Transcript File

Computer Networks
Data & Communication

When we communicate we share information



Local Communication, if Face to Face
Remote, if through Telephone etc
Data

Information presented in any form that is agreed
upon by communicating parties.

Text, Image, Video, Audio
Data Communication


Exchange of data between two devices via some
form of transmission medium such as wire…
OR
Data Communication is the exchange of information
from One entity to another using a transmission
medium





Exchange
Information
Entity
Transmission
Medium
Aims/Characteristics of Data
Communication

Delivery

Data should be delivered to the other party


Accuracy

Data should not be corrupted during transmission


Addressing Mechanisms IP, MAC Address, Routing are used
to make delivery possible
Encoding, Error detection, Error recovery, Amplification of
signal
Timeliness

Data should not be delivered after the time it is required.

Quality of Service Support, Routing Protocols help in this
regard
Simplified Communication Model
Integral Parts of Communication Model…

Source

Generates data to be transmitted


Telephone, Mic, Computer, Web Cam, Scanner, Digital
Camera
Transmitter



Data produced can not be transmitted directly
Data should be converted to signals
Transmitter converts data into transmittable
signals

Modem converts Data Bits into Signals

Modulation
Integral Parts of Communication Model…

Transmission System




It carries data from one party (sender) to another (receiver)
Can be Wired / Wireless medium
Can be complex network like Internet
Receiver


It receives signal
Converts received signal into data (bits)


Modem (demodulation)
Destination

Takes incoming data from receiver.
Simplified Communication Model
Dial-up Internet Example
Key Tasks in Data Communication




Optimal Transmission System Utilization
 Efficient use of Medium
 Medium could be shared by many users
 Multiplexing could be implemented
Interfacing
 Connection of devices to Medium
Signal Generation
 Data Encoding Techniques
 How to represent data through signal
 Amplitude, Frequency, Phase???
Synchronization
 In synchronous communication Timing matters
 If sender sends the data and receiver is not ready/expecting, data
may be lost
Key Tasks in Data Communication

Exchange Management



Connection Management
How to establish, maintain and disconnect?
Error detection and correction


Errors can occur in data during transmission
Amount of error depends on medium / network



Damaged/Missed/Duplicated packets
Some applications can tolerate errors (video/voice), others
can not (text/ email/ file)
Mechanisms should be provided to detect and possibly
correct them or otherwise report them to sender
Key Tasks in Data Communication

Flow Control





Communication of a device that produce data very fast with
a device that accept data at low rate should be possible
Communication medium may not permit fast data transfer
rate
We use some form of Flow Control to avoid data loss in
such case
Techniques like Buffering may help
Addressing and Routing


When more devices share a transmission medium, then we
need addressing mechanisms to specify which device is
destination
Routing is the selection of best path from sender to
receiver
Key Tasks in Data Communication

Recovery



If data transfer or a transaction is interrupted, how
to recover from the damage
Disconnection from server during a file download!
Message formatting

Agreed upon format for the message to be
transferred

Protocols/Standards
Key Tasks in Data Communication

Security



To ensure that only the intended receiver actually
receives the data
Even if the data is captured by some one else he
should not be able to comprehend it
Network Management




Network should be managed
Access control
Resource utilization
Charges for use
Types of Communication/Directions of
Data Flow

Communication modes could be:

Simplex





Half Duplex




One Way (Uni directional) only
One device is sender and other is receiver
Monitor, Speakers etc
Is Keyboard Simplex?
Bi-directional
Only One device can send at a time and other will receive
Traditional Wireless Sets
Full Duplex



Bi-Directional
Both Devices can send/Receive simultaneously
Telephone Network
Need of Networking for Communication

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

Attach all devices to a communication network
Simplified Network Model
Classification of Networks

Networks are classified into two main
categories:



Local Area Network
Wide Area Network
There are some more categories

MAN, PAN etc
Local Area Network (LAN)

Smaller scope




Building or small campus
Usually owned by served organization/company
Data rates much higher
Traditionally it used broadcast systems
instead of switched approach

Now switched systems (Ethernet) and ATM (ATM
LANs) have replaced broadcasting hubs
Wide Area Networks (WAN)





Large geographical area
Connect LANs
Usually Public but may be Private
Slower than LAN
Consist of interconnected switching nodes


Nodes have no concern with data
Just meant for providing switching facility toward
destination
A Typical Network Configuration
Network Implementation

Networks could be implemented in either


Peer-to-Peer Configuration
Client Server Configuration
Client Server Implementation


Servers are distinguished from other systems which are known as
clients and all these are connected over a computer network
Servers offer services which are used by client systems



Server always keep listening for clients
A Server could be used for









Server serves clients
Data Storage
Distributed Application
Resource Sharing
Authorization
Audit-ability
Accountancy
Security & easy Administration
Centralized Control
A Server may require clients to log on before any services may be
provided
Client Server Implementation
Client Server Implementation

What is the difference in Servers and Clients

Physically Different


Separate Kind of Machines?
Actual Difference in Software


Server runs server software while client runs software
module (usually very small in comparison to server
software)
Used Yahoo Messenger?


You have a very tiny module of Yahoo Messenger (Clients)
Actual Yahoo Messenger Server S/W is much heavy
Client Server Implementation
(Advantages)







Centralized Control
Security Policies are easily implemented
Logs could be create
Reliability
Easy to share resources
Stable environment (Both H/W and S/W)
Performance degrade gracefully in higher
loads
Client Server Implementation
(Disadvantages)


Costly to install
Usually require Expert personnel to manage
Peer-to-Peer Networks



Each computer serves both as client as well
as server
No centralized control for user access
Usually useful for SOHO (Small Office/Home
Office)
Peer-to-Peer Networks
Peer-to-Peer Networks
Advantages




Easy to setup
Low H/W, S/W cost
Usually useful for file/print/internet sharing
Useful in environments where security is not
an issue
Peer-to-Peer Networks
Disadvantages



Not Reliable
Performance degrade exponentially as new
nodes add into the network
Compromised network security
Assignment 1

Write a brief report on different types of network
implementation including







WAN (Wide Area Network)
LAN (Local Area Network)
WLAN (Wireless Local Area Network)
MAN (Metropolitan Area Network)
SAN (Storage Area Network)
CAN (Campus/Controlled/Cluster Area Network)
PAN (Personal Area Network)