Class Note’s
Transmission Mode
Transmission mode means transferring data between two devices. It is also known as a
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:-
These are explained as following below.
1. Simplex Mode –
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

2. Half-Duplex Mode
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 directions 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 directions.
Channel capacity=Bandwidth * Propagation Delay

3. Full-Duplex Mode –
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 another direction, this sharing can occur in two ways
 Either the link must contain two physically separate
transmission paths, one for sending and the other
for receiving.
 Or the capacity is divided between signals travelling
in both directions.
Full-duplex mode is used when communication in both directions
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, through which both can
talk and listen at the same time.
Channel Capacity=2* Bandwidth*propagation Delay

Internet
It is a worldwide/global system of interconnected computer networks. It uses the
standard Internet Protocol (TCP/IP). Every computer in Internet is identified by a unique
IP address. IP Address is a unique set of numbers (such as 110.22.33.114) which
identifies a computer’s location.
A special computer DNS (Domain Name Server) is used to provide a name to the IP
Address so that the user can locate a computer by a name.
Internet is accessible to every user all over the world

Intranet
Intranet is the system in which multiple PCs are connected to each other. PCs in intranet
are not available to the world outside the intranet. Usually each organization has its own
Intranet network and members/employees of that organization can access the
computers in their intranet.
Each computer in Intranet is also identified by an IP Address which is unique among the
computers in that Intranet
Personal Area Network (PAN)
A Personal Area Network (PAN) is smallest network which is very personal to a user.
This may include Bluetooth enabled devices or infra-red enabled devices. PAN has
connectivity range up to 10 meters. PAN may include wireless computer keyboard and
mouse, Bluetooth enabled headphones, wireless printers and TV remotes.

For example, Picante is Bluetooth-enabled Personal Area Network which may contain
up to 8 devices connected together in a master-slave fashion.
Local Area Network ( LAN)
A computer network spanned inside a building and operated under single administrative
system is generally termed as Local Area Network (LAN). Usually,LAN covers an
organization’ offices, schools, colleges or universities. Number of systems connected in
LAN may vary from as least as two to as much as 16 million.
LAN provides a useful way of sharing the resources between end users. The resources
such as printers, file servers, scanners, and internet are easily sharable among
computers.

LANs are composed of inexpensive networking and routing equipment. It may contains
local servers serving file storage and other locally shared applications. It mostly operates
on private IP addresses and does not involve heavy routing. LAN works under its own
local domain and controlled centrally.
MetropolitanAreaNetwork (MAN)
The Metropolitan Area Network (MAN) generally expands throughout a city such as
cable TV network. It can be in the form of Ethernet, Token-ring, ATM, or Fibre Distributed
Data Interface (FDDI).
Metro Ethernet is a service which is provided by ISPs. This service enables its users to
expand their Local Area Networks. For example, MAN can help an organization to
connect all of its offices in a city.
Backbone of MAN is high-capacity and high-speed fibre optics. MAN works in between
Local Area Network and Wide Area Network. MAN provides uplink for LANs to WANs or
internet.
Wide AreaNetwork (WAN)
As the name suggests,the Wide Area Network (WAN) covers a wide area which may
span across provinces and even a whole country. Generally, telecommunication
networks are Wide Area Network. These networks provide connectivity to MANs and

LANs. Since they are equipped with very high speed backbone, WANs use very
expensive network equipment.
WAN may use advanced technologies such as Asynchronous Transfer Mode (ATM),
Frame Relay, and Synchronous Optical Network (SONET). WAN may be managed by
multiple administration.
Hub
A hub is a physical layer networking device which is used to connect multiple devices in
a network. They are generally used to connect computers in a LAN.
A hub has many ports in it. A computer which intends to be connected to the network is
plugged in to one of these ports. When a data frame arrives at a port, it is broadcast to
every other port, without considering whether it is destined for a particular destination or
not.

Switch
A switch is a data link layer networking device which connects devices in a network and
uses packet switching to send and receive data over the network.
Like a hub, a switch also has many ports, to which computers are plugged in. However,
when a data frame arrives at any port of a network switch, it examines the destination
address and sends the frame to the corresponding device(s). Thus, it supports both
unicast and multicast communications.

Router
Routers are networking devices operating at layer 3 or a network layer of the OSI model.
They are responsible for receiving, analysing, and forwarding data packets among the
connected computer networks. When a data packet arrives, the router inspects the
destination address, consults its routing tables to decide the optimal route and then
transfers the packet along this route.
References-

1.Data Communication and ,5th Edition, Behrouz A.Forouzan.(
Transmission Mode)
2.https://www.tutorialspoint.com/data_communication (Internet,
Intranet,PAN,LAN,MAN,WAN,Hub,Sawitch,Router)