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Data Communication Basics

Data Communication Basics. Chapter 6. Knowledge Concepts. Applications used in networking The 7-part data circuit Duplex data transmission Transmission channel Synchronous transmission OSI layer responsibilities Error control. Internet Application Software.

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Data Communication Basics

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  1. Data Communication Basics Chapter 6

  2. Knowledge Concepts • Applications used in networking • The 7-part data circuit • Duplex data transmission • Transmission channel • Synchronous transmission • OSI layer responsibilities • Error control

  3. Internet Application Software There are 4 important Internet application software tools: • the Web • electronic mail (e-mail) • FTP • Telnet

  4. How the Web Works • Each client computer needs an applications layer software package called a Web browser • Each server on the network needs an application layer software package called a Web Server • In order to get a page (file) from the Web, the user must first type the Internet Uniform Resource Locator (URL)

  5. How the Web Works

  6. How the Web Works • In order for the request from the Web browser to be understood by the Web server, they must use the same standard protocol • The standard protocol for communication between a Web browser and a Web server is Hypertext Transfer Protocol (HTTP)

  7. How the Web Works An HTTP request from a Web browser to a Web server has three parts. Only the first part is required, the other two are optional • the request line • the request header • the request body

  8. How the Web Works Command URL HTTP version GET http://tcbworks.cba.uga.edu/~adennis/res.htm HTTP/1.1 Date: Mon 03 Aug 1998 17:35:46 GMT User-Agent: Mozilla/3.0 From: adennis@uga.cc.uga.edu Referer: http://tcbworks.cba.uga.edu/~adennis/home.htm ]- Request Line ]- Date ]- Web browser (this is Netscape) Request Header ]- User’s e-mail address URL that contained the link to the requested URL A Request from a Web browser to a Web server using the HTTP standard

  9. How the Web Works • Many people believe that the Web is anonymous • Every Web access must provide the Internet address of the requester’s computer; otherwise the server would not know where to send the requested page

  10. How the Web Works • The format of an HTTP response from the server to the browser is very similar to the browser request • Only the last part is required, the other 2 are optional • the response status • the response header • the response body

  11. A Response From a Web Server to a Web Browser Using the HTTP Standard HTTP version Status code Reason phrase HTTP/1.1 200 OK Date: Mon 03 Aug 1998 17:35:46 GMT Server: NCSA/1.3 Location: http:// tcbworks.cba.uga.edu/~adennis/res.htm Content-type: text/html <html> <head> <title>Business Data Communications and Networking Web Resources </title> </head> <body> <H2>Resources on the Web </H2> <P>This section contains links to other resources on the WEB that pertain to the field of data communications and networking </P> </body> </html> ]- Date ]- Web server Response Header ]- URL ]- Type of file Response Body

  12. E-mail Standards • Several standards have been developed to ensure compatibility between different e-mail software packages • 3 most commonly used standards are: • SMTP • X.400 • CMC • All three e-mail standards work in the same basic fashion

  13. E-mail Clients & Servers

  14. E-mail Standards • Each client computer in the LAN runs an application layer software package called a user agent, which formats the message into two parts: • The header (source & destination address) • The body (message)

  15. E-mail Standards • The user sends the message to a mail server that runs a special application layer software package called a message transfer agent, which reads the header and sends the message through the network to the receiver’s mail server, where it is stored in the receiver’s mailbox.

  16. E-mail Standards The Simple Mail Transfer Protocol (SMTP) is one of the most commonly used e-mail standards simply because it is the e-mail standard used on the Internet

  17. E-mail Standards TO: “Pat Someone” <someone@somewhere.com> From: “Alan Dennis;”<adennis@uga.cc.uga.edu> Date: Mon 03 Aug 1998 17:35:46 GMT Subject: Sample Note DATA: This is an example of an e-mail message Message Header ]- Message Body An example of an e-mail message using the SMTP standard

  18. E-mail Standards • The SMTP standards covers message transmission between message transfer agents • A different standard called Post Office Protocol (POP) defines how user agents operate and how messages to and from mail transfer agents are formatted • POP is gradually being replaced by a newer standard called Internet Mail Access Protocol (IMAP)

  19. E-mail Standards • Two other commonly used e-mail standards are X.400 and CMC, which are different from SMTP, POP and IMAP, so that they cannot be used interchangeably • The X.400 e-mail standards was developed in 1984 • The Common Messaging Calls (CMC) standard is a simpler version of the X.400 standard, developed in 1994

  20. E-mail Directories • Before you can send an e-mail message, you must know the receiver’s e-mail address • There are no universal e-mail directories

  21. File Transfer Protocol (FTP) • File Transfer Protocol (FTP) enables you to send and receive files over the Internet • There are 2 types of FTP sites: • Closed (requires users to have permission before they can connect and gain access to files) • Anonymous (permits any Internet user to login using the account name of Anonymous) • Many files and documents available via FTP have been compressed to reduce the amount of disk space they require

  22. Telnet • Telnet enables users on one computer to login into other computers on the Internet • Telnet can be useful because it enables you to access your server or host computer without sitting at its keyboard

  23. GROUPWARE

  24. Groupware Software that helps groups of people to work together more productively Group support system

  25. Groupware • Groupware allows people to exchange ideas, debate issues, make decisions, and write reports without actually having to meet face-to-face • There are 5 popular types of groupware: • Discussion groups • Document-based groupware • Group support systems • Videoconferencing • IM

  26. Discussion Groups • Discussion groups are Internet users who have joined together to discuss some topic • Two discussion groups commonly used for business: • Usenet Newsgroups • Listservs

  27. Usenet Newsgroups • Usenet Newsgroups are the most formally organized of the discussion groups • The newsgroups are just a series of discussions about each topic

  28. Listservs • Listserver (Listserv) group is similar in concept to the usenet newsgroups but is generally less formal • One part, the listserv processor, processes commands such as requests to subscribe, unsubscribe, or to provide more information about the listserv • The second part is the listserv mailer-- Anymessage sent to the listserv mailer is re-sent to everyone on the mailing list

  29. Document-based Groupware • E-mail lacks a structured way to support an ongoing discussion • A document database (like Lotus Notes) designed to store and manage large collections of text and graphics was the first solution

  30. Document-based Groupware • One of Notes’ greatest strengths is its replication ability (the automatic sharing of information among servers when information changes) • More than 2 million people world-wide now use Lotus Notes (IBM product)

  31. Group Support Systems • Both e-mail and document-based groupware are designed to support individuals and groups working in different places and different times. • Group Support Systems (GSS) are software tools designed to improve group decision making.

  32. Group Support Systems • In a GSS meeting, group members can discuss idea verbally as they could in any meeting room; however, they can also use the computer to type ideas and information, which are then shared with all other group members via the network. • With large groups, however, typing ideas is faster than talking because only one person can speak at a time

  33. Group Support Systems • GSS enables users to make comments anonymously • These systems also provide tools to support voting and ranking of alternatives, so that more structured decision-making processes can be used

  34. Videoconferencing Videoconferencing provides real-time transmission of video and audio signals to enable people in two or more locations to have a meeting

  35. Desktop Videoconferencing • The fastest growing form of videoconferencing is desktop videoconferencing • Small cameras installed on top of each computer permit meetings to take place from individual offices • The key benefits of videoconferencing area the time and cost savings that can result

  36. Desktop Videoconferencing • The transmission of video requires a lot of network capacity • Like e-mail, most videoconferencing systems were originally developed by vendors using different formats so that many products were incompatible • Three commonly used standards for videoconferencing have the promise to reduce many incompatibilities once adopted: H.320, H.323, and MPEG-1 & -2

  37. ELECTRONIC COMMERCE

  38. Electronic Commerce • Almost all large and medium-sized companies use the Internet for electronic commerce - doing business on the Internet • Most people automatically focus on the retail aspects of electronic commerce; that is selling products to individuals

  39. Electronic Commerce There are four major ways in which the Web can be used to support electronic commerce: • Electronic store • Electronic marketing • Information/entertainment provider • Customer service Each requires a different configuration of hardware!

  40. Transmission Channels • Data network is a 7 part data circuit: • DTE Physical interface • Originating DTE • Physical interface • Originating DCE • Transmission channel • Receiving DCE • Physical interface • Receiving DTE

  41. Data Channel Physical Interface Physical Interface DTE DTE DCE Transmission Channel DCE • DTE-Transmits, receives, performs error control • DCE-Provides interface between DTE and channel • Physical Interface is wire connection

  42. Data Flow • One or Two Directional • Simplex - One-way Transmission (Radio, TV) • Half Duplex - Two-way Transmission • One-way at a Time • Control Signals Negotiate Sending and Receiving • 2 wire • Full Duplex - Bi-directional • Simultaneous Transmission • 4 wire

  43. Error Correction • Message Acknowledgment • The mechanism used to effect retransmission is the positive or negative acknowledgment, often referred to as ACK and NAK, respectively • Retry Limit • To cut down on continual retransmission of messages, a retry limit—typically between 3 and 100—can be set. A retry limit of five means that a message received in error will be retransmitted five times; if it is not successfully received by the fifth try, the receiving station either disables the link or disables the sending station itself

  44. Error Detection • Sequence Checks • Sequence check numbers can be assigned to each block of data so that the ultimate receiver can determine that all blocks have indeed arrived, and the blocks can be put back into proper sequence • Error Correction Codes • Some error-detection schemes allow the receiving station not only to detect errors but also to correct some of them. Such codes are called forward error-correcting codes, the most common of which are called Hamming codes

  45. Error Detection • Parity Check • A parity check (also known as vertical redundancy check [VRC]) involves adding a bit—known as the parity bit—to each character during transmission • Longitudinal Redundancy Check (LRC) • With LRC, an additional, redundant character called the block check character (BCC) is appended to a block of transmitted characters, typically at the end of the block • Cyclic Redundancy Check (CRC) • A CRC can detect bit errors better than either VRC or LRC or both. The transmitting station generates the CRC and transmits it with the data

  46. Error Checking

  47. Ports • Need port fast enough for line • 232 Serial port to 115.2 kbps: only V.34, V.90 or ISDN • USB (universal serial bus) • 12 Mbps • Available on all new PCs • Fast enough for DSLs, cable modems • Faster version coming (USB-2, ~480 Mbps)

  48. Ports • Firewire (IEEE 1394) • 400 Mbps and faster • Not available on most new PCs • Fast enough for DSLs, cable modems • Ethernet NIC (10 Mbps) • Network interface card used in PC networks • Printed circuit board • Must be installed inside PC systems unit • Fast enough for DSLs, cable modems

  49. PC 232 Serial Ports • Ports • Connectors at back of PC • Plus related internal electronics to send/receive • PC 232 Serial Port • Follows EIA/TIA 232 standards

  50. PC 232 Serial Ports: 9-Pin and 25-Pin Ports • 9 pins or 25 pins • Parallel ports have 25 holes Pins 9-pin Serial Port 25-pin Serial Port 25-pin Parallel Port Holes

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