Download - ENTC 345 Lecture 5
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Circuit Switching and
Packet Switching
ENTC 345Dr. Ana Goulart
Assistant Professor
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Announcements Reading: Stallings
Chapter 1 and 2
Chapter 10
Office hours: Mondays 5 to 8 pm (T 101)
Hw # 1 due today
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Review M/M/1 example incoming link information
Hw#1: Examples of simulations and
applications
How was the first lab?
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On Opnet TrafficApplications and Profiles
Application Models: generate typical application traffic patterns
Examples: FTP
Email
Remote Login
Video Conferencing
DatabaseHTTP
Print
Voice
Custom
Standard applications
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On Opnet Standard applications
Client/Server Model
Two-tier architecture
Client Server
request
response
* Sessions: single conversation
between client/server
* Traffic organized into sessions
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Applications and ProfilesApplications: simple traffic sources, or
complex protocols, or discrete set of tasks
Application Profile: users behavior
Specify application he/she uses
how long and how often
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Applications and ProfilesApplication Profile: users behavior
Example: start time, duration, repeatability,
parallel applications or serial applications
Email HTTP
FTP
Email HTTP FTP
Profile 1 : Serial
Profile 2 : Parallel
Email
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Application Model Hierarchy
Profile
Application
Tasks
Phase
Profile Object
Application Object
Task Object
(Custom applications)
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Lab 1 Small Internetwork
Application and Profile
Objects database
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Steps: Create application add row 1
Create profile set attributes
Workstation object - Assign profile to desiredworkstations
Server object assign service type (application)
Example: How would you model the traffic at thelibrarys subnet?
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A Network Configuration
R
RR
R
R
Ethernet
switch
ATM
switchFirewall
host
Private WANServer
ISP
LAN PCs
Subscriber
connection
InternetResidential
user
(page 30 - Stallings)
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Wide Area NetworkImportant concepts:
Circuit switching
Packet switching
Frame relay
ATM (Asynchronous Transfer Mode)
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Wide Area NetworksImportant concepts:
Circuit switching
- fixed routes, dedicated path between 2 stations
- on each link, a logical channel is dedicated tothe connection
- data transmitted along the dedicated path as
rapidly as possible
Packet switching - data sent in a sequence of packets
- each packet passed from node to node along
some path
- at each node, the entire packet is received,
stored briefly and transmitted to next node
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Circuit Switching
A
B
- data transmitted along the dedicated path
as rapidly as possible
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Packet Switching
AR
RR
R
B
Internet
At each node, the entire packet is received,
stored briefly and transmitted to next node
What is the primary framework to model
this behavior and analyze delays?
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Circuit switching x Packet switchingTiming of events:
Call request signal
Data
Time
Call accept
signal
A B C D
Pkt 1
Pkt 2
Pkt 3 Propagation delay
Transmission delay
Queuing delay
Time
A B C D
Circuit switching Packet switching
Circuit
establishment
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Delays in Circuit switchingTiming of events:
Call request signal
Data
Time
A B C D
Propagation delay
Circuit switching Packet switching
Circuit
establishmentAfter connection is established,
Information is transmitted at a
fixed data rate.
Node delays are negligible.
Advantages?
Disadvantages?
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Circuit switching x Packet switchingTiming of events:
Call request signal
Data
Time
Call accept
signal
A B C D
Pkt 1
Pkt 2
Pkt 3Propagation delay
Transmission delay
Queuing delay
Time
A B C D
Circuit switching Packet switching
Circuit
establishment
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Packet switching delaysPkt 1
Transmission delay
Queuing delay + Processing
A B C
Packet switching
Propagation delay
Total delay from A to B
Pkt 1
What is the Throughput?
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ThroughputPkt 1
Transmission delay
Queuing delay + Processing
A B C
Packet switching
Propagation delay
T = Total delay from A to B
Pkt 1
What is the Throughput?
L = size of packet (bits)
Throughtput = L / T
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Impact of packet size Effect of packet size on transmission time
(figure 10.11, page 314 Stallings)
Smaller packets => higher service rate (or smaller
transmission times)
Service rate on the outgoing link
= Capacity (bits/sec)
Packet size (bits/packet)
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Virtual Circuit Packet Switching Datagram packet switching
No dedicated route for the conversation or
session
Virtual Circuit Packet Switching
Dedicated route for the conversation orsession
Additional Call setup delay
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Virtual Circuit switching (internal)Timing of events: Call request signal
Data
Time
Call accept
signal
A B C D
Circuit switching
Packet switching
Circuit
establishment
Pkt 1
Pkt 2
Pkt 3
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Virtual circuits (external) Logical path (or connections) between two
stations
Example: X.25 standard
Physical level interface between station and
packet switched network
Link level reliable data transfer across the physical
link (LAP-B)
Network level virtual circuit service, enables users
to set-up logical connectionsPacket switchingNetwork
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Frame relay Designed to eliminate the overhead of X.25
Virtual circuits or logical connections carried at
the link layer
Call control signaling (separate)
No hop-by-hop flow control (error and flow
control should be taken care by another higherlayer protocol