Salam

Tuesday, 29 May 2012

Internet

Internet


The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite (often called TCP/IP, although not all applications use TCP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless and optical networking technologies. The Internet carries an extensive range of information resources and services, such as the inter-linked hypertext documents of the World Wide Web (WWW) and the infrastructure to support email.



The communications infrastructure of the Internet consists of its hardware components and a system of software layers that control various aspects of the architecture. While the hardware can often be used to support other software systems, it is the design and the rigorous standardization process of the software architecture that characterizes the Internet and provides the foundation for its scalability and success. The responsibility for the architectural design of the Internet software systems has been delegated to the Internet Engineering Task Force (IETF). The IETF conducts standard-setting work groups, open to any individual, about the various aspects of Internet architecture. Resulting discussions and final standards are published in a series of publications, each called a Request for Comments (RFC), freely available on the IETF web site. The principal methods of networking that enable the Internet are contained in specially designated RFCs that constitute the Internet Standards. Other less rigorous documents are simply informative, experimental, or historical, or document the best current practices (BCP) when implementing Internet technologies.



Wireless

Wireless Technology

Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few metres for television remote control, or as far as thousands or even millions of kilometres for deep-space radio communications.It is a term used for mobile IT equipment. It is encompasses cellular phones, personal digital assistants (PDA’s) and wireless wiring. Other examples of wireless technology include GPA units, garage door openers and or garage door, wireless computer mice and keyboards, satellite television and cordless telephones. 

  • Wireless PAN
  • Wireless personal area networks (WPANs) interconnect devices within a relatively small area, that is generally within a person's reach.[3] For example, both Bluetooth radio and invisible infraredlight provides a WPAN for interconnecting a headset to a laptop. ZigBee also supports WPAN applications.[4] Wi-Fi PANs are becoming commonplace (2010) as equipment designers start to integrate Wi-Fi into a variety of consumer electronic devices. Intel "My WiFi" and Windows 7 "virtual Wi-Fi" capabilities have made Wi-Fi PANs simpler and easier to set up and configure

Wireless LAN
A wireless local area network (WLAN) links two or more devices over a short distance using a wireless distribution method, usually providing a connection through an access point for Internet access. The use of spread-spectrum or OFDM technologies may allow users to move around within a local coverage area, and still remain connected to the network.
Products using the IEEE 802.11 WLAN standards are marketed under the Wi-Fi brand name. Fixed wireless technology implements point-to-point links between computers or networks at two distant locations, often using dedicated microwave or modulated laser light beams over line of sight paths. It is often used in cities to connect networks in two or more buildings without installing a wired link.
Wireless MAN
Wireless metropolitan area networks are a type of wireless network that connects several wireless LANs.
  • WiMAX is a type of Wireless MAN and is described by the IEEE 802.16 standard

Wireless WAN
Wireless wide area networks are wireless networks that typically cover large areas, such as between neighboring towns and cities, or city and suburb. These networks can be used to connect branch offices of business or as a public internet access system. The wireless connections between access points are usually point to point microwave links using parabolic dishes on the 2.4 GHz band, rather than omnidirectional antennas used with smaller networks. A typical system contains base station gateways, access points and wireless bridging relays. Other configurations are mesh systems where each access point acts as a relay also. When combined with renewable energy systems such as photo-voltaic solar panels or wind systems they can be stand alone systems.


With the development of smartphonescellular telephone networks routinely carry data in addition to telephone conversations:
  • Global System for Mobile Communications (GSM): The GSM network is divided into three major systems: the switching system, the base station system, and the operation and support system. The cell phone connects to the base system station which then connects to the operation and support station; it then connects to the switching station where the call is transferred to where it needs to go. GSM is the most common standard and is used for a majority of cell phones.
  • Personal Communications Service (PCS): PCS is a radio band that can be used by mobile phones in North America and South Asia. Sprint happened to be the first service to set up a PCS.
  • D-AMPS: Digital Advanced Mobile Phone Service, an upgraded version of AMPS, is being phased out due to advancement in technology. The newer GSM networks are replacing the older system.


Network Equipments, Protocol and Cabling

Network Equipments
   Networking hardware includes all computers, peripherals, interface cards and other equipment needed to perform data-processing and communications within the network.


Network Hardware


File Server
In computing, a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files (such as documents, sound files, photographs, movies, images, databases, etc.) that can be accessed by the workstations that are attached to the same computer network. The term server highlights the role of the machine in the client–server scheme, where the clients are the workstations using the storage. A file server is not intended to perform computational tasks, and does not run programs on behalf of its clients. It is designed primarily to enable the storage and retrieval of data while the computation is carried out by the workstations.


Workstation
workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems. The term workstation has also been used to refer to a mainframe computer terminal or a PC connected to a network.


Network Interface Card
In computer networking, a NIC provides the hardware interface between a computer and a network. A NIC technically is network adapter hardware in the form factor of an add-in card such as a PCI or PCMCIA card.
Some NIC cards work with wired connections while others are wireless. Most NICs support either wired Ethernet or WiFi wireless standards. Ethernet NICs plug into the system bus of the PC and include jacks for network cables, while WiFi NICs contain built-in transmitters / receivers (transceivers).



Hub


  1. The messages that are understood by the object.
  1. The arguments that these messages may be supplied with.
  1. The types of results that these messages return.
  1. The invariants that are preserved despite modifications to the state of an object.
  1. The exceptional situations that will be required to be handled by clients to the object.
Cable is the medium through which information usually moves
from one network device to another. Several types of cable are
commonly used with LANs.In some cases,a network will utilize only one type of cable, other networks will use a variety of cable types.There are four types of cables namely :
  1.      Unshielded Twiested Pair (UTP) 
  1.      Shielded Twisted Pair (STP) 
  1.      
  2. Coaxial Cable
  1.      
  2. Fiber Optic Cable
  1.      Wireless LANs

      Unshielded Twiested Pair  (UTP)

  •   four pairs of wires inside the jacket
  •    
  • each pair is twisted with different twist per   inch to help eliminate  interference from adjacent pairs and other electrical devices.










 Shielded Twisted Pair (STP) 



  •  
  • consists of two individual wires wrapped in a foil shielding to help provide a more reliable data communication. 
  • suitable for environments with electrical 
  • interference but the extra shielding can make the cables quite bulky. 
  • often used on networks using Token Ring topology.
Coaxial Cable




  • Coaxial cabling has a single copper conductor at its center. 
  • A plastic layer provides insulation between the center conductor and a braided metal shield. 
  • The metal shield helps to block any outside interference from fluorescent lights, motors, and    other computers.
  • The most common type of connector   
  • used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector. 




  • Fiber Optic Cable  consists of a center glass core surrounded by several layers of protective materials and transmits light rather than electronic signals eliminating the problem of electrical interference. 
  • Fiber Optic Cable is ideal for certain environments that contain a large amount of electrical interference. 
  • It is able to transmit signals over much longer distances than coaxial and twisted pair.

A common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.
Repeater

Network repeaters regenerate incoming electrical, wireless or optical signals. With physical media like Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel.
Actual network devices that serve as repeaters usually have some other name. Active hubs, for example, are repeaters. Active hubs are sometimes also called "multiport repeaters," but more commonly they are just "hubs." Other types of "passive hubs" are not repeaters. In Wi-Fi, access points function as repeaters only when operating in so-called "repeater mode."

Bridges


bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments.
Bridges operate at the data link layer (Layer 2) of the OSI model. Bridges inspect incoming traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects each incoming Ethernet frame - including the source and destination MAC addresses, and sometimes the frame size - in making individual forwarding decisions.
Bridges serve a similar function as switches, that also operate at Layer 2. Traditional bridges, though, support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.
Router
router is a device that forwards data packets between computer networks, creating an overlay internetwork. A router is connected to two or more data lines from different networks. When a data packet comes in on one of the lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey. Routers perform the "traffic directing" functions on the Internet. A data packet is typically forwarded from one router to another through the networks that constitute the internetwork until it gets to its destination node
Switch
network switch or switching hub is a computer networking device that connects network segments or network devices. The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (layer 3) and above are often referred to as layer-3 switches or multilayer switches.

Protocol
In object-oriented programming, a protocol or interface is a common means for unrelated objects to communicate with each other. These are definitions of methods and values which the objects agree upon in order to cooperate.
The protocol is a description of:
If the objects are fully encapsulated then the protocol will describe the only way in which objects may be accessed by other objects.

Cabling

Computer Networking


Computer Network
A collection of computers and other hardware devices that are connected together to share hardware, software, and data as well as to communicate with one another


LAN (Local Area Network) : covers relatively small geographical area : home,
WAN (Wide Area Network) Covers large geographical area. It consists of two or more LAN and connected together using communications technology Internet is the largest WAN
MAN (Metropolitan Area Networks) school, office Network design to service a metropolitan area i.e a city . Consist of multiple LAN Size between LAN and WAN
PAN (Personal Area Networks) Network of personal devices:
printer, mobile devices, etc.. Wired or wireless


computer network can be categorized according to three properties:
  1. typology
  2. protocol
  3. architecture  

Network topology is the layout pattern of interconnections of the various elements (links, notes) of a computer network. It is the geometrical arrangement of the network. The picture below show the different arrangement of the network.






 network protocol defines rules and conventions for communication between network devices. 

The most common network protocols are:
  1. Ethernet
  2. Local Talk
  3. Token Ring
  4. FDDI
  5. ATM

A network architecture is the specification of design principles (including data formats and procedures) for creating a network configuration of data processors. Two most common network are peer- to- peer and server/client network There are two types of transmission media; bounded and unbounded. 

Types of Network Protocols

     • Bounded Media         • Unbounded Media (air or a vacuum)
- Twisted pair wire        - AM and FM radio
- Co-axial cable             - TV broadcasting
- Fiber optic cables        - Satellite communication
- Microwave radio
- Infrared signals 
- Below are some examples of network electronic device and
their properties:
  • network bridge connects multiple network segments.A bridge uses a forwarding database to send frames across network segments.
  •  hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment.
  • gateway is used to interfaced with other network.A gateway is a network point that acts as an entrance to another network
    .