1. Chapter 7 Computer Networks, the Internet, and the World Wide Web
Introduction to Networks
Chapter 7
Computer Networks, the Internet, and the World Wide Web

2. 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
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3. Communication Links In early days of networking:
Most common way to transmit data was via switched, dial-up telephone lines
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
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4. Figure 7.1 Two Forms of Information Representation
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5. Figure 7.2 Modulation of a Carrier to Encode Binary Information
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6. Communication Links (continued)
Broadband
Has rapidly been replacing modems and analog phone lines for data communications
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
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7. Communication Links (continued)
Cable modem
Makes use of links that deliver cable TV signals into your home
Offered by cable TV providers
Ethernet
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
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8. Communication Links (continued)
Gigabit networking
Transmission lines that support speeds in excess of 1 billion bits per second (Gbps)
Ten-gigabit Ethernet standard
Version of Ethernet with data rate of 10 billion bits per second
Adopted by IEEE in 2003
Wireless data communication
Uses radio, microwave, and infrared signals
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9. Figure 7.3 Transmission Time of an
Image at Different Transmission Speeds
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10. 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
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11. 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
Now 4G (up to 10 times faster than 3G)
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12. Local Area Networks Local area network (LAN) Bus topology
Connects hardware devices such as computers, printers, and storage devices that are all in close proximity
Bus topology
All nodes are connected to a single shared communication line
Ring topology
Connects the network nodes in a circular fashion
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13. Figure 7.4 Some Common LAN Topologies
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14. Local Area 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
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15. Figure 7.5 An Ethernet LAN Implemented Using Shared Cables
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16. 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
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17. Figure 7.6 An Ethernet LAN Implemented Using a Switch
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18. Wide Area Networks Wide area network (WAN) Most WANs Packet
Connects devices that are not in close proximity but rather are across town, across the country, or across the ocean
Most WANs
Use a store-and-forward, packet-switched technology to deliver messages
Packet
Information block with a fixed maximum size that is transmitted through the network as a single unit
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19. Figure 7.7 Typical Structure of a Wide Area Network
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20. Overall Structure of the Internet
Individual networks are interconnected via a device called a router
Internet Service Provider (ISP)
Business whose purpose is to provide access from a private network to the Internet
Hierarchical, interconnecting to each other in multiple layers, or tiers, that provide ever-expanding geographic coverage
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21. Figure 7.8(a) Structure of a Typical Company Network
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22. Figure 7.8(b) Structure of a Network Using an ISP
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23. Figure 7.8(c) Hierarchy of Internet Service Providers
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24. 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
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25. 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
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26. Figure 7.10 The Five-Layer TCP/IP Internet Protocol Hierarchy
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27. 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
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28. Figure 7.11 The Concept of a Bit Pipe
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29. 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
Address and solve error handling and framing
Medium access control protocols
Determine how to arbitrate ownership of a shared line when multiple nodes want to send messages at the same time
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30. Figure 7.12 The Medium Access Control Protocols in Ethernet
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31. 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
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32. 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
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33. Figure 7.13 A Message Packet Sent by the Data Link Protocols
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34. 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
Local name server
Checks to see if it has data record containing a specific IP address
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35. Network Layer (continued)
Routing
Process of selecting one specific path
Shortest path
Path via which message can travel the fastest
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36. Transport Layer Transport layer protocols Well-known port numbers
Assigns port numbers to programs
Remembers which program goes with which port
Well-known port numbers
Used by all important applications on the Internet
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37. Figure 7.14 Relationship between IP Addresses and Port Numbers
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38. 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
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39. Figure 7.16 Some Popular Application Protocols on the Internet
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40. Figure 7.17 Behavior of the HTTP Application-Level Protocol
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41. Network Services and Benefits
Electronic 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
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42. 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
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43. Figure 7.18 The Client-Server Model of Computing
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44. 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
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45. 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
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46. 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
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47. Figure 7.19 A Network of Networks
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48. 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
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49. Figure 7.20 State of Networking in the Late 1980s
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50. 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
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51. 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
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52. Figure 7.21 Hypertext Documents
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53. 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)
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54. 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
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