通信网络技术课件：chapter7 The Application Layer

1、Computer Networks1RoadmapIntroductionPhysical LayerData Link LayerTransport LayerNetwork LayerMedium Access SublayerApplication Layer2The Application LayerChapter 73In this chaper,you will learn the following: 7.1 DNS-THE DOMAIN NAME SYTEM 7.2 ELECTRONIC MAIL 7.3 THE WORLD WIDE WEB 7.4 MULTIMEDIA 47

2、.1 DNS The Domain Name SystemThe DNS Name SpaceResource RecordsName Servers5The DNS Name SpaceA portion of the Internet domain name space.6Resource RecordsThe principal DNS resource records types.7Resource Records (2)A portion of a possible DNS database for cs.vu.nl.8Name ServersPart of the DNS name

3、 space showing the division into zones.9Name Servers (2)How a resolver looks up a remote name in eight steps.107.2 Electronic MailArchitecture and ServicesThe User AgentMessage FormatsMessage TransferFinal Delivery11Electronic Mail (2)Some smileys. They will not be on the final exam :-).12Architectu

4、re and ServicesBasic functionsCompositionTransferReportingDisplayingDisposition13The User AgentEnvelopes and messages. (a) Paper mail. (b) Electronic mail.14Reading E-mailAn example display of the contents of a mailbox.15Message Formats RFC 822RFC 822 header fields related to message transport.16Mes

5、sage Formats RFC 822 (2)Some fields used in the RFC 822 message header.17MIME Multipurpose Internet Mail ExtensionsProblems with international languages:Languages with accents (French, German).Languages in non-Latin alphabets (Hebrew, Russian).Languages without alphabets (Chinese, Japanese).Messages

6、 not containing text at all (audio or images).18MIME (2)RFC 822 headers added by MIME.19MIME (3)The MIME types and subtypes defined in RFC 2045.20MIME (4)A multipart message containing enriched and audio alternatives.21Message TransferTransferring a message from elinore to carolyn.22Final Delivery(a

7、) Sending and reading mail when the receiver has a permanent Internet connection and the user agent runs on the same machine as the message transfer agent. (b) Reading e-mail when the receiver has a dial-up connection to an ISP.23POP3Using POP3 to fetch three messages.24IMAP(internet message access

8、protocol)A comparison of POP3 and IMAP.257.3 The World Wide WebArchitectural OverviewStatic Web DocumentsDynamic Web DocumentsHTTP The HyperText Transfer ProtocolPerformance EhnancementsThe Wireless Web26Architectural Overview(a) A Web page (b) The page reached by clicking on Department of Animal Ps

9、ychology.27Architectural Overview (2)The parts of the Web model.28The Client Side(a) A browser plug-in. (b) A helper application.the two ways to extend a browserP-I is a code module browser fetches from a special directory on the disk.H-A-this is a complete program running as a separate process29The

10、 Server sideThe steps the server performs:1.Accept a TCP connection from a client2.Get the name of the file requeseted 3.Get the file(from the disk)4.Return the file to the client5. Release the TCP Connection .The Web Server cannot server more requests per second.one obvious improvement is to mainta

11、in a cache in memory of the n most recently used files. next step for building a faster server is to make the server multithreaded.Seeing the next slide30The Server SideA multithreaded Web server with a front end and processing modules.The front end accepts a request,and build a record,passing it to

12、 one of the processing modules.31The Server Side (2)A server farm.32The Server Side (3)(a) Normal request-reply message sequence.(b) Sequence when TCP handoff is used.33URLs Uniform Resource LocatersSome common URLs.1.what is the page called?2.where is the page located?3.how can the page be accessed

13、?34Statelessness and CookiesSome examples of cookies.The Web is basically stateless,but some Web sites require clients to register to use them.This raises the question of how servers can distinquish between requests from registered users and everyone else.cookie is a small text file.35Static Web Doc

14、umentsHTML HyperText Markup Language(a) The HTML for a sample Web page. (b) The formatted page.(b)36HTML (2)A selection of common HTML tags. some can have additional parameters.37Tables(a) An HTML table. (b) A possible rendition of this table.38Forms (a) The HTML for an order form.(b) The formatted

15、page.(b)39Forms (2)A possible response from the browser to the server with information filled in by the user.40XML and XSLA simple Web page in XML.41XML and XSL (2)A style sheet in XSL.42Dynamic Web DocumentsSteps in processing the information from an HTML form.43Dynamic Web Documents (2)A sample HT

16、ML page with embedded PHP.44Dynamic Web Documents (3)(a) A Web page containing a form. (b) A PHP script for handling the output of the form. (c) Output from the PHP script when the inputs are Barbara and 24 respectively.45Client-Side Dynamic Web Page GenerationUse of JavaScript for processing a form

17、.46Client-Side Dynamic Web Page Generation (2)(a) Server-side scripting with PHP.(b) Client-side scripting with JavaScript.47Client-Side Dynamic Web Page Generation (3)A JavaScript program for computing and printing factorials.48Client-Side Dynamic Web Page Generation (4)An interactive Web page that

18、 responds to mouse movement.49Client-Side Dynamic Web Page Generation (5)The various ways to generate and display content.50HTTP MethodsThe built-in HTTP request methods.51HTTP Methods (2)The status code response groups.52HTTP Message HeadersSome HTTP message headers.53Example HTTP UsageThe start of

19、 the output of /rfc.html.54CachingHierarchical caching with three proxies.55Content Delivery Networks(a) Original Web page. (b) Same page after transformation.56The Wireless WebSteps in looking up a URL when a CDN is used.57WAP The Wireless Application ProtocolThe WAP protocol stack.58WAP (2)The WAP

20、 architecture.59I-ModeStructure of the i-mode data network showing the transport protocols.60I-Mode (2)Structure of the i-mode software.61I-Mode (3)Lewis Carroll meets a 16 x 16 screen.62I-Mode (4)An example of cHTML file.63Second-Generation Wireless WebA comparison of first-generation WAP and i-mod

21、e.64Second-Generation Wireless Web (2)New features of WAP 2.0.Push model as well as pull model.Support for integrating telephony into apps.Multimedia messaging.Inclusion of 264 pictograms.Interface to a storage device.Support for plug-ins in the browser.65Second-Generation Wireless Web (3)WAP 2.0 su

22、pports two protocol stacks.66Second-Generation Wireless Web (4)The XHTML Basic modules and tags.677.4 MultimediaIntroduction to AudioAudio CompressionStreaming AudioInternet RadioVoice over IPIntroduction to VideoVideo CompressionVideo on DemandThe MBone The Multicast Backbone68Introduction to Audio

23、(a) A sine wave. (b) Sampling the sine wave. (c) Quantizing the samples to 4 bits.69Audio Compression(a) The threshold of audibility as a function of frequency.(b) The masking effect.70Streaming AudioA straightforward way to implement clickable music on a Web page.71Streaming Audio (2)When packets c

24、arry alternate samples, the loss of a packet reduces the temporal resolution rather than creating a gap in time.72Streaming Audio (3)The media player buffers input from the media server and plays from the buffer rather than directly from the network.73Streaming Audio (4)RTSP commands from the player

25、 to the server.74Internet RadioA student radio station.75Voice over IPThe H323 architectural model for Internet telephony.76Voice over IP (2)The H323 protocol stack.77Voice over IP (3)Logical channels between the caller and callee during a call.78SIP The Session Initiation ProtocolThe SIP methods defined in the core specification.79SIP (2)Use a proxy and redirection servers with SIP.80Comparison of H.32