THE INTERNET, INTRANETS, AND EXTRANETS
An Overview of Telecommunications and Networks Telecommunications: the electronic
transmission of signals for communications
Telecommunications medium: anything that carries an electronic signal and interfaces between a sending device and a receiving device
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An Overview of Telecommunications and Networks (continued)
Elements of a Telecommunications System
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Transmission Media
Transmission Media Types
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Transmission Media (continued)
Transmission Media Types (continued)
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Telecommunications Devices
Common Telecommunications Devices
Networks Computer network: the
communications media, devices, and software needed to connect two or more computer systems or devices
Network nodes: the computers and devices on the networks
Basic Processing Strategies Centralized processing: all processing
occurs in a single location or facility Decentralized processing: processing
devices are placed at various remote locations
Distributed processing: computers are placed at remote locations but connected to each other via a network
Terminal-to-Host, File Server, and Client/Server Systems Connecting computers in distributed
information processing: Terminal-to-host: the application and database
reside on one host computer, and the user interacts with the application and data using a “dumb” terminal
File server: the application and database reside on the one host computer, called the file server
Client/server: multiple computer platforms are dedicated to special functions, such as database management, printing, communications, and program execution
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Terminal-to-Host, File Server, and Client/Server Systems (continued)
Client/Server Connection
Network Types Personal area network (PAN) Local area network (LAN) Metropolitan area network (MAN) Wide area network (WAN) International network
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Network Types (continued)
A Typical LAN
Network Types (continued)
A Wide Area Network
Communications Software and Protocols Communications software: software
that provides a number of important functions in a network, such as error checking and data security
Network operating system (NOS) Network management software Communications protocol: a standard
set of rules that controls a telecommunications connection
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Communications Software and Protocols (continued)
Common Communications Protocols
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Communications Software and Protocols (continued)
Common Communications Protocols (continued)
Use and Functioning of the Internet Internet: a collection of interconnected
networks, all freely exchanging information ARPANET
The ancestor of the Internet A project started by the U.S. Department of
Defense (DoD) in 1969 Internet Protocol (IP): communication
standard that enables traffic to be routed from one network to another as needed
How the Internet Works The Internet transmits data from one
computer (called a host) to another If the receiving computer is on a network to
which the first computer is directly connected, it can send the message directly
If the receiving computer is not on a network to which the sending computer is connected, the sending computer relays the message to another computer that can forward it
The Internet The internet
A network of networks The internet transmits data from one
computer (called a host) to another Internet networks
Linked networks that work much the same way -- they pass data around in packets, each of which carries the addresses of its sender and receiver
Internet
Unlike online services, which are centrally controlled, the Internet is decentralized by design. Each Internet computer, called a host, is independent. Its operators can choose which Internet services to use and which local services to make available to the global
Internet community. Remarkably, this anarchy by design works exceedingly
There are a variety of ways to access the Internet. It is also possible to
gain access through a commercial Internet Service Provider (ISP).
How the Internet WorksTransport control protocol (TCP)
A protocol that operates at the transport layer and is used in combination with IP by most Internet applications
Backbone An Internet high-speed, long distance
communications links (like a bus; wire that connects nodes)
Uniform resource locator (URL) An assigned address on the Internet for each
computer E.g., http://www.yorku.ca/
Domain AffiliationsDomain
Affiliations
arts cultural and entertainment activitiescom business organizationsedu educational sitesfirm businesses and firmsgov government sitesinfo information service providersmil military sitesnom individuals net networking organizationsorg organizationsrec recreational activitiesstore businesses offering goods for purchaseweb entities related to World Wide Web
activitiesnet networking organizations
Access to the Internet LAN servers
Local servers can provide access to the Internet through normal connections (e.g., Ethernet)
Serial line internet protocol (SLIP) and Point-to-point protocol (PPP)
Communications protocol software that transmits packets over telephone lines, allowing dial-up access to the Internet
Connection via an on-line service Examples are America Online and Microsoft Network.
These services usually require sign-up procedures
Three Ways to Access the Internet
Internet Service Providers Internet service provider (ISP)
Any company that provides individuals or companies with access to the Internet
Thousands of providers including large communications companies
Need an account with the ISP and software that links with TCP/IP
Internet Services E-mail Telnet FTP Usenet and newsgroups Chat rooms Internet phone Internet videoconferencing Content streaming
Internet Services Internet telephony
Also called voice-over-IP (VOIP) Technology that enables network managers to
route phone calls and fax transmissions over the same network they use for data
What is VOIP ?Internet telephony is a category of hardware and software that enables people to use the Internet as the transmission medium for telephone calls. For users who have free, or fixed-price, Internet access, Internet telephony software essentially provides free telephone calls anywhere in the world. To date, however, Internet telephony does not offer the same quality of telephone service as direct telephone connections.
There are many Internet telephony applications available. Some, like CoolTalk and NetMeeting, come bundled with popular Web browsers. Others are stand-alone products. Internet telephony products are sometimes called IP telephony, Voice over the Internet (VOI) or Voice over IP (VOIP) products.
Content Streaming Content streaming
A method for transferring multimedia files over the Internet so that the data stream of voice and pictures plays continuously, without a break, or very few of them
It also enables users to browse large files in real time
The World Wide Web World Wide Web
A collection of tens of thousands of independently-owned computers that work together as one in an Internet service
WWW Terminology Home page
The cover page for a Web site that has graphics, titles, coloured text, etc.
Hypermedia Tools that connect the data on Web pages,
allowing users to access topics in whatever order they wish
Hypertext markup language (HTML) The standard page description language for
Web pages
WWW Terminology Web browser
Software that creates a unique hypermedia-based menu on your computer screen and provides a graphical interface to the Web
Web page A screen of information sent to a requesting
user and presented through a browser Applet
A small program embedded in Web pages
HTML “The” language of WWW pages
Need we say more!!!
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The World Wide Web The Web, WWW or W3 A menu-based system that uses the
client/server model Organizes Internet resources throughout
the world into a series of menu pages, or screens, that appear on your computer
Hypermedia: tools that connect the data on Web pages, allowing users to access topics in whatever order they want
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The World Wide Web Hypertext Markup Language
(HTML): the standard page description language for Web pages
HTML tags: codes that let the browser know how to format the text on a Web page and whether images, sound, and other elements should be inserted
Search Engines Search engines
A search tool for the Web (like card catalogs in libraries)
E.g., Google.comYahoo.comRediff.com
Java Java
An object-oriented programming language Developed by Sun Microsystems Based on C++ Allows small programs -- applets -- to be
embedded within an HTML document
Applets Applets are small java programs that are
downloaded from the server to the local machine
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Developing Web Content
Products that greatly simplify the creation of a Web page For example: .NET platform
Content management system (CMS) Web services
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Web Services Standards and tools that streamline and
simplify communication among Web sites for business and personal purposes
Can also be used to develop new systems to send and receive secure messages between healthcare facilities, doctors, and patients, while maintaining patient privacy
Push Technology Push technology
Technology that enables users to automatically receive information over the Internet rather than searching for it using a browser
Also called Webcasting E.g.,
PointCast InterMind
Webcasting ‘Discussion’
Using the Internet, and the World Wide Web in particular, to
broadcast information. Unlike typical surfing, which relies on a pull
method of transferring Web pages, webcasting uses push
technologies.
What is Push ?
In client/server applications, to send data to a client without the client requesting it. The World Wide Web is based on a pull technology where the client browser must request a Web page before it is sent. Broadcast media, on the other hand, are push technologies because they send information out regardless of whether anyone is tuned in.
Increasingly, companies are using the Internet to deliver information push-style. One of the most successful examples of this is PointCast, which delivers customized news to users' desktops.
Push Mail
Probably the oldest and most widely used push technology is e-mail.
This is a push technology because you receive mail whether you ask
for it or not -- that is, the sender pushes the message to the
receiver.
Intranets and Extranets Intranet
An internal corporate network built using Internet and World Wide Web standards and products that allows employees of an organization to gain access to corporate information
Extranet A network based on Web technologies that
links selected resources of the intranet of a company with its customers, suppliers, or other business partners
What is Intranet ?
A network based on TCP/IP protocols (an internet) belonging to an organization, usually a corporation, accessible only by the organization's members, employees, or others with authorization. An intranet's Web sites look and act just like any other Web sites, but the firewall surrounding an intranet fends off unauthorized access.
Like the Internet itself, intranets are used to share information. Secure intranets are now the fastest-growing segment of the Internet because they are much less expensive to build and manage than private networks based on proprietary protocols.
What is Extranet ?
A new buzzword that refers to an intranet that is partially accessible to authorized outsiders. Whereas an intranet resides behind a firewall and is accessible only to people who are members of the same company or organization, an extranet provides various levels of accessibility to outsiders. You can access an extranet only if you have a valid username and password, and your identity determines which parts of the extranet you can view.
Extranets are becoming a very popular means for business partners to exchange information.
Virtual Private Network (VPN) Virtual Private Network (VPN)
A secure connection between two points across the Internet
Tunneling The process by which VPNs transfer information
by encapsulating traffic in IP packets and sending the packets over the Internet
VPN
Short for virtual private network, a network that is constructed by using public wires to connect nodes. For example, there are a number of systems that enable you to create networks using the Internet as the medium for transporting data. These systems use encryption and other security mechanisms to ensure that only authorized users can access the network and that the data
cannot be intercepted.
Tunneling
A technology that enables one network to send its data via another network's connections. Tunneling works by encapsulating a network protocol within packets carried by the second network. For example, Microsoft's PPTP technology enables organizations to use the Internet to transmit data across a virtual private network (VPN). It does this by embedding its own network protocol within the TCP/IP packets carried by the Internet. (Note: PPTP = point-to-point
tunneling protocol)
Tunneling is also called encapsulation.
Internet Issues Management issues
No centralized governing body for the Internet
Service bottlenecks Phenomenal growth has left a service void Providers underestimating computing
power needed Reconciling router addresses needed to
transverse the network
Privacy & Security Cryptography
The process of converting a message into a secret code and changing the encoded message back to regular text
Encryption The original conversion of a message into a secret
code Digital Signature
An encryption technique used for online financial transactions
Have anice day…
Have anice day…
Encryption software running on sending computer
Decryption software running on Receiving computer
E%$&:”}{|…
Firewalls Firewalls
A method of preventing unauthorized access between a company’s computers and the Internet (looks at the header of a packet)
Assured pipeline An Internet security method that looks at the
entire request for data and then determines whether the request is valid
Firewall
A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware
and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.
Firewall
There are several types of firewall techniques: Packet filter: Looks at each packet entering or leaving the network
and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.
Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.
Circuit-level gateway: Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.
Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses.
Firewall
In practice, many firewalls use two or more of these techniques in
concert.
A firewall is considered a first line of defense in protecting private
information. For greater security, data can be encrypted.
Summary Telecommunications is the electronic
transmission of signals for communications A computer network consists of the
communications media, devices, and software needed to connect two or more computer systems or devices
Ways of connecting computers in distributed information processing: terminal-to-host, file server, and client/server
Summary (continued) Network types: personal area network
(PAN), local area network (LAN), metropolitan area network (MAN), wide area network (WAN), and international network
The Internet is a collection of interconnected networks, all freely exchanging information
Internet Protocol (IP) is a communication standard that enables traffic to be routed from one network to another as needed
Summary (continued) Uniform Resource Locator (URL) is an
assigned address on the Internet for each computer
An intranet is an internal corporate network built using Internet and World Wide Web standards and protocols
An extranet is a network based on Web technologies that links selected resources of a company’s intranet with its customers, suppliers, or other business partners
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