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Domain Name System

Domain Name System. A heirarchial, distributed database A service primarily aimed at mapping names to IP addresses Partitioned for ease of administration. gov. edu. com. utexas. tamu. ibm. austin. cs. mac1. solar. mac1. DNS Structure (partial). DNS -- How it Works.

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Domain Name System

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  1. Domain Name System • A heirarchial, distributed database • A service primarily aimed at mapping names to IP addresses • Partitioned for ease of administration

  2. . gov edu com utexas tamu ibm austin cs mac1 solar mac1 DNS Structure (partial)

  3. DNS -- How it Works • DNS Servers in a logical tree • DNS clients on every host • Iterative Queries • Recursive Queries

  4. ARP • Address Resolution Protocol {translate network layer address to physical address} • Part of general resolution procedure: name {e.g., neuron.cs.tamu.edu} DNS IP Address {e.g., 128.194.133.1} ARP Ethernet address {e.g., 08:00:20:08:58:78}

  5. Application Layer • File Transfer, Access and Management • virtual file store • file servers and requesting clients • Electronic Mail • process to process traffic expected to dominate Internet • actually email dominates the Internet • Virtual Terminals • representing the abstract state of the real terminal • Remote Job Execution • JTM: Job Transfer and Manipulation

  6. ISO Applications • FTAM ~ FTP File Transfer, Access & Manipulation • VTS ~ TELNET Virtual Terminal Service • JTM ~ ??? Job Transfer & Manipulation {maybe rsh, RPC?} • MHS ~ SMTP Message Handling System (X.400)

  7. “applications” SASE SASE CASE ISO Terminology [Specific|Common] Application Service Elements “think of them as programming libraries or APIs”

  8. ISO Service Elements(examples) • Association Control Service Element (primitives) • Commitment, Concurrency and Recovery • atomic actions • two phase commit

  9. File Servers • 1. File Structure • 2. File Attributes • e.g. identifier, size of storage, access control • 3. File Operations • create, delete move • OSI has defined virtual filestore operations

  10. Replicated Files • Why multiple file servers? • 1. To split the workload over multiple servers. • 2. To allow file access to occur even if one file server is down • 3. To increase reliability by having independent backups of each file • Updates • Voting

  11. Electronic Mail • Motis and X.400CCITT has aligned them for compatibilityMay replace SMTP • The user agentuser interface • Message transfer agentpost office

  12. Virtual Terminals • Scroll mode terminalsno local resources; dumb display and transmission • Page mode terminals25 x 80 character displayscreen editing via termcap • Form mode terminalslocal processing enabled • Bitmapped terminals like X stations

  13. Case Study: Internet • File Transfer • Electronic Mail • Virtual Terminals

  14. Getting Started • RARP • BOOTP • TFTP • DHCP

  15. File Transfer Protocol • FTP recognizes four file types: • 1. Image • bit by bit transfer • 2. ASCII • 3. EBCDIC • 4. Logical Byte files • binary files which use byte size other than 8 bits

  16. Electronic Mail • Pioneered by ARPANET • RFC 822 (widely used) • Simple Mail Transfer Protocol (SMTP) • Supports only ASCII text • name@domain addressing

  17. Virtual Terminals - TELNET • Designed for scroll mode terminals • Hit a key , 8-bit bytes are sent • 95 ASCII and 7 control characters legal

  18. USENET--HOW TO AVOID GRADUATION • Internet compatible (now) • Variety of newsgroups • Moderated newsgroups • NNTP, Network News Transfer Protocol, allows selective downloading of messagesto multiple sites

  19. The Web • “the” killer application for the Internet • Two components for popularity • http combines multiple access (gopher, ftp, etc) methods • hypertext interface supports point-and-click interface • Who will organize the information? • No one... • Database experts • Librarians (!)

  20. Web Terminology • Web Browsers • Netscape • Mosaic • Web Servers • http daemon • httd.conf - main server config file • srm.con - server resource config file • access.conf - global access control file • Home Page • Eg., www.cs.tamu.edu • HTML • HyperText Markup Language

  21. HTML Document <HTML> <HEAD> <TITLE>Willis Marti’s Homepage</TITLE> <LINK REV=“OWNER” HREF=“mailto:willis@cs.tamu.edu”> </HEAD> <BODY> <IMG SRC=“my-logo.gif” ALT=“logo”> <H1> Sample HTML Document</H1> <EM> To demonstrate HTML </EM> <HR> ....

  22. Web Future Directions • HTML Enhancements • Secure Transactions • Uniform Naming • Librarians & Brokers • Information “push” or “pull”

  23. Layer 7 Summary • Service Element Model • Not all Apps belong here... • Common Network Services

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