Fundamental Parameters of Data

The effectiveness of data communication system depends upon following four fundamental characteristics:
1. Delivering Data Packets
2. Accuracy
3. Timelessness
4. Jitter
Variation in packet arrival time

Data Communication System Components

1. Message
2. Sender
3. Receiver
4. Medium
5. Protocol

Data Communication System



Data Representation

• It has different forms
Text, number, image, audio, video


Mode of Transmission

• Mode of transmission or data flow between two devices can be
1. Simplex
2. Half Duplex
3. Full Duplex






Networks


• Define Network
– Set of devices connected through communication link.
• Node
– It can be computer, printer or any other device capable of sending/ receiving data.
• Distributed Processing
1. Security
2. Distributed Databases
3. Faster problem solving
4. Security through redundancy
5. Collaborative processing

Network Criteria


Performance

Performance can be measured in many ways including transit and response time.
– Transit time
– Response time
• The performance of network depends upon
– Number of Users
– Type of Transmission Medium
– Hardware( buffer, speed etc)
– Software ( raw data conversion and reassembly)

Reliability ( robustness)
• Frequency of Failure
• Recovery time of a network after a failure
• Catastrophe

Security

• Unauthorized Access
• Viruses
• Hacking etc..
Protocols & Standards

• Define Protocol? ( what, how and when)
• Entity ( data base management, browse, FTP)
– Any thing capable of sending and receiving the information
• Key elements of Protocol
1. Syntax ( format of data)
2. Semantics ( meaning of each section of bits)
3. Timing ( when to send and how fast to send)


Standards


• Standards are essential in creating and maintaining an open and competitive market for the manufacturer
• Standards provide guidelines
• Data communication standards fall into two catagories


• De Jure ( By Law)
– Those standards that has been legislated by an officially recognized body , forums and government agencies.
• De Facto ( By Fact)
– Those standards established by manufacturer, who seek functionality of new product.

Standard Organizations
• Developed by Cooperation among standards creation committees, forums and government regulatory agencies
• Standards Creation Committees
1. ISO
2. ITU
3. ANSI
4. IEEE
5. EIA
6. Telcordia

Forums

• Frame relay Forum
• ATM forum
• Internet Society( ISOC) and Internet Engg Task force
( IETF)



Regulatory Agency
• Purpose is to protect the public interest
• PTA
• FCC
• BTC
Regulatory Agencies
Following are the responsibilities of regulatory agencies
• To review rate and service charge applications made by telegraph and telephone providers.
• To review the technical specifications of communications hardware.
• To establish reasonable common carrier rates of return.
• To divide and allocate radio frequencies.
• To assign carrier frequencies for radio and TV broadcast.




Mesh Topology
Mesh
• Dedicated link
• Robust
• Security
• Fault identification is easier
Disadvantage
• Amount of cabling and I/O ports
• Installation is difficult and reconfiguration too
• Bulk of wiring may be more than spacing

Star Topology


Star
• Less expensive
• Simple due to one I/O port
• Installation and conf is easier
• Robustness
• Self fault identification
Disadvantages
• Hub is down then…..

Tree Topology


Tree
• Same as Star
Bus Topology



Bus
• Ease of installation
• Less cabling
• In same room 4 cables for star where as 1 cable in case of bus
Disadvantage
• Difficult in reconfig and fault isolation
• Low scalability
• When bus is down all network will be down.
Ring
• Fault isolation is simple
• Alarming
Disadvantages
• Ring breaks then…
• Station is dead