the rainless city

Thursday, May 31, 2012

14th week: internet infrastructure

Internet infrastructure

Hierarcy of networks

In order to connect to internet, we need:

¨ Computer

¨ Web browser

¨ Internet access (ISP)

All of this look so easy, what you need to do is just find a computer, connect to a WIFI or internet, click on the web browser which installed in it…that’s all.But the exactly policy and procedures to bring to internet is quite complicated.

Internet protocol (IP)

§ provide a common layer over dissimilar network

§ move packets among “host” computer thru gateways

§ each computer assign a unique IP address

§ IP address consist of 32 bits (shown as 4 octets of numbers from 0-225 represented in decimal form instead of binary)

· 168.212.226.204

· 10101000.11010100.11100010.11001100

§ consists of 2 part:

· Identifying the network

· Identifying the node/host

§ Class of addresses will part it into network add part and node part.

§ All nodes on a given network share the same network prefix have a unique host number

class	Class A	Class B	Class C	Class D	Class E
Binary add	0	10	110	1110	1111
Decimal no	1 to 126	128 to 191	192 to 223	224 to 239	240 to 255
Identify network	First octet, first 8 bits	First 2 octet, first 16 bits	First 3 octet, first 24 bits	support multicasting	experimentation
example	102.168.212.226	102.168.212.226	102.168.212.226	102.168.212.226

§ So where is the decimal no of 127?

§ Number 127 is for loopback, used for internal testing on local machine

Domain name system (DNS)

Internet servise provider (ISP)

ª Or IAPs (Internet access providers)

ª Is an organization that provides access to the internet

ª Two type: community-owned and non-profit, privately owned and for-profit

ª User can access ISP to connect the internet via using wires, wireless or fiber-optic connections.

Hypertext transfer protocol (HTTP)

ª An application protocol for distributed, collaborative, hypermedia information system.

ª Foundation of data communication for the World Wide Web.

ª Hypertext = multi-linear set of objects, building a network by using logical link or hyperlinks between the nodes (text or words).

ª HTTP is the protocol to exchange or transfer hypertext.

Hypertext transfer protocol secure (HTTPS)

ª Combination of HTTP and SSL/TLS protocol.

ª From the name we know that it is in secure.

ª It provides encrypted communication: prevent eavesdropping, securely identify web server communicating.

ª Primarily used for e-payment transactions, e-mail and sensitive transaction in corporate information system.

ª Now, widespread use for protecting page authenticity on all type of websites, securing accounts, keeping user communication, identity and browsing history private.

Thursday, May 10, 2012

12th week:unbounded / unguided media

Different between bounded and unbounded media

· Bounded media are those that use cables for transmitting electricity or light;

· Unbounded media does not require cabling and includes satellite, microwave and radio transmission.

· Wireless connections, including 802.11b and 802.11a, are examples of unbounded media.

· Today, bounded media continue to be more common than unbounded.

Unbounded media / unguided media

- Translate electromagnetic wave without physical conductor.

- Signal = broadcasting thru air/water

- Available for anyone who has a device capable of receiving them

- 2 type of microwave:

1. Terrestrial Microwave

§ Require line-of-sight transmission and reception equipment

§ The taller the antennas, the longer the sight distance

§ The higher, the stronger

§ So…Usually built on hills / mountains

§ One way direction signal

§ Install system(repeater) with antennas to increase distance

§ 2 type of antennas

1. Parabolic dish

o Same as it’s name, in a dish shape

o good at catching a wide range of signal waves

o directing to a common point(focus)

o Every wave parallel to the line of sight reflects back to the focus on a common point

2. Horn

o looks like a gigantic scoop

o broadcasts the assembled signals that are deflected outward in a series of narrow parallel beams by the curve head

o signals are received in a manner are deflected down into the stem

2. Satellite microwave

§ same principle as terrestrial microwave

§ acting as a super tall antenna and repeater

§ single bounce

§ capability = anywhere on earth

§ high quality communication without huge investment in ground-based infrastructure

§ same speed as earth

§ Geosynchronous satellite = orbit speed is based on distance from the planet

§ Minimum 3 satellites to provide full global transmissions

§ earth à satellite = uplink

§ satellite à earth = downlink

Something you might do not know….

Wireless technology

· Technology that does not require any wires. (unbounded media)

· The distances involved may be short such as a few meters as in television remote control

· Long like thousands or millions of kilometers for radio communications.

Wifi

· developed to be used for mobile computing devices

· Transmit data use radio wave

· IEEE802.11 – standard for implementing wifi

· IEEE802.11b standard provides a transmit data size up to 11Mbps (Megabyte per second)

· IEEE802.11a standard provides throughput rates up to 54Mbps

Radio frequency[RF] and cellular phones

· Cellular phone is one of the wireless devices make use of RF

· Cell phones work by sending signals to (and receiving them from) nearby cell towers (base stations) using RF waves

· This is a form of electromagnetic energy that falls between FM radio waves and microwaves

· RF waves are a form of non-ionizing radiation

· RF waves are different from stronger (ionizing) types of radiation such as x-rays, gamma rays, and ultraviolet (UV) light, which can break the chemical bonds in DNA.

· At very high levels, RF waves can heat up body tissues. (This is the basis for how microwave ovens work.)

· But the levels of energy given off by cell phones are much lower, and are not enough to raise temperatures in the body.

Designation	Frequencies	Free-space Wavelengths
Very Low Frequency	9 kHz - 30 kHz	33 km - 10 km
Low Frequency	30 kHz - 300 kHz	10 km - 1 km
Medium Frequency	300 kHz - 3 MHz	1 km - 100 m
High Frequency	3 MHz - 30 MHz	100 m - 10 m
Very High Frequency	30 MHz - 300 MHz	10 m - 1 m
Ultra High Frequency	300 MHz - 3 GHz	1 m - 100 mm
Super High Frequency	3 GHz - 30 GHz	100 mm - 10 mm
Extremely High Frequency	30 GHz - 300 GHz	10 mm - 1 mm