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Web applications. Architecture. Standards. HTTP

Web applications. Architecture. Standarts. HTTP

Volodymyr Yakubovskiy

on 25 September 2013

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Transcript of Web applications. Architecture. Standards. HTTP

Web applications. Architecture. Standards. HTTP
Thank you for your attention!
And one more question?...
TCP (1974)
Transmission control protocol
replacement of Network Control Protocol (NCP)

 'A Protocol for Packet Network Interconnection'
by Vint Cerf and Bob Kahn
 Reliable and ordered transmission of byte stream between two endpoints

 Migration of ARPANET to TCP/IP in 1982
Vint Cerf
Bob Kahn
Volodymyr Yakubovskyy
22 September 2013
World Wode Web
Web applications architecture
ARPANET Map (March 1977)
TCP/IP (1978)
4 abstraction layers
each layer offers functionality to the above layer
separation of concerns
 Application layer
 Transport layer
TCP, UDP, ...
 Internet layer
addressing hosts and packet routing
IP, ...
 Link layer
TCP/IP Layers
OSI Reference Model (1984)
Open Systems Interconnection Reference Model
released by ISO in 1984
dataflow between two computers over network
7 layer model
3 network layers (1-3)
4 host layers (4-7)
aims to simplify network interconnection
standardised interfaces
modular and interchangeable networking components
OSI Reference Model (1984)...
Application layer
enable access to network resources
HTTP, FTP, SMTP, Telnet, ...
 Presentation layer
translation, compression and encryption
 Session layer
establish, synchronise and terminate sessions between systems
 Transport layer
reliable endpoint-to-endpoint message delivery
TCP, UDP, ...
OSI Reference Model (1984)...

Network layer
move packets from a source to a destination
IP, ...
 Data link layer
divide stream of bits into frames (includes error correction)
PPP, ...
 Physical layer
transfer bits over a physical medium (e.g. electrical specifications)
repeaters, hubs, ...
World Wide Web (WWW)
Tim Berners-Lee
Robert Cailliau
Networked hypertext system (over ARPANET) to share information at CERN
first draft in March 1989
The Information Mine, Information Mesh, ...?
Components by end of 1990
HyperText Transfer Protocol (HTTP)
HyperText Markup Language (HTML)
HTTP server software
Web browser called WorldWideWeb
 First public "release" in August 1991
WordWideWeb Browser (1993)

Basic Client-Server Web Architecture
Effect of typing http://google.com in the broswer bar
use a Domain Name Service (DNS) to get the IP address for google.com (answer
create a TCP connection to
send an HTTP request message over the TCP connection
visualise the received HTTP response message in the browser

Web Server
Tasks of a web server
setup connection
receive and process
HTTP request
fetch resource
create and send
HTTP response
The most prominent web servers are the Apache HTTP Server and Microsoft's Internet Information Services (IIS)
 A lot of devices have an embedded web server
printers, WLAN routers, TVs, ...

Example HTTP Request Message

Example HTTP Response Message
HTTP Protocol
Request/response communication model
HTTP Request
HTTP Response
 Communication always has to be initiated by the client
 Stateless protocol
 HTTP can be used on top of various reliable protocols
TCP is by far the most commonly used one
runs on TCP port 80 by default
 Latest version: HTTP/1.1
 HTTPS scheme used for encrypted connections
Uniform Resource Identifier (URI)
A Uniform Resource Identifier (URI) uniquely identifies a resource
 There are two types of URIs
Uniform Resource Locator (URL)
contains information about the exact location of a resource
consists of a
, a
and the
path (resource name)
problem: the URL changes if resource is moved!
idea of Persistent Uniform Resource Locators (PURLs) [http://purl.oclc.org]
Uniform Resource Name (URN)
unique and location independent name for a resource
consists of a
scheme name,
namespace identifier
and a
namespace-specific string
(separated by colons)
HTTP Message Format
start line
header field(s)
blank line (CRLF)
message body (optional)
Request and response messages have the same format
HTTP Request Message
Request-specific start line
 Methods
GET : get a resource from the server
HEAD : get the header only (no body)
POST : send data (in the body) to the server
PUT : store request body on server
TRACE : get the "final" request (after it has potentially been modified by proxies)
OPTIONS : get a list of methods supported by the server
DELETE: delete a resource on the serve
Response-specific start line
HTTP Response Message
Status codes
100-199 : informational
200-299 : success (e.g. 200 for 'OK')
300-399 : redirection
400-499 : client error (e.g. 404 for 'Not Found')
500-599 : server error (e.g. 503 for 'Service Unavailable')
David Gourley et al., HTTP: The Definitive Guide, O'Reilly Media, September 2002
 R. Fielding et al., RFC2616 - Hypertext Transfer Protocol - HTTP/1.1
 N. Freed et al., RFC2045 - Multipurpose Internet Mail Extensions (MIME)
 HTML and JavaScript Tutorials October 7, 2011
W. Jason Gilmore, PHP
 Java Servlet Tutorial October 7, 2011
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