COMPUTER NETWORK

A computer network is a collection of computers and devices connected together via communications devices and transmission media. For examples it may connect computers, printers and scanners.


IMPORTANCE / ADVANTAGES OF COMPUTER NETWORKS

• Sharing of devices such as printer and scanner.
• Sharing of program/ software.
• Sharing of files.
• Sharing of data.
• Sharing of information.
• Sharing of single high-speed internet connection.
• Can access server centered database.
• Better communication using internet services such as e-mail, mailing list and Internet Relat Chat (IRC). 

Types of computer network                   : LAN, MAN, WAN

Network architecture                            : Client/Server, Peer to Peer

Network topologies                               : Star, Bus, Ring

Network communications technology     : Intranet, Extranet, Internet 

TYPES OF COMPUTER NETWORKS

Local Area Network (LAN) ~ A local area network is a network that connects
                                              computers and devices in a limited geographical area
                                              such as a home, school computer laboratory,
                                              office building.

Metropolitan Area Network (MAN) ~ A metropolitan area network (MAN) is a high
                                                          speed network that connects local area
                                                          networks in a metropolitan area such as city
                                                          or town and handles bulk of communications
                                                          activity across the region. 

                                                       ~A MAN typically includes one or more LAN
                                                         but covers a smaller geographic area than a
                                                         WAN.

Wide Area Network (WAN) ~A wide area network is a network that covers a large 

                                             geographical area such as country or the world.

                                           ~WAN combines many types of media such as telephone
                                             lines, cables and radio waves. A WAN can be one
                                             large network or can consist of two or more LANs
                                             connected together.

                                           ~The internet is the worlds largest WAN.

NETWORK ARCHITECTURE 

Client/ Server

• A server is a computer that controls access to the hardware, software and other resources on the network and provides a centralized storage area for program. There are many type of server such as mail server, web server, file server and ftp server.
• A client is a computer that requests services from a server computer.

Peer-to-Peer

• Peer-to-Peer is a simple, inexpensive network that typically connects fewer than 10 computers. All computers it the network have equal capabilities to use the resources (hardware, software, data and files) available on the network.

NETWORK TOPOLOGIES 

Network topology is the physical arrangement of computers in a network. Common network topologies include the bus, star and ring.

* RING TOPOLOGY

- Data transmitted on the ring network travels from device to device around the entire
  ring, in one direction.

Advantages

• A physical ring topology has minimal cable requirements
• No wiring center or closet needed
• The message can be automatically acknowledged
• No collision exist between nodes.

Disadvantages

• If any node goes down, the entire ring goes down
• Troubleshooting is difficult because communication is only one way
• There will be a limit on the distance between nodes

* BUS TOPOLOGY

- The bus in a bus network transmits data, instructions and information in both
   directions.

Advantages

• Easy to implement and extend
• Cost effective as only a single cable is used
• Cable faults are easily identified 

Disadvantages

• Limited cable length and number of stations.
• If there is a problem with the cable, the entire network goes down.
• Maintenance costs may be higher in the long run.
• Performance degrades as additional computers are added or on heavy traffic.
• Proper termination is required (loop must be in closed path).

* STAR TOPOLOGY

- All data that transfers from one node to another passes through the hub, in both
  directions.

Advantages

• Easy to install and wire
• No disruptions to the network then connecting or removing devices
• Easy to detect faults and remove parts
• More suited for larger networks
• Easy to expand network
•  Easy to troubleshoot because problem usually isolates itself

Disadvantages

• Failure of the central hub causes the whole network failure.
• It is slightly more expensive than using bus topology.
• Requires more cable.

NETWORK COMMUNICATIONS TECHNOLOGY

Internet ~ An internet is a public network. It is worldwide collection of networks that
                links millions of businesses, government agencies, educational institutions
                and individuals. 

Intranet ~ An intranet is a private network within an organization that resembles the 

                internet. Organizations use intranets to provide information to their
                employees. 

Extranet ~ An extranet is a private network that connects more than one
                organizations. Many organizations use the Internet technologies to allow
                suppliers, customers and business partner limited access to their networks.  

WIRED COMMUNICATION MEDIA

Wired communication refers to the transmission of data over a wire-based communication technology. Examples include telephone networks, cable television or internet eccess and fibre-optic communication. Also wave guide (electromagnetism), used for high-power applications, is considered as wired line. 


* TYPES OF CABLES

• Twisted Pair Cable

              
          ~ Twisted pair cable consists of two strands of insulated copper wire, twisted
             around each other. Multiple twisted pairs can be combined into a single cable.
             This twisted-pair configuration somewhat reduces  interference from
             electrical field.
          ~ The wires are twisted together to reduce noise. Noise is an electrical
             disturbance that can degrade communications.

• Coaxial Cable

               

         ~ Coaxial cable consists of a single copper wire surrounded by at least three
             layer an insulating material, braided wired, plastic coating.
         ~ Cable television (CATV) network wiring ofter uses coaxial cable because it
             can be cabled over longer distances than twisted-pair cable.
         ~ Most of today's computer networks, however, do not use coaxial cable
            because other transmission media such as fiber-optic cable transmit signals
            at faster rates.  

• Fibre Optic

                

          ~ Fibre optic cable consists of dozens or hundreds of thin strands of glass that
             use light to transmit signal. Each strand, call optical fibre, is an thin as a
             human hair.
          ~ Inside the fibre-optic cable, an insulating glass cladding and a protective
             coating surround each optic fibre.
          ~ Fibre optic cables have the following advantages over cables that use wire,
             such as twisted-pair and coaxial cables:
                     * Capability of carrying significantly more signals than wire cables
                     * Faster data transmission
                     * Less susceptible to noise (interference) from other devices such as
                        copy machine
                     * Better security for signals during transmission because they are less
                        susceptible to noise
                     * Smaller size (much thinner and lighter weight)

          ~ Disadvantages of fibre-optic cable are it costs more than twisted-pair or
             coaxial cable and can be difficult to install and modify. Despite these
             limitations, many local and long-distance telephone companies are replacing
             existing telephone lines with fibre-optic cables. Businesses also are using
             fibre-optic cables in high-traffic networks or as the backbone in a network.

WIRELESS COMMUNICATION MEDIA

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 meters for television remote control, or as far as thousands of even million of kilometer for deep-space radio communications. It encompasses various types of fixed, mobile and portable two-way radios, cellular telephones, personal digital assistants (PDAs) and wireless networking. Other examples of wireless technology include GPS units, Garage door openers or garage door, wireless computer mice, keyboards and Headset (audio), headphones, radio receivers, satellite television, broadcast television and cordless telephones.

SATELLITE

~ A satellite is a place station that receives microwave signals from an earth-based station,

    amplifies (strengthens) the signals and broadcasts the signal back over a wide area to any

    number of earth-based stations.

BLUETOOTH

~ Bluetooth technology uses short-range radio waves to transmit data between two bluetooth

    devices. The data transfers between devices at a rate of 1 Mbps. To communicate each other,

    bluetooth devices often must be within about 10 meters (33 feet).

WiFi (Wireless Fidelity)

~The data transfers between devices at a rate of 11 - 54 Mbps. To communicate each other,

   WiFi devices often must be within about 30 meters (100 feet).

COMMUNICATION PROTOCOL

A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications. A protocol may have a format description. Protocols may includes signaling, authentication and error detection or connection capabilities. A protocol definition defines the syntax, semantics and synchronization of communications; the specified behavior is typically independent of how it is to be implemented. A protocol can therefore be implemented as hardware or software or both.

TCP/IP

~TCP/IP is the communication protocol for communication between computers on the 

  Internet.

~TCP/IP stands for Transmission Control Protocol / Internet Protocol.

~TCP/IP defines how electronic devices (like computers) should be connected to the 

   Internet, and how data should be transmitted between them.

Hart communication protocol

HYPERTEXT TRANSFER PROTOCOL

~ The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, 

   collaborative, hyper media information systems. HTTP is the foundation of data 

   communication for the World Wide Web.

~  Hypertext is a multi-linear set of objects, building a network by using logical links 

   (the so-called hyperlinks) between the nodes (e.g. text or words). HTTP is the 

   protocol to exchange or transfer hypertext.

~ The standards development of HTTP was coordinated by the Internet Engineering 

   Task Force (IETF) and the World Wide Web Consortium (W3C), culminating in the 

   publication of a series of Requests for Comments (RFCs), most notably RFC 2616 

   (June 1999), which defines HTTP/1.1, the version of HTTP in common use.

SIMPLE MAIL TRANSFER PROTOCOL (SMTP)

~ Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. SMTP was first defined by RFC 821 (1982, eventually declared STD10), and last updated by RFC 5321 (2008) which includes the extended SMTP (ESMTP) additions, and is the protocol in widespread use today. SMTP uses TCP port 25. The protocol for new submissions (MSA) is effectively the same as SMTP, but it uses port 587 instead. SMTP connections secured by SSL are known by the shorthand SMTPS, though SMTPS is not a protocol in its own right.

While electronic mail servers and other mail transfer agents use SMTP to send and receive mail messages, user-level client mail applications typically only use SMTP for sending messages to a mail server for relatying. For receiving messages, client applications usually use either the Post office Protocol  (POP) or the Internet Message Access Protocol (IMAP) or a proprietary system (such as Microsoft Exchange or Lotus Notes/Domino) to access their mail box accounts on a mail server.

 Mail processing model

POST OFFICE PROTOCOL (POP)

~ In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by local e-mail clients to retrieve e-mail from a remote server over a TCP/IP connection. POP and IMAP (Internet Message Access Protocol) are the two most prevalent Internet standard protocols for e-mail retrieval. Virtually all modern e-mail clients and servers support both. The POP protocol has been developed through several versions, with version 3 (POP3) being the current standard. Most webmail service providers such as Hotmail, Gmail and Yahoo! Mail also provide IMAP and POP3 service.

REFERENCE

* Book ~ Score A <INFORMATION AND COMMUNICATION TECHNOLOGY
               (SPM)>
            ~ Discovering Computers2007
* Websites ~ http://en.wikipedia.org/wiki/Communications_protocol
                  ~ http://en.wikipedia.org/wiki/Wireless
                  ~ http://en.wikipedia.org/wiki/Wired_communication
                  ~ http://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol
                  ~ http://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol
                  ~ http://en.wikipedia.org/wiki/Post_Office_Protocol