ECE 4450:427/527 - Computer Networks Spring 2015 Dr. Nghi Tran Department of Electrical & Computer Engineering Lecture 2: Overview of Computer Network Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 1

Network Definition Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 2 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

Computer Network Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 3 Definition: A system that carries information between 2 or more entities, in the form of electric signals Commodity? Entities? Connections?

Example: Transportation Vs Computer Network Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 4

Common Networks Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 5 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

How Large is the Internet? Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 6

How Popular is the Internet? Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 7

Traffic of the Internet Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 8

Users of the Internet Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 9

Internet: Further Trend Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 10

Internet: Challenges Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 11 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

Objectives Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 12 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 Not too ambitious in this course!!!

Basic Elements of Network Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 13 Nodes: Links: Divided into two main categories:

What is Network Design Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 14 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 network connectivity, network architecture, protocols, applications, interfaces, policies, usages. As said, we shall take the issues step by step.

Main Factors in Network Design Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 15 What are the most important factors that drive Network Design?

Applications Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 16 Most people know about the Internet (a computer network) through applications – World Wide Web – – Online Social Network – Streaming Audio Video – File Sharing – Instant Messaging – …

Example of Application Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 17 A multimedia application including video-conferencing

Network Performance Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 18 When designing a network, we also need some tools to evaluate the design: Network Performance Metrics

Network Design Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 19 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 network connectivity, network architecture, protocols, applications, interfaces, policies, usages. As said, we shall take the issues step by step. We now start with some Network Connectivity

Network Connectivity Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 20 Directly-connected Network Circuit-switched Network Package-switched Network We have the following three main categories

Directly-connected Network Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 21 (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 Nodes are directly connected

Disadvantages Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 22 What are the main disadvantages of a network in which all nodes are directly connected? Given N nodes, how many connections do we need?

Switched Network Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 23 Fortunately, connection between 2 nodes does not necessary imply a physical connection: connection is achieved among a set of cooperating nodes

Interconnection of Networks Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 24 Two nodes can also be connected by using a set of networks (or clouds): Form an internetwork or internet

Switched Network Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 25 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: ?

Circuit-Switched Network Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 26 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?

Circuit-Switched: Pros and Con? Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 27 Interesting note: Circuit switching currently makes a comeback in optical networking

Packet-Switched Network Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 28 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

Advantages of Packet-Switched Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 29 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

Disadvantages of Packet-Switched Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 30

Multiplexing Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 31 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

Statistical Multiplexing Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 32 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

Comparison Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 33 Example:  1 Mb/s link  each user: 100 kb/s when “active” active 10% of time  circuit-switching:  10 users  packet switching:  with 35 users, probability > 10 active at same time is less than.0004 Packet switching allows more users to use network! N users 1 Mbps link Q: how did we get value ? Q: what happens if > 35 users ? …..

More Detail Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 34 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

Comparison Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 35 Example:  1 Mb/s link  each user: 100 kb/s when “active” active 10% of time  circuit-switching:  10 users  packet switching:  with 35 users, probability > 10 active at same time is less than.0004 Packet switching allows more users to use network! More connections of lesser quality N users 1 Mbps link …..

Recap Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527Computer Networks 36 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