CHAPTER 2 DATA COMMUNICATION

DATA COMMUNICATION

Type of signal

Signal Transmission: 

Signaling is the way data is transmitted across the medium. It uses electrical energy to communicate.

Two types of signaling:

·                     Digital signaling 

·                     Analog signaling

Digital Signaling:
Most computer networks use digital signaling.

Encoding data in a digital signal is called encoding schemes.

·                     Current-state encoding

·                     State-transition encoding

Current-state encoding:

·                     In current-state encoding strategies, data is encoded by the presence or absence of a signal characteristics or state.

·                     The signal is monitored periodically by network

·                     State-transition encoding method use transitions in the signal to represent data.

·                     Presence of transition represents a 1 and the absence of transition indicate a 0.

State-transition encoding schemes:

·                     Bipolar-Alternative Mark Inversion (AMI)

·                     Non-Return-to-Zero (NRZ)Manchester

·                     Differential Manchester

·                     Biphase Space (FM-0)

·                     Comparing Signaling Methods

Advantages of digital signaling:

·                     Fewer errors from noise and interference

·                     Uses less expensive equipment

Disadvantages of digital signaling:

·                     Suffer from attenuation

Advantages of Analog signaling:

·                     Less attenuation than digital signal

·                     Can be multiplexed to increase bandwidth

Disadvantages of analog signaling:

·                     More prone to errors from noise and interference

Bit Synchronization:

The coordination of signal measurement timing is called bit synchronization.

Two major method of bit synchronization:

·                     Asynchronous bit synchronization

·                     Synchronous bit synchronization

Asynchronous bit synchronization:

Asynchronous bit synchronization

Asynchronous communication requires that messages begin with a start bit so that the receiving device can synchronize its internal clock with the timing of the message.

It is normally short and the end of the message is signaled by a stop bit.

Synchronous bit synchronization:

Synchronous communication requires that some kind of clocking mechanism be put into place to keep the clocks of the sender and receiver synchronized.

Methods used for synchronous timing coordination:

·                     Guaranteed state change

·                     Separate clock signal

·                     Oversampling

Baseband and broadband Transmission

Baseband: use the entire media bandwidth for a single channel. Commonly used for digital signaling. Most LANs use baseband signaling.

Broadband: Provide the entire media bandwidth into multiple channels. Since each channel can carry a different analog signal, broadband networks support multiple simultaneous conversations over a singletransmission medium.

Broadband: Provide the entire media bandwidth into multiple channels. Since each channel can carry a different analog signal, broadband networks support multiple simultaneous conversations over a single transmission medium.

Data Transmission Mode

The way in which data is transmitted from one place to another is called data transmission mode. It is also called the data communication mode. It is indicates the direction of flow of information. Sometimes, data transmission modes are also called directional modes.

Types of Data Transmission Modes
Different types of data transmission modes are as follows:

1. Simplex mode
2. Half-duplex mode
3. Full-duplex mode

1.      Simplex Mode
    In simplex mode, data can flow in only one direction. In this mode, a sender can only send data and cannot receive it. Similarly, a receiver can only receive data but cannot send it. Data sent from computer to printer is an example of simplex mode.
In simplex mode, it is not possible to confirm successful transmission of data. It is also not possible to request the sender to re-transmit information. This mode is not widely used. However, this mode is used in business field at certain point-of-sale terminals. The other examples of simplex communication modes are Radio and T.V transmissions.

2.      Half-Duplex Mode
    In half-duplex mode, data can flow in both directions but only in one direction at a time. In this mode, data is sent and received alternatively. It is like a one-lane bridge where two-way traffic must give way in order to cross the other.
The Internet browsing is an example of half duplex mode. The user sends a request to a Web server for a web page. It means that information flows from user's computer to the web server. Web server receives the request and sends data of the requested page. The data flows the Web server to the user's computer. At a time a user can a request or receive the data of web page.

3.      Full-Duplex Mode
    In full duplex-mode, data can flow in both directions at the same time. It is the fastest directional mode of data communication. The telephone communication system is an example of full-duplex communication mode. Two persons can talk at the same time. Another example of fully-duplex mode in daily life is automobile traffic on a two-lane road. The traffic can move in both directions at the same time.

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This week I have learned about data communication. There are three types of communication channels which is formal, non- formal and informal. For me this is a new thing that I learned about this title . In addition, I also learned about the data transmission in which information is transmitted using analog or digital signal. When data is sent to the analog signal, the analog signal will be converted to digital signal before new data can be sent and when it has reached the proper because the data will be converted back to an analog signal.