2013/05/18

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1. Network: A network is a set of nodes connected together by a shared medium.

2. Node (節點) : A node can be a computer or a connecting device.

3. Internet (互聯網) : The Internet is not a single network, but instead is a large collection of individual networks that are all interlinked.

4. Server (伺服器) : A server is computer that performs tasks for other computers and / or manages the network, e.g. sharing of files, sharing of hardware, etc.

5. Networks can be distinguished by the distances that they cover.

    A. Local Area Network (LAN) (局域網):             *Within a relatively limited area.

         There are two popular types of LANs:
                      PEER TO PEER 對等式:                    CLIENT TO SERVER 主從式:
                  
 


Peer to peer: 

Every computer is connected directly to every other computer. Each computer can use information from, and provide information to each other.

Disadvantage: Low network efficiency, Not suitable for a large number of computers, Low security.
Advantage: Network topology (structure) is simple.
                  No need to buy extra software.

缺點;網絡效能較低,電腦數量多便不合用。
優點:架構簡單,使用者不需另購軟件。

Client-server:

Individual computers, called clients or workstations, are connected to a server. Clients request for services and server provide services.

(最少要一台伺服器電腦擔任中央控制角色)
缺點:伺服器若壞了,整個網絡的服務便停止。

    B. Wide Area Network (WAN) (廣域網):             *Span a wide geographical area.

        

6. Communication Hardware and Software.

A. Hardware:

i. Modem (調制解調器):

A modem is a device that converts digital signals (數位訊號) from your computer into analogue signals (類比訊號) (modulation) and also converts analogue signals into digital signals (demodulation).

iv. Network Interface Card (網絡介面卡):

The network interface card (NIC) provides the physical connection between the network and the computer workstation.

iii. Switch (Switching hub 交換式集線器):

Provide a central connection point for cables in a network to connect different computers.

iv. Router (路由器):

A router is a connecting device that routes data from one network to another.
We usually use router to share broadband service (寛頻)  at home. --> (this is why we use router)

v. Links (Network cables and Radio connections)

a. Coaxial cable (同軸電纜):

Coaxial cabling has a single copper conductor at its center and a plastic layer outside.

b. Twisted pair wires (雙扭線):

It looks similar to a telephone cable (Two of them are UTP and STP). The maximum data transmission speed of a Cat6 UTP cable is about 1000 Mbps within 100m distance limit.

c. Optical fibre (fiber-optic) (光導纖維):

It consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference.

Adv: Greater signal-carrying capacity.
        Faster data transmission speed.
        Much thinner, lighter and more durable.
        Reduced susceptibility to noise or interference from other devices.

d. Wi-Fi connections:

Wireless Fidelity refers to the network based on the IEEE802.11 wireless LAN standard (e.g. 802.11a, 802.11g). Data in a Wi-Fi wireless network is transmitted by radio waves. Data transmission speed is 10 to 600 Mbps.

The advantages of it are inexpensive, flexible and easy to install.

e. Microwave 微波 (or Satellite 人造衛星):

They are electromagnetic waves so that rainstorms may affect the signal. Data transmission speed of satellite is 50 Kbps to 500 Kbps. Data transmission speed of microwave is 100 Mbps and the coverage range up to 1.5 km.

B. Software:

i. Web Browser:
e.g. Internet Explorer (IE), Netscape, Firefox, Google Chrome

ii. Communication Protocol:
A protocol is a set of rules that govern the communication between different devices
     
a. HTTP: (HyperText Transfer Protocol)

HTTP is a communications protocol for the transfer of information on the Internet. It is use for retrieving inter-linked text documents (hypertext) led to the establishment of the World Wide Web.

b. FTP: (File Transfer Protocol)
FTP is a network protocol used to transfer data from one computer to another through a network such as the Internet. 

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