Computer Networks, the Internet, and the World Wide Web PDF

Chapter 7 Computer Networks Networks, the Internet Internet, and the World Wide Web INVITATION TO Computer Science 1  Objectives After studying this chapter,...

Chapter 7 Computer Networks Networks, the Internet Internet, and the World Wide Web INVITATION TO Computer Science 1  Objectives After studying this chapter, chapter students will be able to: Describe and compare different network technologies, including dial-up, broadband, and wireless Explain how different kinds of networks (LAN, WAN, WLAN, WWAN) are connected, and how communications works in each Explain the importance of standards and protocols for communications among computing devices Name the layers of the protocol hierarchy, and describe the purpose of each layer Invitation to Computer Science, 6th Edition 2  Objectives (continued) After studying this chapter, chapter students will be able to: Demonstrate how protocols like the ARQ algorithm, DNS, IP,TCP, and HTTP function Explain how the existence of the Internet has led to new modes of communication, such as e-mail, resource sharing and e-commerce sharing, Describe the highlights of the history of the Internet and the Web, and explain how the modern system came into being Invitation to Computer Science, 6th Edition 3  Introduction Computer networks have had revolutionary impact Electronic commerce Worldwide communications Spread of information and data We take for granted: – access to information on any subject – immediate contact with people around the world – streaming audio and video – wired or wireless access from every device Invitation to Computer Science, 6th Edition 4  Basic Networking Concepts Computer network: made up of computing devices, nodes, and interconnections Networks may y be wired or wireless;; communication links use various technology Wired: – Dial-up – Broadband Wireless: – WLAN – WWAN Invitation to Computer Science, 6th Edition 5  Basic Networking Concepts (continued) Switched, Switched dial-up telephone lines Analog lines Transmit digital data Modem modulates carrier wave Speeds up to 56k bps Bandwidth = capacity Invitation to Computer Science, 6th Edition 6  Overview of Modulation Serial link Phone RS -232 Line RJ 11 RJ-11 Computer Modem Digital Analog Slide from Modulation.ppt at web.calstatela.edu/  Amplitude Modulation (AM) 1 = Amp. 1 0 = Amp Amp. 2 1 1 0 0 A B Amp. 1 Amp. 2 Slide from Modulation.ppt at web.calstatela.edu/  Characteristics of Amplitude Modulation Amplitude of the analog signal is modulated One amplitude represents a 0 Another amplitude represents a 1 Frequency remains unchanged in both cases Signals that are modulated at one end are demodulated at the other end Slide from Modulation.ppt at web.calstatela.edu/  Frequency Modulation (FM) 1 = Frequency F1 0 = Frequency F2 1 1 0 0 Freq. 1 Freq. 2 Slide from Modulation.ppt at web.calstatela.edu/  Characteristics of Frequency Modulation Frequency is modulated Frequency f1 – Represents 1 Frequency f2 – Represents 0 The amplitude remains unaltered in both cases Slide from Modulation.ppt at web.calstatela.edu/ The Concept of Phase Shift 90 degrees phase shift 0 90 180 degrees phase shift 0 180 Slide from Modulation.ppt at web.calstatela.edu/  Phase Modulation Technique 1 0 90 Degrees 0 Degree phase shift phase shift Slide from Modulation.ppt at This is also known as phase shift keying. web.calstatela.edu/  Characteristics of Phase Shift Modulation Phase is modulated Phase shift of 0 represents a 0 Phase shift of 90 degrees represents a 1 Both amplitude and frequency remain unaltered is both cases Also known as Phase Shift Keying, it is used in a number of modern modems as well Slide from Modulation.ppt at web.calstatela.edu/  Basic Networking Concepts (continued) Broadband: transmission rate > 256k bps Home users: – Asymmetric download/upload times – Digital subscriber line (DSL) Uses phone lines, but sends digital signal on different frequencies than voice Down: 5-15 Mbps, Up: 1-2 Mbps – Cable modem Uses cable TV lines Down: 10-20 Mbps, Up: 1-3Mbps Invitation to Computer Science, 6th Edition 16  Basic Networking Concepts (continued) Commercial/institutional users: – Ethernet (1970s) Dedicated coaxial cable Operates at 10 Mbps – Fast Ethernet (early 1990s) Dedicated lines (coaxial, fiber-optic, or twisted-pair) Operates at 100 Mbps – Gigabit Ethernet Standard (late 1990s) From gigabit networking research project IEEE standard Operates at 1000 Mbps Invitation to Computer Science, 6th Edition 17 Invitation to Computer Science, 6th Edition 18  Basic Networking Concepts (continued) Wireless data communication Radio, microwave, infrared signals to mobile computers p Laptops, tablet computers, smartphones, etc. Mobile computing: p g deliver data regardless g of location Bluetooth: – Low-power, close range (30-50 feet), connect devices like wireless mice mice, cameras cameras, video games Invitation to Computer Science, 6th Edition 19  Basic Networking Concepts (continued) Wireless local area network (WLAN) Computers transmit wirelessly to base station with wired connection Range of 150-300 feet Terminology: – Wi-Fi (Wireless Fidelity) – IEEE 802.11 wireless network standards – Wi-Fi hot spot: e.g., libraries, campuses, coffee shops – Metropolitan Wi-Fi service: cities provide routers Invitation to Computer Science, 6th Edition 20  Basic Networking Concepts (continued) Wireless wide area network (WWAN) Computers transmit wirelessly to remote base station with wired connection Cellular technology: antennas on towers miles apart Example: 4G: voice and data, transmits at 5-20 Mbps Signal may be blocked when indoors Errors with data transmission can slow performance S Security: wireless signals easy to intercept Invitation to Computer Science, 6th Edition 21  Basic Networking Concepts (continued) Local Area Networks (LAN) Wired connection Computers, Computers printers printers, and servers in close proximity Examples: same room, office building, campus Privately owned and operated Topology: how computers connected, affects how they communicate Invitation to Computer Science, 6th Edition 22  Basic Networking Concepts (continued) Bus topology – Shared lines – Take turns using line Ring topology – Messagesg circulate until reach source Star topology – All send to central node, which routes to destination Invitation to Computer Science, 6th Edition  Basic Networking Concepts (continued) Ethernet LAN with shared cable Bus topology Single g cable over short distances Multiple cables over longer distances Repeater amplifies signal Bridge routes messages only when necessary Invitation to Computer Science, 6th Edition  Basic Networking Concepts (continued) Ethernet LAN with switch Bus topology, still Shared cable is inside switch Wiring closet contains switch and ports Ethernet Eth t jacks j k iin rooms connectt tto switch it h iin closet Wireless base stations also connect to switch in closet Invitation to Computer Science, 6th Edition 25 Invitation to Computer Science, 6th Edition 26  Basic Networking Concepts (continued) Wide Area Networks (WANs) Wired connection Computers located at great distances Examples: across state or country Dedicated point-to-point point to point lines – Computers connect to other computers on individual lines Store-and-forward, packet-switched – Packets go from node to node until reach destination Invitation to Computer Science, 6th Edition 27  Basic Networking Concepts (continued) Routing of packets determined dynamically – A-B-C-D or A-B-F-D or A-E-F-D or A-E-F-B-C-D Redundant paths, paths fault tolerance tolerance, responsive to traffic load Invitation to Computer Science, 6th Edition 28 Invitation to Computer Science, 6th Edition 29  Basic Networking Concepts (continued) Internet structure Combination of LANs and WANs Connected by routers that direct message traffic Internet service provider (ISP) provides access to the Internet for p private individuals and organizations ISPs exist at multiple levels: local, regional, national, international (tier-1 ( network or Internet backbone) Invitation to Computer Science, 6th Edition 30 Invitation to Computer Science, 6th Edition 31 Invitation to Computer Science, 6th Edition 32 Invitation to Computer Science, 6th Edition 33  Basic Networking Concepts (continued) Internet growth has been astonishing: Updated with new graph up to 2020. Invitation to Computer Science, 6th Edition 34  Communication Protocols Protocol: a standard set of rules for communicating Standards evolve over time International agreements make Internet possible Internet Societyy makes standards and ppromotes research: www.isoc.org Protocol hierarchy/protocol stack, TCP/IP – layers of protocols – physical transmission to end application rules and standards Invitation to Computer Science, 6th Edition 36 Invitation to Computer Science, 6th Edition 37  Communication Protocols Physical Layer (continued) Physical layer protocols Rules for exchange of binary data across physical channel ((fiber-optic, p , twisted-pair, p , wireless,, etc.)) – How to know when a bit is present on the line – How much time the bit will remain on the line – Whether the bit is digital or analog in form – What physical quantities represent 0 and 1 – S Shape off the connector between computer and transmission line Create abstract “bit bit pipe” pipe for higher layers to use Invitation to Computer Science, 6th Edition 38 Invitation to Computer Science, 6th Edition 39  From now on, on all you need to know about the communication channel is that when you ask the physical layer to send a bit, it does so, and when you ask the physical layer to get a bit, it retrieves a 0 or a 1. Invitation to Computer Science, 6th Edition 40  Communication Protocols Data Link Layer (continued) Data Link protocols Ensure reliable transmission of bits Error detection and correction: notice failures in transmission and fix them Framing:g determine which bits belongg to one message Two parts: – Layer 2a: Medium Access Control – Layer 2b: Logical Link Control Invitation to Computer Science, 6th Edition 41  Communication Protocols Data Link Layer (continued) Medium Access Control protocols Rules for communicating on shared lines Ethernet: Contention-based Contention based protocol When node wants to send a message – Listen s e to o the e line eaand d wait a uuntil it is s free ee – Begin transmitting as soon as it is free – If collision results, wait a random amount of time – Repeat Advantage: distributed, no master bottleneck Invitation to Computer Science, 6th Edition 42  If your network uses point-to-point links rather than shared lines, we do not need the MAC protocols just described. The MAC protocols turn a shared channel into a point to point link. From now on we have a sender and a receiver, who want to exchange a single message, and these two nodes are directly connected by a channel. Invitation to Computer Science, 6th Edition 44  Communication Protocols Data Link Layer (continued) Logical Link Control protocols Rules for detecting and correcting errors ARQ algorithm (Automatic Repeat Request) Sender: Receiver: Transmit packet and wait for If no error error, return ACK or time out acknowledgement If receive ACK, go on to message (ACK) nextt packet k t Oth Otherwise, i return t nothing thi Otherwise, repeat on current packet Invitation to Computer Science, 6th Edition 45  Communication Protocols Data Link Layer (continued) Packet contains: – Markers for start and end of packet (SOP and EOP) – Sequence q number for p packet ((e.g., g , 2 of 5)) – Packet data – Error-checking bits Invitation to Computer Science, 6th Edition 46  Communication Protocols Data Link Layer (continued) Purpose of Data Link layer Create virtual error-free message pipe – Messages go in one end – Come out the other correct and in the right order Invitation to Computer Science, 6th Edition 47  The data link layer protocols create an error-free “message pipe,” in which messages go in one end and always come out the other end and in the proper sequence. Invitation to Computer Science, 6th Edition 48  Communication Protocols Network Layer (continued) Network layer protocols Transmit message across multiple nodes in a network “Good faith” transmission Requirements: q – Standard for addressing all network nodes – Routing method for finding route from any node to any other node Internet network layer: IP (Internet Protocol) Invitation to Computer Science, 6th Edition 49  Communication Protocols Network Layer (continued) Addressing Host name: human-friendly name for node IP address: unique numerical address used by computer, 141.140.1.5 Domain Name Service ((DNS): ) mapp host names to IP addresses – Symbolic host name goes to local DNS server – If it has no record, goes to remote servers until one has the host name and retrieves the IP address Invitation to Computer Science, 6th Edition 50  Communication Protocols Network Layer (continued) Routing Picking a path through network from source to destination Seek shortest/best path: fastest travel Massive network requires q efficient p path-seeking g Networks are dynamic: nodes come online and go offline all the time. Routing must adapt quickly Invitation to Computer Science, 6th Edition 51  From now on, on we no longer have just a bit pipe or a message pipe, but a true “network delivery service” in which message are delivered between any two nodes in the network, regardless of their location. Invitation to Computer Science, 6th Edition 52  Communication Protocols Transport Layer (continued) Transport layer protocols Application-to-application, reliable packet delivery Port number: unique identifier for program Invitation to Computer Science, 6th Edition 53  Communication Protocols Transport Layer (continued) Application types have standard port numbers – Web server: port 80 – Domain Name Service: pport 42 – SMTP, sending e-mail: port 25 TCP (Transport Control Protocol) – Ensures no errors – Establishes ordered delivery of packets – Another version of ARQ algorithm – Virtual direct, quality connection between programs Invitation to Computer Science, 6th Edition 54 Invitation to Computer Science, 6th Edition 55  We now have a complete end-to-end delivery service to transmit a message from a program anywhere in the network to another program anywhere in the network. The only thing left to specify is the “content” of those messages. th Invitation to Computer Science, 6th Edition 56  Communication Protocols Application Layer (continued) Application layer protocols Handle formatted data transmitted between application pp p programs g Invitation to Computer Science, 6th Edition 57  Communication Protocols Application Layer (continued) Hypertext Transfer Protocol (HTTP) Web page/service identified by unique URL ((Uniform Resource Locator)) – protocol://host name/page – Multiple protocols: http, mailto, news, ftp Web browser uses TCP to send formatted messages to Web server, and vice versa – TCP uses networkk layer l (IP), (IP) data d link li k llayer, and d physical layer Invitation to Computer Science, 6th Edition 58  Communication Protocols Application Layer (continued) Process: http://hostname/page Browser reads protocol, extracts host name (and requests q IP address from DNS server)) Sends a connect message to port 80 on that machine After connection established, sends “Get” message with page information Server S responds with message containing page contents, size, and indicates connection closes at end of message Invitation to Computer Science, 6th Edition 59  Network Services and Benefits Interpersonal Communications Electronic mail (e-mail) – Send message to be read at recipient’s recipient s convenience – Fast, multimedia, broadcast medium Bulletin board system y ((BBS)) – Public forum for shared communications – Evolved into Internet forums, chat rooms Instant messaging and texting Social networking – Online social groups designed for rich interaction Invitation to Computer Science, 6th Edition 61  Network Services and Benefits (continued) Resource sharing Print server serves all computers on a LAN File server provides storage to all users Client/server computing – Some So e nodes odes provide p o de se services, ces, o other e nodes odes use those services Distributed databases and data warehouses – Massive data stored in various sites online Groupware or wiki – Support collaborative knowledge/data construction Invitation to Computer Science, 6th Edition 62 Invitation to Computer Science, 6th Edition 63  Network Services and Benefits (continued) Electronic commerce (e-commerce) Early applications – Automatic paycheck deposit – ATMs – Checkout scanners and inventory systems Current applications – Online stores for everything – Electronic bill payment – Online payment systems (Paypal) F t ? Future? Invitation to Computer Science, 6th Edition 64  A Brief History of the Internet and the World Wide Web “A A Brief History of the Internet Internet”, 1997, 1997 by some of the founders Early y years y – Licklider’s “Galactic Network”, 1962 – ARPA-funded ARPANET, 1966 – E-mail, 1972 – Many networks (e.g., HEPNet, DECNet) 1970s/80s Internetworking: standards for communication Gateway: device for translating between networks Invitation to Computer Science, 6th Edition 65 Invitation to Computer Science, 6th Edition 66  A Brief History of the Internet and the World Wide Web (continued) Middle years – TCP/IP established standard – Telnet,, FTP (File ( Transfer Protocol)) – NSFNet, broadens access (1984) ARPANET only open to ARPA grant recipients NSFNet open to universities, government agencies, libraries, museum, schools – Networks begin to connect connect, late 1980s ARPANET ceases to be as separate network NSFNet turns over to private p providers, p 1995 Invitation to Computer Science, 6th Edition 67  A Brief History of the Internet and the World Wide Web (continued) World Wide Web High-energy physicist at CERN: Tim Berners-Lee Wanted user user-friendly friendly information and data exchange Hypertext: yp documents containing g links to other documents Web protocols made public; rapid expansion Invitation to Computer Science, 6th Edition 69 Invitation to Computer Science, 6th Edition 70  Summary Computing devices can communicate through various wired and wireless media Computer p networks vary y in size and form,, including g LANs, WANs, WLANs, and WWANs LANs are configured differently from WANs, and use different communication methods The Internet is a WAN of WANs Protocols are necessary to standardize communications across different media and among different computers Invitation to Computer Science, 6th Edition 71  Summary (continued) The protocol hierarchy breaks down network communications into different layers of abstraction – physical, p y data link, network, transport, p and application Protocols like the ARQ algorithm and TCP/IP provide id rules l ffor th the ttransfer f off information i f ti The Internet has permitted new kinds of connections among people: e-maile-mail, e-commerce e-commerce, resource sharing The Internet and Web grewg from ARPAnet and NSFNet as new network applications developed Invitation to Computer Science, 6th Edition 72