Networks and Networking Background EMC 165 Computer Network

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

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.

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.

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.

Network Examples

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.

The Internet Concept

The Internet Concept (Cont’d)

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.

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.

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.

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.

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.

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 third generation of the cellular phones coming to the market. • New phones allow users to do much more than hold phone conversations.

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, MP 3 Players, etc. )

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

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.

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.

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.

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 Wi. Fi; it is also known as 802. 11 networking.

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.

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

Wi-Fi Components (Cont’d) • Hotspot: a connection point for a Wi. Fi 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 Wi. Fi 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.

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

Wi-Fi: A Network in the Network of Networks Internet ss e l e s il nk Wi-Fi Access Point/Router W ir WLAN Wi-Fi Ready Devices

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).

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. )

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

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.

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.

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 p. H Conductivity Structural Vibrations Bio. Toxins Etc.

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.

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 Wireless Links Radio Antenna Sensor Wired Connections

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

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.

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).

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.

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

Example of Present Home Networks

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.

Important Terminology & Concepts

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.

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).

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.

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“.

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

Quantization • This sampling process is called quantization. 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.

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).

Bits (Cont’d) • For example, 6, 957 has four digits. 7 is hold the 1 s place, 5 is holding the 10 s, 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.

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 dig. IT. A binary digit is a sequence of 0’s and 1’s that represent numbers. 1110101010101010011011111010100010101010

More on Bits 0=0 1=1 2 = 10 3 = 11 4 = 100 5 = 101 6 = 110 7 = 111 8 = 1000 9 = 1001 10 = 1010 11 = 1011 12 = 1100 13 = 1101 14 = 1110 15 = 1111 16 = 10000 17 = 10001 18 = 10010 19 = 10011 20 = 10100 There are simple rules that have been developed to convert a digit to a bit.

Some Decimal Number Rules • To understand binary numbers, begin by recalling elementary school math. When we first learned about numbers, we were taught that, in the decimal system, things are organized into columns: H|T|O 1|9|3 • Here, "H" is the hundreds column, "T" is the tens column, and "O" is the ones column. So the number "193" is 1 -hundreds plus 9 -tens plus 3 ones.

Decimal Number Rules (Cont’d) • Years later, we learned that the ones column meant 100, the tens column meant 101, the hundreds column 102 and so on, such that 102|101|100 1| 9|3 • Thus, the number 193 is really (1*102)+(9*101)+(3*100) = 1*100+9*10+3*1.

Binary Number Rules • The binary system works under the exact same principles as the decimal system, only it operates in base 2 rather than base 10. In other words, instead of columns being 102|101|100 they are 22|21|20 • For example, the binary sequence 11, is 1*21+1*20 = 3. • While the binary sequence 10010 is (1*24)+(0*23)+(0*22)+(1*21)+(0*20) = (1*16)+(0*8)+(0*4)+(1*2)+(0*1) = 18.

Bytes • Bits are rarely seen alone in computers. • They are typically grouped together into 8 bit collections, called bytes. • With 8 bits in a byte, a byte can represent values ranging from 0 to 255: 0 = 0000 1 = 00000001 2 = 00000010. . . 254 = 11111110 255 = 1111

How is Quantized Digital Signal converted to Bits? • After quantization, a digital signal takes on one of a discrete set of values {y 1, y 2, …. y. N}. • Each possible discrete value can be represented in binary format. • Whenever the digital signal takes on particular value yi, the value yi is converted to binary format, i. e. , a sequence of 0’s and 1’s. • Result is a binary (digital) signal.

Packets • In communication networks, bits are transported in groups called packets. • Packets can vary in length (depending on the type of network), e. g. , from hundreds of bits to thousands of bits. • To understand this, consider the process of sending an email message.

Email Example • An email message is written using characters on a keyboard. • These characters only take on one of a set of a possible values (are thus inherently digital). • There is a standard method for converting text messages to bits, called ASCII conversion.

Brief Aside: ASCII • American Standard Code for Information Interchange (ASCII) is a standard method for converting text characters (including !@#$%. . ) into binary format. • Standard method means all systems, software packages, operating systems, etc. use same conversion process. • Standard method is preferred because once converted to binary format, message can be understood by all software applications.

Email Example (Cont’d) • Once the message has been converted to bits, the bits are groups into packets. • These packets are then sent over the wired or wireless connection to the router, which is connected to the internet. • The packets then move through the internet to the destination. • At the destination, the packets are reassembled into a stream of bits and then reconverted from bits to a text message.

Packet and Circuit Switched Networks • In packet switched networks, each packet is independently routed from the source terminal to the destination terminal (e. g, Internet). As a result, packets from the same data stream (e. g. , email message) can take different paths through the network. • In circuit-switched networks, each packet in a bit stream takes the same exact path from source to destination.

Circuit-Switched Network connections (wired or wireless) Fixed Route Network Routers … ts Packe 2 1

Circuit-Switched • In circuit switched networks, a path from source to destination is fixed by reserving network resources from source to destination for the duration of the message transmission. • As a result, packets arrive in order at the destination. • This is different from packet-switched networks.

Packet-Switched Route for Packets 1 & 2 Route for Packet 3 2 1 Route for Packet 4 … 2 1 4 3

Packet-Switched • In packet-switched networks, no route reservations are made. This way each link can support more than one message stream (implies more information can be packed into each link). • Independent routing for each packet implies that data traffic can be distributed more evenly over all network devices. • Result: packets can arrive out of order at destination, thereby requiring reassembly.

Review of Today’s Lecture • We introduced some relevant communication networks, which we will review in greater detail during the semester. • We learned some important networking concepts that characterize modern computer and communication networks.

Some References for Today’s Lecture • http: //www. math. grin. edu/~rebelsky/Courses/152 /97 F/Readings/student-binary. html • http: //www. techonline. com/community/ed_resour ce/feature_article/4153 • http: //www. howstuffworks. com