Category Archives: COMPUTER NETWORKING

COMPUTER NETWORKING

COMPUTER NETWORKING.

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Ethernet Cabling

CATERGORY 3 CABLE

Catergory 3 cable is used as telephone cable and has a 100mhz bandwidth, using an RJ11 connector. It is UTP cable, with a max distance of 100M (300 feet) before the signal starts to degrade and can use 10Base-T LAN applications with a max speed of 4mbps.

CATERGORY 4 CABLE

Catergory 4 cable is rarely used anymore, and has been wiped out by Cat5+ and has a 100mhz bandwidth. It is UTP cable, with a max distance of 100M (300 feet) before the signal starts to degrade and can use 10Base-T LAN applications with a max speed of 16mbps.

CATERGORY 5 CABLE

Catergory 5 cable is a little old nowadays, but it still used widely in networks and has a 100mhz bandwidth. Cat 5 is UTP cable, with a maximum length of 100M (300 feet) before the signal starts to degrade. Cat 5 can be used in 10BaseT, 100Base-Tx, ATM and CDDI LAN applications.

CATERGORY 5e CABLE

Catergory 5e cable is the most common type of cable used today in networks and has a 100mhz bandwidth. Cat 5e is UTP cable, with a maximum length of 100M (300 feet) before the signal starts to degrade, and can be used in 10Base-T and 100Base-T LAN applications.

CATERGORY 6 CABLE

Catergory 6 cable is the up and coming cable with a 250mhz bandwidth. It is full duplex cable which means that it can be used with gigabit routers. It has two 4 wires paths instead of 2 2-wire paths like the cabling before. Cat 6 is UTP cable, with a maximum length of 100M (300 feet) before the signal starts to degrade. Cat 6 can be used in 10BaseT, 100Base-T, and 1000Base-T LAN applications.

CATERGORY 7 CABLE

Catergory 7 is not being used yet. It is a hybrid cable with a 600mhz bandwidth. It is ScTP cable with a maximum length of 100M (300 feet) before the signal starts to degrade. Cat 7 can be used in 1000Base-T LAN applications.

BLOCK AMPLIFIER

A device attached to a long cable run, which works just like a repeater to re-boost the signal so that the signal can be carried over a longer distance.

Hub And Bridges

In general, a hub is the central part of a wheel where the spokes come together. The term is familiar to frequent fliers who travel through airport “hubs” to make connecting flights from one point to another. In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub usually includes a switch of some kind. (And a product that is called a “switch” could usually be considered a hub as well.) The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data

is forwarded from the place where data comes together. Regarded in its switching aspects, a hub can also include a router.

1) In describing network topologies, a hub topology consists of a backbone (main circuit) to which a number of outgoing lines can be attached (“dropped”), each providing one or more connection port for device to attach to. For Internet users not connected to a local area network, this is the general topology used by your access provider. Other common network topologies are the bus network and the ring network. (Either of these could possibly feed into a hub network, using a bridge.)

2) As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for connections to a local area network (for example, an Ethernet or a token ring), and a connection to a line (the main line in this example).

BRIDGES

A bridge is used to connect two networks together. Just like a bridge connects two roads, this bridge can join two different networks to extend the network. Say you have two home networks, one in the basement and one upstairs. You can put a bridge in the middle of the house, and then transfer files between networks while still having two seperate networks. The only disadvantage to doing is, is that the collision domain becomes larger (more chance of packets colliding) since the network is much larger.

REPEATERS

A repeater is like a router, but is used to re-strengthen a signal over a long distance. There are analog repeaters, which can only amplify the signal and there are digital repeaters that can restore a signal to near original quality. Some hubs can act as repeaters aswell. Repeaters cannot route internet like a router can though, they are strictly used to regenerate a signal. A repeater should be used when cat5e cabling is over 300feet (100metres) in length. A wireless repeater can be placed between the router and the computer, when length is an issue and the signal is degraded.

linksys bridge

Network Topologies

In computer networking, topology refers to the layout of connected devices. This article introduces the standard topologies of networking.

Topology in Network Design

Think of a topology as a network’s virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.

Network topologies are categorized into the following basic types:

  • bus
  • ring
  • star
  • tree
  • mesh

More complex networks can be built as hybrids of two or more of the above basic topologies.

Bus Topology

Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.

Ethernet bus topologies are relatively easy to install and don’t require much cabling compared to the alternatives. 10Base-2 (“ThinNet”) and 10Base-5 (“ThickNet”) both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either “clockwise” or “counterclockwise”). A failure in any cable or device breaks the loop and can take down the entire network.

To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses.

Illustration – Ring Topology Diagram

Star Topology

Many home networks use the star topology. A star network features a central connection point called a “hub” that may be a hubswitch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer’s network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

Tree Topology

Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the “root” of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

Mesh Topology

Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.

A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

net topologies

net topologies

The Internet And How It Works

It seems like everyone’s talking about the Internet these days. But what is it really? How does it work? How do you access it? And most important, what can it do for you at work or at home?

Fortunately, accessing and using the Internet is fairly simple. Let this tutorial be your guide to the Internet as you connect for the first time and explore the network’s vast and useful resources.

How Does the Internet Work?

The Internet is a worldwide collection of computer networks, cooperating with each other to exchange data using a common software standard. Through telephone wires and satellite links, Internet users can share information in a variety of forms. The size, scope and design of the Internet allows users to:

  • connect easily through ordinary personal computers and local phone numbers;
  • exchange electronic mail (E-mail) with friends and colleagues with accounts on the Internet;
  • post information for others to access, and update it frequently;
  • access multimedia information that includes sound, photographic images and even video; and
  • access diverse perspectives from around the world.

An additional attribute of the Internet is that it lacks a central authority—in other words, there is no “Internet, Inc.” that controls the Internet. Beyond the various governing boards that work to establish policies and standards, the Internet is bound by few rules and answers to no single organization.

In February 1996, President Clinton signed into law the Communications Decency Act, which provides criminal penalties for those who post or transmit “indecent” material via the Internet. This law, however, has been challenged in U.S. courts by those who feel it would unfairly prohibit many legitimate uses of the Internet, and was ruled unconstitutional in July 1996. The federal government, however, is preparing an appeal.

The History of the Internet

Many people think that the Internet is a recent innovation, when in fact the essence of it has been around for over a quarter century. The Internet began as ARPAnet, a U.S. Department of Defense project to create a nationwide computer network that would continue to function even if a large portion of it were destroyed in a nuclear war or natural disaster.

During the next two decades, the network that evolved was used primarily by academic institutions, scientists and the government for research and communications. The appeal of the Internet to these bodies was obvious, as it allowed disparate institutions to connect to each others’ computing systems and databases, as well as share data via E-mail.

The nature of the Internet changed abruptly in 1992, when the U.S. government began pulling out of network management, and commercial entities offered Internet access to the general public for the first time. This change in focus marked the beginning of the Internet’s astonishing expansion.

According to a survey conducted by CommerceNet and Nielsen Media Research in early 1997, nearly one out of every four Americans over the age of 16 is an Internet user. And the number of users worldwide is believed to be well into the tens of millions. Other statistics are equally startling:

  • A CNN report stated that Internet traffic in 1996 was 25 times what it was just two years earlier.
  • The market research group IntelliQuest pegged the number of Internet users in the U.S. in late 1996 at 47 million – a 34 percent increase over the first quarter of that year.
  • According to IBM, 146 countries currently have at least some level of Internet access.
  • The technology research firm IDG estimates that by century’s end, one billion people worldwide will have access to personal computers—more than doubling the computer-savvy population of 1996.

The Internet explosion coincides with the advent of increasingly powerful yet reasonably priced personal computers with easy-to-use graphical operating systems. The result has been an attraction of recent computer “converts” to the network, and new possibilities for exploiting a wealth of

What Kinds of Information are Available?

In addition to text documents, the Internet makes available graphics files  (digitized photographs and artwork), and even files that contain digitized sound and video. Through the Internet, you can download software, participate in interactive forums where users post and respond to public messages, and even join “chats,” in which you and other users type (and, in some cases, speak) messages that are received by the chat participants instantly.

How Do People Use the Internet?

Obviously, the Internet can bring you a whole host of capabilities. But how can they be put to practical use?

Among the ways that users like yourself are taking advantage of the Internet are:

  • Sharing research and business data among colleagues and like-minded individuals.
  • Communicating with others and transmitting files via E-mail.
  • Requesting and providing assistance with problems and questions.
  • Marketing and publicizing products and services.
  • Gathering valuable feedback and suggestions from customers and business partners.

The Internet’s potential is limited only by users’ vision and creativity. And as the Internet grows, new and innovative uses will surely follow.

The Sum of Many Parts

Unlike many computer networks, the Internet consists of not one but multiple data systems that were developed independently. The most popular and important systems are:

  • E-mail, for exchange of electronic mail messages.
  • USENET newsgroups, for posting and responding to public “bulletin board” messages.
  • File Transfer Protocol (FTP), a system for storing and retrieving data files on large computer systems.
  • Gopher, a method of searching for various text-based Internet resources (largely obsolete).
  • TELNET, a way of cornecting directly to computer systems on the Internet.
  • Internet Relay Chat (IRC), a system for sending public and private messages to other users in “real time”—that is, your message appears on the recipient’s screen as soon as you type it.
  • CU-SeeMe, a videoconferencing system that allows users to send and receive sound and pictures simultaneously over the Internet.
  • The World Wide Web.

The final component listed here is perhaps the most exciting element of the Internet today. We will learn more about the World Wide Web—and how you can benefit from it.

Internet

Internet

Local Area Network

local area network (LAN) supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN.

Most local area networks are built with relatively inexpensive hardware such as Ethernetcables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist.

Specialized operating system software may be used to configure a local area network. For example, most flavors of Microsoft Windows provide a software package called Internet Connection Sharing (ICS)that supports controlled access to LAN resources.

The term LAN party refers to a multiplayer gaming event where participants bring their own computers and build a temporary LAN.

Also Known As: local area network

Examples:

The most common type of local area network is an Ethernet LAN. The smallest home LAN can have exactly two computers; a large LAN can accommodate many thousands of computers. Many LANs are divided into logical groups called subnets. An Internet Protocol (IP) “Class A” LAN can in theory accommodate more than 16 million devices organized into subnets.

Lan

Lan

 

 

Types of Network

 

 

 

 

There are three types of network. These are:

  • Local Area Network (LAN)
  • Wide Area Network (WAN)
  • Metropolitan Area Network (MAN)

Local Area Network

A local area network is a network system in which computers are interconnected in a limited geographical area, such as network of computers in college computer laboratory or network of computers in office building etc.

Wide Area Network

A wide area network is a network system that covers a large geographical area such as different cities of country or different countries of the world. In WAN telephone lines, satellites, microwave, fiber optic etc. are used as transmission media. If you enjoy learning about computer networks and want to become an IT professional, a CCNA Training Course might be right for you.”

Metropolitan Area Network

A Metropolitan area Network is a network system that covers area of a single city. Usually, MAN connects more than one LANS in a city or town and covers a smaller geographical area than a WAN. The cable television, telephone companies or local corporations use MAN.

Internet

The internet is a worldwide collection of networks that connects millions of computers, business, government agencies, educational institutions. It is a global network and source of information. Information can be communicated from one country to another through internet. More than two and half billion people around the world use the internet daily for different purposes. For example, to communicate with other people around the world, access information and latest news around the world. The computers are the main source through which information can be electronically sent and received from one location to another.

TCP/IP

In this protocol data transmission is managed by dividing the data into different pieces called packets. Each packet of data contains a part of actual data, source computer address, destination address, and information for reassembling data at destination computer. These packets of data travel along the fastest available path in the network. This type of data transmission is called packet switching and is used in internet communication.

IP Addressing

IP stands for internet protocol. Basically it is a unique identifier for a computer on the internet. It is numerical address with four numbers separated with dots and the format of an IP address is a 32-bit.Each number can be start from 0 and ends with 255. For example  IP address looks like this: 131.200.1.1

Every computer on the internet using unique IP address and this IP address can be static and dynamic. A server has a static IP address that does not change. When a computer dialing internet through modem then that computer has a IP address that is assigned by the local ISP. Your local ISP assigned you unique IP address for each session and it may be different each time.

What is Packets?

The transfer of data from one place to another place in the form of digital signals and this data is broken into small data segment before being transmitted from one computer to another computer. These small data segments are called packets. Each packets contains the information about its source and destination (sender’s and receiver’s information). A normal packets size between 1000 to 1500 bytes. The packets send to its destination using best possible path and this makes a network more efficient.

Network Devices

Digital Modem

The modem that is used to send and to receive data to and from a digital telephone line is called digital modem. ISDN modem and DSL modem are the best example of digital modem. These modem are used to send and receive the digital data to and from the digital line, So there is no need to convert to analog signals because digital lines already use the digital signals.

Bridge

It is an electronic device that connects two same type of networks and control the traffic between them. A bridge basically split an overloaded network into two separate network for reducing the amount of traffic on each segment and increase the performance of each network. A bridge looks at the information in each packet header and forwards data from one LAN to another.

Router

An electronic device that connects many computers together and transmits data to its correct destination using the available path on the network is called router. It stores the information of each node on the network and to use these information to transfer date between nodes.

Routable Protocols

There are not all protocols works with routers. Routable protocols are

  • IP
  • IPX
  • OSI
  • DECnet
  • XNS

Like a bridge, a router looks at each packet’s header to determine the destination of packet and thus reach its destination. Some routers also have built-in antivirus protection. Similarly, some routers also support wireless communication

Type of Routers

Static Router.

An administrator manually set up the router path and configuration of static router.

Dynamic Router.

A dynamic router automatically find the path to its destination with minimal configuration.

Gateway

A gateway is an electronic device that can perform logical function. A gateway is a device or system (because it may be a hardware or software) that connects two or more networks to share their information from one to the other. Packets from different networks have different type of information in their headers, and information in different format. The gateway can take a packet from one type of network, read the header, and then encapsulates the entire packet into a new one, adding a header that is understood by the network.