Chapter 7. The Application Layer. DNS The Domain Name System. DNS Resource Records. The DNS Name Space Resource Records Name Servers

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1 DNS The Domain Name System Chapter 7 The Application Layer The DNS Name Space Resource Records Name Servers The DNS Name Space DNS Resource Records A portion of the Internet domain name space. (1) MX: the name of the host prepared to accept for the specified domain; e.g. mail.tu-berlin.de for jsli@tu-berlin.de; (2) Domain_name Time_to_live Class Type Value; (3) cs.mit.edu IN(Internet Info.) CNAME lcs.mit.edu (4) CNAME: a macro definition; PTR: a regular DNS type (lookups of the IP and return the name, reverse lookups)

2 Resource Records (2) Name Servers A portion of a possible DNS database for cs.vu.nl. Part of the DNS name space showing the division into zones. Name Servers (2) Electronic Mail A resolver on flits.cs.vu.nl wants to know the IP address of the host linda.cd.yale.edu; Architecture and Services The User Agent Message Formats Message Transfer Final Delivery

3 Architecture and Services The User Agent Basic functions Composition Transfer Reporting Displaying Disposition Envelopes and messages. (a) Paper mail. (b) Electronic mail. Reading Message Formats RFC 822 An example display of the contents of a mailbox; Flags: K read and kept in the mailbox; A answered; F forwarded; Return-Path: added by the final message transfer agent and was intended to tell how to get back to the sender; rarely used in this way, simply the sender s address;

4 Message Formats RFC 822 (2) MIME Multipurpose Internet Mail Extensions Some fields used in the RFC 822 message header. Problems with international languages: Languages with accents (French, German). Languages in non-latin alphabets (Hebrew, Russian). Languages without alphabets (Chinese, Japanese). Messages not containing text at all (audio or images). MIME (2) MIME (3) RFC 822 headers added by MIME. The MIME types and subtypes defined in RFC 2045.

5 MIME (4) Message Transfer C: Client; S: Server Transferring a message from elinore@abc.com to carolyn@xyz.com; A multipart message containing enriched and audio alternatives. Final Delivery POP3 (a) 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 when the receiver has a dial-up connection to an ISP. Using POP3 to fetch three messages.

6 IMAP The World Wide Web Architectural Overview Static Web Documents Dynamic Web Documents HTTP The HyperText Transfer Protocol Performance Ehnancements The Wireless Web A comparison of POP3 and IMAP. Architectural Overview Architectural Overview (2) (a) A Web page (b) The page reached by clicking on Department of Animal Psychology. The parts of the Web model.

7 The Client Side The Server Side (a) A browser plug-in.(e.g., self-extracting zip) (b) A helper application.(e.g., Adobe s Arcobat Reader or Microsoft Word; A multithreaded Web server with a front end and processing modules. The Server Side (2) The Server Side (3) A server farm. (a) Normal request-reply message sequence. () q py g q (b) Sequence when TCP handoff is used.

8 URLs Uniform Resource Locaters Statelessness and Cookies Some common URLs. Need login session. (1) clients have to register ( for paying money); (2) e-commerce; (3) customized Web portals; observing IP addresses, not work for NAT; cookies: when a client requests a Web page, pg, the server can supply ppy additional information (cookies, small, only at most 4KB). Cookies are treated as data; Path: which parts of the server s file tree may use the cookie; Secure: the browser may only return the cookie to a secure server; Before request, the browser sends all the cookies placed by that domain; HTML HyperText Markup Language g HTML (2) (b) (a) The HTML for a sample Web page. (b) The formatted page. A selection of common HTML tags A selection of common HTML tags. some can have additional parameters.

9 Forms Forms (2) (a) An HTML table. (b) A possible rendition of this table. (a) The HTML for an order form. (b) The formatted page. (b) Forms (3) XML and XSL A simple Web page in XML. A possible response from the browser to the server with information filled in by the user.

10 XML and XSL (2) Dynamic Web Documents A style sheet in XSL. Steps in processing the information from an HTML form. Dynamic Web Documents (2) Dynamic Web Documents (3) A sample HTML page with embedded PHP. (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.

11 Client-Side Dynamic Web Page Generation Client-Side Dynamic Web Page Generation (2) Use of JavaScript for processing a form. (a) Server-side scripting with PHP. (b) Client-side scripting with JavaScript. Client-Side Dynamic Web Page Generation (3) Client-Side Dynamic Web Page Generation (4) A JavaScript program for computing and printing factorials. An interactive Web page that responds to mouse movement.

12 Client-Side Dynamic Web Page Generation (5) HTTP Methods The various ways to generate and display content. The built-inin HTTP request methods. HTTP Methods (2) HTTP Message Headers The status code response groups. Some HTTP message headers.

13 Example HTTP Usage Caching The start of the output of Hierarchical caching with three proxies. Content Delivery Networks Content Delivery Network (a) Original Web page. (b) Same page after transformation. Steps in looking up a URL when a CDN is used.

14 WAP The Wireless Application Protocol WAP (2) The WAP protocol stack. The WAP architecture. I-Mode I-Mode (2) Structure of the i-mode data network showing the transport protocols; LTP: lightweight Transport Protocol; Structure of the i-mode software.

15 I-Mode (3) I-Mode (4) Lewis Carroll meets a 16 x 16 screen. An example of chtml file. Second-Generation Wireless Web Second-Generation Wireless Web (2) New features of fwap 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. A comparison of first-generation WAP and i-mode.

16 Second-Generation Wireless Web (3) Second-Generation Wireless Web (4) WAP 2.0 supports two protocol stacks. The XHTML Basic modules and tags. Multimedia Introduction to Audio Audio Compression Streaming Audio Internet Radio Voice over IP Introduction to Video Video Compression Video on Demand The MBone The Multicast t Backbone Introduction to Audio (a) Asinewave (b) Sampling the sine wave (a) A sine wave. (b) Sampling the sine wave. (c) Quantizing the samples to 4 bits.

17 Audio compression Streaming Audio Perceptual coding (psychoacoustics, MP3): frequency masking: jackhammer might mask flute (only jackhammer coded); temporal masking: after jackhammers stop, the ear must take a finite time to turn it up again; (a) The threshold of audibility as a function of frequency. :(no need to encode any frequency whose power falls below the threshold of audibility) (b) The masking effect. A straightforward way to implement clickable music on a Web page. Streaming Audio (2) Streaming Audio (3) When packets carry alternate samples, the loss of a packet reduces the temporal resolution rather than creating a gap in time. The media player buffers input from the media server and plays from the The media player buffers input from the media server and plays from the buffer rather than directly from the network.

18 Streaming Audio (4) Internet Radio RTSP commands from the player to the server. A student radio station. Voice over IP Voice over IP (2) The H323 architectural model for Internet telephony. The H323 protocol stack.

19 Voice over IP (3) SIP The Session Initiation Protocol Logical channels between the caller and callee during a call. The SIP methods defined in the core specification. SIP (2) Comparison of H.323 and SIP Use a proxy and redirection servers with SIP.

20 The JPEG Standard The JPEG Standard (2) The operation of JPEG in lossy sequential mode. ()24 (a) 24-bit RGB input data. (b) After block preparation.y=0.30r+0.59g+0.11b;i=0.60r- 0.28G-0.32B; Q=0.21R-0.52G+0.31B; (square blocks of four pixels are averaged in I and Q) The JPEG Standard (3) The JPEG Standard (4) (a) (a) One block of the Y matrix. (b) The DTC coefficients. (b) Comp tation of the q anti ed DTC coefficients Computation of the quantized DTC coefficients. Table1/Table2 ~ Table3

21 The JPEG Standard (5) The MPEG Standard The order in which the quantized values are transmitted.(run (run-length econding: (38 times) 38 0 s Synchronization of the audio and video streams in MPEG-1 1. The MPEG Standard (2) Video on Demand Three consecutive frames. Overview of a video-on-demandon demand system.

22 Video Servers Video Servers (2) A video server storage hierarchy. The hardware architecture of a typical video server. The MBone The Multicast Backbone MBone consists of multicast islands connected by tunnels.

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