Networks and Networking Background

1. Networks and Networking Background EMC 165: Computer & Network Engineering Spring 2005 Profs. Chuah & Kishore

2. Last Time/Today • Last time, we motivated study of computer & network engineering using some case studies. • Today, we introduce • Several types of networks we will discuss in greater detail during the semester; and • Important concepts and terminology related to study of modern networks.

3. What is a Communication Network? • A collection of devices that can exchange information between each other. • Devices can be computers, phones, other appliances, sensors, etc. • Information can be all kinds of data: computer files, voice, video stream, etc. • Information is exchanged over wires (copper, optical fibers) or wirelessly using radio signals that are transmitted and received by antennas, or both.

4. What is a Communication Network? (Cont’d) • To fully connect all devices in a network, additional equipment may be needed. • These additional devices (e.g., access points, routers) form interconnections (wired and/or wireless) over which information can traverse as it moves from a source device to a destination device. • The path a data stream takes from source to destination is called a route.

5. Network Examples

6. 1. Internet • One of the greatest things about the Internet is that nobody really owns it. • It is a global collection of networks, both big and small. • These networks connect together in many different ways to form the single entity that we know as the Internet. In fact, the very name comes from this idea of interconnected networks.

7. The Internet Concept

8. The Internet Concept (Cont’d)

9. Internet: Network of Networks • Every computer that is connected to the Internet is part of a network, even the one in your home. • For example, you may use a modem and dial a local number to connect to an Internet Service Provider (ISP). • At school/work, you may be part of a local area network (LAN), but you most likely still connect to the Internet using an ISP that your school/company has contracted with.

10. Internet: Network of Networks (Cont’d) • When you connect to your ISP, you become part of their network. • The ISP may then connect to a larger network and become part of their network. • The Internet is simply a network of networks.

11. Connecting Network of Networks • The amazing thing here is that there is no overall controlling network. • Instead, there are several high-level networks connecting to each other through Network Access Points or NAPs. • All the networks that make up the Internet rely on NAPs, backbones and routers to talk to each other.

12. Internet: Clients & Servers • Internet servers make the Internet possible. All of the machines on the Internet are either servers or clients. • The machines that provide services to other machines are servers. • The machines that are used to connect to those services are clients. • There are Web servers, e-mail servers, FTP servers and so on serving the needs of Internet users all over the world.

13. Internet: Clients & Servers (Cont’d) • When you connect to www.cnn.com to read a page, you are a user sitting at a client's machine. • You are accessing the cnn Web server. The server machine finds the page you requested and sends it to you. • Clients locate servers using addresses called Internet Protocol (IP) addresses. • We will cover these and more details in the upcoming weeks.

14. 2. Cellular Networks • Cellular telephony is one of the fastest growing technologies on the planet. • It has been around roughly 15-20 years now. Presently, we are starting to see the third generation of the cellular phones coming to the market. • New phones allow users to do much more than hold phone conversations.

15. Beyond Voice • Store contact information • Make task/to-do lists • Keep track of appointments • Calculator • Send/receive email • Send/receive pictures • Send/receive video clips • Get information from the internet • Play games • Integrate with other devices (PDA’s, MP3 Players, etc.)

16. Cells, Bases, and Mobiles Base station: local radio tower to which a mobile sends its signals. Mobile: User handset. Sends/receives all signals from base station. Normal Telephone System Wired connection Cell: coverage area of base station

17. Multiple Cells • Over a region, say a city, a cellular service provider will typically install multiple base stations, leading to multiple interconnected cells. • As mobiles move from one cell to another, the phone call is handed from one base station to the next.

18. Multiple Cells (Cont’d) • A base station provides coverage (communication capabilities) to users on mobile phones within its coverage area. • Users outside the coverage area receive/transmit signals with too low power for reliable communications. • Users within the coverage area transmit and receive signals from the base station. • The base station itself is connected to other base stations and to the wired telephone network.

19. How it all works • In the upcoming weeks, we will review how cell phones operate, learn about cellular network components, the differences in the generations of cellular technology, etc. • In the process, we will learn how wireless signals are generated, how they move through the air, and how receivers can extract these signals from the air.

20. 3. Wireless Local Area Networks (WLANs) • A Wireless local area network is a network of computers that communicate with each other without wires within a 100 feet or so. • Most popular WLAN is WiFi; it is also known as 802.11 networking.

21. More on Wi-Fi • You can connect computers anywhere in your home or office without the need for wires. The computers connect to the network using radio signals, and computers can be up to 100 feet or so apart. • In order to form such networks, the computers have to have special equipment. • This typically comes in the form of a Wi-Fi card, which are collection of computer chips that enable Wi-Fi connections.

22. Wi-Fi Components • Many new laptops already come with a WiFi card built in -- in many cases you don't have to do anything to start using WiFi. • It is also easy to add a WiFi card to an older laptop or a desktop PC. • Once a Wi-Fi card is available, you just have to access a hotspot.

23. Wi-Fi Components (Cont’d) • Hotspot: a connection point for a WiFi network. It is a small box (called an access point) that is hardwired into the Internet. The box contains an 802.11 radio that can simultaneously talk to up to 100 or so 802.11 cards. • There are many WiFi hotspots now available in public places like restaurants, hotels, libraries and airports. For example, Starbucks. • The number of hotspots in the world is growing daily. • You can also create a hotspot at home.

24. Wi-Fi Hotspots • One way to find a hotspot is to go on-line. • For example, the following websites:

25. Wi-Fi: A Network in the Network of Networks Internet Wi-Fi Access Point/Router Wireless links WLAN Wi-Fi Ready Devices

26. More on Wi-Fi • In the next few weeks, we will see how Wi-Fi works, how you can set one up at home/work, how Wi-Fi networks can be extended to cover larger areas, etc. • We will also see how existing Wi-Fi technology is being used to create ad-hoc, self-configuring networks (more on this later).

27. 4. Ad-Hoc/Sensor Networks • Thus far, all the wireless networks we have mentioned have a centralized architecture: user terminals communicate strictly with a base station or an access point. • Currently, there is a lot of research work being conducted in ad-hoc wireless networks, where terminals can communicate directly with each other. (It is not necessary that terminals talk with access points first.)

28. Wi-Fi Example • For example, Wi-Fi cards can operate in both centralized (or infrastructure) mode as well as ad-hoc mode. • Peer-to-peer communication is enabled.

29. Ad-Hoc Mode • Ad Hoc connections can be used to share information directly between devices. This mode is also useful for establishing a network where wireless infrastructure does not exist. • Some uses, • Synchronize data between devices. • Retrieve multimedia files from one device and “play” them on another device. • Print from a computer to a printer without wires. • Ad Hoc wireless networking has very important application in sensor networks.

30. Sensors • Most basic definition: sensors are devices that are able to detect changes in a physical quantity or event. • Another definition: sensors are electronic or electromechanical devices that are used to detect and supply either physical or environmental information.

31. More on Sensors For example, sensors can measure: Air Temperature Barometric Pressure Distance Evaporation Fuel Moisture & Temp Leaf Wetness Position (GPS) Precipitation Relative Humidity Soil Heat Flux Soil Moisture Solar Radiation Soil/Water Temperature Snow Depth Wind Speed & Direction Water Quality pH Conductivity Structural Vibrations BioToxins Etc.

32. Sensor Networks • Sensors there have important applications in transportation, healthcare, manufacturing, environmental monitoring, homeland security,… • In most of these applications, a large number of sensors are installed in a region over which pertinent data has to be collected. • Sensors have to report their measured data back to a central unit, which processes and monitors data collection and may make control decisions, e.g., alert users of high/low measured data.

33. Sensor Network (Cont’d) The communication required to forward collected data to a central processor occurs over a peer-to-peer network, i.e., an ad-hoc network. Data Collection Data Collection Wireless Links Radio Antenna Sensor Wired Connections

34. Sensor Networks (Cont’d) • This semester, we will discuss several existing/emerging sensor networks, design of ad-hoc networks, etc. • In the process, we will also review the important research areas in this emerging networking topic.

35. 5. Satellite Systems: GPS • Several key communication networks rely on satellite links. • An important satellite system is Global Positioning System (GPS). • GPS is primarily a navigation tool, giving users with GPS terminals accurate measurements of location, velocity, etc. These terminals obtain the measurements by receiving signals from satellites located several thousand miles in the space.

36. GPS Components • Three basic components: • User terminal (gives navigation measurements). • 24 Satellites (used as artificial/intelligent stars to determine location of user terminals) • 5 Ground stations (collectively control and monitor the satellites).

37. More to Come on GPS • During the semester, we will learn how GPS works, how user terminal uses satellites to give highly accurate navigation data, etc. • In the process, we will discuss satellite systems in general, how satellites are launched into space, learn about different types of satellites, the components required in communication satellites, etc.

38. 5. Home Networks A Network connecting devices within a home, e.g., computers, printers, TV, DVD players, music servers, (even) refrigerators, microwave ovens, etc. Gateway Between 1 &3 Broadband Connection (e.g., DSL, Cable, Wireless, etc.) Home Network

39. Example of Present Home Networks

40. More on Home Networking • In the future, more and more devices can be connected on the home network. • We will discuss these possibilities and demonstrate how sensor networks may converge with present day home networks to give smart homes.

41. Important Terminology & Concepts

42. Packet and Circuit Switched Networks • Most of the networks we have talked about thus far are packet-switched networks. • To understand this concept, we must compare these types of networks to circuit-switched networks. • To under both packet and circuit switched networks, we must begin with comparing analog to digital.

43. Analog Versus Digital • The data or information we can communicate over a network can be qualified as either analog or digital. • Imagine plotting the information as a function of time. • Analog signals can take on a continuous range of values (e.g., voice). • Digital signals can only take on one of a possible set of values (e.g., text message).

44. Analog to Digital Conversion • Most modern networks carry digital information. • Thus, analog signals, like voice, have to be converted from analog to digital. • We now overview this process.

45. Analog Speech Signal • Microphone outputs an analog electrical signal. • For example, here is a graph showing the analog wave created by saying the word "hello“.

46. A to D Conversion • In digital systems, this analog signal is converted to a sequence of 0’s and 1’s. • One way this can be done is to sample the analog signal in fixed time intervals: Sampling instances

47. Quantization • This sampling process is called quantization. • The quantized values that make up the digital signal (say {0, 0.1, 0.2, …, 1}) are then converted to binary format, i.e, into bits. Quantization

48. Bits • Binary signals can only take on one of two values: 0 or 1, commonly known as bits. • To understand bits, we first look at digits. • A digit is a single place that can hold numerical values in the range of 0 to 9. • Digits are normally combined together to make larger numbers (called decimal numbers).

49. Bits (Cont’d) • For example, 6,957 has four digits. 7 is hold the 1s place, 5 is holding the 10s, 9 is holding the 100’s place, and 6 is holding the 1000’s place. • Each digit is placeholder for the next higher power of ten. • Each place can have 10 different values; this implies that digits use a base-10 number system. • Bits use a base-2 (binary) number system.

50. Bits (Cont’d) • Reason computers and communication systems use binary number system is that electronic components that perform binary operations are cheap. • Bit stands for Binary digIT. A binary digit is a sequence of 0’s and 1’s that represent numbers. 1110101001010101010101010100110111110101000101010010101010