A computer network, often simply referred to as a network, is a collection of computers A computer is a programmable machine that receives input, stores and manipulates data//information, and provides output in a useful format and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of types and categories and also presents the basic components of a network.
Contents |
Introduction
A computer network allows sharing of resources and information among devices connected to the network. The Advanced Research Projects Agency (ARPA The Defense Advanced Research Projects Agency is an agency of the United States Department of Defense responsible for the development of new technology for use by the military. DARPA has been responsible for funding the development of many technologies which have had a major effect on the world, including computer networking, as well as NLS, which) funded the design of the Advanced Research Projects Agency Network (ARPANET ARPANET , created by a small research team at the head of the Massachusetts Institute of Technology and the Defense Advanced Research Projects Agency (DARPA) of the United States Department of Defense, was the world's first operational packet switching network, and one of the networks that came to compose the global Internet. The packet switching) for the United States Department of Defense. It was the first operational computer network in the world.[1] Development of the network began in 1969, based on designs developed during the 1960s. For a history see ARPANET ARPANET , created by a small research team at the head of the Massachusetts Institute of Technology and the Defense Advanced Research Projects Agency (DARPA) of the United States Department of Defense, was the world's first operational packet switching network, and one of the networks that came to compose the global Internet. The packet switching, the first network.
Purpose
Computer networks can be used for several purposes:
- Facilitating communications. Using a network, people can communicate efficiently and easily via e-mail, instant messaging, chat rooms, telephony, video telephone calls, and videoconferencing.
- Sharing hardware. In a networked environment, each computer on a network can access and use hardware on the network. Suppose several personal computers on a network each require the use of a laser printer. If the personal computers and a laser printer are connected to a network, each user can then access the laser printer on the network, as they need it.
- Sharing files, data, and information. In a network environment, any authorized user can access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.
- Sharing software. Users connected to a network can access application programs A computer program is a sequence of instructions written to perform a specified task for a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute the instructions. The same program in its human- on the network.
Network classification
The following list presents categories used for classifying networks.
Connection method
Computer networks can be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as optical fiber An optical fiber is made up of the core , the cladding (reflecting the light pulses back into the core) and the buffer coating (protecting the core and cladding from moisture, damage, etc). Together, all of this creates a fiber optic which can carry up to 10 million messages at any time using light pulses. Fiber optics is the overlap of applied, Ethernet Ethernet is a family of frame-based computer networking technologies for local area networks . The name came from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model as well as a common addressing format and Media Access Control at the Data Link Layer, Wireless LAN A wireless local area network links devices via a wireless distribution method (typically spread-spectrum or OFDM) and usually provides a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network, HomePNA The HomePNA Alliance is an incorporated non-profit industry association of companies that develops and standardizes technology for home networking over the existing coaxial cables and telephone wiring within the home, Power line communication Power line communication or power line carrier , also known as Power line Digital Subscriber Line (PDSL), mains communication, power line telecom (PLT), or power line networking (PLN), or Broadband over Power Lines (BPL) are systems for carrying data on a conductor also used for electric power transmission or G.hn G.hn is the common name for a home network technology standard being developed under the International Telecommunication Union and promoted by the HomeGrid Forum and several other organizations. and several other organizations. It supports networking over power lines, phone lines and coaxial cables with data rates up to 1 Gbit/s.
Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers. Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light. Naturally-occurring radio waves are made by lightning, or by astronomical objects. Artificially-generated radio waves are used for fixed and mobile or infrared signals as a transmission medium. ITU-T The Telecommunication Standardization Sector coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland G.hn G.hn is the common name for a home network technology standard being developed under the International Telecommunication Union and promoted by the HomeGrid Forum and several other organizations. and several other organizations. It supports networking over power lines, phone lines and coaxial cables with data rates up to 1 Gbit/s technology uses existing home wiring (coaxial cable Ethernet over Coax is a family of technologies that supports the transmission of Ethernet frames over coaxial or coax cable, phone lines and power lines Power line communication or power line carrier , also known as Power line Digital Subscriber Line (PDSL), mains communication, power line telecom (PLT), or power line networking (PLN), or Broadband over Power Lines (BPL) are systems for carrying data on a conductor also used for electric power transmission) to create a high-speed (up to 1 Gigabit/s) local area network.
Wired technologies
- Twisted pair Twisted pair cabling is a type of wiring in which two conductors are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. It was invented by Alexander Graham Bell and he wire is the most widely used medium for telecommunication. Twisted-pair wires are ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or channel, to another and electromagnetic induction Electromagnetic induction is the production of voltage across a conductor situated in a changing magnetic field or a conductor moving through a stationary magnetic field. The transmission speed ranges from 2 million bits per second to 100 million bits per second.
- Coaxial cable Coaxial cable, or coax, is an electrical cable with an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, is widely used for cable television systems, office buildings, and other worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.
- Optical fiber An optical fiber is made up of the core , the cladding (reflecting the light pulses back into the core) and the buffer coating (protecting the core and cladding from moisture, damage, etc). Together, all of this creates a fiber optic which can carry up to 10 million messages at any time using light pulses. Fiber optics is the overlap of applied cable consists of one or more filaments of glass fiber wrapped in protective layers. It transmits light which can travel over extended distances without signal loss. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed may reach trillions of bits per second. The transmission speed of fiber optics is hundreds of times faster than for coaxial cables and thousands of times faster than for twisted-pair wire.
Wireless technologies
- Terrestrial Microwave Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band ( – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx. 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.
- Communications Satellites In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
- Cellular and PCS Systems – Use several radio communications technologies. The systems are divided to different geographic area. Each area has low-power transmitter or radio relay antenna device to relay calls from one area to the next area.
- Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. An example of open-standards wireless radio-wave technology is IEEE 802.11b.
- Bluetooth – A short range wireless technology. Operate at approx. 1Mbps with range from 10 to 100 meters. Bluetooth is an open wireless protocol for data exchange over short distances.
Scale
Networks are often classified as local area network A local area network is a computer network covering a small physical area, like a home, office, or small groups of buildings, such as a school, or an airport. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased (LAN), wide area network A wide area network is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries ). This is in contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs) which are usually limited to a (WAN), metropolitan area network A metropolitan area network is a large computer network that usually spans a city or a large campus. A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks and the Internet (MAN), personal area network A personal area network is a computer network used for communication among computer devices, including telephones and personal digital assistants, in proximity to an individual's body. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal (PAN), virtual private network A virtual private network is a computer network that is layered on top of an underlying computer network. The private nature of a VPN means that the data travelling over the VPN is not generally visible to, or is encapsulated from, the underlying network traffic. Similarly, the traffic within the VPN appears to the underlying network as just (VPN), campus area network A campus area network is a computer network that interconnects local area networks throughout a limited geographical area, such as a university campus, a corporate campus, or a military base. It could be considered a metropolitan area network that is specific to a campus setting. A campus area network is, therefore, larger than a local area (CAN), storage area network A storage area network is an architecture to attach remote computer storage devices (such as disk arrays, tape libraries, and optical jukeboxes) to servers in such a way that the devices appear as locally attached to the operating system. A SAN typically is its own network of storage devices that are generally not accessible through the regular (SAN), and others, depending on their scale, scope and purpose. (e.g., Controller Area Network Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer (CAN)) Usage, trust level, and access right often differ between these types of network. For example, LANs tend to be designed for internal use by an organization's internal systems and employees in individual physical locations (such as a building), while WANs may connect physically separate parts of an organization and may include connections to third parties.
Functional relationship (network architecture)
Computer networks may be classified according to the functional relationships which exist among the elements of the network, e.g., active networking Active network architecture is composed of execution environments , a node operating system capable of supporting one or more execution environments. It also consists of active hardware, capable of routing or switching as well as executing code within active packets. This differs from the traditional network architecture which seeks robustness and, client–server and peer-to-peer A peer-to-peer, commonly abbreviated to P2P, is any distributed network architecture composed of participants that make a portion of their resources directly available to other network participants, without the need for central coordination instances (such as servers or stable hosts). Peers are both suppliers and consumers of resources, in (workgroup) architecture.
Network topology
Computer networks may be classified according to the network topology Network topology is defined as the interconnection of the various elements of a computer network. Network Topologies can be physical or logical. Physical Topology means the physical design of a network including the devices, location and cable installation. Logical topology refers to how data is actually transferred in a network as opposed to its upon which the network is based, such as bus network A bus network topology is a network architecture in which a set of clients are connected via a shared communications line, called a bus. There are several common instances of the bus architecture, including one in the motherboard of most computers, and those in some versions of Ethernet networks, star network Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages. Thus, the hub and leaf nodes, and the transmission lines between them, form a graph with the topology of a star. If the central node is passive,, ring network A ring network is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node - a ring. Data travels from node to node, with each node along the way handling every packet, mesh network Mesh networking is a type of networking wherein each node in the network may act as an independent router, regardless of whether it is connected to another network or not. It allows for continuous connections and reconfiguration around broken or blocked paths by “hopping” from node to node until the destination is reached. A mesh network whose, star-bus network Network topology is defined as the physical interconnection of the various elements of a computer network. Network Topologies can be physical or logical. Physical Topology means the physical design of a network including the devices, location and cable installation. Logical topology refers to the fact that how data actually transfers in a network, tree or hierarchical topology network Network topology is the physical interconnections of the elements of a computer network. A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN has one or more links to one or more other nodes in the network and the mapping of these links and nodes in a graph. Network topology is the coordination by which devices in the network are arranged in their logical relations to one another, independent of physical arrangement. Even if networked computers are physically placed in a linear arrangement and are connected to a hub, the network has a star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.
Types of networks
Common types of computer networks may be identified by their scale.
Personal area network
A personal area network A personal area network is a computer network used for communication among computer devices, including telephones and personal digital assistants, in proximity to an individual's body. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless connections between devices. The reach of a PAN typically extends to 10 meters.[2] A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.[3]
Local area network
A local area network A local area network is a computer network covering a small physical area, like a home, office, or small groups of buildings, such as a school, or an airport. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on Ethernet Ethernet is a family of frame-based computer networking technologies for local area networks . The name came from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model as well as a common addressing format and Media Access Control at the Data Link Layer technology, although new standards like ITU-T The Telecommunication Standardization Sector coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland G.hn G.hn is the common name for a home network technology standard being developed under the International Telecommunication Union and promoted by the HomeGrid Forum and several other organizations. and several other organizations. It supports networking over power lines, phone lines and coaxial cables with data rates up to 1 Gbit/s also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines)[4].
Typical library network, in a branching tree topology and controlled access to resourcesAll interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP The Internet Protocol is a protocol used for communicating data across a packet-switched internetwork using the Internet Protocol Suite, also referred to as TCP/IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.
The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and no need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 IEEE 802.3 is a collection of IEEE standards defining the Physical Layer and Data Link Layer's media access control sublayer of wired Ethernet. This is generally a LAN technology with some WAN applications. Physical connections are made between nodes and/or infrastructure devices (hubs, switches, routers) by various types of copper or fiber cable LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE The Institute of Electrical and Electronics Engineers or IEEE is an international non-profit, professional organization for the advancement of technology related to electricity. It has the most members of any technical professional organization in the world, with more than 395,000 members in around 150 countries has projects investigating the standardization of 40 and 100 Gbit/s.[5]
Home area network
A home area network is a residential LAN which is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a CATV or Digital Subscriber Line Digital Subscriber Line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term Digital Subscriber Line is widely understood to mean Asymmetric Digital Subscriber Line (ADSL), the most commonly (DSL) provider.
Campus network
A campus network is a computer network made up of an interconnection of local area networks (LANs) within a limited geographical area. The networking equipments (switches, routers) and trasmission media (optical fiber, copper plant, Cat5 cabling etc.) are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc.).
In the case of a university campus-based campus network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls.
Wide area network
A wide area network A wide area network is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries ). This is in contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs) which are usually limited to a (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.
|
Tue, 24 Aug 2010 19:53:44 GMT+00:00
EnterpriseNetworkingPlanet Then in the 1970s, ARPA was renamed DARPA with addition of "Defense," and its researchers developed the computer network protocols that became the ... Remarks by Vice President Joe Biden at the Recovery Act Innovation Report Event Whitehouse.gov (press release)
338px x 450px | 37.60kB
[source page]
Hi My Dear Readers In my previous posts i show you spiderman 3 computer case
Computer Network Security
Mon, 16 Aug 2010 00:06:21 GM
Apple has released QuickTime 7.6.7 for Windows to address a vulnerability. This vulnerability is due to a stack buffer overflow that exists in.
Q. My husband has both a bachelors and a master in music education and has 8 years experience as a band director. He's considering changing careers and wants to work with computers. He's very knowledgable about computers and troubleshooting. He thinks he would like to work as a network administrator, but other computer-type jobs might be considered. What kind of qualifications would he need (mind you he has no experience, so education type of qualifications)? And what kind of salaries are normal for a job like this?
Asked by SMicheleHolmes - Sun Aug 26 07:37:15 2007 - - 3 Answers - 0 Comments
A. I have two sons in this field. They are highly experienced and both have 2 year degrees in the field. They are not well paid but really enjoy their work. They both say that experience counts for more than degrees in this field, but I'm thinking that for him to get started in the field, he should have at least a 2 year degree and as many certifications as he can get. If he takes some classes in this field, he will hear about the certification tests and when and where he can take them. They are sometimes expensive, but his teachers should be able to guide him toward the most important ones.
Answered by leslie b - Sun Aug 26 07:55:06 2007
