1. Data Communications and Networking Overview
Chapter 1
Data Communications and Networking Overview
Data Communication

2. A Communications Model
Key elements of a simple model of communications:
(Purpose: the exchange of data between two parties)
Source
generates data to be transmitted (e.g. telephones & PCs)
Transmitter
Converts data into transmittable electromagnetic signals
Transmission System
Carries data (single transmission line or network)
Receiver
Converts received signal into data
Destination
Takes incoming data
Data Communication

3. Simplified Communications Model - Diagram
TUNALI
Data Communication

4. Communications Tasks Transmission system utilization
Make efficient use of transmission facilities
Interfacing
A device must interface to cummunicate
Signal generation
Capable of being propagated through the transmission system, interpretable as data at the receiver
Synchronization
The receiver must be able to determine when a signal begins to arrive and when it ends
Exchange management
The two parties must cooperate (transmit simultaneously or take turn, data format)
Error detection and correction
In all communications systems, there is a potential for error
Data Communication

5. Communications Tasks Flow control
Sending data faster than destination can be processed
Addressing
Only intended destination system must receive the data
Routing
Specific route through the network
Recovery
Resume activity at the point of interruption or restore the state
Message formatting
Form of the data to be exchanged
Security
Receiver may wish the data have not been altered in transit, ..
Network management
Configuring the system, monitoring its status
Data Communication

6. Simplified Data Communications Model

7. Networking Point to point communication not usually practical
Devices are too far apart
Large set of devices would need impractical number of connections
Solution is a communications network
Wide Area Network (WAN)
Local Area Network (LAN)
Data Communication

8. Wide Area Networks Large geographical area
Crossing public rights of way
Consists of a number of interconnected switching nodes
Alternative technologies
Circuit switching
Packet switching
Frame relay
Asynchronous Transfer Mode (ATM)
Data Communication

9. Circuit Switching
Dedicated communications path established for the duration of the conversation
Path: a connected sequence of physical links between nodes
e.g. telephone network
Data Communication

10. Packet Switching Data sent out of sequence
Small chunks (packets) of data at a time
Packets passed from node to node between source and destination
Used for terminal to computer and computer to computer communications
Data Communication

11. Frame Relay
Packet switching systems have large overheads to compensate for errors
Modern systems are more reliable
Errors can be caught in end system
Most overhead for error control is stripped out
Data Communication

12. Asynchronous Transfer Mode
ATM
Evolution of frame relay
Little overhead for error control
Fixed packet (called cell) length
Constant data rate using packet switching technique (by using small – fixed sized cells)
By using a fixed packet length, the processing overhead is reduced
Data Communication

13. Local Area Networks Smaller scope
Building or small campus
Usually owned by same organization as attached devices
There may be a substantial capital invesment for both purchase and maintenance
One user for network management responsibility
Data rates much higher
Data Communication

14. LAN Configurations Switched Wireless Switched Ethernet ATM LAN
May be single or multiple switches
ATM LAN
Fibre Channel
Wireless
Mobility
Ease of installation
Data Communication

15. Metropolitan Area Networks
MAN
Middle ground between LAN and WAN
Private or public networks that provide high capacity at low costs
Large area
Data Communication

16. Networking Configuration
Data Communication

17. Further Reading
Stallings, W. Data and Computer Communications (7th edition), Prentice Hall, Upper Saddle River NJ, chapter 1
Data Communication