Data Communication  and Networking Notes – OSI, TCP/IP Model

Data Communication is the exchange of data between two devices via some form of transmission medium such as wire cable.Communication can be defined as the exchange of information between one group or person and another group or person. This communication can be between people within the same organisation(internal communication) or with people or groups outside the organization(external communication).

The effectiveness of data communication system depends on four fundamental characteristics such as Delivery, accuracy, timeliness, and jitter.

• Delivery :  The system must deliver data to the correct destination. Data must be recovered by user and only by the device.
• Accuracy : The system must deliver the data accurately.
• Timeliness : The system must deliver data in a timely manner. Data delivered late are useless.
• Jitter : Jitter refers to the variation in the packet arrival time.

In Data communication there are 4 basic terms-

• Data :   Data are entities that convey meaning. Data are representation whereas information refer to the content or interpretation of data.
• Signal:  Signals are electric or electromagnetic encoding of data.
• Signalling: Signalling is propagation of signal along suitable communication medium.
• Transmission:  Transmission is communication  of data by the proposition and processing of signals.

Components :  A data  communication system has five components.

• Message:  The message is the information to be communicated , Information include text, number,pictures audio and video.
• Sender: The sender is the device that sends the data message. It can be a computer, worstation, telephone, video camera etc.

 

 

• Receiver : The receiver is the device that receive the message. It  can bea computer, workstation, telephone, video camera etc.
• Transmission medium :  Transmission medium is the physical path by which a message travels from sender and to receive . examples are twisted  pair cable.
• Protocol :  A protocol is a set of rules ( written in the form of program ) to perform specific task or action Eg. HTTP, FTP etc. that govern data communication . It represents a agreement between the  communicating devices

Concept of Data Communication :  The concept of Data Communication evolved from sharing the computation  power of a computer along with various resources available in a computer environment such as printer , hard disk etc. Data Communication can be used to transfer as exchange confirmation within on building one city, across cities countries and continents.

Data Communication Code (Data encoding ): Every character (Letter, Number, symbol) is composed of a group of bits called Codes.  The most widely used  codes are  the ASCII (American Standard code for Information Interchange), EBCDIC ( Extended Binary Coded decimal Interchange Code), 

Char	7 bit ASCII	Hex
A	100 0001	41
B	100 0010	42
C	100 0011	43
D	100 0100	44
E	100 0101	45
F	100 0110	46
G	100 0111	47
H	100 1000	48
I	100 1001	49
J	100 1010	4A
K	100 1011	4B
L	100 1100	4C
M	100 1101	4D
N	100 1110	4E
O	100 1111	4F
P	101 0000	50
Q	101 0001	51
R	101 0010	52
S	101 0011	53
T	101 0100	54
U	101 0101	55
V	101 0110	56
W	101 0111	57
X	101 1000	58
Y	101 1001	59
Z	101 1010	5A
a	110 0001	61
b	110 0010	62
So on…

ASCII and Hex Codes of Characters

Communication Protocol/ Standard :  Protocol is a set of rules that perform specific task. In other words, protocols are technical customs or guide -lines that govern the exchange of signal transmission and reception between equipments. Both hardware and software are designed to handle specific protocols.

Communication Speed or Rate : The speed at which two computers exchange or transmit data is called communication rate  on transmission  speed. The unit of measurement of the speed is measured in bits per second (bps) or band. Normal PC based communication  transferred using 300 to Mbps whereas mainframe  computers uses 19,200 baud.

Communication protocols are usually defined and approved by some International body  such as ISO, CCITT or IEEE. Some of function on protocols regulates are :

• Control and Information  transfer
• Structure and formats of data
• Error recoveries
• Retransmission
• Interface management

Protocol Layers :

The OSI (Open System Interconnection ) Data Model :  It is ISO standard for computer  networks design and functioning. It has 7 Layers and each layer playing a specific role when applications are communicating  over the net.

OSI LAYER DIAGRAM

7. Application	End User Layer HTTP, FTP, IRC, SSH, DNS
6. Presentation	Syntax Layer SSL, SSH, IMAP, FTP, MPEG, JPEG
5. Session	Synch & send to port API’s, Sockets, WinSock
4. Transport	End-to-end conections TCP, UDP
3. Network	Packets IP, ICMP, IPSec, IGMP
2. Data Link	Frames Ethernet, PPP, Switch, Bridge
1. Physical	Physical structure Coax, Fiber, Wireless, Hubs, Repeaters

• The TCP / IP Model : It consists of only four layers Application, Transport, Internet and Network LayerPhysical Layer: Ensures a safe and efficient transmission of data; consists of electronic circuits for data transmission.
• Data Link Layer:  In charge of data encapsulation under the form of frame and their interpretation at the physical Layer.
• Network Layer:  In charge of packets transmission from a source A to a destination B.
• Transport Layer: In charge of delivery of packets from a source process A to a destination process B
• Session layer:  In charge of the management of dialogue  between source and destination.
•  Presentation Layer:  Determines the format of the data transmitted to application, data compressing / decompressing ,encryption etc
• Application Layer:It contains the application which are used by a end- user, such as MicroSoft-Power Point, MicroSoft-Word etc.

TCP/IP Model :

Application

Transport

Internet

Network Interface

• Network Interface Layer: Provide the same functionality as the physical layer , data link layer and network layers in the OSI model and mapping between IP addresses and network physical addresses, Encapsulation of IP datagram, e.g. packets, in formats understandable by the network.
• Internet Layer: Based on the Internet Protocol(IP), which provides the frame for transmitting data from place A to place B.
• Transport Layer: Based on two main protocols: TCP (Transmission Control Protocol ) and UDP ( User Datagram Protocol )
• Application Layer: Combines the function of OSI application , presentation , and session layers, And Protocols involve in this layer : HTTP, FTP,  SMTP,  DNS etc.

Bandwidth : The number of bits that can be transmitted over a network in a given time, usually measured Hz(Hertz).

Broadband : Broadband is a term referred to some technologies that offers high speed internet connectivity depending on framework and environment. It is network connection with high enough bandwidth to allow  for streaming audio and video. Broadband basically works through its bandwidth.  As you increase the width of the band, so you get the speedy access to the internet.

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Analog and Digital Transmission: 

• Analog Signal: An analog signal is one that is continous with respect to time and may take on any value within a given range of values. Human voice, video and music when converted to electric signalusing suitable devices produce analog signals. Its is denoted by sine waves. Landline phone uses analog signal.
• Digital signal:  Digital signals are discrete time signals generated by digital modulation. It is denoted by square waves. Computers, CDs, DVDs, and other digital electronic devices uses digital signal.

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