Chapter 11

The Internet

Data Communications andComputer Networks: A Business User’s Approach

Data Communications and Computer Networks Chapter 11

Introduction•Today’s Internet is a vast collection of thousands of networks and their attached devices.

•The Internet began as the Arpanet during the 1960s.

•One high-speed backbone connected several university, government, and research sites.

•The backbone was capable of supporting 56 Kbps transmission speeds and eventually became financed by the National Science Foundation (NSF).

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

Internet ServicesThe Internet provides many types of services, including several very common ones:

• File transfer protocol (FTP)

• Remote login (Telnet)

• Internet telephony

• Electronic mail

Data Communications and Computer Networks Chapter 11

Internet ServicesThe Internet provides many types of services, including several very common ones:

• Listservs

• Usenet

• Streaming audio and video

• The World Wide Web

Data Communications and Computer Networks Chapter 11

File Transfer Protocol (FTP)Used to transfer files across the Internet.

User can upload or download a file.

The URL for an FTP site begins with ftp://…

The three most common ways to access an FTP site is:

1. Through a browser

2. Using a canned FTP program e.g. WS-FTP

3. Issuing FTP commands at a text-based command prompt.

Data Communications and Computer Networks Chapter 11

Remote Login (Telnet)Allows a user to remotely login to a distant computer site.

User usually needs a login and password to remote computer site.

User saves money on long distance telephone charges.

Data Communications and Computer Networks Chapter 11

Internet TelephonyThe transfer of voice signals using a packet switched network and the IP protocol.

Also known as packet voice, voice over packet, voice over the Internet, and voice over Internet Protocol (VoIP).

VoIP can be internal to a company or can be external using the Internet.

VoIP consumes many resources and may not always work well, but can be cost effective.

Data Communications and Computer Networks Chapter 11

Electronic MailE-mail programs can create, send, receive, and store e-mails, as well as reply to, forward, and attach non-text files.

Multipurpose Internet Mail Extension (MIME) is used to send e-mail attachments.

Simple Mail Transfer Protocol (SMTP) is used to transmit e-mail messages.

Post Office Protocol version 3 (POP3) and Internet Message Access Protocol (IMAP) are used to hold and later retrieve e-mail messages.

Data Communications and Computer Networks Chapter 11

ListservsA popular software program used to create and manage Internet mailing lists.

When an individual sends an e-mail to a listserv, the listserv sends a copy of the message to all listserv members.

Listservs can be useful business tools for individuals trying to follow a particular area of study.

Data Communications and Computer Networks Chapter 11

UsenetA voluntary set of rules for passing messages and maintaining newsgroups.

A newsgroup is the Internet equivalent of an electronic bulletin board system.

Thousands of Usenet groups exist on virtually any topic.

Data Communications and Computer Networks Chapter 11

Streaming Audio and VideoThe continuous download of a compressed audio or video file, which can be heard or viewed on the user’s workstation.

Real-time Protocol (RTP) and Real Time Streaming Protocol (RTSP) support streaming audio and video.

Streaming audio and video consume a large amount of network resources.

Data Communications and Computer Networks Chapter 11

World Wide WebThe World Wide Web (WWW) is an immense collection of web pages and other resources that can be downloaded across the Internet and displayed on a workstation via a web browser.

The most popular service on the Internet.

Basic web pages are created with the HyperText Markup Language (HTML).

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

World Wide WebWhile HTML is the language to display a web page, HyperText Transport Protocol (HTTP) is the protocol to transfer a web page.

Many extensions to HTML have been created. Dynamic HTML is a very popular extension to HTML.

Common examples of dynamic HTML include mouse-over techniques, live positioning of elements (layers), data binding, and cascading style sheets.

Data Communications and Computer Networks Chapter 11

World Wide WebExtensible Markup Language (XML) is a description for how to create a document - both the definition of the document and the contents of the document.

The syntax of XML is fairly similar to HTML.

You can define your own tags, such as <CUSTOMER> which have their own, unique properties.

Data Communications and Computer Networks Chapter 11

e-CommerceThe buying and selling of goods and services via the Internet.

Many agree that e-commerce consists of four major areas:

1. e-retailing – electronic selling and buying of merchandise using the Web

2. Electronic Data Interchange (EDI) – electronic commercial transaction between two companies

Data Communications and Computer Networks Chapter 11

e-Commerce (cont.)3. Micro-marketing – gathering and use of potential and current customer borrowing habits

4. Electronic security – the security system that supports all Internet transactions

Data Communications and Computer Networks Chapter 11

Cookies and State InformationA cookie is data created by a web server that is stored on the hard drive of a user’s workstation.

This state information is used to track a user’s activity and to predict future needs.

Information on previous viewing habits stored in a cookie can also be used by other web sites to provide customized content.

Many consider cookies to be an invasion of privacy.

Data Communications and Computer Networks Chapter 11

Intranets and ExtranetsAn intranet is a TCP/IP network inside a company that allows employees to access the company’s information resources through an Internet-like interface.

When an intranet is extended outside the corporate walls to include suppliers, customers, or other external agents, the intranet becomes an extranet.

Data Communications and Computer Networks Chapter 11

Internet ProtocolsTo support the Internet and all its services, many protocols are necessary.

Some of the protocols that we will look at:

• Internet Protocol (IP)

• Transport Control Protocol (TCP)

• Address Resolution Protocol (ARP)

• Domain Name System (DNS)

Data Communications and Computer Networks Chapter 11

Internet ProtocolsRecall that the Internet with all its protocols follows the Internet model.

An application, such as e-mail, resides at the highest layer.

A transport protocol, such as TCP, resides at the transport layer.

The Internet Protocol (IP) resides at the Internet or network layer.

A particular media and its framing resides at the interface layer.

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

The Internet Protocol (IP)IP prepares a packet for transmission across the Internet.

The IP header is encapsulated onto a transport data packet.

The IP packet is then passed to the next layer where further network information is encapsulated onto it.

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

The Internet Protocol (IP)Using IP, a subnet router:

• Makes routing decision based on the address in the IP datagram.

• May have to fragment the datagram into smaller datagrams.

• May determine that the current datagram has been hopping around the network too long and delete it.

To perform these functions, an IP header is encapsulated onto each transport layer packet.

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

The Transport Control Protocol (TCP)The TCP layer creates a connection between sender and receiver using port numbers.

The TCP layer can ensure that the receiver is not overrun with data (end-to-end flow control).

TCP can multiplex multiple connections (using port numbers) over a single IP line.

TCP can perform end-to-end error correction.

TCP allows for the sending of high priority data.

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

Internet Control Message Protocol (ICMP)ICMP, which is used by routers and nodes, performs the error reporting for the Internet Protocol.

ICMP reports errors such as invalid IP address, invalid port address, and the packet has hopped too many times.

Data Communications and Computer Networks Chapter 11

User Datagram Protocol (UDP)A transport layer protocol used in place of TCP.

Where TCP supports a connection-oriented application, UDP is used with connectionless applications.

UDP also encapsulates a header onto an application packet, but the header is much simpler than TCP.

Data Communications and Computer Networks Chapter 11

Address Resolution Protocol (ARP)When an IP packet has traversed the Internet and encounters the destination LAN, how does the packet find the destination workstation?

Even though the destination workstation may have an IP address, a LAN does not use IP addresses to deliver frames. A LAN uses the MAC layer address.

ARP translates an IP address into a MAC layer address so a frame can be delivered to the proper workstation.

Data Communications and Computer Networks Chapter 11

Tunneling ProtocolsThe Internet is not normally a secure system.

If a person wants to use the Internet to access a corporate computer system, how can a secure connection be created?

One possible technique is by creating a virtual private network (VPN).

A VPN creates a secure connection through the Internet by using a tunneling protocol.

Data Communications and Computer Networks Chapter 11

Locating a Document on the InternetEvery document on the Internet has a unique uniform resource locator (URL).

All URLs consist of four parts:

1. Service type

2. Host or domain name

3. Directory or subdirectory information

4. Filename

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

Locating a Document on the InternetWhen a user running a web browser enters a URL, how is the URL translated into an IP address?

The Domain Name System (DNS) is a large, distributed database of URLs and IP addresses.

The first operation performed by DNS is to query a local database for URL/IP address information.

If the local server does not recognize the address, the server at the next level will be queried.

Data Communications and Computer Networks Chapter 11

Locating a Document on the InternetEventually the root server for URL/IP addresses will be queried.

If the root server has the answer, the results are returned.

If the root server recognizes the domain name but not the extension in front of the domain name, the root server will query the server at the domain name’s location.

Data Communications and Computer Networks Chapter 11

IP AddressesAll devices connected to the Internet have a 32-bit IP address associated with it.

There are basically four types of IP addresses: Classes A, B, C and D.

A particular class address has a unique network address size and a unique host address size.

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

IP AddressesSometimes a device is permanently assigned an IP address. This is called static assignment.

Sometimes a device is assigned an IP address only when it accesses the Internet. This is called dynamic assignment.

Dynamic assignment of IP addresses is more flexible in that many devices can share a smaller pool of IP addresses.

The disadvantage is that you may run out of IP addresses and not have enough to assign every device that connects to the Internet at the same time.

Classfull and Classless IP Addressing

Data Communications and Computer Networks Chapter 11

The Future of the InternetVarious Internet committees are constantly working on new and improved protocols.

Examples include:

• Internet Printing Protocol

• Internet fax

• Extensions to FTP

• Common Name Resolution Protocol

• WWW Distributed Authoring and Versioning

Data Communications and Computer Networks Chapter 11

IPv6The next version of the Internet Protocol.

Main features include:

• Simpler header

• 128-bit IP addresses

• Priority levels and quality of service parameters

• No fragmentation

Data Communications and Computer Networks Chapter 11

IPv6

Data Communications and Computer Networks Chapter 11

Internet2A new form of the Internet is being developed by a number of businesses and universities in the US.

Internet2 will support very high speed data streams.

Applications might include:

• Digital library services

• Tele-immersion

• Virtual laboratories

Data Communications and Computer Networks Chapter 11

The Internet In Action: A Company Creates a VPNA fictitious company wants to allow 3,500 of its workers to work from home.

If all 3,500 users used a dial-in service, the telephone costs would be very high.

Data Communications and Computer Networks Chapter 11

Data Communications and Computer Networks Chapter 11

The Internet In Action: A Company Creates a VPNInstead, the company will require each user to access the Internet via their local Internet service provider.

This local access will help keep telephone costs low.

Then, once on the Internet, the company will provide software to support virtual private networks.

The virtual private networks will create secure connections from the users’ homes into the corporate computer system.

Data Communications and Computer Networks Chapter 11