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Internet and Intranet Fundamentals

Internet and Intranet Fundamentals. Class 5 Session B. Topics. NNTP Mid-Term Review. NNTP. NNTP = Network News Transfer Protocol Internet bulletin board system 1986 RFC 977 (Kantor & Lapsley) “News” means bulletins, information, data, messages from individuals

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Internet and Intranet Fundamentals

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  1. Internet and Intranet Fundamentals Class 5 Session B

  2. Topics • NNTP • Mid-Term Review

  3. NNTP • NNTP = Network News Transfer Protocol • Internet bulletin board system • 1986 • RFC 977 (Kantor & Lapsley) • “News” means bulletins, information, data, messages from individuals • not news agencies (although this is not precluded)

  4. NNTP • Facilitates rapid dissemination of software bug fixes, technical tips, product reviews, discussions, rumors • distribution • inquiry • retrieval • posting • USENET News System

  5. NNTP • Model: Centralized storage of postings or news articles • clients / server model • USENET News • TCP • Port 119

  6. NNTP • Info Organized into Newsgroups • hierarchical, like a file directory system • rec.sports.football.nfl • Master-Slave Relationship between News Servers • dependent news servers can request that only certain postings (e.g., since a certain time) are transmitted • equivalent of caching

  7. NNTPCommands • ARTICLE <message-id> or [nnn] Responses: 220 n <a> article retrieved - head and body follow (n = article number, <a> = message-id) 221 n <a> article retrieved - head follows 222 n <a> article retrieved - body follows 223 n <a> article retrieved - request text separately 412 no newsgroup has been selected 420 no current article has been selected 423 no such article number in this group 430 no such article found

  8. NNTPCommands • LIST • lists valid newsgroups • GROUP ggg • selects a valid newsgroup • response returns first and last article numbers • LAST • current article pointer set to previous article • NEXT

  9. NNTPCommands • NEWSGROUPS date time • list of newsgroups created since date and time • NEWNEWS newsgroups date time • returns list of articles posted to any one of the newsgroups specified since date and time • POST • post article in format specified by RFC 850

  10. NNTPUSENET News-Related Services • http://www.dejanews.com • http://www.intellinews.com

  11. Mid-Term Review • Covers Everything Up Through Class 5 • Selections from Previous Presentations

  12. Open Systems Interconnection Model • Seven Layers • Application (S/W) • Presentation (S/W) • Session (S/W) • Transport (S/W) • Network (S/W and H/W) • Data Link (F/W and H/W) • Physical (H/W)

  13. OSI Reference Model Application Application Presentation Presentation Session Session Transport Transport Network Network Network Data Link Data Link Data Link Physical Physical Physical

  14. OSI Application Layer • Application and User Interfaces • File Transfer • E-Mail • Database Access • Program to Program Communication • http, ftp, gopher, smtp, telnet

  15. OSI Transport Layer • Host-to-Host Layer • Error Free End-to-End Connections • virtual connections • doesn’t know about intervening routers • TCP in TCP/IP • Often Implemented in Operating System

  16. OSI Network Layer • Communications Subnet Layer • Network Routing • Packets • Congestion and Flow Control • Accounting • IP in TCP/IP • Typically Implemented as I/O Driver

  17. OSI Data Link Layer • Breaks Up Input Data from Network Layer and Transmits as Data Frames • Typically an Interface Card with Firmware • Ethernet card • Acknowledgement • Error Handling • Retransmission • Flow Control

  18. OSI Physical Layer • Transmits Raw Bits • Includes Communication Channel • copper wire • fiber • microwave • Signaling Levels • voltages, timing • Pin Configurations

  19. DefinitionsClient / Server • Client • makes request • initiates communication • may have a GUI and human • but not always • Server • fulfills request • passively waits for requests • usually multitasking machine

  20. DefinitionsClient / Server • Fat Clients • full-featured, large applications • use servers as data servers • not much computational power on the server side • Thin Clients • small applications • downloaded from the network • relies on computational power of server

  21. DefinitionsClient / Server • Fat Client Example • Web Browser • Eudora • Visio • Thin Client • Java Applets • JavaScript Applications inside of HTML Pages • Note dependence on Fat Client (i.e., the browser)

  22. DefinitionsTCP / IP Berkeley Sockets • Five Basic Attributes of a Socket Connection • Local Port (chosen by OS on client side) • Local IP Address • Remote Port • Remote IP Address • Protocol (“tcp”, “udp”, etc.) • Each Connection Has Own 5-tuple

  23. DefinitionsTCP / IP Berkeley Sockets • Server Listens on (Well-Known) Port • Clients Attempts Make a Connection • Server Accepts the Connection • Server Receives Request from Client • Server Interprets Request • performs some action • Sends Response to Client • Shuts Down the Connection

  24. Internet ProtoclsTCP/IP Overview • TCP / IP = Transmission Control Protocol / Internet Protocol • Early 1970s • ARPANET • Distributed with UC Berkeley UNIX in Early 1980s • Public Domain, Non-Proprietary, Open Source

  25. Internet ProtocolsLayers • Five Layer Model • Application • Transport (TCP / UDP) • contains some Session features • Network (IP) • actually there are three sublayers • internet (IP) • convergence • subnet • Data Link and Physical

  26. Internet ProtocolsLayers • Packet Switching • datagrams • Nodes • hosts • end-user machines • clients or servers • routers • connecting different networks • a router is also a host of sorts

  27. Internet ProtocolsLayers • Connection-Oriented • TCP • reliable two-way, byte stream protocol • Connectionless • UDP = User Datagram Protocol • also known as the “Unreliable Datagram Protocol”

  28. Internet ProtocolsTCP • Reliable, Bidirectional Byte Stream • like a UNIX pipe • End-to-End Reliability • Bandwidth Optimization (flow control) • Ports • source • destination

  29. Internet ProtocolsUDP • User Datagram Protocol • Ports (like TCP) • Length, Checksum, Data • no sequencing or acknowledgment structure • error handling left to applications protocol • DNS uses UDP

  30. Internet ProtocolsDNS • Domain Name System • Distributed • database scattered across thousands of nameservers • Top-Level Domains • root domain: . • net, edu, com, org, mil, and country codes (jp) • FQDN: Fully Qualified Domain Name

  31. TCP / IP • ICMP = Internet Control Message Protocol • routers generate most ICMP traffic • most common types • destination unreachable: can’t find routing table entry • routing redirect: better route exists • time expired: ttl = 0; traceroute uses this • echo request / echo reply: ping uses this

  32. TCP / IPRouting Architecture • Autonomous Systems (AS) • collection of routers under single administration • use same routing protocol • Interior Gateway Protocol (IGP) • keeps routers informed of interior routes • AS-to-AS connection uses a different protocol • Exterior Gateway Protocol • policy routing, transit traffic, local traffic (originating within)

  33. TCP / IPRouting Architecture • Routing Protocols • Reachability Protocols • whether path exists • EGPs and BGPs (Border Gateway Protocol) • Distance Vector Protocol • distance metric to remote network • RIP = Routing Information Protocol • broadcast exchange of routing information • uses UDP • OSPF = Open Shortest Path First

  34. Internet ArchitectureOverview • A Network of Networks • internetworking • The Big Picture • http://navigators.com/internet_architecture.html

  35. ISPs • Points of Presence (POPs) • Dial-Up and Dedicated Network Connections • variety of underlying technologies • PPP (Point-to-Point Protocol) • modems • ISDN (Integrated Services Digital Network) • Frame Relay, Dedicated T-1 • ADSL and Cable Modems

  36. Regional Networks • BARRNet: Northern Central California (CA) • CERFnet: Western US and International • CICnet: Midwest US (MN, WI, IA, IN, IL, MI, OH) • MIDnet: Mid-US (NE, OK, AR, MO, IA, KS, SD) • NEARNET: Northeastern US (ME, NH, VT, CT, RI, MA) • NYSERNet: Northeastern US (NY...) • SURAnet: Southeastern US (WV, VA, SC, NC, TN, KY, LA, MS, AL, GA, FL, Washington, D.C., MD, DE) • Westnet: Western US (AZ, CO, ID, NM, UT, WY)

  37. NAPs and MAEs • NAP = Network Access Point • originally NFS • MAE = Metropolitan Area Exchange • MCI Worldcom has a service mark on this • Tier-1 • MAE-East (D.C.) and MAE-West (San Jose) • Tier-2 • LA, Chicago, Dallas, Houston, New York • Giant LAN switch (FDDI)

  38. DNS • Function of DNS? • Function of central registry and what does it hold. • Why aren’t we drowning in DNS requests? • What is a “root domain”, a “fully qualified domain name”.

  39. TopicsRegulation • Documentation • RFCs and STD • Organizations • ISOC (IAB, IESG) • IETF • W3C • InterNic • IAB Standards Process

  40. DocumentationRFCs • RFC = Request for Comments • series of notes • ARPANET 1969 • anyone can write an RFC • two paths • as Internet Draft • through IETF • through RFC Editor • http://www.rfc-editor.org/

  41. Organizational Hierarchy ISOC IAB IESG IETF Working Group Working Group Working Group Areas

  42. OrganizationsIETF • IETF = Internet Engineering Task Force • technical worker bees • Applications Area • General Area • Internet Area • Operations and Management Area • Routing Area • Security Area • Transport Area • User Services Area

  43. IAB Standards Process • Informational • Experimental • Proposed Standard • Draft Standard • Internet Standard

  44. HTTPOverview • HyperText Transfer Protocol • Applications Layer Protocol • Generic Protocol • gateway to SMTP, NNTP, FTP, Gopher, WAIS • Uses TCP Port 80 (by default) • presumes reliable transport

  45. HTTPOverview • Language of the World Wide Web • Provides Open-Ended Set of Methods • indicating purpose of request • Builds on URI, URL, URN disciplines

  46. HTTPOverview • URI = Uniform Resource Identifier • identifies points of content • mechanism used to access resource • specific computer housing the resource • specific name of resource on computer • formatted strings which indicate characteristics of a resource

  47. HTTPOverview • URL = Uniform Resource Locator • a particular form of URI • Web page address • URN = Uniform Resource Name • institutional persistence • identifies agency responsible for a definition, for example, but not the location

  48. HTTP/1.0 • Shortcomings of HTTP/1.0 • weak on proxies, caching, persistent connections, and virtual hosts • proliferation of imposters: • incompletely implemented applications • stateless • new connection for each request/response exchange

  49. How HTTP WorksRequest/Response Protocol • Response from server contains … • status line • message protocol version • success or error code • MIME-like message • server info • entity meta-information • possible entity body content

  50. How HTTP WorksRequest/Response Protocol • More Sophisticated Interactions • proxies • forwarding agent • gateways • receiving agent • tunnels • relay point between two connections • firewalls • non-caching

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