2013/06/18

Reminder:
-In this note, I will add more information and details, also I need to thank you for +Ala Go to provide the helpful information.


1. Network:
A network is a set of nodes connected together by a shared medium.
網絡是一個由共享性質連接在一起的一組節點。

2. Node (節點) :
A node can be a computer or a connecting device.
一個節點可以是計算機或連接裝置。

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.
互聯網並不是一個單一的網絡,而是的收集大量個人網絡,他們都是相通的。

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.
伺服器是一部電腦,它向其他電腦執行作業並管理網絡。

5. Networks can be distinguished by the distances that they cover.
網絡可以被所覆蓋的距離區分。

    A. Local Area Network (LAN) (局域網):             *Within a relatively limited area.
                                                                                        *在一個相對有限的區域。

         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.
                                                                                         *跨越廣闊地理的區域

        

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.

【註解 1】

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.à (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.

【註釋 2】

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: (網站瀏覽器)
e.g. Internet Explorer (IE), Netscape, Firefox, Google Chrome

ii. Communication Protocol (通訊協定):

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.

c. TCP/IP: (Transmission Control Protocol / Internet Protocol)

TCP/IP is the communication protocol suite of the Internet. TCP/IP is a set of rules that determine how the data is broken up into packets, how the packets are routed and how they are recombined. When a message is sent, it is broken up into small packets by the sender computer. Each packet is directed by a series (many different) of routers across the Internet.

C. Others:

i. ISP:

Internet Service Provider (網絡服務供應商) is a company that provides access to the Internet. ISP can provide us the service such as e-mail, web hosting and firewall protection.

ii. URL:

A Uniform Resource Locator (劃一資源定位器 = 網址) refers to a particular web page or a particular file residing on a web site.

【註釋 3】

iii. IP Address:

Internet protocol addresses can identify every computer on a network. Therefore, each IP address must be unique in the network. The address is usually expressed as four denary numbers separated by periods. Each number must fall between 0 and 255 inclusively. For example, 210.0.212.3

【註釋 3】

iv. Domain Name Server:

Translates domain names (hk.yahoo.com) to IP addresses 106.10.165.51

e.g. Google.com    74.125.128.138

7. Advantages and Disadvantages of networking:

A. Advantages:

i. Networks allow user to communicate. (e.g. through e-mail)

ii. Provide fast data transfer Speed. Networks provide a very rapid method for sharing and transferring files.

iii. Sharing and transferring files.

iv. Sharing of software.

v. Sharing of data.

vi. Sharing of Internet access.

B. Disadvantages:

i. Computer virus (病毒) spreading.

ii. Problem of Privacy (私隱).

iii. Computer Crime (電腦犯罪) (Hacking 黑客 is the act of gaining unauthorized access to a remote computer system. E.g. Attacking the system causing damage of files. Changing the content of a web site.)

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【註解 1】


Switching hub 交換式集線器

- 俗稱的分享器,以前都統稱 hub
- Switch用途將不同的網路線插在一起
- 以前不管是否需要設定才能上網的分享器,都統稱 hub
- 但後來還是做了區別,比較專業一點的才叫 hub,而非高手也能用的叫做 switch
- hub 能透過192.168.1.1 的主頁,來設定一些專用的 port
- 但一般家庭使用者其實用不到這些功能,他就是想上網而已,所以簡單的 switch 也開始熱賣
- 只要連接 switch 電腦,做點簡單的連線設定就能上網
- 大部分的 switch 當然也能設定區網( LAN  
- 而比較需要專業設定的 就比較偏向 router
- 如果硬要以專業度來區分 就是 router > hub > switch
- 但這是以理論而言,實際上,現在其實沒有 hub
- 而是只有兩端的 router switch hub
- router 路由器  switch hub 交換器

- switch 跟 hub分別?
- 現今 hub 只是集線器的統稱,意思是所有網路線都接到這一台機器上 ,就好像 USB hub,意思就是所有USB設備接在同一個機器上
- 以前還沒有switch出現,那麼收集網路線的機器就直接稱為hub
- 以現在而言,hub 就是只有「收集線路的機器」這樣而已
- 所以 switch 正式名稱才會叫做 switch hub
- hubswitchrouter
- 現在實際的情況是,router hub switch hub,兩種 
- (分別就是專業人士用與非專業人士用)
- 一般家用的 à switch就可以,設定簡單,不需要複雜功能  à不用密碼
- 公司行號、學校、公家機關就需要 router à有密碼
- 而 hub就是剩下個名稱---集線器

WI-FI à無線網路 à router à無線基地台(ap)「Access Pointà 指的是可提供
- (W / LAN)登入、存取的路由器,又可稱為無線網路基地台。
- 可以說 aprouterswitch,差別只在於 ap另外有無線功能 (發射訊號)
- AP 例子如:http://lasjargon.blogspot.com/2013/06/tl-wr740n-ver-421tp-linkcp-router.html
- ap + router + switch à 統稱  à Hub (分享器)
- node (節點à 簡單說一台電腦,一個OS (operating system ),就是一個點
- 兩個os互相溝通,就是節點對節點了
- 作業系統=os
- Mac, Microsoft, liun, 手機 就是os
- (鍵盤是一個 node,滑鼠也是,以此類推,透過i/o設備跟os溝通)

【註釋 2】


網路速度測試speedtest.net
網速:ping: 4ms ; download speed: 94.50 Mbps ; upload speed: 54.30 Mbps

à速度為 Optical fibre (fiber-optic) (光導纖維)

【註釋 3】

- 網址就是ip à每個網址對應一個 ip
- 每個網站的 url = ip address , 就像每台電腦的ip address一樣的 , 要有唯一的地址,才能找到對方
- 四個一組的ip  xxx.xxx.xxx.xxx
- 電腦 IP à獨一無二
- rul、電腦都是一樣的IP (同一類 / IP) à都必須有一個實體的電腦, 就像檔案伺服器,伺服器本身就是電腦
- URL = 電腦 = 網絡 = 網路上任何東西
- 問題:三部電腦 à 同一個IP
- Ans : 因為是由一個實體ip出去(接在同一台分享器上)
- For example
1.     有信寄到你家
2.     如果沒屬名怎麼知道這封信給誰?  à 所以我們會寫上收件者
假設郵箱是分享器,你、爸爸、媽媽、弟弟是四個收件者,那當然是寄到同一個地址,但分享器自己會幫每台電腦再另給一組ip

- URL = IP?
- 原本url就是一組ip,但不好記憶,於是就演變成網址 (基本上都是做匹配 )
- 譬如說,isp配給我的ip 1.2.3.4,而我的網站網址是 super.com.tw
- 這兩者可以透過 isp的服務去匹配,如果沒匹配就是自動配發了

- isp=網路服務提供者,就是你每個月付錢給網路公司那個就叫isp 
- 這裡有詳細的解釋, http://zh.wikipedia.org/wiki/%E5%9F%9F%E5%90%8D
- 而這個網址可以查 http://tracker.derekr.com/whois/
但只能查大網站,像的blogger是附屬在google底下à這種就不能查

額外知識
網址正確說法叫做網域名稱(Domain Name
(e.g. .tw 是台灣  .jp是日本)

Click here and you can refer the other article about internet!

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