01-09-2012, 12:42 PM
Data communication CIS-175
Data communication.ppt (Size: 3.63 MB / Downloads: 68)
Introduction
What is Data communication
Communication model (e.g. Human communication)
Source
Generates data
Transmitter
Converts data into transmitting signals
Transmission system
Carries data
Receiver
Converts received signals into data
Destination
Takes incoming data
Data Representation
Text
Represented in bits patterns e.g. 0,1
Different Bit patterns called code.
Present Coding system: Unicode, 32 bits
Numbers
Represented in bit patterns
Converted into binary for calculations
Images
Represented into matrix of pixels/bits
Audio/Video
Continuous data
Flow of Data
Simplex
One way traffic only, one device transmits and one receives e.g. Keyboard->monitor
Half-duplex
Both stations can transmit and receive but one at time. e.g. Bus topology
Only one path from source to destination.
collisions may occur
Full-duplex
Both can receive and send at the same time. e.g. Star topology.
Two separate transmission lines.
collisions free
Point to point connections
Not peer to peer
Dedicated communication circuit
Fixed configuration
Direct link between devices
B and C can be intermediate device to connect A and D
Connection formed in different sections between users, end to end connection in series and forms circuit.
So point to point forms simple connection
If number of users increased then hard to provide circuit that connects each user with other users.
So we need switching which could provide sharing of transmission circuits.
Circuit switching network
This allows the communication circuits to be shared among users.
E.g. Telephone exchange
Switching
It allows equipments and circuits to be shared among users.
Establishes dedicated circuit between users before communication.
When circuit is free other users can use this. e.g. telephone calls.
Telephone exchange is an example of circuit switching.
Replacement conference calls
Packet switching network
Similar to message switching
but divides message into packets/datagram packets of equal lengths.
Headers are added to each packets.
Header contains information about source and destination.
No need for dedicated circuit.
As length of packet is small so each link is established for small time and then it is available for other messages.
Another benefit is pipelining.
RING
All nodes connected to one another in form of closed loop.
Expensive and difficult to install but offers high bandwidth, not robust.
Point to point connection with only two devices.
Signal is passed in one direction only, moves until it reaches to its destination.
Each device connected with a repeater.
One signal always circulates for fault detection. If device don’t receives signal for specified time it generates alarm.
TCP/IP
Transmission control protocol:
Guarantees end to end delivery of data segments
Arrange segments in order.
Used to check transmission errors.
Connection oriented (same route, in order) doesn’t mean circuit.
Reliable process to process communication service.
Made reliable through sequence number and acknowledgement
Internet Protocol (IP)
Data sent over internet from source to destination.
IP is connection less (packets independent, different routes, out of order).
TCP/IP Layers
Application layer of TCP/IP includes
functionality of session and presentation
layer of OSI model. Like encoding, dialog
control. Application layer includes
file transfer, email, remote login, network
Management, name management
Transport layer includes QoS, Flow control
Processes to processes communication
IP layer includes ARP,RARP, ICMP
Network layer physical link to media.