The document provides an overview of packet switching, a method for sending data by dividing it into packets with headers for routing. It explains two approaches: datagram networks, which are connectionless and treat packets independently, and virtual circuit networks, which combine characteristics of both circuit and datagram networks but require setup phases. The efficiency and delay issues involved in both approaches are discussed, highlighting the operational differences between them.

1. Introduction to Data communication
Topic: Packet Switching
Lecture #7
Dr Rajiv Srivastava
Director
Sagar Institute of Research & Technology (SIRT)
Sagar Group of Institutions, Bhopal
http://www.sirtbhopal.ac.in

2. Unit 2
Lecture 7
Course Lecture 23
Packet Switching

3. PACKET SWITCHINGPACKET SWITCHING
 Packet switching is a method for sending data wherein the data
is divided in packets.
 Each packet is given a header containing information of the
destination. Each packet is forwarded through the network to
the destination using this information.
 At the destination the data has to be reassembled from the
received packages.
 It uses packets of fixed or variable size.
 Each packet contains header with source & destination
addresses
 The size of the packet is determined by the network and the
governing protocol.
 Individual packets take different routes to reach the destination
 it uses two methods for transmission
1. Datagram Approach
2. Virtual Circuit Approach

5. • In a datagram network, each packet is treated independently
of all others.
• Packets in this approach are referred to as datagrams.
• each packet is separately addressed & treated as
independent
• Switches devices route for each packet independently, each
intermediate node defines next route for this packet
• No dedicated connection is established between sender &
receiver
• Resources are not allocated for any packet so there is no
reserved bandwidth or no scheduled processing time for each
packet
DATAGRAM PACKET SWITCHING

6. • When a switch receives a packet, it has to
wait if there are any other packets being
processed. This increases delay.
• Packet transfer processing takes place at
network layer. These packets are called as
Datagram
• Figure explains the theory of datagram
transmission clearly.

7. A Datagram network with four switches (Routers)
4 3 2 1
1
4
3
2
1
1
2
3
4
432 1

8. • The datagram networks are also referred as
connectionless networks, which means it need
to keep track of connections status.
• There are no tear down phases as circuit
switching
• Each packet is treated the same by a switch
regardless of its source or destination.

9. Figure Routing table in a datagram network
 Since there are no set up
or teardown phases, so to
maintain status of packet a
routing table is required.
 A switch in a datagram
network uses a routing
table that is based on the
destination address

10. Destination address
• Every packet in the datagram network carries
a header that contains destination address
along with some other information. This
address is used to route the packet to its
destination
• The destination address in the header of the
packet remains unchanged throughout its
journey in the network.

11. Efficiency
• the efficiency of the datagram network is
better than that of circuit switched network
• Resources are allocated only when the
packets are to be transferred
• If a source sends a packet & there is a delay
of few minutes before another packet can
be sent then the resources can be
reallocated during these minutes for other
packets from other resources.

12. Delay
• There may be greater delay in datagram
network than virtual circuit network
• There are no setup & tear down phases
• Each packet may experience delay at a switch
before it is forwarded
• Since all packets travel through different
routes/switches so delay is also not identical.

13. Delays in a datagram network
Total Delay = 3 T + 3 + w1 + w2
Where 3T : 3 transmission time
3 :3 propagation delays
w1+w2 : 2 waiting times

14. 2nd
Approach
Virtual Circuit Network
• Virtual circuit network is implemented at the
data link layer
• a circuit switch network is implemented at
physical layer
• datagram is implemented at network layer.
• A virtual circuit network is a cross between a
circuit switched network & a datagram network.
It has some characteristics of both.

15. • Similarities with circuit switch:
– Setup & tear down phases
– Resources allocation during setup phase
– All packet follow the same path established during
connection
• Similarities with datagram approach:
– Resources may be allocated on demand
– Data are packetized & each packet carries an
address in the header. However, address in the
header has local jurisdiction, not end to end
jurisdiction

16. Switched Virtual Circuit

17. Switched Virtual Circuit

18. Switched Virtual Circuit

19. Virtual-circuit network

20. Addressing in Virtual Circuit Network
• Global Addressing
• Local (virtual Circuit Identifier) VCI
– VCI – it is actual identifier used for data transfer
– It is a small number that has only switch scope
– It is used by frame between two switches
– When a frame arrives at a switch it has different
VCI & when it leaves switch it has another VCI

21. Virtual-circuit identifier

22. Thank You
Dr Rajiv Srivastava
Director
Sagar Institute of Research & Technology (SIRT)
Sagar Group of Institutions, Bhopal
http://www.sirtbhopal.ac.in