Faculty Of Engineering and Technology
Department of Computer Science
Course: Data Communication and Networking
Course Code : CS-108
(Lecture-10)
Lecturer: Nazir Ahmad Qayoom
Department: Computer Science
Email: n.qayoom@kardan.edu.af
Mobile: +93(0) 706338869
CONTENTS
• Types of Multiplexing
• Switching
• Types of Switching
2
OUTCOMES
At the end of this lecture, students will be able to understand the concepts of;
➢ Switching
➢ Types of Switching
➢ Types of Multiplexing
3
Multiplexing
• Multiplexing (Muxing) is a technique used to combine and send the multiple data
streams over a single medium.
• The process of combining the data streams is known as multiplexing and hardware used
for multiplexing is known as a multiplexer.
• Multiplexing is achieved by using a device called Multiplexer (MUX) that combines n
input lines to generate a single output line.
• Multiplexing follows many-to-one, i.e., n input lines and one output line.
Continue…
Cont…
• There are three types of Multiplexing:
• FDM
• WDM
• TDM
WDM
• Wavelength Division Multiplexing is same as FDM except that the optical signals are
transmitted through the fiber optic cable.
• WDM is used on fiber optics to increase the capacity of a single fiber.
• Optical signals from different source are combined to form a wider band of light with
the help of multiplexer.
Cont…
Cont…
• At the receiving end, de-multiplexer separates the signals to transmit them to their
respective destinations.
• Multiplexing and De-multiplexing can be achieved by using a prism.
• Prism can perform a role of multiplexer by combining the various optical signals to
form a composite signal, and the composite signal is transmitted through a fiber optical
cable.
• Prism also performs a reverse operation, i.e., de-multiplexing the signal.
• It is an analog multiplexing technique.
Time Division Multiplexing (TDM)
• In Time Division Multiplexing technique, the total time available in the channel is
distributed among different users.
• Therefore, each user is allocated with different time interval known as a Time slot at
which data is to be transmitted by the sender.
• A user takes control of the channel for a fixed amount of time.
• It is a digital technique
Cont..
• In Time Division Multiplexing technique, data is not transmitted simultaneously rather
the data is transmitted one-by-one.
• It can be used to multiplex both digital and analog signals but mainly used to multiplex
digital signals.
Cont..
There are two types of TDM:
• Synchronous TDM
• Asynchronous TDM
Cont..
Synchronous TDM:
• A Synchronous TDM is a technique in which time slot is preassigned to every device.
• In Synchronous TDM, each device is given some time slot irrespective of the fact that
the device contains the data or not.
• If the device does not have any data, then the slot will remain empty.
• The most popular Synchronous TDM are T-1 multiplexing, ISDN multiplexing, and
SONET multiplexing.
Cont..
• In Synchronous TDM, signals are sent in the form of frames. Time slots are organized
in the form of frames. If a device does not have data for a particular time slot, then the
empty slot will be transmitted.
• If there are n devices, then there are n slots.
Cont..
• Concept of Synchronous TDM:
• In the figure, the Synchronous TDM technique is implemented. Each device is allocated
with some time slot. The time slots are transmitted irrespective of whether the sender
has data to send or not.
Statistical (Asynchronous) TDM
• An asynchronous TDM is also known as Statistical TDM.
• An asynchronous TDM is a technique in which time slots are not fixed as in the case of
Synchronous TDM.
• Time slots are allocated to only those devices which have the data to send.
• Therefore, we can say that Asynchronous Time Division multiplexor transmits only the
data from active workstations.
Statistical (Asynchronous) TDM
• Concept of Statistical (Asynchronous) TDM:
• In the diagram, there are 4 devices, but only two devices are sending the data, i.e., A
and C. Therefore, the data of A and C are only transmitted through the transmission line.
Asynchronous TDM
• In Asynchronous TDM, each slot contains an address part that identifies the source of
the data.
• The difference between Asynchronous TDM and Synchronous TDM is that many slots
in Synchronous TDM are unutilized, but in Asynchronous TDM, slots are fully utilized.
• This leads to the smaller transmission time and efficient utilization of the capacity of the
channel.
Switching
• When a user accesses the internet or another computer network outside their immediate
location, messages are sent through the network of transmission media.
• This technique of transferring the information from one computer network to another
network is known as switching.
• Switching in a computer network is achieved by using switches.
• A switch is a small hardware device which is used to join multiple computers together
with one local area network (LAN).
Switching
• Switches are used to forward the packets based on MAC addresses.
• A Switch is used to transfer the data only to the device that has been addressed. It
verifies the destination address to route the packet appropriately.
• It is operated in full duplex mode.
Why Switching
• Bandwidth: It is defined as the maximum transfer rate of a cable. It is a very critical and
expensive resource.
• Therefore, switching techniques are used for the effective utilization of the bandwidth
of a network.
• Collision: Collision is the effect that occurs when more than one device transmits the
message over the same physical media, and they collide with each other.
• To overcome this problem, switching technology is implemented so that packets do not
collide with each other.
Types of Switching
• There are three types of Switching:
• Packet Switching
• Circuit Switching
• Message Switching
Cont..
• Circuit Switching:
• Circuit Switching is a dedicated path establishes between two communicating nodes
before actual data transfer begins. The path means that connected sequence of physical
links in which logical channel is dedicated to the connection.
• Example: Telephonic Communication.
• Phase of Circuit Switching:
• There are three phases of circuit switching.
• 1. Circuit Establishment
• 2. Data Transfer
• 3. Circuit Disconnect
Cont…
• Packet Switching:
• In Packet Switching, the sender breaks the whole message into several packets of
suitable length and consisting of sequential packet numbers. No dedicated path
establishes between the two end parties before data communication. The sender sends
packets to the next node sequentially. Each node after receiving a packet decides the
next route for the packet, the routing decision done by a node in the path before sending
every packet.
Cont…
• Message Switching:
• Message Switching is a combination of circuit switching and packet switching. Like
packet switching, the message is not broken into packets rather it is sent to the next
node as a whole. Like circuit switching, no dedicated path establishes between the two
end parties before data communication. The routing decision done at each node for the
whole message.
Thank You…!
