Networking Concepts and Components
At its most elementary level, a network consists of two computers connected to each other bycable so that they can share data. All networking, no matter how sophisticated, stems from that simple system. While the idea of two computers connected by a cable may not seem extraordinary, in retrospect, it was a major achievement in communications.
Networking arose from the need to share data in a timely fashion. Personal computers are wonderful business tools for producing data spreadsheets, graphics and other types of information. But they do not allow you to quickly share the data you have produced without a network. The documents have to be printed out so that copy to their computers if others make changes to the document there is no way to merge the changes. This was, and still is, called working in a stand-alone environment. Computers that are part of network can share the following:
· ata
· Message
· Graphics
· Printers
· fax machines
· Modems
· Other hardware resources
This list is constantly growing as new ways are found to share and communicate by means of computers.
Local Area Network
Networks started out small, with perhaps ten computers connected together with a printer. The technology limited the size of the network. Including the number of computers connected as well as the physical distance that could be covered by the network. For example, in the early 1980’s the most popular cabling method would allow about 30 users on a maximum cable length of just over 600 feet. Such a network might be on a single floor within one small company. For very small companies today, this configuration is still adequate. This type of network, within a limited area, is known as a local area network (LAN).
Wide Area Network
Local area networks work well but have physical and distance limitations. Because they are not adequate for all business communications there must be connectivity between LANs and other types of environments.
Using components such as bridges, routers and communication service providers, LAN can be expanded from an operation that serves a local area to one that can support data communications over a state, a country or even around the globe. When a network does this, it is called a wide area network (WAN).
To the user, WAN appears to function in the same way as a local area network. In fact, if the WAN has been properly implemented, there will appear to be no difference between a LAN and a WAN.
Most WANs are combination of LANs and other types of communication components connected by communication links called WAN links. WAN links can include the following:
· Packet-Switching Networks
· Fiber-Optic Cable
· Microwave Transmitters
· Satellite Links
· Cable Television Coaxial Systems
WAN links such as wide-area telephone connections are too expensive and complex for most private companies to purchase, implement and maintain at their own. Therefore, they are usually leased from service providers. Communication between LANs will involve one of the following transmission technologies:
· Analog Transmission
· Digital Transmission
· Packet Switching
Network Topologies
A Topology defines how the devices are connected together. Some commonly used topologies are mentioned here.
BUS Topology
Each device is connected to a single strand of co-axial cable via vampire tap. As the network site gets bigger, the LAN will need to grow. Cable in the bus topology can be extended by one of the two following methods.
· A component called a barrel connector can connect two pierces of cable together to make a longer piece of cable, however, connectors weaken the signal and should be used sparingly. It is much better to purchase one continuous cable than to connect several smaller ones with connectors. In fact, using too many connectors can prevent the signal from being correctly received.
· A device called a repeater can be used to connect two cables. A repeater actually boosts the signal before it sends the signal on its way. A repeater is better than a connector or a longer piece of cable because it allows a signal to travel even farther and still be correctly received.
Star Topology
In the star topology, computers are connected by cable segments to a centralized component called hub. Signals are transmitted from the sending computer through the hub to all computers on the network. This topology originated in the early days of computing with computers connected to a centralized mainframe computer. The star network offers centralized resource management. However, because each computer is connected to a central point, this topology requires a great deal of cable in a large network installation. Also, if the central point fails, the entire network goes down.
If one computer or the cable that connects it to the hub fails on a star network, only the failed computer will be able to send or receive network data. The rest of the network continues to function normally.Ring Topology
The ring topology connects computers on a single circle of cable. There are no terminated ends. The signals travel around the loop in one direction and pass through each computer. Unlike the passive bus topology, each computer acts like a repeater to boost the signal and send it on to the next computer. Because the signal passes through each computer, the failure of one computer can impact the entire network.
IP Addressing
IP stands for Internet Protocol. It is the unique 32 bits (4 bytes) address of all devices in the network.
Composition
IP address is composed of three parts :-
Bit Values
In binary addressing each bits represents a specific values i.e. power of 2.
231 20
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
255 255 255 255
Above all Octects (bytes) have range of addressing 0-255 total 256 different combinations (addresses)
Classes of Addresses
Classes are defined for globally standardization of the IP addressing.
Classes
Class is shown by the value of left most byte of IP address.
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
(a) CLASS ‘A’ 1-126
(b) CLASS ‘B’ 128-191
c) CLASS ‘C’ 192-223
(d) CLASS ‘D’ 224-239
(e) CLASS ‘E’ 240-254
‘0’ ADDRESS IS RESERVED FOR ALL NETWORKS
‘127’ IS RESERVED FOR LOOPBACK
‘255’ IS RESERVED FOR BROADCAST ADDRESS
Evolution of the Internet
Internet communication is possible between networks on different platforms and in different environments. This dynamic exchange of data is in part due to the development of communication protocols agreed-upon standard for exchanging data, and enables users to communicate between different networks. This section describes how the evolution of network protocols has contributed to the growth of the Internet.
1960s
In the 1960s, Transmission Control Protocol and the Internet Protocol (TCP/IP) were developed to provide high-speed communication between two network devices. These network protocols were to provide a communication link, even if some of the connecting links between devices were to fail. The RAND Corporation, in conjunction with the Massachusetts Institute of Technology and the University of California, Los Angeles developed this technology for the United States Department of Defense. This government agency needed a fail-safe network to ensure communications in the event of a nuclear war in 1969. The Department of Defense began using ARPANET the first network based on the protocol technology. ARPANET initially connected four supercomputers.
1970s
During 1970s, educational and research institutions began to connect to ARPANET to create a community of networks. In the late 1970s, TCP/IP became the official protocols to use on the Internet.
1980s
In the 1980s, the U.S. National Science Foundation replaced ARPANET with a high-speed network. This is the network that now serves as the backbone for the Internet today, When ARPANET was first used in 1969, it consisted of only 213 registered hosts. By 1986, there were over 2,300 host computers.
1990s
In the early 1990s, the U. S. National Science Foundation transferred the maintenance and funding of the Internet to private foundations and corporations. Today, the Internet has several million-host computers worldwide. The development of other protocols and other technologies such as the World Wide Web has contributed to this growth. You’ll learn more about the development of these technologies later in this chapter. For more information on the history as well as the future of the Internet see the homepage for the National Center for Supercomputing (NCSA) at the University of Illinois Urbana - Champaign.
Internet and Intranet
The most common use of Internet technologies by businesses and organizations is internally on their local area networks (LANs) or on a large wide area network (WAN). A LAN or WAN that uses Internet technologies is called an Intranet. Intranets enable groups to dynamically share internal resources in the same way Internet users share information. To use an Intranet, client computers typically should have:
- TCP/IP installed
- A Web browser installed such as Internet Explorer.
- Also, if the LAN is not connected to the Internet, an internal Web server needs to be established.