Multiplexing techniques such as time division multiplexing (TDM) and frequency division multiplexing (FDM) allow multiple users to share network links. TDM divides time into slots that are allocated to users on a fixed or dynamic basis. FDM assigns each user a unique frequency band to transmit in simultaneously. Switching networks move data packets through intermediate nodes using either circuit switching, which establishes a dedicated path, or packet switching, which breaks messages into packets that travel independently through the network.

1. Multiplexing and Switching

2. Multiplexing
Sharing the link among multiple users

3. Multiplexing
Time Division Multiplexing (TDM)
 Synchronous TDM
 Statistical TDM
Frequency Division Multiplexing (FDM)

4. Time Division Multiplexing
The Basic Idea:
 As the name suggest, Divide time amongst the
users
 Give each user some time to transmit his data
 This process is periodic in a round robin fashion
 The time given to a each user is referred to as
Time Slot or Time Quantum

5. Time Division Multiplexing

6. MUX
12
1
3
23
123
THE TRANSMITTER

7. 12 13 23 123
THE LINK

8. DEMUX
THE RECEIVER

9. There should be no Timing difference between
the
MUX and DEMUX
WARNING………!!!!!!!

10. DEMUX
Or else……..!!!!
Something like this will happen……!!!!!

11. Therefore, the two devices
should be synchronized……
And so it is called Synchronous TDM

12. The problem with Synchronous TDM
What if host2 has only one packet to send
and host3 has two packet to send……..
MUX
12
1
3
12

13. 12 13 12
THE LINK

14. Time slots are being
wasted….!!

15. The solution is
Statistical TDM

16. Statistical TDM
Here Time slots are given on
demand……….rather than in round robin
fashion
Each User can get 2 or more consecutive
time slots
If time slot is not required, it is not
allocated
Hence, not wasted

17. Frequency Division
Multiplexing

18. Frequency Division Multiplexing Diagram

19. FDM
Sharing is done by assigning each user a
specific frequency (Carrier Frequency)
Modulation equipment is used to move
each signal to the required frequency
band.
Multiplexing equipment is needed to
combine the modulated signal

20. User 1
User 2
User 3
M
O
D
U
L
A
T
O
R
f1
f2
f3

21. All the users transmit their data simultaneously….
f1 f2 f3

22. The Received data at the Receiver
f1 f2 f3
f1 f2 f3
The Filter
The output
f1 f2 f3

23. fc
y(f)
Demodulate to get the original signal back

24. Switching

25. Switching Networks
A network is made up of end hosts and
intermediate switching nodes
Data is usually passed through a
network of intermediate switching
nodes
The Switching nodes:
Not concerned with the contents of the data;
• Provide a switching facility that will move
data from node to node until they reach their
destination

26. A
1
7
2
5
3
4
6
B
C
D
E
F
Switching Nodes
End Hosts

27. Some Notes…
 Some nodes only connect to other nodes
 Some nodes connect to end hosts also
 Usually the network is not fully connected; there
is not a direct link between each pair of nodes
 If there are more than one paths between any
pair of nodes; this increases the reliability of the
network
 Node-Node links are usually multiplexed

28. Two Technologies for Switching
Circuit Switching
Packet Switching
They differ in the way the nodes switch
information from one link to another on the
way from source to destination

29. Circuit Switching
A dedicated communication path between the
hosts

30. A
1
7
2
5
3
4
6
B
C
D
E
F
Switching Nodes
End Hosts

31. Three Phases
 Circuit Establishment
• Host-B send a connection request towards Host-D
• Intermediate nodes route the request to Host-D based
on measures of availability and cost
• If ready, D accepts the connection and a dedicated path
(generally full duplex) is established from B through the
intermediate nodes to D
 Data Transfer
• The data (analog/digital) is carried on the dedicated
path
 Circuit Disconnect
• Done by any one station
• Signals are propagated to intermediate nodes to de-
allocate the dedicated resources

32. Principles
• Circuit switching designed for voice
– Resources dedicated to a particular call
– Much of the time a data connection is idle
– Data rate is fixed
• Both ends must operate at the same rate

33. Packet Switching

34. Problems in Circuit Switching
 Circuit Switching approach is inefficient
 Since data rate is constant, therefore the
devices interconnected must transmit and
receive at the same data rate, This limits the
interconnection of variety of hosts
 Further calls are blocked when all the lines are
busy

35. Packet Switching…...A quick overview
 Data is transmitted in short packets
 If a source has larger message to send, the message is broken
up into a series of packets
 Each packet contains user’s data plus some control
information (header)
 The control information, at a minimum includes the
information that the network requires to be able to route the
packet through the network and deliver it to the intended
destination
 At each node the packet is received, stored briefly and passed
on to the next node

36. Advantages
 Line efficiency is greater
 A packet switching network can perform data rate
conversion
 In Circuit Switching, calls are blocked whereas in P.S.
packets are still accepted but delivery delay increases
 Priorities can be used, thus a higher priority packet
experiences less delay

37. Types of Packet Switching
Datagram Approach
Virtual Circuit Approach

38. Datagram Packet Switching
 Each packet is treated independently, with no reference to packets
that have gone before
 Each packet contains the address of its destination
 The packets with the same destination do not always follow the
same route
 Some packets can get late and some can get destroyed in the
network
 Therefore, packets can be received out of order at the destination
 There must be some mechanism of re-ordering at the receiver
 Each packet, treated independently, is referred to as datagram

39. A
B

40. Virtual Circuit Packet Switching
A preplanned route is established before
any packets are sent
All the packets follow that route
Just like circuit switching, the route
should be terminated after the
transmission of data

41. DisconnectData
Connect Accept

42. Packets will be received in order
However, packets can get lost on the way

43. Event Timing