Chapter 1
Internet
Contents
• Overview of Internet
• History and Evolution of Internet • Uses of Internet
• Internet Addresses • Services of Internet
• Types of Internet connections • Connecting Internet
Objectives
After completion of this module you will be able to know: • What is Internet and how it works?
• History and Evolution of Internet • Services of the Internet.
• Types of Internet connections
• Choose the best connection suitable for you. • How to connect to the Internet
1.1 Overview of Internet
The Internet is a global computer network made up of smaller computer networks; it has been called a "Network of Networks."
These smaller networks include:
Local Area Networks (like networked offices or computer labs, and campus-wide
networks)
Wide Area Networks (like city-wide networks)
State and Regional Networks (including regional service providers and others) National and International Networks
There is no one inventor of the Internet. The Internet was created in the 1960s as a huge network linking big university and government computers. The science behind the Internet was invented during the Cold War, when the United States was in competition against Russia for weapons and technology. So the Internet is actually pretty old--around forty years. Much of Internet’s initial development was supported by American governmental research and network development (beginning with the American military's ARPANET in 1969).
In fact, email has been around since 1972! In 1989 that Tim Berners-Lee, a scientist at the European Laboratory for Particle Physics in Geneva, proposed the World Wide Web. Now Internet Service Providers (ISPs) offer Internet access to their clients, at costs ranging from Rs 150/- per 6 months to hundreds of rupees per year, depending on the types of service they offer.
1.2 What are the uses of the Internet?
There are three fundamental uses of the Internet:Communication Information Retrieval Presentation of Information
1.2.1 Communication
The Internet is used both for one-to-one communications (email and real-time "chat" programs) and one-to-many.
1.2.2 Information Retrieval
The Internet allows access to public domain information, bibliographic databases, libraries, and entertainment services, as well as to proprietary information services .
1.2.3 Presentation of Information
Any organization connected to the Internet can provide access to its own in-house information (library catalogs, faculty information, etc.) to millions of people world-wide. Individuals can also develop and provide their own information packages via their own home pages.
1.3 Internet Addresses
Every computer, file of information, and person on the Internet is identified by a unique "address."
1.3.1 Computer Addresses
Computer addresses are made up of three parts (or, in some cases, two parts), separated by "dots," like this:
computer-name.institution.domain
The computer name is a name given locally to identify a particular computer; it is, in some cases, omitted from the address. The institution name is the name (or an abbreviation) of the name of the school, company, or other institution housing the computer. The domain name specifies either the type or the geographic location of the computer.
1.3.2 Domain Names
There are several possible "domain" names, including some that identify the type of institution, and some that identify a geographical location. They include:
edu educational institution
com commercial and profitable organizations org non-profitable organizations
net Internet infrastructure and service providers gov governmental agency/department
mil American military agency int International organizations us United States in India my Malaysia ca Canada jp Japan biz Business aero aeronautics
1.3.3 Personal Addresses
A person's address (or their email address) places the user's "username" (or "login") and the symbol "@" before the computer address. For example, a user whose username is "sundar", who is accessing email from the "bsnl" server of India, would have the following address:
1.3.4 Uniform Resource Locators (URL)
Sources of information that are on the World Wide Web or FTP server are identified by an extended address called a "Uniform Resource Locator" (URL). Here is a typical URL:
http://www.win.org/workshops/internet.shtml
The first part of the URL ("http://") identifies the type of information or protocol (in this case, it is a hypertext document, available from a HyperText Transport Protocol (http) server on the World Wide Web). The middle part ("www.win.org") is the basic address, as described above. The final part ("/workshops/internet.shtml") identifies the directories within which the document resides ("workshops"), as well as the exact name of the document ("internet.shtml").
1.4 Internet Services
”Internet services” serve more sophisticated and multi-purpose purposes, and increasingly make the Internet a truly useful information resource.
1.4.1 Email
It is the Internet's version of the postal service. Using the Internet, it provides the ability to send a message, reply to a message, send a file created in another program and/or even send the same message to a group of people.
Some benefits of Email are:
• Speed: A message can be sent from Chennai to Australia in a matter of seconds. • Cost: Emails are cheap. You are usually only charged for the telephone call time
(local call rate) for sending the message into the Internet, and not the cost associated with transferring the message across the Internet.
• Flexibility: It is easy to send duplicates of your messages to other people or groups for the cost of a single message.
• Record keeping: Messages sent and received can be easily stored for future reference.
In order to use Email, you will need Internet access arranged through an Internet Service Provider (ISP), who will allocate you one or a number of Email accounts. To be able to retrieve and send mail from these addresses, a user will need what is known as Email client software and your ISP usually provides this although nowadays most computers come with it pre-installed.
1.4.2 Mail Lists
These use email to support discussion groups on a wide range of specific subjects. Once you are becoming a subscriber of a mailing list, you will receive lot of emails related to the subject covered by the mailing list.
1.4.3 FTP
FTP was the original Internet mechanism for the storage and retrieval of information. There are still many FTP Sites around the Internet, although many of them
have been melded into the World Wide Web. In computer science, FTP stands for "File Transfer Protocol," which is a way of transferring files between computers. A file can be anything -- a spreadsheet, a word document, a song, or a picture. When someone says "Please FTP me that file," for instance, that means "Please transfer that file from your computer to mine." To FTP, you usually need to download a special program, or application. You also usually need a password to be able to access or send information to someone else's computer.
1.4.4 Gopher
Gopher was developed at the University of Minnesota, primarily to support its own Campus Wide Information Server (CWIS). It provides access to information available either locally or elsewhere on the Internet by means of a simple series of uniformly designed menus.
1.4.5 Instant Messaging (IM)
IM is a way for you to communicate instantly with your friends over the Internet. That might not sound so different to email. Have you ever noticed how cumbersome it is to have a brief conversation via email? You have to click Reply to each message, then find the right spot in the message to type something new, then send it. Then you have to wait for the next message to arrive! IM lets you to have a conversation almost as naturally as on the phone or face to face, by typing messages into a window shared between you and your friend's screens.
Another difference between IM and email is that with IM you can see your friends' presence, that is, whether they are actually on-line at the same time as you. This lets you send messages truly instantly, instead of sending off a mail and having to wait for your friend to check their mailbox. An IM message pops up on the other person's screen as soon as you send it. Of course, if you'd rather not be interrupted, you can change your own presence so others will know not to disturb you.
There are lots of other fun and useful IM features you can explore, like group chats, file transfers, voice calls, video conferencing and emoticons that reflect your mood.
1.4.6 IRC
IRC stands for "Internet Relay Chat". It has been used in many countries around the world. IRC is a multi-user chat system, where people meet on "channels" (rooms, virtual places, usually with a certain topic of conversation) to talk in groups, or privately. There is no restriction to the number of people that can participate in a given discussion, or the number of channels that can be formed on IRC.
1.4.7 Newsgroups
The Internet has a place where we can gather, question, and discuss our experiences within a wide variety of topics. It's called Usenet News. Some users also call it Net News.
Think of Usenet News as a giant, worldwide bulletin board. Anyone can freely post something on this bulletin board. Everyone else can read the posted items and add their own items. These voluntary contributions and free exchange of
information are the foundation of the Internet. Usenet News allows people on the Internet to share their opinions and experiences, openly and freely, on a level playing field. No one has priority or seniority over anyone else. Usenet News gives everyone an equal opportunity to participate in the discussions.
When you send an e-mail message, the only people who can read it are the recipients (for the most part). When you post an article on Usenet News, every person on the Internet could read it and respond to it. Not that they ever would, but they could. That's a lot of people and a lot of opinions, and only a few of them come from true experience.
There are tens of thousands of newsgroups. Some of them are applicable to a global audience; others are more applicable to a country, city, or organization. Most of the newsgroups are available to everyone on the Internet. However, some of the newsgroups have a limited audience.
1.4.8 Voice over IP
Voice over IP (Voice over Internet Protocol or "VoIP") technology converts voice calls from analog to digital to be sent over digital data networks. In Voice over IP, or VoIP, voice, data, and video all travel along the network.
1.4.9 World Wide Web (WWW)
The newest information application on the Internet, the WWW provides standardized access to Gopher, FTP, Telnet and more by means of home pages designed either by institutions or by individuals. By means of the HyperText Markup Language (HTML), it allows users to "point" at highlighted terms, following "links" to whatever information interests them. It is a multimedia environment, allowing Internet users access to audio and video materials. There are a number of client software packages (or browsers), including Lynx (a text-only browser), Netscape, and Microsoft's Internet Explorer, (which are multimedia browsers).
1.5 Types of Internet connections
The options for providing user connectivity to the Internet are given below: 1. Terminal Dialup/Modem (Shell connection)
Most common option
User requirements limited to modem and communications software Text-only access
Shell accounts were more popular before the advent of the Web. A shell account lets you use your computer much as if it were a virtual console associated with a remote computer. You can type commands, which are interpreted by the remote computer, and view the resulting output on your
computer. Although a few web browsers, such as Lynx, can operate via a shell account, they don’t generally support the highly graphical, multimedia pages which web surfers have come to expect.
2. SLIP (Serial Line Internet Protocol)
Computer is treated as though it were directly connected for the period it is online
Utilizes telephone lines
User must have modem, TCP software, SLIP software, & software for Internet applications
Multimedia access 3. PPP (Point-to-Point Protocol)
Computer is treated as though it were directly connected for the period it is online
Utilizes telephone lines
User must have modem, TCP software, PPP software, & software for Internet applications
Multimedia access
While your computer is connected to the Internet, you can use it to surf the Web with your favorite browser. If your ISP allows, you can even run a web server, providing pages that can be viewed by others around the world.
4. ISDN (Integrated Services Digital Network)
Most often used to connect remote telecommuters to office LANs Requires ISDN phone line access
Faster than analog terminal dialup/modem service
User must have ISDN phone line, ISDN card, communications software,
TCP software & SLIP or PPP software multimedia connectivity 5. DIAS
The DIAS offers a wire-line solution for high speed symmetrical Internet
access on the existing telephone lines. It provides an "always on" internet access that is permanently available at customer's premises. DIAS combines voice and internet data packets on a single twisted pair wire at subscriber premises that means you can use telephone and surf internet at the same time.
6. Cable Modem
The term “Cable Modem” is quite new and refers to a modem that
operates over the ordinary cable TV network cables. Basically you just connect the Cable Modem to the TV outlet for your cable TV, and the cable TV operator connects a Cable Modem Termination System (CMTS) in his end (the Head-End).
Actually the term “Cable Modem” is a bit misleading, as a Cable Modem works more like a Local Area Network (LAN) interface than as a modem.
In a cable TV system, signals from the various channels are each given a
6-MHz slice of the cable’s available bandwidth and then sent down the cable to your house. When a cable company offers Internet access over the cable, Internet information can use the same cables because the cable modem system puts downstream data – data sent from the Internet to an
individual computer – into a 6-MHz channel. On the cable, the data looks just like a TV channel. So Internet downstream data takes up the same amount of cable space as any single channel of programming. Upstream data – information sent from an individual back to the Internet – requires even less of the cable’s bandwidth, just 2 MHz, since the assumption is that most people download far more information than they upload.
Putting both upstream and downstream data on the cable television system
requires two types of equipment: a cable modem on the customer end and a cable modem termination system (CMTS) at the cable provider’s end. Between these two types of equipment, all the computer networking, security and management of Internet access over cable television is put into place.
7. Digital Subscriber Line (DSL) connection.
DSL is a very high-speed connection that uses the same wires as a regular telephone line.
Here are some advantages of DSL:
1. You can leave your Internet connection open and still use the phone line for voice calls.
2. The speed is much higher than a regular modem
3. DSL doesn’t necessarily require new wiring; it can use the phone line you already have.
4. The company that offers DSL (e.g. BSNL) will usually provide the modem as part of the installation.
But there are disadvantages:
1. A DSL connection works better when you are closer to the provider’s central office.
2. The service is not available everywhere.
Other types of DSL include:
1. Asymmetric DSL (ADSL) line – The connection is faster for receiving data than it is for sending data over the Internet
2. Very high bit-rate DSL (VDSL) – This is a fast connection, but works only over a short distance.
3. Symmetric DSL (SDSL) – This connection, used mainly by small businesses, doesn’t allow you to use the phone at the same time, but the speed of receiving and sending data is the same.
4. Rate-adaptive DSL (RADSL) – This is a variation of ADSL, but the modem can adjust the speed of the connection depending on the length and quality of the line.
8. Direct Connection (Leased circuit)
Most often used to connect sites within a specific organization; such as a
university or business requires owning or leasing of cable (from 64 kbps to T-3) users typically connected via Ethernet LANs multimedia connectivity at its fastest.
9. Satellite connections
This connection allows you to download Internet files via a satellite connection. This is an efficient method for receiving large Web graphics and other items, but you still need a modem connection for other features.
You must purchase the connection hardware as well as subscribe to the service.
10. Wireless connections
Pagers, cellular phones and personal digital assistants (PDAs) now allow varying levels of Internet access, from notification of E-mail to limited Web connections. Many of these services remain in the experimental stage. The PPP connection is called as TCP/IP connection or PSTN dial-up connection. ISDN connection is called as ISDN dial-up connection. Cable Modem, DSL and Direct Connection are always-on connection.
The words “connection” and “account” related to Internet are interchangeable.
1.6 Comparisons of Internet accounts
You can compare the two types of Internet accounts - shell and PPP - with two kinds of postal service.
Imagine that no mail carrier actually comes to your home to pick and deliver mail. Instead, every time you want to conduct postal business, you go to the post office. This resembles a shell account: The computer that connects you to the Internet is remote, and every time you want to do something on the Internet you must open a terminal, or telnet, session to that computer. PPP, on the other hand, is like home delivery: The Internet comes right to your doorstep, and your computer is literally placed on the Internet by the machine at your ISP that you connect to.
Under Microsoft Windows, you use hyperterminal to access a shell account and Dial-Up Networking to access a PPP account. Under Linux, you can choose from among several programs that let you access a shell account. The most commonly used programs are minicom and seyon. To access a PPP account under Linux, you use the PPP daemon, pppd.
If you are one of the first users to connect to the Internet through a particular cable channel by using Cable Modem Internet connection, then you may have nearly the entire bandwidth of the channel available for your use. As new users, especially heavy-access users, are connected to the channel, you will have to share that bandwidth, and may see your performance degrade as a result. It is possible that, in times of heavy usage with many connected users, performance will be far below the theoretical maximums. The good news is that this particular performance issue can be resolved by the cable company adding a new channel and splitting the base of users.
Another benefit of the Cable Modem for Internet access is that, unlike ADSL, its performance doesn't depend on distance from the central cable office.
ADSL is a distance-sensitive technology: As the connection's length increases, the signal quality decreases and the connection speed goes down. The limit for
ADSL service is 18,000 feet (5,460 meters), though for speed and quality of service reasons many ADSL providers place a lower limit on the distances for the service. At the extremes of the distance limits, ADSL customers may see speeds far below the promised maximums, while customers nearer the central office have faster connections and may see extremely high speeds in the future.
1.7 Choosing an Internet Connection
(Modem, ISDN, Cable, DSL - ASDL/SDSL)
As the Internet becomes increasingly popular with every day that passes, it is now considered as one of the best ways to do business (e-commerce), network (by email), and build partnerships (on-line collaboration).
It is arguably, some would say, the most efficient way of gathering information for a wide range of business uses and to interact with customers. One of the main issues today is what is the best way to connect to and use the Internet to its full potential with a view to speed and reliability?
Unfortunately, because of the poor quality of the existing telephone network that connects us to the Internet, the speed at which information (web pages, images etc) appears on your screen is slow compared to the latest technology available.
Ultimately, DSL (see below) will be the solution that will provide us all with a connection up to ten times faster than the speed at which information arrives to you with a regular modem.
As new technology becomes available almost every week, the awareness of the difference between the performance (speed), costs and availability is still unknown to many people and consequently we face problems deciding which connection is best for our business needs.
(i) PC Modem - up to 56kbps
The PC Modem is the standard way of connecting to the Internet but is now the slowest. The fastest type of standard modem is 56kbps, these are included as standard with all new PC's; but if you do not have one they can be bought from around £15-20 upwards.
If you are currently using a modem below 56k (which is unlikely) then the difference in speed will be very noticeable. There is nothing negative about using standard PC modems but the speed may be a crucial factor if time is valuable to your business or if downloading large or numerous files (images, emails, etc) is what you require.
ISDN provides a solution by offering two high-speed lines capable of running at 64kbps each through your existing phone network. The advantage of this is that each line can be connected to a different source (e.g. two computers, a computer and a telephone/fax or two telephones). Another feature that may interest you is that the lines can be used simultaneously from a single computer giving a speed of 128kbps. This would be useful should you need the extra speed to work quicker over the Internet at a specific time, or for downloading large images and files.
This service requires you to remove your existing modem (if you have one) and replace it with an ISDN card that can be found from most large PC stores.
ISDN appears expensive in comparison to ADSL/broadband, but the two phone lines that come with it can be invaluable to a small business. If ADSL is not available in your area, then ISDN offers an effective solution.
(iii) Cable Modem- up to 600kbps
Cable offers greater speeds but has the initial problem of availability. Just like Cable TV, you can only receive the service if you live within a cable operator's franchise area. Should you find that you are one of the 'chosen few' you may consider this over ADSL (see below) because of the cheaper operating costs; although you should check carefully because prices are always changing.
In cable Modem connection, speeds of up to 2Mbps can be achieved in the future.
In order to use cable you will need two things: A cable modem and a Network Interface Card (Sometimes referred to as NIC's).
You do have to bear in mind the future and consider the following: Once all subscribers in your area have all been connected to the Cable Modem connection, the speed of the service will run at slower rates (kbps). This is because the amount of information that the Cable can carry at one time is shared with all those connected to it. However, you could also consider that there may be further advances in the technology to change this.
(iv) ADSL - Over 256 kbps
This connection improves the speed at which you can download/upload dramatically compared to the standard PC modem. ADSL uses your existing phone line but gives you the added advantage of being able to use the phone/fax at the same time as being connected to the Internet: the connection time to the Internet is instant as ADSL is "always on" meaning that you can start surfing the net as soon as you turn on your computer.
Using such a connection will involve extra hardware such as a box that fits to your wall that you plug a USB modem (also needed) into which will then connect to your computer.
When you connect to ADSL you also get a new phone line, which can be beneficial to many small businesses. The use of this line does not affect the ADSL connection either.
Broadband is available in all cities. However, you should check availability in your area before discounting ISDN or 56k.
ADSL gives faster downloading speeds (receiving) than uploading speeds (sending).
(v) SDSL - upto 2Mbps
This service was released in early 2004 -- aimed at businesses -- allowing users to enjoy the same uploading (sending) speeds as it was capable of downloading (receiving).
This service is beneficial to businesses that frequently send large files via the internet: the current connection may be causing the network to suffer huge strain when transporting such files.
Subscribers can sign up for speeds varying from 256kbps to 2Mbps, depending on preference.
This service is much more expensive than ADSL broadband and should only be considered if there is an instant need for the service.
1.8 How to Connect to the Internet and World Wide Web
Before you can connect to the Internet and access the World Wide Web, you need to have certain equipment. In brief, you must have a computer (preferably running an up-to-date operating system); a modem and access to a telephone line or a local area network (LAN) that is in turn connected to the Internet; and connection software that will allow you to establish an account with a service provider and access the Internet.A modem is not needed when accessing the Internet through a LAN.
1.8.1 The Right Hardware
To operate most of the current Web browsers and on-line services, you should have a computer with at least 32 megabytes (MB) of random access memory (RAM) and 2 GB of free hard disk space. If you are unsure of how much RAM and disk space your computer has, consult your user's manual.
If you are accessing the Internet outside of a LAN environment, you will need a modem that will connect you with other computers and interpret the data being sent back and forth. Any modem that is compatible with your computer will do, though the higher the kilobits per second (kbps) rate of your modem, the faster it will transmit data. Modem speed is an important consideration when accessing
sites on the Web that contain lots of digitized data. If you are looking to purchase a modem, buy the fastest model you can afford.
You must also have access to a live telephone line. Most modems accept the same jacks as do ordinary household telephones, allowing you to connect your modem to a wall jack using standard phone cord. Some cable TV providers have begun offering Internet connections via cable. Such connections provide much faster transmission speeds than standard phone lines, though you will need a special modem that allows you to link your computer with the cable. If you are interested in a cable Internet connection, contact your local cable operator to see if the service is available in your area.
You have to purchase ADSL modem/router if you are going for ADSL Internet connection.
You can also connect to the Internet through a LAN with Internet access. If you are unsure as to the capacities of your LAN to do this, contact your site's systems administrator.
1.8.2 The Right Software
For best results, make sure that your computer is running the most up-to-date operating system that it can handle. If you have an IBM PC/PC compatible computer, it should be running Microsoft Windows NT, Windows 95/98/Me, Windows 2000 or Windows XP. You can use Linux Operating System also. If you have a Macintosh, it should be running System 8 or higher.
To make your connection complete, you will need connection software that allows your computer to dial into an Internet access provider, establish an account, and work with the data in a straightforward manner. Many access providers will give you software that will allow you to access their systems using an all-in-one custom interface. Some software are bundles with Operating System also. Others may give you a collection of separate software packages that can be used together. But whatever software they provide, be sure that it is compatible with your computer and operating system before attempting to use it.
1.8.3 The Browser
As you surf the Web, you will come across sites that state, "This site is best viewed with…" and then name a particular browser. Many will even provide a link to a site where you can download the specified browser.
Sites make these recommendations because some browsers use special protocols, allowing site creators to offer extra features beyond the standard capabilities of hypertext markup language (HTML). Chief among these browsers are Netscape Navigator' Microsoft Internet Explorer, Opera and Mozilla Firefox.
The Netscape Navigator, Mozilla Firefox and Microsoft Internet Explorer browsers allow for the use of plug-ins, or extra software applications that run as if they were an integral part of the browser.
Browsers also use helper applications that, while not as integral as plug-ins, enhance the browser's capabilities by launching when needed. Helper applications allow your browser to play sound and video files, display animation and other graphic formats, or access special Internet features such as TELNET. Most Web sites that require the use of helper applications will provide links to sites where you can download the necessary software.
Chapter 2
Internet Account Tariff
Contents
• Types of Internet connections offered by BSNL • Tariff for the various connections
Objectives
After completion of this module you will be able to know: • Types of Internet connections offered by BSNL • Different tariff for different Internet connections 2.1 Internet Accounts
The different type of Internet accounts offered by BSNL is given below:
Leased line access
Enjoy round the clock internet connectivity at speeds varying from 64 Kbps to 45 Mbps. various plans are available to suit different needs. ISDN dial backup packages for Internet Leased Line Customers are also available.
Direct Internet Access (DIAS)
BSNL also provides DIAS in selected cities of the Country. The DIAS offers a wire-line solution for high speed symmetrical Internet access on the existing telephone lines. It provides an "always on" internet access that is permanently available at customer's premises. DIAS combines voice and internet data packets on a single twisted pair wire
at subscriber premises that means you can use telephone and surf internet at the same time.
Account free Internet dial up access based on CLI
Duration based Dialup Internet Service(CLI based) is a unique method providing Internet service in which the Customer can access the Internet service from any telephone through dial up. The service allows automatic registration on first LOGIN. The authentication will be based on CLI of the telephone with the password supplied by the caller. The charging is totally usage based and the service is a post paid service like normal PSTN. The billing will be separating based on the duration of use and will be charged to telephone bill (CLI based) as Internet access charge at the prescribed rate. The service is available in selected cities. The access no. of this service is '172222' in all cities. CLI based dial up internet service is also available for ISDN customers now. The access no. of this service is '172223'
BROADBAND connection
Broadband service is based on DSL technology (on the same copper cable that is used for connecting telephone). This provides high speed internet connectivity upto 8Mbps. This is always - on internet access service with speed ranging from 256Kbps to 8 Mbps.
SANCHARNET CARD
BSNL has also launched ”SANCHARNET CARD" recently. The Sancharnet Card" is a prepaid Internet Access Card with following features for customers:
• Self-register for internet access with your choice of user id
• Renew your existing Sancharnet Account
• Wide Range of Internet Access Packages
2.2 Tariff for various Internet accounts
The tariff for various Internet accounts offered by BSNL is given below:
2.2.1 Tariff for Direct Internet Access Services (DIAS)
DIAS is presently available in 42 cities across India.
Plan-0
(Starter) Plan-I Plan-II Plan-III Activation Charges (non refundable) Rs.500 Rs. 500 Rs.500 Rs. 500
Security Deposit Nil Nil Nil Nil
Monthly Rental Per user Rs.300 Rs.500 Rs.900 Rs. 3000 Free Usages per month 0.5 GB 1.0 GB 2.0 GB Unlimited Additional Usages charges per MB Rs.2 Rs.2 Rs.2 N.A
• The DIAS services shall be offered to the PSTN subscribers of BSNL, on the same copper pair as is being used for their DELs at present.
• In case of disconnection of BSNL PSTN connection this DIAS connection is also to be surrendered. In case of disconnection of telephone for non-payment etc., DIAS facility should also be disconnected.
• This tariff includes internet usage charges. The subscriber need not pay any additional amount for
(i) PSTN Dialup Access for internet (ii) Port charges for Internet Leased Line.
• This tariff is for connection of subscribers to Internet nodes of BSNL.
• Wherever it is not technically feasible to measure the usage, the present tariff will remain applicable. However, whenever it will be technically possible to apply usages based tariff, subscribers of DIAS should be intimated well in time by giving time period of one month for switchover from existing tariff to the tariff based on usage as above.
• This tariff will be reviewed after six months.
2.2.2 Tariff for Account free Internet Dial up access based on CLI
• Usage charges for Internet access through BSNL's sancharnet: 10 paise per minute
Note: The subscribers will be charged at these usage charge over and above normal PSTN dial up charges.
• The tariff of CLI service for ISDN (with effect from 1st September 2005): ISDN Type Tariff for CLI (Rs. Per Minute)
64 kbps 0.20
128 kbps 0.40
192 kbps 0.60
Note: The above CLI based Internet tariff is in addition to the already applicable ISDN tariff.
2.2.3 Tariff for Internet Access Local Calls
The tariff for internet access local calls [Calls made to internet access numbers like
172XXX] are given below:
Peak Hours Off Peak Hours Packages
Period (Hr) Pulse (Seconds) Period (Hr) Pulse (Seconds) Standard (TRAI) 0800-2000 120 2000-0800 180 BSNL Package
(with effect from 21.10.2004)
0730-2230
450 2230-0730 900*
* 600 seconds for E10B exchanges Service Tax as applicable shall be extra
2.2.4 PSTN & ISDN Limited Access Dialup packages with 4 MB
E-mail space
The uniform tariff shall be applicable for all new customers. All new connection shall be provided as per the tariff applicable on the date of new connection/renewal. All
instructions issued from time to time by BSNL shall remain applicable. PSTN Dialup Access - Limited Access
Free access from 1100 PM to 0800 AM on Weekdays and for full day on Sunday and National Holidays
S.N. Brand Name Denomination Hrs Validity Charges
1. Corporate 1000 2 yr 4500 2. Gold Pass 500 2 yr 2300 3. Silver Pass 200 2 yr 1000 4. Executive 100 2 yr 500 5. Regular 50 1 yr 250 6. Temporary 25 6 months 150
ISDN Dialup Access at 64 kbps - Limited Access
S.N. Brand Name Denomination Hrs Validity Charges
1. Corporate 1000 2 yr 8000
2. Professional 500 2 yr 4500
3. Personal 100 2 yr 1000
ISDN Dialup Access at 128 kbps - Limited Access
S.N. Brand Name Denomination Hrs Validity Charges
1. Corporate 1000 2 yr 16000
2. Professional 500 2 yr 9000
3. Personal 100 2 yr 2000
• Service Tax as applicable shall be extra
• One User ID and e-mail ID per package except for Corporate Package where it is 2.
• Simultaneous logins per user ID shall be 2.
• E-mail space per e-mail ID shall be 4 Mb
• Free web space for user ID shall be 1 MB
• Free access between 2300 hrs to 0800 hrs on weekdays and for full day on Sundays and National Holidays.
2.2.5 PSTN & ISDN Limited Access Dialup packages with 10 MB
E-mail space
PSTN Dialup Access - Limited Access
S.N. Package Hours Validity Charges Rs.
1. Corporate 1000 1 yr 5000
2. Gold Pass 500 1 yr 2500
ISDN Dialup Access at 64 kbps - Limited Access
S.N. Package Hours Validity Charges Rs.
1. Corporate Mail 1000 1 yr 9000
2. Professional Mail 500 1 yr 5000
ISDN Dialup Access at 128 kbps - Limited Access
S.N. Package Hours Validity Charges Rs.
1. Corporate Plus Mail 1000 1 yr 18000
2. Professional Plus Mail 500 1yr 10000
• Service Tax as applicable shall be extra
• One User ID and e-mail ID per package except Corporate Package.
• One user ID and two E-mail IDs with Corporate Package.
• Simultaneous logins per user ID shall be 2.
• E-mail space per e-mail ID shall be 10 Mb
• Free web space for user ID shall be 1 MB
• Free access between 2300 hrs to 0800 hrson weekdays and for full day on Sundays and National Holidays.
2.2.6 PSTN & ISDN UNLIMITED ACCESS Dialup packages with
10 MB E-mail space
PSTN Dialup Access - Unlimited Access
S.N. Package Hours Validity Charges Rs.
1. Enterprise Mail Unlimited 6 months 9000 ISDN Dialup Access at 64 kbps - Unlimited Access
S.N. Package Hours Validity Charges Rs.
1. Enterprise Mail Unlimited 6 months 16000 ISDN Dialup Access at 128 kbps - Unlimited Access
S.N. Package Hours Validity Charges Rs.
• Service Tax as applicable shall be extra
• One User ID and one e-mail ID per package.
• Simultaneous logins restricted to one.
• Access restricted from two specified telephone numbers (CLIP restriction).
• 10 MB e-mail space
• 1 MB webspace
2.2.7 ISDN UNLIMITED ACCESS Dialup with FIXED IP
and 10 MB E-mail space
ISDN Dialup Access at 64 kbps-Unlimited Access
Package Denomination Hrs Validity Charges Rs.
Fixed IP Address Unlimited 6 months 30,000
ISDN Dialup Access at 128 kbps-Unlimited Access
Package Denomination Hrs Validity Charges Rs.
Fixed IP Address Unlimited 6 months 54,000
• Service Tax as applicable shall be extra
• One User ID and one e-mail ID per package.
• Simultaneous logins restricted to one.
• Access restricted from two specified telephone numbers(CLIP restriction)
• Fixed IP address assigned on access (customer has to apply for IP address separately)
• 10 MB e-mail space
• 1 MB webspace
2.2.8 Tariff for Broadband services
BSNL has decided to revise packages of ADSL Broadband Services 'DataOne' for Home and Business users
with different Bandwidth (BW) options and download capacities with effect from 16-08-2005. The revise offer and new packages are as under:
A. Initial and other charges:
Installation charges Rs 250 (In case of modem from BSNL) Modem Rental
(a) Monthly Rental
(b) Security Deposit (Refundable)
Rs 100 (Type I Modem) Rs 500
Shifting Charges Nil (Withdrawn w.e.f. 15/07/05) Change of Plan Charges Nil (Withdrawn w.e.f. 09/06/05)
B. Demand Note to New Dataone Customers:
At the time of issue of Demand Note, following charges are to be collected: a) Installation charges (As applicable)
b) Security Deposit of the Modem (If Applicable)
c) Refundable Security Deposit for One month rental as per the plan (As applicable) subject to maximum of Rs. 5000. No Security deposit is to be collected for Home 250 & Home 500 plans.
C. DataOne - Home Plans
Tariff in Rs. Particulars Home 250 (New) Home 500 Home 1000 Home 1800 Home 3300 Bandwidth 256 Kbps 256 Kbps 384 Kbps 512 Kbps 1 Mbps Monthly Charges (Rs) 250 500 1000 1800 3300
Annual Payment Option to Customers (Rs)
2500 5000 10000 18000 33000
Download/ Upload Limit (GB) 0.4 GB 1.0 GB 2 GB 5 GB 10 GB Additional Usage Charges/MB
Beyond free Download/Upload Limit (Rs)
1.40 1.20 1.00 0.80 0.80
Free mail IDs/Space (Per
E-mail ID) 1/5 MB 1/5 MB 1/5 MB 1/5 MB 2/5 MB
Security Deposit NIL NIL 1 month
rental 1 month rental 1 month rental Night Unlimited (0200- 0800 Hrs) Not Available
Available Available Available Available Minimum Hire period Three
months Three months One month One month One month D. DataOne - Business Plans
Tariff in Rs. Particulars Business 700 (New) Business 1200 Business 3000 Business 5000 Business 9000 Bandwidth 256 Kbps 256 Kbps 512Kbps 1 Mbps 2 Mbps
Single /Multi User-(SU/MU) SU SU MU MU MU
Annual Payment Option to Customers (Rs)
7000 12000 30000 50000 90000 Download/ Upload Limit (GB) 2 GB 4 GB 10 GB 20 GB 40 GB Additional Usage Charges/MB
Beyond free download/upload limit (Rs)
1.20 1.00 0.80 0.60 0.60
Free mail IDs/Space (Per E-mail ID)
1/5 MB 1/5 MB 2/5 MB 2 / 5 MB 4 / 5 MB Static IP Address (On request) Not
Available Not Available Not Available One One Web hosting space (On request) Not
Available Not Available Not Available 5 MB 5 MB Domain Name (On request) Not
Available Not Available Not Available One One
Security Deposit 1 Month
rental 1 months rental 1 month rental 1 month rental Rs 5000 Minimum Hire period One
month One month One month One month One month - Service Taxes extra.
- Billing for the service will be included in the normal Bfone bill. The billing cycle shall be monthly for Dataone customers. Monthly rentals and usage charges will be billed in arrears.
E. Modem on Outright purchase:
Only Modem Type I with One ethernet port will be available for sale / rental to customers for the present.
F. Conditions for providing Home plan or Business plan:
1. Either Plan can be taken by the subscribers having telephones in individual names working at homes/residences used for personal use/purpose.
2. Subscribers having telephones in the name of Company, firms, shops, educational institutes or any other commercial entity can take only Business Plan. They are not eligible for Home Plan.
3. Telephones working in individual names at commercial/ business/ office premises are also not entitled for Home Plans.
4. Home plan can be taken on Bfones in name of Government/company but actually working at residences of their employees. An undertaking shall have to be given by the customer in this regard.
A registration fee of Rs. 100 shall be charged which will be adjusted in the first demand note. H. Waiver of Installation charges:
Installation charges of Rs. 250 are waived off for all new broadband customers between 16th August 2005 and 30th September 2005.
Chapter 3
MODEM
Contents
• MODEM fundamental • Types of MODEMS • Interface • ConnectionsObjectives
After completion of this module, you will be able to know: • MODEM fundamental
• The two types of MODEMS • Different types of interfaces • Different types of connections
3.1 MODEM fundamental
Acronym for MODulator / DEModulator which describes the method used to convert digital data used by computers into analog signals used by the phones and then back into digital data once received by the other computer.
The above pictures help represent a digital signal and an analog signal. All computer data is stored and transmitted within the computer in digital format 1s and 0s. In order for this data to be transmitted over analog phone lines the data must be transmitted into an analog signal which is the noise you hear when connecting to another computer. Once the other computer receives this signal it will then translate the signal back into its original digital format.
Typical modems are referred to as an asynchronous device. Meaning that the device transmits data in a intermittent stream of small packets. Once received the receiving system then takes the data in the packets and reassembles it into a form the computer can use. Stop 1 bit Data 8 bits Start 1 bit Stop 1 bit Data 8 bits Start 1 bit Packet
10 bits Packet 10 bits
The above chart represents how an asynchronous transmission would be transmitted over a phone line. In asynchronous communication 1 byte (8 bits) is transferred within 1 packet which is equivalent to one character. However for the computer to receive this information each packet must contain a Start and a Stop bit therefore the complete packet would be 10 bits. An example of what the above chart would transmit is the word HI which is equivalent to 2 bytes (16 bits).
3.2 Types of MODEMs
There are two types of modems used in all computers.
Internal: Modem which would be plugged into a slot located within or on the computer.
External: Modem which is located within a box and is hooked up externally to the computer generally VIA the Serial Ports.
3.3 Purchasing Tips
Before purchasing a modem take the following into consideration. Today with the popularity of the Internet and multimedia over the Internet, broadband is becoming widely available. If available in your area you may want to consider purchasing a broadband solution such as DSL available through BSNL or third party company, Cable available through your local cable provider, Satellite available through a third party . If a broadband connection is not available in your area, then modem can be purchased. The details about modems are given below:
3.3.1 Standards
Originally when the 56k connection was introduced there was not a set standard between two major modem manufactures causing there to be two different technologies, X2 and KFlex. Each of these technologies allowed for a modem to connect to higher speeds however only if the Internet Provider supported the technology. Because of the difficulties and issues with these two different technologies one technology emerged out of the two called V.90. This technology will allow users of any brand of modem to connect at higher speeds.
Today all modems (purchased new) are V.90 and this is no longer a concern.
Interface can be an important when considering purchasing a modem. It is important that your computer has the available connections and resources when purchasing a modem. 3.3.2.1 PCI / ISA (Internal)
PCI / ISA modems are modems which are found in most computers today. These modems are installed internally into the computer with an available connection on the back of the modem for the phone line.
When purchasing this type of modem it is important that you verify your computer has the available connection for this modem within the computer (PCI or ISA). In addition verify that your computer has the available resources. You can sometimes see difficulties installing a modem if a serial device such as a Serial mouse or Serial PDA is connected to the computer.
3.3.2.2 Serial (External)
A serial modem connects to the serial port located on the back of the computer. These modems are generally easy to install however cost more then an internal modem as you can pay additional money for the plastic cover.
When purchasing this type of modem it is important that you verify your computer has an available serial connection on the back of the computer, devices such as a serial mouse may already be utilizing your serial port. Some computers may have two serial ports, if this is the case and only one serial port is currently being utilize, verify that the second port can be enabled or is already enabled in CMOS.
3.3.2.3 PC Card (PCMCIA)
Solution used with portable computers PC Card modems are fairly cheap and relatively easy to install in the computer.
If a modem is already present in your portable computer however you wish to upgrade or the internal modem has gone bad it is important that you verify the pre-existing modem can be disabled before installing the new modem.
3.3.2.1 USB
A new solution USB allows a user to install up to 127 devices on the computer and is available for PC and Mac. Before purchasing this solution verify that your computer has a USB connection. If no USB connection is available an additional card will need to be installed in the computer.
3.3.3 Connection
The connection can differ depending upon the type of modem purchased with the computer.
3.3.3.1 Internal / External / USB modem
Today all modems have a RJ-11 connection which is a standard phone connection on the modem. If important to you, verify that the modem has two available RJ-11 connections. One of these connections will connect the modem to the phone and the other can be used for an office phone. This can be very useful for home or office computer that may need a phone next to it.
3.3.3.2 PC Card modem
When purchasing a PC Card modem the connection can be a very important factor consideration. Below we have listed the pros and cons of each of these connection types. 3.3.3.3 Dongle
A commonly found solution for PC Card modems, however a very burdensome solution. The Dongle is an additional card that connects from the PC Card to a small opening for a RJ-11 connection. While a good thought we find that these connections get lost often. The pro of this solution is a very sturdy connection and a solution that will allow only a Type II slot to be used allowing and additional slot free for another card.
3.3.3.4 Standard
Standard connection like a desktop modem allows for a phone line to be connected directly to the modem. This solution allows for no additional cables. The con to this solution is that these cards will generally occupy your complete PCMCIA slot.
Chapter 4
Windows XP Dialup Networking
Contents
• Configuring Dialup Networking in Windows XP
Objectives
• After completion of this module, you will be able to know how to configure Dialup Networking in Windows XP
4.1 Configuring Dialup Networking in Windows XP
These instructions assume your modem is properly installed and configured. See information provided by the modem manufacturer for instructions for installing the modem.
Windows XP has multiple methods for reaching dialup settings, and your screen shots may vary slightly from those shown below because XP allows users to customize screen settings.
Start the "New Connection Wizard" from the start menu -
Click Start ÖAll Programs ÖAccessories Ö CommunicationsÖNew Connection Wizard. You will get a figure like this:
Click Next and the next screen will appear like this:
Chose the radio button next to Set up my connection manually and click Next to see the Internet Connection window.
Select "Connect using a dial-up modem and Click Next to get the Connection Name window
For the ISP name click in the box and enter the name you want to see for the icon for the connection, in this example we use the Sancharnet name. Click Next to continue.
Enter the phone number as you want it to be dialed for your connection. Choose Next to continue when done.
If multiple unrelated users are sharing a connection you may want to make this setting 'My use only', but if every user of the system is allowed to use this dialup select Anyone's use. Then click Next.
The Internet Account Information window options are left blank - doing this means you will need to provide your id and password every time you connect. If you want to make your connection less secure you can fill in and save the user name and password information. Turning on Internet Connection Firewall is most likely appropriate for most users, but users using a VPN (like an Oracle connection) may find that it will not work with Internet Connection Firewall selected. Click Next
In the 'Finish' screen you can add a shortcut to this connection to your desktop. You may want to do that, if not, you can reach the connection through the start menu. Click Finish (but you may not really done.) If you are going to use the Home Directory service continue with the Advanced configuration below.
If all you use the dialup connection for is email and web access then the connections defined this way will probably work just fine without additional setup. To start a dialup session go to the Start Ö Connect To Ö Sancharnet (the name you haven for the Internet connection).
Choosing the connection from the menu will bring a login screen that will take your Dialup Networking ID and password and will make your modem dial in to get your connection.
4.1.1 Advanced configuration
If you have problems connecting, or if you plan to use the Home Directory service via your dialup connection, the following steps may be required to force appropriate settings. Go to Start Ö Connect to Ö Sancharnet (or what ever you named the connection) and right-click to get the menu to choose properties - left click on Properties.
The Properties window will looks similar to the following:
The "Connect Using" box should have the name of your modem.
If you understand the use of dialing rules feel free to use them, otherwise uncheck the 'Use dialing rules' box and put the full number, as you want it dialed, in the "Phone number" box. You can use the "Alternates" button to provide numbers which should be tried if the first one fails to connect.
Your settings on the Options tab should be the same as above, in particular be sure "Include Windows logon domain" MUST NOT be checked or your user name will be sent incorrectly for logon. Redial attemps are optional.
Your securities settings should look like those above to connect to the UVA dialup. Select the Networking tab
Advanced users may want to change some of the settings to be different than those above, but in general the screen should match the one above. Note: for Home Directory users -
Client for Microsoft Networks MUST BE CHECKED. (If you scroll through the screen
'This connection uses the following items, no additional items need to be checked.) Click on the Internet Protocol (TCP/IP) line and then click on the 'Properties' button on the Network properties window.
If you have previously set up any network connections on this system some of the settings on the TCP/IP properties window may be different (and this window may change with later changes we will make.) The Obtain and IP address automatically is mandatory. Click on the Advanced button, then click on the "DNS" tab for the Advanced TCP/IP Settings.
Click on the Add button below the DNS Server address window - a window will pop up - add 128.143.2.7 and 128.143.22.119. Only 2 can be specified so if you make an error select the wrong entry and click on remove.
Select the Append these DNS suffix and click add and add virginia.edu (this lets you leave off the virginia.edu part of host names when you specify them in other programs) If you use the Home directory service, click on the WINS tab to bring up the WINS setting window. Initially it is unlikely to look like the one below.
Home Directory users MUST click in the Enable NetBIOS over TCP/IP button. The WINS server settings should not be necessary for Home Directory, but if you are having difficulties, the correct servers for UVa and Home Directory are 128.143.3.199 and 128.143.22.189.
If you use a WINS server (ESERVICES users and some HSC users) on the WINS tab and add the appropriate WINS server information. Contact your server administrator for the correct WINS settings for your domain. (Those given above are for the ESERVICES domain.)
When finished click OK, you will be taken back to the "Internet Protocol (TCP/IP) Properties" window, some information may be filled in for you.
From this window click OK to get back to the main network connection properties window, and OK again on that window to exit the configuration. Then you should be able to retry your connection.
If you have difficulties following these directions or need any other help getting your connection to a UVa modem, please call us at 924-3731. That's the ITC Help Desk. Have your University Computing ID (that's your Email ID) ready and give us as clear a description as possible of what you have done and what is not working.
Chapter 5
ISDN Terminal Adapter
Contents
• What is Terminal Adapter • Types of Terminal Adapters • Features of Terminal Adapter
Objectives
After completion of this module, you will be able to know: • What is Terminal Adapter
• What are the types of Terminal Adapters • What are the features of Terminal Adapter
5.1 Terminal Adapter
In telecommunications, a terminal adapter is an interfacing device employed at the "R" reference point in an ISDN environment that allows a non-ISDN terminal at the physical layer to communicate with an ISDN network.
It performs a similar role for ISDN to that which a modem performs for the PSTN.
A terminal adapter (TA) is a hardware interface between a computer and an Integrated Services Digital Network line. It's what replaces a modem when you are using an ISDN connection. Unlike "plain old telephone service," which carries signal in analog (voice) form between your computer and the telephone company's office, ISDN carries signals in digital form so there is no need to modulate and demodulate between analog and digital signals. The terminal adapter is what you have to install on a computer so that data can be fed directly into the ISDN line in digital form. Since ISDN service is not available from telephone companies in all areas, the terminal adapter is not usually built into a computer. You purchase and install it when you sign up for ISDN service.
Some manufacturers and telephone companies use the term ISDN modem, instead.
Note: Typically, a terminal adapter will support standard RJ-11 (or other country-specific)
telephone connection plugs for voice and RS-232C, V.35 and RS-449 interfaces for data.
5.2 Types of Terminal Adapters
There are two main types of ISDN terminal adapters. You can either buy an internal or external terminal adapter. It really depends on what features you want supported with your ISDN line. But as ISDN becomes more common, future computers will probably have terminal adapters built it.
5.2.1 External terminal adapters
External adapters are better if your are going to use your ISDN line for "voice" (phone, fax, analog isdn modem, etc.). One has to be careful when purchasing an external TA because vendors claim to give you speeds of up to 64K. However, many external TAs cannot convert synchronous 64 Kbps data into 57.6 kbps asynchronous data. These TAs can only communicate in asynchronous mode at 38.4 kbps.
5.2.2 Internal terminal adapter
Internal terminal adapters usually go inside your computer like any other internal card. If you are going to be using ISDN strictly for Internet access, then an internal adapter is the right choice. The internal models are normally cheaper than external, because the manufacturers do not need to include a power supply or enclosure. The internal adapters do not have the serial port bandwidth constraints that the external ones do; hence you do not need to buy any special accessories to squeeze the maximum out of them. However, the internals are not set up well to provide ringers, and they need an
external power connection (or your PC powered on) in order to use them to make a voice call.
Features External TAs Internal TAs To use voice Works as long as TA is
powered
PC must be on, or additional equipment purchased
Ringer for other devices (fax, phone, etc.)
Can usually provide for six devices
Often requires additional equipment.
DTE speed Serial port speed constraint Much higher speed.
Cost More expensive Less expensive.
5.3 Some of the features to look out for in a TA
• Easy to install and use : Installation of TAs is easy and there should be an installation wizard that walks you through the configuration and setup, making the TA up and running in minutes with plug and play support for Windows 95/98/2000/Me/XP and NT.
• Support for WAN Protocol : TAs should support a full-range of WAN protocols, including X.75, CLEAR (synchronous), CHAP, MD5, PPP, ML-PPP, MP+TM, V.120, X.75 and PAP so that you can connect to a variety of servers on the corporate LAN or Internet.
• Call Bumping : TAs should support call bumping features that automatically adjust a data call from 128 K to 64 K. It should be able to reduce the data link to one channel to make or receive a phone call while communicating data with two B channels (at 128K).
• Battery back up : They should provide a built-in battery which supplies power for 2-3 hours in case of power failure.
• Simultaneous Voice and Data : TAs should be capable of transmitting and receiving data on your computer over one ISDN channel and use the other B-channel for your phone or fax machine using the analog port.
• Call line identification : For incoming calls from digital lines, the caller's number appears in the telephone display when the phone rings. This feature of TAs will enable to trace anonymous calls over ISDN.
Chapter 6
Proxy Servers
Contents
• Introduction of Proxy Server • Functions of Proxy Servers • Protocols of Proxy Servers • Host Identifiers and Ports
• Configuration of browser to use Proxy Server
Objectives
After completion of this module, you will be able to know: • What is a Proxy Server?
• What are the functions of Proxy Servers? • Protocols of Proxy Servers
• Host Identifiers and Ports
6.1 Introduction of Proxy Servers
A proxy is a device which allows connection to the Internet. It sits between workstations on a network and the Internet, allowing for a secure connection, allowing only certain ports or protocols to remain open. When a client requests a page, the request is sent to the proxy server, which relays it to the site. When the request is received from the site, it is forwarded back to the user. Proxy servers can be used to log internet use and block access to prohibited sites.
Some home networks, corporate intranets, and Internet Service Providers (ISPs) use proxy servers (also known as proxies). Proxy servers act as a "middleman" or broker between the two ends of a client/server network connection. Proxy servers work with Web browsers and servers, or other applications, by supporting underlying network protocols like HTTP.
6.2 Key Features of Proxy Servers
Proxy servers provide three main functions:1. Firewalling and filtering 2. Connection sharing 3. Caching
The features of proxy servers are especially important on larger networks like corporate intranets and ISP networks. The more users on a LAN and the more critical the need for data privacy, the greater the need for proxy server functionality.
6.2.1 Proxy Servers, Firewalling and Filtering
Proxy servers work at the Application layer, layer 7 of the OSI model. They aren't as popular as ordinary firewalls that work at lower layers and support application-independent filtering. Proxy servers are also more difficult to install and maintain than firewalls, as proxy functionality for each application protocol like HTTP, SMTP, or SOCKS must be configured individually. However, a properly configured proxy server improves network security and performance. Proxies have capability that ordinary firewalls simply cannot provide.
Some network administrators deploy both firewalls and proxy servers to work in tandem. To do this, they install both firewall and proxy server software on a server gateway. Because they function at the OSI Application layer, the filtering capability of proxy servers is relatively intelligent compared to that of ordinary routers. For example, proxy Web servers can check the URL of outgoing requests for Web pages by inspecting HTTP GET and POST messages. Using this feature, network administrators can bar access to illegal domains but allow access to other sites. Ordinary firewalls, in contrast, cannot see Web domain names inside those messages. Likewise for incoming data traffic, ordinary routers can filter by port number or network address, but proxy servers can also filter based on application content inside the messages.
6.2.2 Connection Sharing with Proxy Servers
Various software products for connection sharing on small home networks have appeared in recent years. In medium- and large-sized networks, however, actual proxy servers offer a more scalable and cost-effective alternative for shared Internet access. Rather than give each client computer a direct Internet connection, all internal connections can be funneled through one or more proxies that in turn connect to the outside.
6.2.3 Proxy Servers and Caching
The caching of Web pages by proxy servers can improve a network's "quality of service" in three ways. First, caching may conserve bandwidth on the network, increasing scalability. Next, caching can improve response time experienced by clients. With an HTTP proxy cache, for example, Web pages can load more quickly into the browser. Finally, proxy server caches increase availability. Web pages or other files in the cache remain accessible even if the original source or an intermediate network link goes offline.
Figure 6.1
6.2.3.1 Proxy caching
Imagine two people at a office -- let's call them Ram and Latha -- surfing the Net for business research. Suppose Ram has an interest in computer networking books, visits www.oreillynet.com in an attempt to learn more about them.
Now it's Latha's turn. Latha is very interested in computer programming. She navigates to www.oreillynet.com and, because this page was cached during Ram's very recent visit, she is surprised at how quickly this content-rich page pops into her browser window. With a great first impression, Latha is now ready to immerse herself in the wonderful world of computer programming.
The potential benefits of proxy server caching loom even larger if Ram and Latha have a few hundred coworkers that share the same proxied Internet access and similar interests
