Download ECE 4400:427/527 - Computer Networks Spring 2012

ECE 4450:427/527 - Computer Networks
Spring 2017
Dr. Nghi Tran
Department of Electrical & Computer Engineering
Lecture 2: Overview of Computer Network
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Network Definition
• Definition: A system that carries a commodity
between 2 or more entities via connections
• Entities: People, Computers, Cities etc.
• Connections: Relationships, Wires, Road etc.
• Examples of Network:
– Transportation
– Computer
– Many others
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Computer Network
• Definition: A system that carries information
between 2 or more entities, in the form of
electric signals
• Commodity?
• Entities?
• Connections?
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Example: Transportation Vs Computer
Network
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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Common Networks
• Ethernet (LAN)
• WiFi, WiMAX, 3G/4G: Mobile wireless
network
• The Internet:
• Internet: Internetwork - interconnecting
computer networks with special gateways
or routers
• Largest communication network adopting
IP technology
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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How Large is the Internet?
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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How Popular is the Internet?
Dr. Nghi Tran (ECE-University of Akron)
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Traffic of the Internet
Dr. Nghi Tran (ECE-University of Akron)
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Users of the Internet
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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Internet: Further Trend
Dr. Nghi Tran (ECE-University of Akron)
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Internet: Challenges
• Internet has grown rapidly and evolved to
unprecedented size
• With a significant increase in the number of
users, providers, and services, the Internet of
the future is facing many problems:
• How to manage/design a very large system
with limited resources
• Yet still provide a guaranteed performance
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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Objectives
Not too ambitious in this course!!!
• We take things step by step to help you
uunderstand communication network design
principles
• And to pave an initial road for you to:
• Design/operate Comm. Network
• Design client/server software
• Design equipments
• Doing research
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Basic Elements of Network
Divided into two main categories:
• Nodes:
• Links:
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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What is Network Design
• A task to make connections among nodes via links so that
packages can be exchanged:
• Timely, reliably
• Using as low resources as possible
• etc
• To this end, a huge of work required: We need to define 1)
network connectivity; 2) network architecture; 3) protocols;
4) applications, 5) interfaces, 6) policies, usages.
• As said, we shall take the issues step by step.
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Main Factors in Network Design
What are the most important factors that drive
Network Design?
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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Applications
• Most people know about the Internet (a computer
network) through applications
–
–
–
–
–
–
–
World Wide Web
Email
Online Social Network
Streaming Audio Video
File Sharing
Instant Messaging
…
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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Example of Application
A multimedia application including video-conferencing
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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Network Performance
When designing a network, we also need some
tools to evaluate the design:
Network Performance Metrics
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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Network Design
• A task to make connections among nodes via links so that
packages can be exchanged:
• Timely, reliably
• Using as low resources as possible
• etc
• To this end, a huge of work required: We need to define 1)
network connectivity; 2) network architecture; 3) protocols;
4) applications, 5) interfaces, 6) policies, usages.
• As said, we shall take the issues step by step.
• We now start with some Network Connectivity
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
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Network Connectivity
We have the following three main categories
• Directly-connected Network
• Circuit-switched Network
• Package-switched Network
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Directly-connected Network
Nodes are directly connected
(a) Point-to-Point: Each node is directly
connected to all others via a link
(b) Multiple-Access: All nodes share the same
physical medium
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Disadvantages
What are the main disadvantages of a network in
which all nodes are directly connected?
Given N nodes, how many connections do we
need?
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Switched Network
• Fortunately, connection between 2 nodes does not
necessary imply a physical connection: connection is
achieved among a set of cooperating nodes
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Interconnection of Networks
• Two nodes can also be connected by using a set of networks
(or clouds): Form an internetwork or internet
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Switched Network
• Circuit-Switched
– A dedicated circuit is
established between two
communicating nodes
– Example: ?
• Packet-Switched
– Data is split into blocks called
packets or messages.
– Store-and-forward strategy:
Switches to store and forward
packets
– Example: ?
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Circuit-Switched Network
• Designed in 1878: reserve a dedicated channel
for entire communication
• No need for a destination address since a path
is already established
• Once communication is complete, connection
is ended and links are released
• How many switches do we need?
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Circuit-Switched: Pros and Con?
Interesting note: Circuit switching currently
makes a comeback in optical networking
Dr. Nghi Tran (ECE-University of Akron)
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Packet-Switched Network
• Data is divided into packets
• Each packet can be delivered independently over
the network
• Each packet contains identification info
(source/destination address seq. number)
• Store-and-forward: Key strategy
• Each node receive complete package
• Store in memory
• Forward package to the next node
Dr. Nghi Tran (ECE-University of Akron)
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Advantages of Packet-Switched
• Efficiency in using resources, which is a key
requirement of computer network
• Flexible multiplexing methods
– What is multiplexing?
• Service
– More connections of lesser quality
– No blocking of users
• Adaptation
– Can adapt to network congestion and failures
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Disadvantages of Packet-Switched
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Multiplexing
• Fundamental concept: resources are shared
among user, e.g., data of users be multiplexed
over links that make up network
• Two common methods: Time and Frequency
Division Multiplexing
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Statistical Multiplexing
• Shortcomings of TDM/FDM:
• If no data to send: Link is idle – wasteful
• Maximum number of flows is fixed and known
ahead of time – not practical to add additional
quanta/frequencies
• Statistical multiplexing: Division of the
communication medium into channels of variable
bandwidth: Resource allocated on demand rather
than pre-allocated
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Comparison
Packet switching allows more users to use network!
Example:
 1 Mb/s link
 each user:
N
users
• 100 kb/s when “active”
• active 10% of time
1 Mbps link
 circuit-switching:
 10 users
 packet
Q: how did we get value 0.0004?
switching:
 with 35 users, probability >
10 active at same time is less
than .0004
Dr. Nghi Tran (ECE-University of Akron)
Q: what happens if > 35 users ?
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More Detail
Packet switching allows more users to use network!
• Assume there are total N users
• The probability for each user to be active is p
• Now we need to calculate two probabilities:
• What is the probability that we exactly n active
users
• What is the probability that we have more than n
active users
• Let start with some simple cases: N=3 and n=1
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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Comparison
Packet switching allows more users to use network!
Example:
 1 Mb/s link
 each user:
N
users
• 100 kb/s when “active”
• active 10% of time
1 Mbps link
 circuit-switching:
 10 users
 packet
switching:
 with 35 users, probability >
10 active at same time is less
than .0004
Dr. Nghi Tran (ECE-University of Akron)
More connections of lesser
quality
ECE 4450:427/527
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Recap
• We have taken an overview about Network
• We also define CONNECTIVITY in a Network:
• Packet switching with statistical multiplexing
• Next step: We shall look at NETWORK ARCHITECTURE
• Layering
• Protocols
• Internet Architecture
Dr. Nghi Tran (ECE-University of Akron)
ECE 4450:427/527
Computer Networks
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