2. What is Computer Network?
Goals of Computer Network.
Protocols, Standards, Standard
Organizations.
Data Flow.
3. A computer network often simply referred to
as a network, is
a collection of hardware components, which are
interconnected by communication channels that
allow sharing of resources and information with
respect to certain set of rules / protocols via OS
/ software.
Elements of Network;
1. Hardware equipments
2. Network OS / software
3. Communication channel
4. Information / Data / Recourse
5. 1. Resource Sharing –
Many organization has a substantial number of
computers in operations, which are located
apart. Ex. A group of office workers can share a
common printer, fax, modem, scanner etc.
2. High Reliability –
If there are alternate sources of supply, all files
could be replicated on two or, machines. If one
of them is not available, due to hardware failure,
the other copies could be used.
6. 3. Inter-process Communication –
Network users, located geographically apart,
may converse in an interactive session through
the network. In order to permit this, the
network must provide almost error-free
communications.
4. Flexible access –
Files can be accessed from any computer in
the network. The project can be begun on one
computer and finished on another.
7. A set of rules governing data
communications.
1. Syntax: format of data block
2. Semantics: meaning of each section
3. Timing: speed and sequencing
Standards: A common set of rules.
1. De facto (in practice) standards
(not approved but widely adopted)
2. De jure (in law) standards
(approved by an organization)
8. IEEE (Institute of Electrical and Electronics
Engineers)
ANSI (American National Standards
Institute)
ITU (International Telecommunications
Union – formerly
CCITT)
ISO (International Organization for
Standards)
EIA (Electronic Industries Association)
9. Transmission mode(Data Flow) means
transferring of data between two devices.
It is also known as communication mode.
Buses and networks are designed to allow
communication to occur between
individual devices that are interconnected.
There are three types of transmission
mode.
10.
11. In Simplex mode, the communication is unidirectional, as
on a one-way street.
Only one of the two devices on a link can transmit, the
other can only receive.
The simplex mode can use the entire capacity of the
channel to send data in one direction.
Example: Keyboard and traditional monitors. The
keyboard can only introduce input, the monitor can only
give the output.
12. In half-duplex mode, each station can both transmit and
receive, but not at the same time.
When one device is sending, the other can only receive,
and vice versa.
The half-duplex mode is used in cases where there is no
need for communication in both direction at the same
time.
The entire capacity of the channel can be utilized for
each direction.
Example: Walkie- talkie in which message is sent one at
a time and messages are sent in both the directions.
13. In full-duplex mode, both stations can transmit and
receive simultaneously.
In full_duplex mode, signals going in one direction share
the capacity of the link with signals going in other
direction, this sharing can occur in two ways:
1. Either the link must contain two physically separate
transmission paths, one for sending and other for receiving.
2. Or the capacity is divided between signals travelling in
both directions.
Full-duplex mode is used when communication in both
direction is required all the time.
The capacity of the channel, however must be divided
between the two directions.
Example: Telephone Network in which there is
communication between two persons by a telephone line,
