Transcript cis 484 communication systems

Chapter
Packet and Circuit Switching
Chapter Objectives
• Explain the concept of packet switching
• Give sample application areas of packet
switching
• Describe circuit switching
• Compare and contrast packet switching
with circuit switching
Chapter Modules
• Packet switching
• Packet switching applications
• Circuit switching applications
Module
Packet Switching
Packet Switching Preview
• Explain the concept of a path or a route taken
by a packet
• Study the difference between static and
dynamic paths?
• Relate appropriately the terms packet
switching and circuit switching to the terms
dynamic and static paths
• Explore the path taken by a packets in
dynamic routing when a packet travels from
its origin to its destination
The Concept of Path in
Communication
• A path is a route for data to travel between
two nodes in a network
• Dynamic path
– In this case, the path often changes from packet to
packet
– Example: Packet Switching
• Static path
– Path is initially established and it remains
unchanged for the duration of the communication
session
– Example: Circuit Switching
Packet Switching Network
Packet 2
New
York
Los
Angeles
Packet 1
Miami
Salient Points of Packet
Switching
• Path
– Each packet may take a different path to its
destination
– Best path is heuristically determined at
each node
• Packet switching
– Path may be switched among packets
– Hence, the term packet switching
Key Words
• Packet and circuit switching
• Dynamic and static paths
End of Module
Module
Advantages and Disadvantages of
Packet Switching
Questions
• What are the major advantages and
disadvantages of packet switching?
• Could the Internet be called a packet
switching network?
• How does packet switching help in
supporting multiple communication
sessions?
• How does a web server support multiple
access to its contents? Explain in terms of
packets that travel from the web server to
their various destinations.
Questions (continued)
• What are the implications of packet
switching to the transmission of audio
and video in real time?
• How are the above problems addressed
in streaming?
Major Advantages
• Better utilization of the network
segments in terms of the usage of the
network paths
• Ability to engage in multiple
communication sessions
Dynamic Assignment of Paths
New
York
Los
Angeles
Las
Vegas
Miami
Support for Multiple
Communication Sessions
Session 1
New
York
Session 2
Los
Angeles
Las
Vegas
Miami
Disadvantage or a Concern
• Packets may not arrive at their
destination in the order in which they
were originally transmitted
• The above possibility exists because of
the different paths that are taken by the
different packets
Order of Arrival of Packets
Packet 2
New
York
Packet 1
Los
Angeles
Packet 2 may arrive earlier than Packet 1.
Miami
Packet Assembly
• Packets are assembled to preserve the
order of transmission
• Packets arriving earlier are held in a
buffer
• The order of arrival is critical and in
certain cases the order is time sensitive
as well
Transmission of Audio and Video
in Packet Switching
• Transmission of audio and video are time
sensitive
– Timely arrival of packet is important
• The process that would ensure the orderly
and timely arrival of data packets is known as
streaming
• Streaming also compresses the data to
minimize bandwidth requirements thus
ensuring that the packets have adequate
bandwidth to travel to the destination in the
order in which they are supposed to arrive at
the destination
Buffering in Streaming
• Streamed audio or video is often
buffered to ensure that the audio or
video is played continuously
Advantages And Disadvantages
• Advantages
– Efficient use of the network paths
– Engage in multiple sessions
• Disadvantages
– Additional hardware and software
resources are required to assemble and
route the packets
– If real-time continuity is stipulated then the
data must be subjected to a process known
as streaming
Special Concerns
• Audio and video transmission
– Streaming is used
• Voice Over IP (VoIP) is designed
deploy telephony over the Internet
Newer Advancements for Real Time
Transmission of Information
• Faster Internet speed
• Better technology
– IPv6
– Better streaming technologies
Questions
• What are the major advantages and
disadvantages of packet switching?
• Could the Internet be called as a packet
switching network?
• How does packet switching help in
supporting multiple communication
sessions?
• How does a web server support multiple
access to its contents? Explain in terms of
packets that travel from the web server to
their various destinations on the Internet.
Questions (continued)
• What are the implications of packet
switching to the transmission of audio
and video in real time?
– Relate the above to Voice over IP
transmission.
• How are the above problems addressed
in streaming?
End of Module
MODULE
Packet Switching Applications
Questions
• Give a simple example of packet
switching application
• Relate packet switching to multiple
session applications on the Internet and
give examples of multiple session
applications
• Describe audio transmission challenges
on packet-switched networks
Questions (Continued)
• List the packet switching technologies
used in WANs
• Explain the emergence of the concept of
fixed length packets or cells in packet
switching networks
– Name a cell based transmission technology
and state its applications
Internet: An Application of
Packet Switching
Internet
Server
Packet N1
New
York
Ramp
Los
Angeles
Packet M1
Miami
Server in Los Angeles supports multiple access to the web
over a packet switched connection.
Support for Multiple Sessions
Packet 2
Session LA
Session HU
New
York
Los
Angeles
Packet 1
Houston
Miami
Packets are displayed on different sessions on the screen.
Applications Using MultipleSessions
• Sharing
• Collaboration
• Multiple access to an Internet server
• etc.
Packet Delivery
SCREEN
Packets from
origin 1:
N1, N2
Sharing of Word
document on
Internet under
Microsoft
NetMeeting
Packets
from
Origin 2:
M1, M2
Audio Transmission Over
Packet Switching Network
• Relatively high speeds are required on
the network
• Data compression and other techniques
are used to ensure continuity know as
streaming
• Sample applications:
– Audio streaming on the Internet
• RealAudio is an example of a streaming
software
Usage of Packet Switching
• Large computer networks with multiple
routers
• WAN in general
• Internet in particular
Packet Switching WAN
Technologies
• Past and Present
– X.25 Packet Switching
• Present and Near Future
– Frame Relay
• Present and Future
– Asynchronous Transfer Mode (ATM)
– ATM is also known as Cell Relay
ATM
• Asynchronous Transmission Method
(ATM)
• Based on fixed length packets
• Switches instead of routers are used to
route the information on a network
• This is the emerging technology in
WAN transmission
• (Include more information on ATM)
Recollecting the Concept of Cell
Data
Packet varies in size
Data
Cell is of fixed length
Questions
• Give a simple example of packet
switching application
• Relate packet switching to multiple
session applications on the Internet and
give examples of multiple session
applications
• Describe audio transmission challenges
on packet-switched networks
Questions (Continued)
• List the packet switching technologies
used in WANs
• Explain the emergence of the concept of
fixed length packets or cells in packet
switching networks
– Name a cell based transmission technology
and state its applications
End of Module
MODULE 5
Circuit Switching
Questions
• Explain the concepts of circuit
switching. How does it function?
• What are the advantages and
disadvantages of circuit switching?
• Name some applications of circuit
switching
• Compare circuit switching with packet
switching
Circuit Switching Network
Switch
Established Circuit
New
York
Los
Angeles
Circuit established and maintained for
entire duration of communication.
Defining Characteristics of
Circuit Switching
• Establish (switch) a path (circuit)
between two nodes of communication
• Maintain the circuit for the full duration
of communication session
Advantages of Circuit Switching
• Continuity assured in the order of
transmission
• Audio can be transmitted without
streaming provided adequate
bandwidth is available
– Otherwise streaming is necessary
• The overhead is low in switching a
circuit
Disadvantages of Circuit
Switching
• Inefficient use of the paths that are
available within a network
– This may lead to circuit saturation
• Users can be locked out of the network
• Multiple sessions cannot easily be
implemented although it is possible to
have multiple sessions
Circuit Saturation
Established Circuit
New
York
Los
Angeles
Miami
Saturation point.
Areas of Applications
• Voice/Video communications
– Telephone network
• Both analog and digital
telecommunication lines can be circuit
switched
• ISDN
More on ISDN
• ISDN has two B channels and one D
channel
– B channel is used for data and D channel is
used for monitoring and control of the data
transmission
• B channels are circuit switched and the
D channels are packet switched
Comparison
Packet Switching
Circuit Switching
_______________________________________________
•Efficient use of network
•High overhead
•Computer data
•Audio and video
transmissions are,
however, possible
•Multiple sessions possible
are easily implemented
Inefficient use
Low overhead
Audio and video
Multiple sessions
are possible, however
it requires additional
hardware and software
Questions
• Explain the concepts of circuit
switching. How does it function?
• What are the advantages and
disadvantages of circuit switching?
• Name some applications of circuit
switching
• Compare circuit switching with packet
switching
END OF MODULE
END OF MODULE 5
END OF CHAPTER