter 2
Internet & TCP/IP

2.1 Introduction to the Internet

The term “Internet” may be defined as a network of networks that, together may create a one large world-wide network. The whole local Internet connection  within the Sri Lanka  is part of the whole Internet. The Internet is truly an organic network: it is always growing; new networks and computers are being added to the Internet every moment.  

As so many people share so much of information over the Internet, it is referred to as the main component of the Information Superhighway. It virtually simulates Our road system’s infrastructure. As more and more people share their knowledge over the Internet, its value, population, and resources all increase, and hence its usefulness to each user increases.

Fig 2.1 Alternate Internet Access Scenarios

 2.2 Internet Tools

 To use the Internet efficiently and usefully, tools are indispensable. Some of the tools are

·         Electronic Mail
·         Usenet
·         FTP
·         Telnet
·         Gopher
·         World Wide Web

2.2.1        Electronic Mail

 Electronic Mail (e-mail for short) is a way for Internet users to correspond with each others in a way similar to the normal postal service. As in the standard postal service, here we need to know the person’s e-mail address for whom we want to send an e-mail.   The e-mail is really a computer file, sent over the Internet using a special program (Email Software). Again at the other end an Email software must be used to receive the e-mail. There are wide range of Email software available in the market, like MS Outlook, MS Outlook Express, Eudora, Pine and Pegasus.

An Email address is made up of two parts: viz. a userid (unique to each person that has an account on a particular computer) and a computer address .The following are some examples for typical Email addresses:

jeya@jhc.lk
asiri@arthursl-as.com

2.2.2        UseNet News 

UseNet is a set of international bulletin boards that allow users to discus topics of interest regardless of time and location. Within UseNet News, the bulletin boards are referred to as news groups. 

These news groups allow users to correspond with other Internet users with similar interests. In the News, we are free to read and reply to messages,  or  post new messages relevant to the particular news group, and they will be read and may be responded by people all over the world.  There are more than 8,000 news groups ranging from Arts to Zoology. They are arranged in a hierarchical manner that indicates the topic of the news group. The top level may give a broad topic name, and may then step down to more particular and specific topics.  

The main hierarchies of news groups are,

2.2.3        File Transfer Protocol (FTP)

FTP is an Internet tool which permits to transfer files from one computer to another over the Internet. If we transfer files from our computer to another, it is referred to as uploading and if its other way around, it’s downloading.  FTP can be used to transfer workings to office  machine, or to obtain software updates from software vendors.  Before we use the FTP, we must know the file and its location. Then we must log in to the computer from which we are going to download or to which we are going to upload the file. Many sites, allow “anonymous ftp” logins; that is, we are allowed to log in to the system, even though we do not have an account on that machine, and transfer files from that system. In short, anonymous FTP allows those with the Internet access the to log in to remote computers for the purpose of transferring publicly accessible files.  While some sites, permit both uploading and downloading, certain sites only permit downloading for security reasons.

2.2.4        Telnet and Gopher

While FTP permits us to transfer files, Telnet allows to really log in to a remote computer and use it. Telnet may be used to get to services like Gophers, Line mode Web servers, libraries and WAIS servers.

Gopher is an Internet navigation tool that allows us to find and retrieve information using a hierarchy of menus and files. Gopher Software (Gopher Client) connects to the Gopher Server and displays the relevant information by means of menus and files.

2.2.5        World Wide Web

World Wide Web (WWW) is another Internet Navigation tool that helps us to find and retrieve information, using links to other Web pages. These tools are often referred to as Web Browsers. Popular browsers are NetScape, Microsoft Internet Explorer, and Mosaic. As each web page may have many links, ultimately, there is no end to these links.  Web links are stored within the page itself and when we wish to jump to the page, that is linked, we select the “hypertext”. Usually these hypertext are colored or underlined in the web browser. The latest versions of web browses include, FTP too. This basically makes us to  simply download files even without knowing the location of the files. And in further Gopher is almost being replaced by the Web browsers  Using web browsers, we can simply search for a topic over the Internet, we can download files, or even we can search for people’s e-mail address. 

Web pages may contain simple text, sound, images and even motion pictures. But all the web clients are not capable of handling all these media types. Some may handle only the text, while some may handle upto images and some may handle all the media available.

Each web browser will have a Home page , from where we will start to surf the web. We can customize the homage  for our browser. Each web page displayed by the browser has an address called URL (Uniform Resource Locator) and really is the citation of the web page being displayed. As long as we know the URLs, we may simply locate the place without following the heavily nested links. Typical  examples for URLs are http://www.asiasoftonline.com, http://www.jhc.lk and  http://www.pdn.ac.lk.  

2.3 TCP/IP and other Protocols

The fundamental technology at the root of the Internet is a set of communication protocols known as Transmission Control Protocol/Internet Protocol, more familiarly known as TCP/IP. TCP/IP's three main characteristics are rich functionality, openness and  pervasiveness. Its functionality is well documented, the result of a flexible design that has allowed it to evolve to meet new needs. As an open communications standard, TCP/IP is not controlled by any single company, a characteristic that makes it appealing to many organizations that wish to preserve flexibility in where they purchase their computer and hardware. LISL never buys, any product if it lacks the support for TCP/IP.

The TCP/IP protocol suite got its name from its two most important protocols, the Transmission Control Protocol (TCP) and the Internet Protocol (IP). The IP datagram is the most basic communication element within TCP/IP, consisting primarily of source and destination address information and application data. IP datagrams are  transmitted from source to destination using routers-computers that are optimized to select the most efficient path through a network as complex as the Internet. To accomplish this, routers use special routing protocols. In addition to this routers often use routing tables. However, IP has no provisions to guarantee that data will reach its destination. That's the job of TCP, which includes information that applications depend upon to ensure  delivery of data.  

2.3.1 Addressing

In TCP/IP-based network, one of the  fundamental concerns will be addressing. Unlike protocols such as IPX, which derives its network addresses dynamically, usually by reading the MAC-layer address of the network interface card (NIC), TCP/IP addresses must be assigned to devices on the network. A TCP/IP address is a 32-bit entity made up of a network address and a node address, usually represented in dotted-decimal notation. Although it is fairly common to divide this address space evenly with 16 bits for the network address and 16 bits for the node address, this may vary depending on the number of computers connected to the network.

2.3.2  Getting an Address

Since all computers attached to the Internet must have unique addresses, some entity must assume responsibility for assigning these addresses. These responsibilities are currently handled by the Internet Network Information Center, or InterNIC (www.internic.net), which is managed by Network Solutions Inc. (US). Addresses are divided into classes depending on the number of nodes on the network. For example, a Class C Internet address provides enough addresses for up to 255 computer systems. A Class B address provides enough addresses for more than 65,000 computers. Although InterNIC controls the allocation of official Internet addresses, anyone can build a corporate network around TCP/IP using any set of addresses they choose, as long as they don't want to connect to the Internet. 

Fig 2.2 Internet IP Address Classes  

2.3.3     Domain Name Server 

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