Invitation to Computer Science 6th Edition Chapter 7 Computer Networks, the Internet, and the World Wide Web

Objectives In this chapter, you will learn about: Basic networking concepts Communication links Computer Networks Communication protocols Network services and benefits The Internet and the World Wide Web Invitation to Computer Science, 6th Edition

Introduction Networking Might foster growth of democracy and global understanding Can equalize access to information and eliminate the concept of “information haves” and “information have-nots” Twitter revolution Students Physicians medical records, test results specialists Invitation to Computer Science, 6th Edition 3

Basic Networking Concepts Computer network Set of independent computer systems connected by telecommunication links Individual computers on the network Referred to as nodes, hosts, or end systems Invitation to Computer Science, 6th Edition 4

Communication Links In early days of networking: Most common way to transmit data was via switched, dial-up telephone lines Transmission rate: 56,000 bps (56 Kbps) Voice-oriented dial-up telephone network Originally a totally analog medium Modem Modulates, or alters, a standard analog signal called a carrier so that it encodes binary information Invitation to Computer Science, 6th Edition

Figure 7.1 Two Forms of Information Representation Invitation to Computer Science, 6th Edition

Figure 7.2 Modulation of a Carrier to Encode Binary Information Invitation to Computer Science, 6th Edition

Communication Links (continued) Broadband Has rapidly been replacing modems and analog phone lines for data communications Transmission rate: Exceeding 256,000 bps (256 Kbps) kilobit (kbit) 210 megabit (Mbit) 220 gigabit (Gbit) 230 terabit (Tbit) 240 Home users Invitation to Computer Science, 6th Edition

Communication Links (continued) Options for broadband communications Home use Digital subscriber line (DSL), asymmetric, Cable modem Commercial and office environment Ethernet Fast Ethernet Gigabit Ethernet Home users Invitation to Computer Science, 6th Edition

Communication Links (continued) Digital subscriber line Provided by either your local telephone company or someone certified to act as their intermediary Asymmetric digital subscriber Does not have the same transmission speed in the download direction as in the upload direction Cable modem Makes use of links that deliver cable TV signals into your home Offered by cable TV providers Home users Invitation to Computer Science, 6th Edition

Communication Links (continued) Ethernet (commercial and office) Designed to operate at 10 Mbps using coaxial cable Fast Ethernet Transmits at 100 Mbps across coaxial cable, fiber-optic cable, or regular twisted-pair copper wire Gigabit networking Transmission lines that support speeds in excess of 1 billion bits per second (Gbps) Invitation to Computer Science, 6th Edition

Communication Links (continued) Ten-gigabit Ethernet standard Version of Ethernet with data rate of 10 billion bits per second Adopted by IEEE in 2003 Figure 7.3 Transmission Time of an Image at Different Transmission Speeds Invitation to Computer Science, 6th Edition

Communication Links (continued) Wireless data communication Uses radio, microwave, and infrared signals Enables “mobile computing” Types of wireless data communication Wireless local access network Wireless wide-area access network Invitation to Computer Science, 6th Edition

Communication Links (continued) Wireless local access network User transmits from his or her computer to a local wireless base station Wi-Fi (Wireless Fidelity) Used to connect a computer to the Internet when it is within range of a wireless base station Metropolitan Wireless Local Access Network Routers provide convenient, low cost wireless Internet access to all residents Invitation to Computer Science, 6th Edition

Communication Links (continued) Bluetooth Often used to support communication between wireless computer peripherals Wireless wide area access network Computer transmits messages to a remote base station provided by a telecommunications company 3G Offers voice services as well as data communication at rates of 0.5 to 2.4 Mbps Invitation to Computer Science, 6th Edition

Computer Networks Local area network (LAN) Connects hardware devices such as computers, printers, and storage devices that are all in close proximity The owner of the devices is also the owner of the means of communications Common wired LAN topologies Bus Ring Star Invitation to Computer Science, 6th Edition

Computer Networks Bus topology Ring topology Star topology All nodes are connected to a single shared communication line Ring topology Connects the network nodes in a circular fashion Star topology A single central node that is connected to all other sites Invitation to Computer Science, 6th Edition

Figure 7.4 Some Common LAN Topologies Invitation to Computer Science, 6th Edition

Invitation to Computer Science, 6th Edition

Computer Networks (continued) Ethernet Most widely used LAN technology Uses the bus topology Two ways to construct an Ethernet LAN Shared cable Switch: The most widely used technology Invitation to Computer Science, 6th Edition

Computer Networks (continued) Shared cable A wire is strung around and through a building Users tap into the cable at its nearest point using a transceiver Repeater Device that simply amplifies and forwards a signal Bridge (switch) “Smarter” device that has knowledge about the nodes located on each separate network It examines every message to see if it should be forwarded Invitation to Computer Science, 6th Edition

Figure 7.5 An Ethernet LAN Implemented Using Shared Cables Invitation to Computer Science, 6th Edition

Local Area Networks (continued) Switch Located in a room called a wiring closet Contains a number of ports, with a wire leading from each port to an Ethernet interface Invitation to Computer Science, 6th Edition

Figure 7.6 An Ethernet LAN Implemented Using a Switch Invitation to Computer Science, 6th Edition

Invitation to Computer Science, 6th Edition

Invitation to Computer Science, 6th Edition

Computer Networks Wide area network (WAN) Connects devices that are not in close proximity but rather are across town, across the country, or across the ocean Users must purchase telecommunications services from an external provider Dedicated point-to-point lines Most use a store-and-forward, packet-switched technology to deliver messages Invitation to Computer Science, 6th Edition

Computer Networks Packet Information block with a fixed maximum size that is transmitted through the network as a single unit Figure 7.7 Typical Structure of a Wide Area Network Invitation to Computer Science, 6th Edition

Overall Structure of the Internet All real-world networks, including the Internet, are a mix of LANs and WANs Example: A company or a college One or more LANs connecting its local computers Individual LANs interconnected into a wide-area company network Invitation to Computer Science, 6th Edition

Figure 7.8(a) Structure of a Typical Company Network Invitation to Computer Science, 6th Edition

Overall Structure of the Internet Individual networks are interconnected via a device called a router Internet Service Provider (ISP) A wide-area network Provides a pathway from a specific network to other networks, or from an individual’s computer to other networks ISPs are hierarchical Interconnect to each other in multiple layers to provide greater geographical coverage Invitation to Computer Science, 6th Edition

Figure 7.8(b) Structure of a Network Using an ISP Invitation to Computer Science, 6th Edition

Figure 7.8(c) Hierarchy of Internet Service Providers Invitation to Computer Science, 6th Edition

Overall Structure of the Internet (continued) International ISP Also called tier-1 network or an Internet backbone Provides global coverage Internet Huge interconnected “network of networks” that includes nodes, LANs, WANs, bridges, routers, and multiple levels of ISPs Early 2011 818 million nodes Hundreds of thousands of separate networks located in over 230 countries Invitation to Computer Science, 6th Edition

Communication Protocols Mutually agreed upon set of rules, conventions, and agreements for the efficient and orderly exchange of information Internet Society Nonprofit, nongovernmental, professional society composed of more than 100 worldwide organizations Internet protocol hierarchy Also called a protocol stack Has five layers 1. To have meaningful communications, we need a set of procedures that specifies how the exchanges will take place. Talk on the telephone. Telephone etiquette. conventional requirements 2. Millions of machines, exchange messages correctly and efficiently, one reason, they have all agreed to use the same protocols to govern that exchange. 3. Managed by the governments or international agency like the united Nations. Operated by the Internet society. (foundations, governmental agencies, educational institutions, companies) 4. Subcommittees establishes and enforces network protocol standards. 5. The protocols are set up as a multilayered hierarchy, with each layer addressing one aspect of the overall communications task. This hierarchy is also referred to as TCP/IP. Two important protocols Invitation to Computer Science, 6th Edition

Figure 7.10 The Five-Layer TCP/IP Internet Protocol Hierarchy Wifi , 3G, physical layer Invitation to Computer Science, 6th Edition

Why need layers? The layered concept of networking was developed to accommodate changes in technology. Each layer of a specific network model may be responsible for a different function of the network. Each layer will pass information up and down to the next subsequent layer as data is processed. Invitation to Computer Science, Java Version, Third Edition

Physical Layer Physical layer protocols Goal of the physical layer Govern the exchange of binary digits across a physical communication channel Goal of the physical layer To create a “bit pipe” between two computers How we know when a bit is present on the line How much time the bit will remain on the line Whether the bit is in the form of a digital or an analog signal What physical quantities are used to represent a binary 0 and a binary 1 The shape of the connector between the computer and the transmission line Invitation to Computer Science, 6th Edition

Figure 7.11 The Concept of a Bit Pipe Moderm, dsl , mobile phone with wireless data capabitlites. No concerned about the voltage levels, wavelengths or radio frequencies. Send a bit and receive a bit Invitation to Computer Science, 6th Edition

Data Link Layer Error detection and correction problem Framing problem How do we detect when errors occur, and how do we correct them? Framing problem Identifying the start and end of a message Data link protocols (layer 2a, layer 2b) Address and solve error handling and framing Medium access control protocols (layer 2a) Determine how to arbitrate ownership of a shared line when multiple nodes want to send messages at the same time The link is not an error-free channel, Due to interference or weather or any number of other factors. Not exact copy of the bits that went in Want to receive complete messages, not raw streams of bits, which bits in the incoming stream belong together. Invitation to Computer Science, 6th Edition

Figure 7.12 The Medium Access Control Protocols in Ethernet A collision occurs, stop sending, wait a random amount of time Exact same random waiting period One reason the ethernet protocal is so popular is that control is distributed. Centralized manner takes a good deal of time. Send requests to master, reply the decision. Fault tolerant Invitation to Computer Science, 6th Edition

Data Link Layer (continued) Collision Two or more messages transmitted at exactly the same time Common occurrence in contention-based networks like Ethernet Layer 2b logical link control protocols Ensure that message traveling across this channel from source to destination arrives correctly ARQ algorithm Basis for all data link control protocols in current use Arq automatic repeat request. Adds some additional information to form a packet, sequence number uniquely identifying each packet. Adds some error-checking bits, whether corrupted during transimission Finally, adds a start of packet (SOP) and end of packet (EOP) delimiter to determine exactly where the packet begins and ends. SOP and EOP will not be the same as the content of the message in the packet ACK acknowledgement message Disassemble Invitation to Computer Science, 6th Edition

Figure 7.13 A Message Packet Sent by the Data Link Protocols Invitation to Computer Science, 6th Edition

Invitation to Computer Science, 6th Edition

Network Layer Network layer protocols Deliver message from the site where it was created to its ultimate destination Responsibilities of the network layer Creating a universal addressing scheme for all network nodes Delivering messages between any two nodes in the network Great majority of nodes are not directly connected. It is often said that the network layer is the glue that holds the entire network together. Invitation to Computer Science, 6th Edition

Network Layer (continued) Provides a true network delivery service Messages are delivered between any two nodes in the network, regardless of where they are located IP (Internet Protocol) layer Network layer in the Internet Invitation to Computer Science, Java Version, Third Edition

Network Layer (continued) Nodes identify each other using a 32-bit IP address Domain Name System (DNS) Converts from a symbolic host name such as macalester.edu to its 32-bit IP address 141.140.1.5 Local name server Checks to see if it has data record containing a specific IP address The DNS is a massive database, distributed over literally thousands of machines. Symbolic name, forward to a computer called a local name server. Invitation to Computer Science, 6th Edition

Network Layer (continued) Routing Process of selecting one specific path Shortest path Path via which message can travel the fastest As the number of network nodes increases, the solution time for these “brute force” algorithm grows exponentially. For tiniest network. Invitation to Computer Science, 6th Edition

Invitation to Computer Science, 6th Edition

Invitation to Computer Science, 6th Edition

Invitation to Computer Science, 6th Edition

Transport Layer Provides a high-quality, error-free, order- preserving, end-to-end delivery service Transport layer protocols Assigns port numbers to programs Remembers which program goes with which port Well-known port numbers Used by all important applications on the Internet Invitation to Computer Science, 6th Edition

Transport Layer UDP (User Datagram Protocol) TCP (Transport Control Protocol) Primary transport protocol on the Internet Requires the source and destination programs to initially establish a connection Use port number UDP (User Datagram Protocol) Not a reliable protocol TCP uses the same ARQ algorithm described in our discussion of the data link level. Invitation to Computer Science, Java Version, Third Edition

Figure 7.14 Relationship between IP Addresses and Port Numbers With these four protocol layers in place, we now have a complete end to end delivery service. The only thing left to specify is the content of those messages, what does a program want to say to another program. What types of applications do we want to give to our network users and exactly how do we implement them. Figure 7.14 Relationship between IP Addresses and Port Numbers Invitation to Computer Science, 6th Edition

Application Layer Implements the end-user services provided by a network There are many application protocols The appearance of exciting new and critically important applications (often called killer apps) has fueled the rapid growth of networking and the Internet E-mail in the 1970s, chat room in 1980s, the web and e-commerce int 1990s And social networking in the twenty-first century. Invitation to Computer Science, Java Version, Third Edition

Application Layer Application layer protocols Rules for implementing end-user services provided by a network Uniform Resource Locator (URL) protocol://host address/page HTTP request message Sent on the TCP connection from the client to the server, specifying the name of a Web page HTTP response message Returned from the server to the client along the same TCP connection Use the HTTP protocol as a general model for how application layer services. A single web page is identified by a symbolic string called a uniform resource locator Invitation to Computer Science, 6th Edition

Figure 7.17 Behavior of the HTTP Application-Level Protocol Invitation to Computer Science, 6th Edition

Browse http://www.gsu.edu 1. Convert domain name to IP address by using DNS protocol 2. Establish TCP connection at 80 port 3. Send HTTP Get Meesage 4. Get HTTP Reponse Message Invitation to Computer Science, Java Version, Third Edition

Network Services and Benefits Electronic mail (e-mail) Single most popular application of networks for the last 30 years Bulletin boards Shared public file where anyone can post messages and everyone is free to read the postings of others Social networks Systems that create communities of users who share common interests Invitation to Computer Science, 6th Edition

Network Services and Benefits (continued) Resource sharing Ability to share physical and logical resources Client-server computing Some nodes provide services, while the remaining nodes are users of those services Information sharing A network is an excellent way to access scientific, medical, legal, and commercial data files Invitation to Computer Science, 6th Edition

Figure 7.18 The Client-Server Model of Computing Invitation to Computer Science, 6th Edition

Network Services and Benefits (continued) Information utility (data warehouse) Nodes contain massive amounts of information that can be electronically searched for specific facts Collaborative software (groupware) Facilitates the efforts of individuals connected by a network and working on a single shared project Electronic commerce (e-commerce) Use of computers and networking to support the paperless exchange of goods, information, and services Invitation to Computer Science, 6th Edition

A Brief History of the Internet and the World Wide Web ARPA Small research office of the Department of Defense charged with developing technology that could be of use to the U.S. military ARPANET Formally demonstrated to scientific community at an international conference in 1972 Internetworking Any WAN is free to do whatever it wants internally Invitation to Computer Science, 6th Edition

A Brief History of the Internet and the World Wide Web (continued) Robert Kahn and his colleagues needed to create: A standardized way for a node in one WAN to identify a node located in a different WAN A universally recognized message format for exchanging information across WAN boundaries Telnet Allows users to log on remotely to another computer and use it as though it were their own local machine Invitation to Computer Science, 6th Edition

Figure 7.19 A Network of Networks Invitation to Computer Science, 6th Edition

A Brief History of the Internet and the World Wide Web (continued) FTP (file transfer protocol) Provides a way to move files around the network quickly and easily NSFNet Used TCP/IP technology identical to the ARPANET Interconnected six NSF supercomputer centers with dozens of new regional networks set up by the NSF Internet service providers Offered Internet access once provided by ARPANET and NSFNet Invitation to Computer Science, 6th Edition

Figure 7.20 State of Networking in the Late 1980s Invitation to Computer Science, 6th Edition

The World Wide Web Tim Berners-Lee Hypertext Uniform Resource Locator Researcher at CERN First developed the idea for a hypertext-based information distribution system in 1989 Hypertext Collection of documents interconnected by pointers, called links Uniform Resource Locator Worldwide identification of a Web page located on a specific host computer on the Internet Invitation to Computer Science, 6th Edition

The World Wide Web (continued) Completed and made available to all researchers at CERN in May 1991 Mosaic Web browser developed in late 1993 and made available to the general public Invitation to Computer Science, 6th Edition

Figure 7.21 Hypertext Documents Invitation to Computer Science, 6th Edition

Summary Computer network Options for transmitting data on a network Set of independent computer systems connected by telecommunication links Options for transmitting data on a network Dial-up telephone lines, DSL, cable modem, Ethernet, Fast Ethernet Types of networks Local area network (LAN) and wide area network (WAN) Invitation to Computer Science, 6th Edition

Summary (continued) The Internet TCP/IP World Wide Web Huge interconnected "network of networks" TCP/IP Internet protocol hierarchy, composed of five layers: physical, data link, network, transport, and application World Wide Web An information system based on the concept of hypertext Invitation to Computer Science, 6th Edition

Test 4 Chapter 6, 7, 9; time: Apr 24, 3pm-4:15pm 15 questions: Assembly language programming Transmission rate Routing Communication protocol Java programming Software development life cycle Question types single answer choice, short answer, programming Invitation to Computer Science, 6th Edition