2012年5月28日星期一

Internet Infrastructure

Today we are learning about Internet Infrastructure.


Hierarchy Of Networks
-from a single computer to LAN.
-from LAN to ISP.
-from ISP to www.


There are a few things that needed in order to connect to internet. The things are:
-computer
-web browser
-Internet access


However,policy and procedure to bring to internet is complicated.


Internet Protocol
-is the internet standard protocol that provides a common layer over dissimilar network.
-to more packet among 'host', computer through gateways.
-every computer assign unique IP address.
IP address consist of 32 bits, also equal to 4 octets of number from 0-225, represent in decimal form instead if binary.
-IP address consist of 2 part:

  1. Identifying network.
  2. Identifying the node/host.
-class of address determined which part belongs to network and             which part belongs to node.
-all node on a given network share the same network pretix but must have a unique host number.

DOMAIN NAME SYSTEM (DNS)
-internet service that translate domains name like www.yahoo.com into numerical IP address like 204.62.131.129.

INTERNET SERVICE PROVIDER(ISP)
- an organization that provides access to the Internet. 
-  can be either community-owned and non-profit, or privately owned and for-profit.

               


Hypertext Transfer Protocol Secure 
(HTTP)
-combination of the Hypertext Transfer Protocol (HTTP) with 

the SSL/TLS protocol.

-It provides encrypted communication to prevent 

 eavesdropping and to securely identify the web server with     
 which you are actually communicating 

                    \




                        




-it can protect against eavesdropping and tampering with the contents of the site or with the information you send to the site.

-makes it possible to know whether you are talking to the right server and protects from passive and active network attacks

















2012年5月10日星期四

Week 11
  Today Dr. Dayang seem like a bit upset because last week we didn't attend her class due to our course activity at Pulau Tioman and she had no been inform about that. and we are very sorry about that and for sure there will be no more next time.
   Today we are learning about



Terrestrial Microwave
                       
                                     

-required line of sight transmission and reception equipment.
-the taller the atennas,the longer the sight distance.
-there are the TOWERS on the hills ad mountains.
-signal transmmit one way direction at one time.
-to increase the distance, a system ( repeater ) can be installed with antenna.




Sattlite
-same principle as terrestrial microwave.
-acting as a super tall antenna and repeater.
-single bound.
-capability =any location on earth no matter low remote.
-high quality communication without requiring a huge investment in ground based infrastructure.
-same speed as the earth.
-geosynchronous satellite=orbit speed is based on distance from planet.
-minimum 3 satelite to provide full global transmission.
-transmission from earth to satellite= Uplink
-transsmission from satellite to earth-downlink



Radio Frequency
-Radio-frequency identification (RFID) is the use of a wireless non-contact system that uses radio-frequency electromagnetic fields to transfer data from a tag attached to an object, for the purposes of automatic identification and tracking. Some tags require no battery and are powered by the electromagnetic fields used to read them. Others use a local power source and emit radio waves (electromagnetic radiation at radio frequencies). The tag contains electronically stored information which can be read from up to several metres (yards) away. Unlike a bar code, the tag does not need to be within line of sight of the reader and may be embedded in the tracked object.
RFID tags are used in many industries. An RFID tag attached to an automobile during production can be used to track its progress through the assembly line. Pharmaceuticals can be tracked through warehouses. Livestock and pets may have tags injected, allowing positive identification of the animal. RFID identity cards can give employees access to locked areas of a building, and RF transponders mounted in automobiles can be used to bill motorists for access to toll roads or parking.

                                        

Cellular Phone


                                             
         
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How Cell Phones Work



They say that the era of communication technology has provided one of the major catalysts in developing a modern human society. Let us take a look at one of the most prominent communication devices, the mobile phone.
When Alexander Graham Bell developed the first telephone in the latter part of the 19th century, the industrial revolution suddenly changed as more and more people became interconnected to one another thus fueling business transactions. The same era also gave birth to the radio which was initially presented by the Italian Guglielmo Marconi out of the initial works of Nikolai Tesla. It seems to be the perfect combination of discoveries and invention, but the two devices were not actually combined into a single more powerful device up to the early 1950’s when the development of a cellular or mobile phone started.
Today, cellular phones are simply the most common telecom device around the world. Basically, it provides both the basic features of the telephone and a radio in providing the best communication service yet. Let us talk about how this device works.

My Phone is a Radio?
Basically, the mobile phone is a radio. It relies on a radio signal in order to transmit and receive voice and data information. Previously, the radio device can only receive a signal from a commercial station making it a one way communication apparatus. However, by integrating the principles behind Bell’s telephone, the simple radio became a communication device which can also serve as a small transmitter thus giving it the capability to become a mobile phone.
Develop Web/App Phone & Server/PBX For Desktop OS & Mobile-Phones
Mobile phones are small radios imbedded with mini transmitters. This means that it actually transmits radio signals when powered on. This is a very important component because it readily gives up your electronic radio location so that calls can be diverted to you or make them.
So how am I able to talk with my friend using a cell phone?
One crucial part in the mobile phone communication is the establishment of relay centers called “base stations”. These stations are actually smaller versions of transmitter towers that you will see around the neighborhood in almost any places. The base station serves as the electronic bridge between two mobile phones.
The principle is basically simple, because your mobile phone transmits a certain amount of radio signal, whatever base station nearest to you will capture its presence. Therefore, this gives you an “always online” mode ready to receive calls and texts. When another mobile phone user wants to contact you, his mobile phone will transmit a signal to the nearest base station in his location. This base station will then transmit to a series of telecom relay equipments such as channel towers or satellites until it reaches your local base station wherever you are. The same procedure goes when you are the one to call out to another number.
So how are base stations able to locate me? Won’t these stations become confused considering that there must be millions of cell site towers out there?
Actually, when you dial a particular number, the base station will automatically identify that number and assign an encrypted code on its transmission. Therefore, when the stations send out transmissions, it will only be transmitted to the shortest possible relays that will connect to the exact number you have dialed.
I presume that base stations also have a limited range of transmission, so what if I suddenly change locations?
Actually, the term cellular phone is derived from the “cell” principle of radio transmission. Each base station provides a single “cell” or radio signal span radius. Combining all of these signals in a location makes it appear as cellular compartments. Therefore, when you change your location, you go out of a single cell and enter a new one. With each change in locality, the base station nearest to you will provide you a signal. In some cases, you may arrive at a location when no signal from any base stations is present; this is called a “dead spot”.
For more information about cell phones, read about the disadvantages of cell phone tracking.

Cellular Radio Signal Diagram

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