History of internet -- Introduction:

• The Internet is a gigantic collection of millions of computers, all linked together on a computer network.
• The network allows all of the computers to communicate with one another.
• A home computer is usually linked to the Internet using a normal phone line and a modem that talks to an Internet Service Provider (ISP).
• A computer in a business or university has a Network Interface Card (NIC) that directly connects it to a Local Area Network (LAN) inside the business.
• The business then connects its LAN to an ISP using a high-speed phone line like a T1 line.
• A T1 line can handle approximately 1.5 million bits per second, while a normal phone line using a modem can usually handle 30,000 to 50,000 bits per second.
• ISPs then connect to larger ISPs, and the largest ISPs maintain fiber-optic "backbones" for an entire nation or region. Backbones around the world are connected through fiber-optic lines, undersea cables or satellite links .
• In this way, every computer on the Internet is connected to every other computer on the Internet.


• Backbones are typically fiber optic trunk lines.
• The trunk line has multiple fiber optic cables combined together to increase the capacity.
• Fiber optic cables are designated OC for optical carrier, such as OC-3, OC-12 or OC-48. An OC-3 line is capable of transmitting 155 Mbps while an OC-48 can transmit 2,488 Mbps (2.488 Gbps). Compare that to a typical 56K modem transmitting 56,000 bps and The National Science Foundation (NSF) created the first high-speed backbone in 1987. Called NSFNET, it was a T1 line that connected 170 smaller networks together and operated at 1.544 Mbps (million bits per second).
• IBM, MCI and Merit worked with NSF to create the backbone and developed a T3 (45 Mbps) backbone the following year.
• Most large communications companies have their own dedicated backbones connecting between various regions .
• In each region, the company has a Point of Presence (POP). The POP is a place for local users to access the company's network, often through a local phone number or dedicated line.
• The amazing thing here is that there is no overall controlling network. Instead, there are several high-level networks connecting to each other through Network Access Points or NAPs

• In the real Internet, dozens of large Internet providers interconnect at NAPs in various cities, and trillions of bytes of data flow between the individual networks at these points.
• The Internet is a collection of huge corporate networks that agree to all intercommunicate with each other at the NAPs.
• In this way, every computer on the Internet connects to every other.

Bridging the Network :
All of these networks rely on NAPs, backbones and routers to talk to each other. In this process, a message can leave one computer and travel halfway across the world through several different networks and arrive at another computer in a fraction of a second!
The routers determine where to send information from one computer to another. Routers are specialized computers that send your messages and those of every other Internet user speeding to their destinations along thousands of pathways. A router has two separate, but related, jobs.

• It ensures that information does not go where it is not needed. This is crucial for keeping large volumes of data from clogging the connections of "innocent bystanders."
• It makes sure that information does make it to the intended destination.

In performing these two jobs, a router is extremely useful in dealing with two separate computer networks. It joins the two networks, passing information from one to the other. It also protects the networks from one another, preventing the traffic on one from unnecessarily spilling over to the other. Regardless of how many networks are attached, the basic operation and function of the router remains the same. Since the Internet is one huge network made up of tens of thousands of smaller networks, its use of routers is an absolute necessity

Every machine on the Internet has a unique identifying number, called an IP Address. The IP stands for Internet Protocol, which is the language, that computers use to communicate over the Internet. A protocol is the pre-defined way that someone who wants to use a service talks with that service. The "someone" could be a person, but more often, it is a computer program like a Web browser.
A typical IP address looks like this:
151.8.151.16

To make it easier for us humans to remember, IP addresses are normally expressed in decimal format as a dotted decimal number like the one above. But computers communicate in binary form. Look at the same IP address in binary:
10010111.00001000.10010111.00010000
The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form.

• If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers.
• Since each of the eight positions can have two different states (1 or zero), the total number of possible combinations per octet is 28 or 256.
• Therefore, each octet can contain any value between zero and 255.
• Combine the four octets and you get 232 or a possible 4,294,967,296 unique values!
  Out of the almost 4.3 billion possible combinations, certain values are restricted from use as typical IP addresses.
• For example, the IP address 0.0.0.0 is reserved for the default network and the address 255.255.255.255 is used for broadcasts.
• The octets serve a purpose other than simply separating the numbers. They are used to create classes of IP addresses that can be assigned to a particular business; government or other entity based on size and need.
• The octets are split into two sections: Net and Host.
• The Net section always contains the first octet. It is used to identify the network that a computer belongs to.
• Host (sometimes referred to as Node) identifies the actual computer on the network. The Host section always contains the last octet.
• There are five IP classes plus certain special addresses.

When the Web is accessed or used for sending an e-mail message, a domain name is used . For example, the Uniform Resource Locator (URL) "http://laptop-computers-desktop.blogspot.com/" contains the domain name blogspot.com. So does this e-mail address: xyz@blogger.com. Every time a domain name, is used the Internet's DNS server translates the human-readable domain name into the machine-readable IP address.
Top-level domain names, also called first-level domain names, include .COM, .ORG, .NET, .EDU and. GOV. Within every top-level domain, there is a huge list of second-level domains. For example, in the COM first-level domain there is:

• Yahoo
• Microsoft

Every name in the COM top-level domain must be unique. The left-most word, like www, is the host name. It specifies the name of a specific machine (with a specific IP address) in a domain. A given domain can, potentially, contain millions of host names as long as they are all unique within that domain. DNS servers accept requests from programs and other name servers to convert domain names into IP addresses. When a request comes in, the DNS server can do one of four things with it

1. It can answer the request with an IP address because it already knows the IP address for the requested domain.
2. It can contact another DNS server and try to find the IP address for the name requested. It may have to do this multiple times.
3. It can say, "I don't know the IP address for the domain you requested, but here's the IP address for a DNS server that knows more than I do."
4. It can return an error message because the requested domain name is invalid or does not exist.

When the URL http://laptop-computers-desktop.blogspot.com/ is typed in the browser.

1. The browser contacts a DNS server to get the IP address. A DNS server would start its search for an IP address by contacting one of the root DNS http://laptop-computers-desktop.blogspot.com/ servers.
2. The root servers know the IP addresses for all of the DNS servers that handle the top-level domains (COM, NET, ORG, etc.).
3. The DNS server would ask the root for , and the root would say, "I don't know the IP address for www.hclinfosystems.com, but here's the IP address for http://laptop-computers-desktop.blogspot.com/ of the blogger.COM DNS server." The server then sends a query to the COM DNS server asking it if it knows the IP address for http://laptop-computers-desktop.blogspot.com/.
4. The DNS server for the COM domain knows the IP addresses for the name servers handling the http://laptop-computers-desktop.blogspot.com/ domain, so it returns thoseThe server then contacts the DNS server for http://laptop-computers-desktop.blogspot.com/and asks if it knows the IP address for http://laptop-computers-desktop.blogspot.com/. It actually does, so it returns the IP address to the DNS server, which returns it to the browser, which can then contact the server for http://laptop-computers-desktop.blogspot.com/ to get a Web page.
5. One of the keys to making this work is redundancy. There are multiple DNS servers at every level, so that if one fails, there are others to handle the requests.
6. The other key is caching. Once a DNS server resolves a request, it caches the IP address it receives. Once it has made a request to a root DNS server for any COM domain, it knows the IP address for a DNS server handling the COM domain, so it does not have to bug the root DNS servers again for that information.
7. DNS servers can do this for every request, and this caching helps to keep things from bogging down.
8. Even though it is totally invisible, DNS servers handle billions of requests every day and they are essential to the Internet's smooth functioning. The fact that this distributed database works so well and so invisibly day in and day out is a testimony to the designThus the whole complex network though seems complex, works fine .

• It is now more than a decade since the announcement of CD-ROM standard for the computer storage.

• From its origins as a music format, CD has enjoyed unprecedented success and has grown to encompass computer applications, imaging applications (Photo CD), and the video game applications.

• Over the years, we have seen significant advance in the enabling technologies that support the Compact Disc.

• Laser optics, reflective films and disc replication have all made major strides. Digital coding and compression algorithms have become vastly more sophisticated.

• Moreover, integrated circuits and drive mechanisms have made impressive advances.

• All of these advances came into play when work began on the next generation of the optical media.

• The goal:

  • vastly increased capacity, with the ability to feature an entire movie in high-quality digital video on a single side of the disc. This was the start of DVD, a new optical storage technology with far greater capacity than current compact discs.

  • What is DVD? The letters don't officially stand for anything. They are commonly assumed to represent "Digital Video Disk", but that term has already been trademarked.

  • Some vendors use "Digital Versatile Disk". "DVD" simply means "Very Large Capacity CD with Advanced Multimedia Support". It is a storage technology that will change how people buy movies, music, and software

• DVD-R is a write-once format, meaning that data can be written to a disc and stored without fear of accidental erasure. similar.
• DVD-R, like CD-R, uses a constant linear velocity ration technique to maximize the storage density on the disc surface.
• This results in a variable number of revolutions per minute (RPM) as disc writing/reading progresses from one end to the other.
• Recording begins at the inner radius and ends at the outer. At "1X"speeds, rotation of the disc varies from 1,623 to 632 RPM on 3.95 Gbyte media and 1,475 to 575 RPM on 4.7 byte media, depending on the record/playback head's position over the surface.
• On 3.95 Gb media, the track pitch, or the distance from the center of one part of the spiral information "track" to an adjacent part of the track, is 0.8 microns, one-half that of CD-R. 4.7 Gbyte media uses an even smaller track pitch of 0.74 microns.

• DVD Recordable (DVD-R) technology allows anyone to create DVD discs at the desktop.

• Similar in concept to
  • Compact Disc Recordable (CD-R), DVD-R is a write-once medium that can contain any type of information normally stored on mass produced DVD discs – video, audio, images, data files, multimedia programs, and so on.
  • Depending on the type of information recorded, DVD-R discs are usable on virtually any compatible DVD playback device, including DVD-ROM drives and DVD Video players.
• A DVD-R disc is able to contain a maximum of either 4.7 or 3.95 billion bytes of information on each side, depending on the type of blank media used.
• Since the DVD format supports double-sided media, up to 9.4Gbytes can be stored on a single double-sided DVD-R disc.
• Data can be written to a disc at a DVD "1X" equivalent of 11.08 megabits per second (Mbps), which is roughly equivalent to nine times the transfer rate of CD-ROM's "1X" speed.
• After recording, DVD-R discs can be read at the same rate as mass-produced replicated discs, depending on the "X" factor of the DVD-ROM drive used.
• These transfer rates, coupled with DVD-R's capacity and conformance to worldwide DVD standards, makes it an extremely viable and cost effective storage medium.

Expected Life of DVD-R Media:

• Life expectancy is a key issue when considering the use of DVD-R for applications such as document imaging and other archival applications.

• Although each disc media manufacturer has its own life expectancy rating, Pioneer DVD-R media is currently rated at better than 100 year

DVD File system and MPEG software:

• Recorded DVD Video discs can be played on a DVD video player, as well as a computer that is equipped with a DVD-ROM drive, a DVD-compliant MPEG decoder card (or decoder software like POWER DVD MPEG Software) and application software that emulates a video player's control functions.

• A recorded DVD-ROM disc can be read by a computer equipped with a DVD-ROM drive, as well as a computer equipped for DVD video playback as described above.

• Recorded DVD-R discs support a new file system called "UDF- Bridge" .

• This is a hybrid approach that provides both the newer UDF (Universal Disc Format) system as well as the older ISO-9660 system used by the CD-ROM format.

• This allows DVD discs to be used with computer operating systems that do not have any provision for UDF support.

Looks Familiar, still new and Different:

The DVD standard defines a disc that maintains the overall dimensions, look and feel of the current Compact Disc. Some of these similarities will be unmistakable to consumers experiencing DVD for the first time. Others are less apparent, but equally important to the rapid and successful introduction of DVD.

Ø Like CD, DVD is 120mm (4-3/4 inches) in diameter and 1.2mm thick.

Ø Both store information as pits arranged along concentric, circular tracks embedded in a reflective material, which is bonded to a clear disc. A laser reflects differently from pits and from "land" (space without a pit). The player spins the disc, focuses a laser on a track, and "reads" reflections of pits and land as 0's and 1's.

Ø The new DVD players will be able to play the billions of existing music CDs.

Ø DVD software can be replicated using existing CD production facilities.

Ø Using the existing form factor reduces the re-tooling required to manufacture DVD players and DVD-ROM drives.

Ø A disc-based format means the kind of split-second random access that no tape format can match.

Ø Non-contact laser optics means playback without wear and tear.

Ø As with Compact Disc, DVD will be durable, and tolerant of dust, dirt and fingerprints. Under the surface, of course, DVD reveals some substantial differences.

Ø DVD holds seven times the data of CD: 4.7 gigabytes per layer, as compared to 680 megabytes for CD.

Ø DVD offers a dual-layer, single-side option, for even higher capacity: 8.5 gigabytes on a single side.

Ø Every DVD is a bonded disc, composed of two 0.6mm substrates joined together.

• 1. A one-sided digital video disc (DVD) is made up of four main layers. First there's a thick polycarbonate plastic that provides a foundation for the other layers. Next, a much thinner layer of opaque, reflective material is laid on the base. Then come a thin layer of transparent film, and finally a surface layer of clear, protective plastic. Data, including video, audio, text, or programs, is represented, as with a CD-ROM, by a combination of flat areas (lands) and indentations (pits) on two of the surfaces—the transparent film and the shiny opaque layer

• The DVD pits, however, are much smaller, which is part of the reason the DVD holds as much as 8.5MB of data, the capacity of 13 compact discs.

• 2. Like a CD-ROM drive, a DVD drive uses a laser to read the lands and pits. But the DVD laser uses light that has a shorter wavelength, which makes the laser beam narrow enough to accurately read the smaller pits and lands on the DVD surfaces.
• 3. By changing the amount of current flowing through a magnetic coil surrounding the laser beam, the DVD read head focuses the beam so that it's concentrated on only the surface of the transparent film.
• 4. Where the laser beam hits a pit, the indentation scatters the light in all directions.
  
• 5. But when the beam of light hits a flat area, it is reflected back to the read head, where a prism deflects the light to a device that converts the bursts of light energy into bursts of electricity. The computer interprets those electrical pulses as code and data.
• 6. The layer of transparent film accounts for only half the data DVD can contain.
• By adjusting the amount of current in the coils surrounding the laser, the read head can change the focal length of the laser beam so that it passes through the transparent layer with little distortion.
• The beam then strikes the opaque layer and reads the pits and lands on it the same as it does with the transparent layer.
• 7. The capacity of a single-sided DVD is doubled when the same layers of opaque and transparent materials are applied to the other side of the disc. But because current DVD drives have only one read head, you must remove the doubled-side DVD and flip it over to read data on the second side.

Mass Data Delivery and Storage:

• Every day there are more ideas for using mass storage in a small, portable medium.

• For example, content that currently fills several CDs would fit on one DVD.

• Write able DVD, as a data backup medium, provides far shorter seek and retrieval times than magnetic tape.

• Instead of shipping multiple units, software companies could encrypt multiple titles, distribute them all one DVD, and charge consumers for decryption keys.

Single standard for the World:

• DVD consortium, formed to create a single, unified standard for the emerging DVD format, consists of 11 electronic companies.
• These companies are Hewlett-Packard, JVC, Kodak, Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson, Time Warner, and Toshiba.
• The format enjoys the enthusiastic support of the world's major electronics & computer companies. As a movie playback format, it meets the specific and detailed requests of the motion picture Industry's Studio Advisory Committee.
• As a computer ROM format, it meets the specifications of the computer Industry's Technical Working Group.
• No other product has enjoyed such broad international support across so many industries prior to launch

Ultimate Multimedia:

• The design of DVD reflects the widespread success of CD-ROM as a data carrier for computer programs, databases, multimedia software and video games.

• As computer-processing power continues to increase, the need for higher capacity media is becoming increasingly apparent. And expanding markets for high-resolution graphics and full motion video continue to push the limits of existing storage media.

• In this environment, DVD-ROM will help satisfy the constant demand for the increased storage. With all the advantages, DVD-ROM is poised to become the undisputed leader in next-generation optical media for computers, multimedia and video games.

• DVD is poised to spark new opportunities and creative applications that we can only imagine today.

DVD-RAM and DVD-R Standards:

• High capacity, Recordable optical disk technology took a big step last month when the DVD Consortium announced it had finalized the DVD-RAM and DVD-R formats.

• The new systems offer up to 5.2 GB of data storage.

• The DVD-RAM standard will utilize the wobble-land-groove recording method to enable the users to store 2.6 GB on a single sided disk and 5.2GB on a double-sided disk.

• The wobble-land-groove method combines the land-groove recording method, in which data is recorded in grooves in the disk and lands, the areas between the grooves, and the wobble method, in which the disk tracks are not perfectly circular but move slightly from left to right as they run round the disk.

• The DVD-R system, which is write-once version for computer use, will have the capacity to store 3.95 GB on a single-sided disk, and 7.9 GB on a double-sided disk.

• The difference in format is due to a different recording method, where in a laser records to an organic dye on the disk.

• Besides the 12-cm version, DVD-R will also have a smaller 8-cm cousin.

Manufacturer:

• The leader in the world who is making the DVDROM drives are

  1. Pioneer 2. Aopen 3. Samsung 4. Philips