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CE80N Introduction to Networks & The Internet Dr. Chane L. Fullmer UCSC Winter 2002.

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Presentation on theme: "CE80N Introduction to Networks & The Internet Dr. Chane L. Fullmer UCSC Winter 2002."— Presentation transcript:

1 CE80N Introduction to Networks & The Internet Dr. Chane L. Fullmer UCSC Winter 2002

2 March 12, 2002CE80N -- Winter'2 -- Final Review2 Class Information Web page tutorial available on-line Web page submission: – to Subject: cmpe080n-assgn4 –Must be ed on or before March 15 No extensions can be granted – don’t be late Final Exam –Last class session March 14, 2002 –Similar to midterm – open notes/open book

3 March 12, 2002CE80N -- Winter'2 -- Final Review3 Review Telephone analogy for development of the Internet Telephone History –1876: Alexander Graham Bell obtains patent for the telephone –1877: The first commercial telephone service, Bell Telephone, is in operation –1881: The first long-distance line for public use opens between Boston and Providence –1915: Formal opening of line between New York and San Francisco –1927: Commercial telephone service by radio between New York and London opens for the first time –1947: Onset of use of microwave radio, later to become dominant carrier for long-distance telephony in U.S.

4 March 12, 2002CE80N -- Winter'2 -- Final Review4 Review The Telephone Network –Provides Universal Service Any individual user may call up any other user. –Ubiquitous –Interconnects billions of phones world-wide –Designed specifically for voice: two-way conversations small end-to-end delays dedicated circuit is set up between two endpoints

5 March 12, 2002CE80N -- Winter'2 -- Final Review5 Review Its an Analog World –Analog devices –An analog device maintains an exact physical analog of information. Phonograph – Physical image (grooves) Tape recorder/player – Magnetic image Early telephone handset – mic./speaker –Not Perfect – Prone to distortion –Hiss, cracks, pops

6 March 12, 2002CE80N -- Winter'2 -- Final Review6 Review Digital and Analog –Digital signals can be any one of a finite number of discrete values –Analog signals can be any one of an infinite number of values –Digital generally has better performance Regenerative repeaters –Analog - distortion and noise cumulative –Digital - true regeneration –Analog simpler (lower cost)

7 March 12, 2002CE80N -- Winter'2 -- Final Review7 Review Sampling and Quantization –Sampling: Recording of voltage levels at prescribed time intervals. Nyquist’s Theorem: If an analog signal is sampled at 2x(highest frequency), we can adequately reproduce the signal. –Quantization: Round up the voltage level to the nearest of 256 predetermined levels –Quantization error (difference between actual level and level the voltage was rounded to) AKA lossiness –Every sound over the telephone is one of 256 unique pitches and volumes.

8 March 12, 2002CE80N -- Winter'2 -- Final Review8 Review The Digital Network –The Telephone System began as analog, but has now transformed over time to a digital network. –The Internet is digital – so are the computers that you use…. Uses a binary encoding system –Two symbols – 0 or 1

9 March 12, 2002CE80N -- Winter'2 -- Final Review9 Review Circuit Switching –Network consists of switches –Each user is connected to a switch –To connect two users, a circuit must be established through the network –Provides guaranteed bandwidth –Disadvantages Setup/Teardown time Wastes bandwidth during idle periods

10 March 12, 2002CE80N -- Winter'2 -- Final Review10 Review Basic Communication –Signals An electrical signal reflects from the end of a metal wire the same way that light reflects from a mirror. –Modulation Modulation means imposing information on an electrical signal (called the carrier) –Amplitude/Frequency/Phase modulation

11 March 12, 2002CE80N -- Winter'2 -- Final Review11 Review Modems … –Allows two-way communication Designed to either use two different signals or Agree to take turns sending data –In either case, data appears to flow simultaneously in both directions. Encoding the data –Voice, music (sounds) are quantized to numeric values represented as bits.. –Text is represented by ASCII..

12 March 12, 2002CE80N -- Winter'2 -- Final Review12 Review Transmission errors can (and do) occur –Bits can get reversed: 0  1, 1  0… –Error detection Parity bits -- odd, even –Bits in a message are summed –Parity bit is set to complete sum for either odd or even total (0 is even, 1 is odd) –Parity bits alone are not sufficient Checksum –Bytes are summed to total –Total is included with message and the sums “checked” Corrupted messages are dropped

13 March 12, 2002CE80N -- Winter'2 -- Final Review13 Review The Local Are Network (LAN) –Early data transfers were accomplished by physically “moving the data” around Magnetic tapes, disk packs –“Never underestimate the bandwidth of a station wagon loaded full of mag tapes headed for LA” --- anonymous Interconnecting the computers –Circuit boards Specific to hardware platform Specific to physical medium and protocol

14 March 12, 2002CE80N -- Winter'2 -- Final Review14 Review LANs A computer communication technology is classified as a Local Area Network (LAN) if it provides a way to interconnect multiple computers across short distances. –Modern day LANs are inexpensive, reliable and convenient to install and manage

15 March 12, 2002CE80N -- Winter'2 -- Final Review15 Review LANs have changed the economies of computing –LANs allow the sharing of resources Use of inexpensive computers to access expensive resources Printers, disks… –Remote printing is common LANs came along just in time.. –Internet design assumed many LANs would be interconnected via the Internet…

16 March 12, 2002CE80N -- Winter'2 -- Final Review16 Review Various LAN technologies are basically incompatible –Ethernet != AppleTalk != Fiber Optic –Protocols, encoding, electrically Wide Area Networks (WAN) –First WANs used dialup technology to form a set of long-haul transmission lines –Uses a dedicated machine (gateway) at each local site to unify the transmission lines into a coordinated system

17 March 12, 2002CE80N -- Winter'2 -- Final Review17 Review  A WAN differs from a disjoint set of transmission lines because of the inclusion of a special computer (Gateway) at each site that connects to the transmission lines and keeps communication independent of the computers that use the WAN

18 March 12, 2002CE80N -- Winter'2 -- Final Review18 Review The Early Years –Many WANs and LANs were installed, but machines on the WANs could not access information on the LANs.. Remote access was separated from local access –A single cohesive network was desirable. –The DoD funded network research in the early ’70s through (D)ARPA creating various network technologies, including a research WAN called ARPANET.

19 March 12, 2002CE80N -- Winter'2 -- Final Review19 Review The Early Years –ARPANET allowed researchers the opportunity to build a working test-bed for networking ideas. Solved incompatibility issues Solved interoperability issues Created an internetwork of LANs and the WANs –The Internet is born

20 March 12, 2002CE80N -- Winter'2 -- Final Review20 Review Internet Software –Internet Protocol (IP) Provides basic communication –Transmission Control Protocol (TCP) Provides services for applications to communicate –The “TCP/IP Internet Protocol Suite” aka TCP/IP

21 March 12, 2002CE80N -- Winter'2 -- Final Review21 Review ARAPA placed the research and software into the public domain. Internet documentation freely available –On-line and accessible from the Internet ARPA negotiated with UCB to add the TCP/IP suite to the BSD UNIX release. –Gave large number of universities access to study networking, and deploy it in their departments the ARPANET began running TCP/IP exclusively.

22 March 12, 2002CE80N -- Winter'2 -- Final Review22 Review The Growth of the Internet –Incredible growth from day one.. In 1982 ~200 machines were connected By 1983 the number had doubled –The IAB (Internet Activities Board) Original controlling body to coordinate TCP/IP research and Internet development. –The IETF (Internet Engineering Task Force) Now is responsible for most of the Internet technical development –Working groups meet and create the RFCs Manet, ipsec, tcp…

23 March 12, 2002CE80N -- Winter'2 -- Final Review23 Review Growth of the Internet –The NSFNET Backbone 1988 WAN established as main backbone of the Internet –The ANS Backbone (Advanced Networks and Services) Consortium of MCI, IBM & MERIT –Allowed the US Government to begin privatization of the Internet

24 March 12, 2002CE80N -- Winter'2 -- Final Review24 Review Exponential growth ……. –By 1999, the Internet was growing so fast that, on average, a computer was added to the Internet every second – and the rate continues to increase. The Hard limit – Address space –The IPv4 protocol is limited to a number contained in 4 bytes (32 bits)… This limits the number of possibilities to 2 32 = 4,294,967,296 There are solutions – IPv6, NAT

25 March 12, 2002CE80N -- Winter'2 -- Final Review25 Review How does the network work? –Circuit switching Network resources reserved and dedicated from sender to receiver (circuit) Control signaling and data transfers are separated Control information processing at circuit setup and termination –Packet Switching Packetize data to transfer Multiplex it onto the wire

26 March 12, 2002CE80N -- Winter'2 -- Final Review26 Review: How Does the Network Work? Packet Switching Example C DDDD CC A D B C

27 March 12, 2002CE80N -- Winter'2 -- Final Review27 Review Packet Switching… –Avoids some delays Resource is shared by multiplexing packets Short messages do not have to wait for long ones to complete. –Overhead Packetizing does not come for free –Header with labeling information is added

28 March 12, 2002CE80N -- Winter'2 -- Final Review28 Review Packet Switching… –Labeling (Header information) Source (sender’s) address Destination (recipient’s) address Packet size Sequence number Error checking information –Packet sizes are variable There is a maximum packet size –Maximum transmission unit (MTU) No minimum size –But, header size is fixed -- ~40 bytes

29 March 12, 2002CE80N -- Winter'2 -- Final Review29 Review: Circuit vs Packet switched Circuit-Switched –guaranteed transmission –large setup delays –reliable connection –quality-of-service –idle time is wasted –bandwidth granularity problem Packet-Switched –small setup delays, header overhead –unreliable connection –efficient use of available bandwidth –congestion (queues) result in dropped packets

30 March 12, 2002CE80N -- Winter'2 -- Final Review30 Review Packet Switching and the Internet All data is transferred across the Internet in packets. A sender divides a message, or document, into packets and transfers the packets across the Internet. A receiver reassembles the original message from the packets that arrive. Packets from many machines traverse the Internet at the same time.

31 March 12, 2002CE80N -- Winter'2 -- Final Review31 Review Interconnecting Networks –A dedicated computer –Special software Restarts automatically on power up –Goal is to forward packets from one network to another – quickly, efficiently and correctly Process is called routing Computers are called routers

32 March 12, 2002CE80N -- Winter'2 -- Final Review32 Review Routers – Building blocks of the Internet The Internet is not a conventional network. It consists of thousands of computer networks interconnected by dedicated special purpose computers called routers –Routers can interconnect LANs and/or WANs

33 March 12, 2002CE80N -- Winter'2 -- Final Review33 Review Communication Protocols –A common language computers use to exchange messages. Specifying exact format and meaning of each message Sending and receiving –Complex protocol stacks use the layering model for simplification.

34 March 12, 2002CE80N -- Winter'2 -- Final Review34 Review -- The Layering Model Purpose is to divide and conquer complex software and hardware needed to implement services Partition services and functions needed in system into layers Each layer of service is provided by peer protocol entities Extensibility (new protocols and services easily added) Communication can be point-to-point or multipoint Layer-N Protocol Entity Layer-N Protocol Entity Layer-(N - 1) Protocol Entity Layer-(N - 1) Protocol Entity (virtual communication) Layer N packets interface NODE A NODE B protocol

35 March 12, 2002CE80N -- Winter'2 -- Final Review35 Internet protocol stack application: supporting network applications –ftp, smtp, http transport: host-host data transfer –tcp, udp network: routing of datagrams from source to destination –ip, routing protocols link: data transfer between neighboring network elements –ppp, ethernet physical: bits “on the wire” application transport network link physical

36 March 12, 2002CE80N -- Winter'2 -- Final Review36 Layering: physical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data

37 March 12, 2002CE80N -- Winter'2 -- Final Review37 Protocol layering and data Each layer takes data from above adds header information to create new data unit passes new data unit to layer below application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame

38 March 12, 2002CE80N -- Winter'2 -- Final Review38 Review Internet Protocol (IP) –Found at Network Layer –IP defines computer communication details. Specifying how packets are formed Specifying how routers forward each packet –IP Forwarding –Computers connecting to the Internet must follow the IP rules.

39 March 12, 2002CE80N -- Winter'2 -- Final Review39 Review Any computer can send IP datagrams to any other computer providing they both have IP software installed (Universal Service) The Internet operates like a virtual network. Each computer attached to the Internet must be assigned a unique address. –One computer must know the address of another before it can communicate

40 March 12, 2002CE80N -- Winter'2 -- Final Review40 Review IP Addresses –The unique number assigned to a computer is its Internet (IP) address. –Each computer (including routers) need to have an IP address. –IP addresses are not random. –Computers on the same network have the same prefix.

41 March 12, 2002CE80N -- Winter'2 -- Final Review41 IP Addresses 0 network host 10 network host 110 networkhost 1110 multicast address A/8 B/16 C/24 D class to to to to bits given notion of “network”, let’s re-examine IP addresses: “class-full” addressing:

42 March 12, 2002CE80N -- Winter'2 -- Final Review42 IP addressing: CIDR Classful addressing: –inefficient use of address space, address space exhaustion –e.g., class B net allocated enough addresses for 65K hosts, even if only 2K hosts in that network CIDR: Classless InterDomain Routing –network portion of address of arbitrary length –address format: a.b.c.d/x, where x is # bits in network portion of address network part host part /23

43 March 12, 2002CE80N -- Winter'2 -- Final Review43 Review IP Addresses – Assignment –hard-coded by system admin in a file –DHCP: Dynamic Host Configuration Protocol: dynamically get address: “plug-and-play” ISP Address assignment ICANN: Internet Corporation for Assigned Names and Numbers allocates addresses manages DNS assigns domain names, resolves disputes

44 March 12, 2002CE80N -- Winter'2 -- Final Review44 Review Routing in the Internet –A router must choose between two paths that both lead to the destination. Choosing the shortest path, or least cost –Algorithms Link State –Each node has global information Distance Vector –Each node only has information from direct neighbors

45 March 12, 2002CE80N -- Winter'2 -- Final Review45 Review: Transport services and protocols provide logical communication between processes running on different hosts transport protocols run in end systems transport vs network layer services: –network layer: data transfer between end systems –transport layer: data transfer between processes relies on, enhances, network layer services application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical logical end-end transport

46 March 12, 2002CE80N -- Winter'2 -- Final Review46 Review UDP: User Datagram Protocol –“no frills,” “bare bones” Internet transport protocol –“best effort” service, UDP segments may be: lost delivered out of order to app –connectionless: no handshaking between UDP sender, receiver each UDP segment handled independently of others Why is there a UDP? no connection establishment (which can add delay) simple: no connection state at sender, receiver small segment header no congestion control: UDP can blast away as fast as desired

47 March 12, 2002CE80N -- Winter'2 -- Final Review47 Review TCP: Transport Control Protocol –TCP software makes it possible for two computer programs to communicate across the Internet. Establishes a connection Exchanges data Terminates communication –Ignores duplicate copies –Recovers lost datagrams Uses timers Sends an acknowledgement back to the source

48 March 12, 2002CE80N -- Winter'2 -- Final Review48 Review TCP and IP work well together.. –TCP handles the problems that IP does not handle without duplicating the work that IP does. Designed at the same time to work as a unified system Engineered to: –Cooperate with each other –Compliment each other

49 March 12, 2002CE80N -- Winter'2 -- Final Review49 Review Client-Server Computing –Any program that offers a service is a server; any program that contacts a service is a client. –A server program must always be ready to receive requests

50 March 12, 2002CE80N -- Winter'2 -- Final Review50 Review Computer Names Must Be Unique –Each computer on the Internet must have a unique name. –The Internet uses a familiar idea. Extends name by adding strings Appends a suffix to the name Qualifies each name by giving the type of organization

51 March 12, 2002CE80N -- Winter'2 -- Final Review51 Review Translating A Name To An Equivalent IP Address –Internet communication software must use IP addresses to send and receive datagrams. Translates names to IP addresses automatically –Called the Domain Name System (DNS)

52 March 12, 2002CE80N -- Winter'2 -- Final Review52 Review Electronic Mail –The first “Killer App”… –Allowed users to communicate via computer – asynchronously systems follow the client server approach. –Cooperate to send an message From sender to recipient’s mailbox Sender’s computer is the client

53 March 12, 2002CE80N -- Winter'2 -- Final Review53 Review Impact And Significance Of Electronic Mail –After using it, benefits become apparent. Combines benefits of instantaneous communication with freedom from interruption Provides a way for (remote) groups to share common interests Can communicate with more people

54 March 12, 2002CE80N -- Winter'2 -- Final Review54 Review Electronic Bulletin Boards –An electronic bulletin board service combines the features of many communication mechanisms: Allows anyone to post –Conventional bulletin board Distributes to many subscribers –Newspaper Focuses on single topic –Club

55 March 12, 2002CE80N -- Winter'2 -- Final Review55 Review Network News –A newsgroup is a bulletin board in a netnews system. –An article is a message in a newsgroup. –USENET: A loose consortium of network news sites All sites participate in the exchange of network news.

56 March 12, 2002CE80N -- Winter'2 -- Final Review56 Review Browsing the World Wide Web –A browsing service can perform many tasks. Obtain textual information, recorded sounds or graphics Display the retrieved information automatically Store a copy of retrieved information on disk Print a copy of retrieved information on paper Follow a reference found in a document

57 March 12, 2002CE80N -- Winter'2 -- Final Review57 Review The WWW is a service that links together information stored on many computers. –Allows references in a document on one computer to refer to information stored on another computer. –The Web is the most popular service on the Internet

58 March 12, 2002CE80N -- Winter'2 -- Final Review58 Review The World Wide Web –The WWW uses client-server interaction. Uses HTTP (HyperText Transfer Protocol) –The client: Uses the Internet to contact a remote server –The server: Returns a copy of the requested page with additional information –The URL determines the location of the server. Computer name is part of the URL

59 March 12, 2002CE80N -- Winter'2 -- Final Review59 Review URL: Uniform Resource Locator

60 March 12, 2002CE80N -- Winter'2 -- Final Review60 Review URL parts –Prefix: type prefix is implied –Server Name: www. server name is often implied –Item: Index.html page name is implied for home pages –Not all parts are always necessary in the URL Example: entering “ucsc.edu” –Retrieves: “http://www.ucsc.edu/index.html”

61 March 12, 2002CE80N -- Winter'2 -- Final Review61 Review Web documents –A Web page is created to be used with any display hardware. –Each web page is written in HyperText Markup Language (HTML). Has its own grammar rules Uses punctuation symbols in unusual ways Does not show spaces on displayed page –uses free format input.

62 March 12, 2002CE80N -- Winter'2 -- Final Review62 Review HTML is the language of the Web. HTML is hidden to the average user. Browsers and servers handle the details and display the results HTML is significant in that: Sufficiently general to be widely used Useable by people without computer programming knowledge

63 March 12, 2002CE80N -- Winter'2 -- Final Review63 Review Web pages can be static or dynamic Frame technology allows for regions on a page to display independently Common Gateway Interface (CGI) allows for dynamic pages FORMS technology allows for interaction with web pages.

64 March 12, 2002CE80N -- Winter'2 -- Final Review64 Review Shopping carts allow for intermittent shopping on-line.. Cookies.. Information exchanged between your system and theirs… –Should you always allow cookies ? Active documents – a program to run locally from your browser.. –Java programming language –JavaScript

65 March 12, 2002CE80N -- Winter'2 -- Final Review65 Review Automated Web Search –An automated search service allows one to find information that resides on remote computers. –Search engines: gather information globally store it locally –Search services: Accessed through a Web site Require user interaction Use forms technology

66 March 12, 2002CE80N -- Winter'2 -- Final Review66 Review Automated Web Search –The search engine creates a Web page that has a link to each found topic. Uses CGI technology to create pages dynamically –The user enters a topic, the search engine finds Web pages that contain that topic string. –Automated search engines have become an essential part of finding information. Growing rapidly on the Internet A gigantic, freely accessible, global database at your disposal, 24/7…..

67 March 12, 2002CE80N -- Winter'2 -- Final Review67 Review Multimedia Networking –Live audio or video require high bandwidth. Requires a multimedia computer with: –microphone, speakers, camera… –high-speed processor –Problems Overall bandwidth – no QoS, Jitter, congestion loss rate…

68 March 12, 2002CE80N -- Winter'2 -- Final Review68 constant bit rate transmission Cumulative data time variable network delay (jitter) client reception constant bit rate playout at client client playout delay buffered data Review -- Delay Jitter Client-side buffering, playout delay compensate for network-added delay, delay jitter

69 March 12, 2002CE80N -- Winter'2 -- Final Review69 Review Internet Multimedia: bag of tricks –Audio/video compression lossy/lossless –use UDP to avoid TCP congestion control (delays) for time-sensitive traffic –client-side playout delay to compensate for network delay/jitter –server side matches stream bandwidth to available client-to-server path bandwidth chose among pre-encoded stream rates dynamic server encoding rate –error recovery (on top of UDP) FEC retransmissions, time permitting mask errors: repeat nearby data

70 March 12, 2002CE80N -- Winter'2 -- Final Review70 Review Internet Multimedia – Collaboration –Whiteboard service Allows all users to see changes on their own screens, as well as reflected on the screens of others –Audio/Video Teleconferencing –Teleconferencing becomes more interesting when combined with a whiteboard service. Provides the most flexibility

71 March 12, 2002CE80N -- Winter'2 -- Final Review71 Review Facsimile –The first facsimile transmission: 1843 by Alexander Bain’s “Recording Telegraph” –1984 – Standardized by the CCITT (The International Telegraph and Telephone Consultative Committee) Uses basic telephone (POTS) for interconnections –The Internet can be used to send a fax. FAX is converted to/from image and treated as a file

72 March 12, 2002CE80N -- Winter'2 -- Final Review72 Review Files –The network can transfer a file from one computer disk to another. Uses software developed early in ARPANET called file transfer Uses a protocol called File Transfer Protocol (FTP) Today, the application software itself is also called ftp. FTP uses the client-server approach. –Uses TCP/IP for data transfer Web browsers can use FTP

73 March 12, 2002CE80N -- Winter'2 -- Final Review73 Review Remote Login –TELNET is the Internet remote login application –Remote login resembles conventional login Login account and password required Client-server architecture TCP/IP used for transport of data

74 March 12, 2002CE80N -- Winter'2 -- Final Review74 Review Security in the Internet –Networks in general, and especially The Internet, are not absolutely secure –Messages can be “snooped” or even modified as they traverse the network –Public Key Encryption is the fundamental technology used to provide security in the Internet Public/private key pairs are used

75 March 12, 2002CE80N -- Winter'2 -- Final Review75 Review PK Encryption –Key Pairs are used One key is public and posted at large One key is private – never given out Called Public Key (PK) Encryption –One key is to encrypt messages. Use the public key to encrypt Public key cannot be used to decrypt the message –The other key is to decrypt messages Use the private key

76 March 12, 2002CE80N -- Winter'2 -- Final Review76 Review E-Commerce: all commercial transactions conducted over the Internet –The most common form of e-commerce transaction consists of a retail purchase from a catalog. –Consumers would not have confidence in the process without security of their data (credit card and personal info) Secure Socket Layer (SSL) Uses PK Encryption

77 March 12, 2002CE80N -- Winter'2 -- Final Review77 Review Digital Signatures are specially encrypted messages –Verifies sender of a document Digital Cash is an electronic equivalent of cash

78 March 12, 2002CE80N -- Winter'2 -- Final Review78 Review Firewall: filters out unauthorized packets coming into and leaving a network. –Similar to a router/bridge Sits at network ingress/egress Sniffs packets that come across it Rejects (filters out) packets for unauthorized TCP/UDP ports (ie. ftp, telnet, etc.)

79 March 12, 2002CE80N -- Winter'2 -- Final Review79 So…. What is the Internet? “The Internet is a wildly-successful, rapidly growing, global, digital library built on a remarkably flexible communication technology.”

80 Class Final Exam: March 14, :00PM


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