The Architecture of the World Wide Web Min Song IS NJIT

Internet Architecture  Today’s Internet  Thousands of networks  Connected by legal agreements and commercial contracts  Uses TCP/IP protocol  Internet service providers (ISPs)  Provide most individual users with access to the Internet  Dialup connections  Modems and conventional phone lines  xDSL and cable modems provide broadband access

Packet Switching  Most modern Wide Area Network (WAN) protocols, including TCP/IP, X.25, and Frame Relay  Packet switching is more efficient and robust for data that can withstand some delays in transmission, such as messages and Web pages.  Circuit-switching: Normal telephone service is based on a circuit-switching technology  a dedicated line is allocated for transmission between two parties.  data must be transmitted quickly and must arrive in the same order in which it's sent.  real-time data, such as live audio and video. real-timevideo

Use of Packets

Internet Protocols:TCP/IP  Communications protocol suite  Packet switched protocol  No end-to-end connection is required  Each message broken down into small pieces called packets  Packets possibly routed to destination over different paths  Transmission Control Protocol (TCP)  Breaks messages into packets  Numbers packets in order  Reorders packets at the destination  Internet Protocol (IP)  Routes packets to the proper destination

Domain Names  Every computer connected to the Internet must have a unique IP address  IP address format is xxx.xxx.xxx.xxx where xxx is a number between 0 and 255  How do we know that is Microsoft?  Domain Name Service(DNS)  A database of Internet names  DNS Servers convert Internet names to IP addresses  Top level domains  Ping: to test whether a particular host is reachable across an IP network.  Tcpdump: to sniff network packets and make some statistical analysis out of those dumps

The World Wide Web  Collection of hyperlinked computer files on the Internet  Client-server application  Web servers  Web browsers as clients  WWW standards  Hypertext markup language (HTML)  Current standard for writing Web pages  Implementation of SGML specifically for Web pagesSGML  Tags in HTML instruct the client browser how to format and display the Web page content  Hypertext transfer protocol (HTTP)  Protocol that establishes a connection between Web server and client  Extensible markup language (XML)  A meta-markup language  Gives meaning to the data enclosed within XML tags

Static versus Dynamic Web Pages  HTML and XML only display and exchange data  No interactivity; no processing of data  Scripting languages  Provides basic interactivity  Rollovers  Crawling text  JavaScript  VBScript  Full-featured Web programming  Java  Client side scripting or browser side scripting  Applets  J2EE  Common Gateway Interface (CGI)  Allows passing of data between a static HTML page and a computer program

Searching the WWW  Most data on the Internet is part of the WWW  Search engines – large databases that index WWW content  Building the search engine database  Submit a site to the search engine administrator for listing  Spiders  Metatags  Google Google  Yahoo Yahoo

Hypertext Transfer Protocol  A protocol (syntax and semantics) for transferring representations of resources  usually across the Internet using TCP  Design goals  speed(stateless, cachable, few round- trips)  simplicity  extensibility  data (payload) independence  A true network-based API

HTTP/0.9 (pre-1993)  Absolute Simplicity GET /url-path Hello World  No Extensibility  only one method (GET)  no request modifiers  no response metadata

HTTP/1.0 (1993-present)  Simple and (mostly) Extensible GET /Test/hello.html HTTP/1.0 Accept: text/html User-Agent: GET/5 libwww-perl/0.40 HTTP/ OK Date: Fri, 12 Jan :02:49 GMT Server: Apache/1.0.5 Content-type: text/html Content-length: 38 Last-modified: Wed, 10 Jan : Hello Hello out there!

HTTP/1.0 Deficiencies  No complete specification until end of `94  No minimum standard for compliance  Poor network behavior  one request per connection  no reliable transfer of dynamic content  no control over response caching  failed to anticipate proxies and gateways  created huge demand for vanity addresses  misuse/misunderstanding of MIME

HTTP/1.1  Culmination of two years work, RFC2068  with Henrik Frystyk, Jim Gettys, Jeff Mogul  designed at UCI and W3C; expanded in IETF  Improved Reliability  chunked transfer of dynamic content  recognition of proxy and gateway requirements  explicit cachability of responses  Improved Network Behavior  persistent connections  virtual hosts (many names, one address)

HTTP/1.1 (1997-????)  Less Simple, More Extensible, but Compatible GET /Test/hello.html HTTP/1.1 Host: kiwi.ics.uci.edu:8080 User-Agent: GET/7 libwww-perl/5.40 HTTP/ OK Date: Fri, 07 Jan :40:09 GMT Server: Apache/1.2b6 Content-type: text/html Transfer-Encoding: chunked Etag: “a797cd-465af” Cache-control: max-age=3600 Vary: Accept-Language …

HTTP/1.x Deficiencies  MIME is too verbose (overhead per message)  Control mixed with metadata  Metadata restricted to header or trailer  Fixed request/response ordering can block progress  Incurs frequent round-trip delays due to connection establishment.

HTTP/2.x  Tokenized transfer of common fields  reducing bandwidth usage, latency  removal of MIME syntax limitations  self-descriptive for extensions  Multiplexing control, data, metadata streams  reducing desire for multiple connections  enabling multi-protocol connections  per-stream priority or credit mechanism  Layered streams for meta-metadata, encryption...

XML to the rescue?  “X” for extensible:  self-descriptive syntax  semantics by reference (doctype, namespaces)  rendering by reference (style sheets)  An XML representation is an object turned inside-out, with behavior-by-reference  However, network application performance will demand standards for domain-specific doctypes and style sheets

Future Work  Dynamic application architectures  Architectural analysis and performance bounds  Impact of future network architectures (ATM)  Balancing secure transfer with firewall visibility  Protocol for manipulating resource mappings  HTTP-NG (W3C/Xerox PARC)  rHTTP (UCI)