week 4 : Physical Layer

Composite signal - a combination of sine waves with different frequencies, phases(the position of the wave at time 0) and amplitudes.
Bandwidth - the difference between the highest and lowest frequencies contained in that signal (the higher bandwidth, send faster)

log2L = N
L - number of level
N - number of bits that can send in period

8 Kbps - 8 kilo bits per sec
8 KBps - 8 kilo byte per sec
1 byte - 8 bits

Baseband transmission - use full capacity of channel to send data
low-pass channel - lowest frequency is 0
wide bandwidth - very high frequency
narrow bandwidth - not high frequency(send data very slow)
Bandpass channel - don't have to start from 0(the lowest can be any number, include 0)

Medium
analog bandwidth - hertz
digital bandwidth - bits per second

Nyquist Bit Rate
Bitrate = 2 * bandwidth * log2L
L = the number of signal level used to represent data

Shannon Capacity
capacity = bandwidth * log2(1 + SNR)
SNR = Signal to Noise Ratio

week 3 : Data and Signals

guided = wire
unguided = wireless

Radio link types
- terrestrial microwave (have microwave towel)
- LAN (WiMax)
- wide-area (cell phone)
- satellite (Geosynchronous orbit)

Data
- Analog data (continuous - voice)
- Digital data (discrete - data in computer (0 and 1))
Data(from computer) must be transformed to electromagnetic signals (use to carry along medium) and signals can also be analog(infinite number) and digital(limited number).

Can't send data without signal and cam combine to 4 combination
- analog data, analog signal
- analog data , digital signal
- digital data, analog signal
- digital data, digital signal

Periodic analog signals (look the same every period)
A sine wave is fundamental periodic analog signal that use in data comm.
- Peak amplitude
- frequencies (number of wave in 1 signal, number of wave in 1 sec. - Hz)
- period (represent time of 1 wave, sec)

week 1 : Introduction to Data Communication

What is Data Communication?
The word Data Communication is come from Telecommunication and Data.
Meaning of Telecommunication is "The Communication at a distance", and the meaning of Data is "Information presented in whatever form is agreed upon by the parties creating and using the data".So, Data communication are the exchange of data between two devices via some form of transmission medium (like wire cable, fiber optics)

In Data Communication, We have mainly have 5 network type (base on scale) which is
1. Local Area network (LAN)
- LANs is a group of PCs that share a circuit. This type of network can be seen in computer room or building.
2. Backbone Networks
- A high speed backbone linking the LANS at various locations.
3. Metropolitan Area Network (MAN)
- This network type is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities.
4. Connects LANs and BNs at different locations
5. Wide Area Networks (WANs)
- Same as MAN but more wider scale.

Data Flow
Data flow is a group of traffic, identified by a combination of source address/mask, destination address/mask, IP next protocol field, and source and destination ports, where the protocol and port fields can have the values of any.

General type of Data flow
- Simplex (Data can be sent one way only, from Server to client.)
- Half-Duplex (Data can be sent from sender and receiver but can send only one at the time.)
- Full-Duplex (Data can be sent and received at the same time.)

week 2 : Introduction cont. & Network Models

Introduction cont.
Intranet vs. Extranet
Intranet is a LAN network that open only inside the organization
Extranet is a LAN network that open only for user outside the organization and allow user to access the network through the internet

Protocols and Standards (Protocols must have standards)
The key elements of protocol
- Syntax(language)
- Semantics
-Timing

Types of standards for Protocols
- Formal standards (developed by industy or goverment)
- De-facto standards(developed by big company)

Major Standard Bodies
- ISO (develop OSI)
- ITU-T (formal name - CCITT)
- ANSI (approve standard)
- IEEE
- IETF
-W3C

Network Models
Implementation of Communication Function
- Single layer
Put everything in one modul, if have something wrong and it already fix. The entire network need to be checked again
- Multi layer
Solve the problem that Single layer have, if it have something wrong in any layer it can modify and fix just the layer that has problem

OSI Model
- Application (providing service to user)
- Presentation (translation compression and encyption)
- Session (dialog control and synchronization)
- Transport (send program data from machine to another program on another machine)
- Network (send frame from source host to the destination host)
- Data link (moving frame from node to node)
- Physical (just send the data and move data from computer to target computer)