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

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 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

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

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

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

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

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

Users of the Internet Dr. Nghi Tran (ECE-University of Akron)

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

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

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

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

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

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

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

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

Network Performance Metrics 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

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

We have the following three main categories 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

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

Given N nodes, how many connections do we need? 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

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

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

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

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

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

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) ECE 4450:427/527

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

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

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

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

Comparison Packet switching allows more users to use network! ….. 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 N users ….. 1 Mbps link Q: how did we get value 0.0004? Q: what happens if > 35 users ? Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527

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

Comparison Packet switching allows more users to use network! ….. 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 N users ….. 1 Mbps link More connections of lesser quality Dr. Nghi Tran (ECE-University of Akron) ECE 4450:427/527

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