Transcript - University of Surrey

Introduction to
Web Technologies
Introduction to the Internet and TCP/IP
21th January 2005
Dr Bogdan L. Vrusias
[email protected]
Introduction to
Web Technologies
Open Systems
Systems whose architecture is not a secret (open source)
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Operating Systems (Unix, Linux)
Programming Languages (Java)
Web Servers
Protocols (TCP/IP, HTTP)
Databases
The Internet supports the idea of Open Systems
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Introduction to
Web Technologies
Network Concepts: Topology
• Bus network
– Simple
– Based on component id
• Ring network
– Central unit carries out the process of sending and forwarding
messages in the network.
• Hub network (most popular)
– Backplane cable
– Ports
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Introduction to
Web Technologies
Bus network
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Introduction to
Web Technologies
Ring network
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Introduction to
Web Technologies
Hub network
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Introduction to
Web Technologies
Network Concepts: Layered Models
• Network protocols are partitioned into layers corresponding to the type
and level of functionality that each layer carries out.
• Layers in the OSI (Open System Interconnection) model:
– Application: where applications reside
– Presentation: acts as a buffer between the application layer and the
remaining layers
– Session: synchronises the exchange of data between applications
– Transport: responsible for the transfer of data through a network
– Network: carries out the physical routing of data from one computer to
another
– Data Link: carries out the process of managing the transmission of lowlevel items of data such as bytes
– Physical: responsible for the low-level process of sending the electrical
signals
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Introduction to
Web Technologies
What the Web is
• Web is the network of computers that contain information
that one can view from a browser.
• The Internet is not a network of computers but, rather, it is
a network which consists of a number of other subnetworks
• The internet consists of computers that communicate
through an Internet Service Provider (ISP).
• The intranet is a private network that allows access only to
computers directly connected to it.
• An extranet extends the intranet by allowing specific
customers to access parts of the intranet.
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Introduction to
Web Technologies
What the Web is
• The World Wide Web (WWW) is the collection of
interlinked documents (also called Web pages) over the
Internet.
• The Web pages can be viewed through a Web browser
(such as Microsoft Internet Explorer, Netscape, Mozilla,
Opera, etc.)
• The Web pages are located on a Web server, from which a
Web browser downloads the page to the client and displays
it.
• The collection of Web pages is called a Web site.
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Introduction to
Web Technologies
History: The Internet
• 1960… beginning of the Net
• The Advanced Research Projects Agency (ARPA) of the
Department of Defence implemented the ARPAnet
(grandparent of today's Internet).
• Multiple users where able to send and receive information
over a common communication path simultaneously.
• Internet and Intranet evolved very fast and ARPA created
the TCP/IP as a combined set of protocols for
communication.
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Introduction to
Web Technologies
History: WWW
• The information carrying capacity (bandwidth) and the
popularity has increased tremendously over the years, and
lots of businesses rapidly realised the benefits of the
Internet.
• 1990… Tim Berners-Lee of CERN (the European
Laboratory of Particle Physics) developed the World Wide
Web (WWW).
• WWW allowed businesses and everyday users to browse
or even create multimedia-based documents over the Web.
• FUTURE: The GRID?
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Introduction to
Web Technologies
Network Concepts: Internet Structure
• Popular Internet protocols:
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Telnet
FTP (File Transfer Protocol)
SMTP (Simple Mail Transfer Protocol)
Kerberos
DNS (Domain Name System)
TCP (Transmission Control Protocol)
UDP (User Datagram Protocol)
IP (Internet Protocol.)
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Introduction to
Web Technologies
Network Concepts: Internet Structure
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Introduction to
Web Technologies
Network Concepts: Ports
• Given a destination computer address, data is transferred
via a protocol suite such as TCP/IP over a network.
• A port is a conduit into a computer through which data
flows.
• A port on a computer is identified by a unique number
– 0 to 1023 are reserved for special services
– 1024 and above can be used for any user application
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Introduction to
Web Technologies
Network Concepts: Ports
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Introduction to
Web Technologies
Network Concepts: Internet Addresses
• How does a computer specify a possible destination
computer?
• The IP address is the dotted quad notation
– E.g.
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131.227.68.110
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Introduction to
Web Technologies
Network Concepts: Domain Names
Top-level domain name
Organisation
com
Commercial company
edu or ac
Educational
gov
Governmental
mil
Military
biz
Show business
org
Organisations not catered for above
aero
Aeronautics
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Introduction to
Web Technologies
Internet domain name system
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Introduction to
Web Technologies
Network Concepts: Name Servers
• A Name Server is a computer that contains Internet
addresses and provides the service of translating a
symbolic name into some address.
• The collection of name servers is known as the Internet
Domain Name System or DNS.
• One of the most used part of the Internet!
• Every time someone sends e-mail or consults a Web
document then the service is consulted.
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Introduction to
Web Technologies
Network Concepts: Clients and Servers
• A server is a computer on a network which carries out
some service for another computer known as a client.
– E.g. A computer with a browser (client) requesting a Web page
from another computer that holds Web pages (server or specifically
Web server).
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Introduction to
Web Technologies
Clients and Servers
• A server is a computer which carries out a service such as
printing out a file or responding to a web page.
– A file server provides files for the clients that ask for its service.
– Database servers are computers which store large collections of data which are
structured.
– Groupware is software which organises the work of a number of staff in some
enterprise.
– A web server is a typical type of file server that contain files which store the
various components of a web site.
– A mail server is a computer which has the task of receiving, storing, and sending email.
– Object servers are design to hold distributed objects and provides facilities for
programs executing on a client computer.
– A print server is a computer which receives requests from clients for printing.
– An application server is a server which is dedicated to one or more particular
applications and contains special-purpose programming code that is specific to that
application.
• A client is some computer which requires a service.
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Introduction to
Web Technologies
Web Server
• A Web server is a server which dispenses documents that
reside on the World Wide Web.
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Introduction to
Web Technologies
Protocols
• A language which embodies the functions required by an
entity in a distributed system (usually a client) which
another entity provides (usually a server)
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Introduction to
Web Technologies
How the Web Works
• The user requests to view a Web page from the Web Server by opening
a Transport Control Protocol (TCP).
• Each Web page has a Uniform Resource Identifier (URI), which is a
uniform naming scheme for all the resources on the Internet (or
Intranet). There are two types of URIs the Uniform Resource Locator
(URL) and the Uniform Resource Name (URN).
– URL: http://www.computing.surrey.ac.uk/courses/
– URN: urn:def://JavaScript
• Each Web server has a unique Internet Protocol (IP) address (e.g.
University of Surrey has 131.227.76.230).
• The URI is translated into the corresponding IP address through the
Domain Name System (DNS).
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Introduction to
Web Technologies
How the Web Works
• The user communicates with the server through the HyperText
Transport Protocol (HTTP), the network protocol for the Web.
• The server then processes the client's request and sends the response to
the client's browser
• The browser then parses the HTML it receives, and then it displays it's
content.
1. Author writes
instructions
5. HTML stream returned to browser
6. Browser processes HTML
and displays page.
3. Web server
locates instructions
file
4. Web server
processes
instructions to
create HTML
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2. Client requests a web page
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Introduction to
Web Technologies
Tiered Architectures
A tier is a logically separated and encapsulated set of
processes.
• two-tier
– presentation and logic layer and a database layer
• three-tier
– presentation layer, processing layer (or application server layer)
and data layer
• n-tier
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Introduction to
Web Technologies
Middle Tier
• The middle layer enables the developer to isolate the main
part of an application that can change over time.
• In this layer can be found objects known as business
objects.
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Introduction to
Web Technologies
Three-Tier Architecture
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Introduction to
Web Technologies
Class Exercise
• Consider the following scenarios:
– A) A Web application for displaying pages (containing any
subject), comprising lots of information, and presentation is
important.
– B) A Web application that allows users to buy books online.
• What architecture would you choose for developing each
Web application, how many tiers?
• How would you distribute the processing in each tier?
Consider the cases where the website is expected to receive
lots of hits constantly and the case where the website is
expected not to get busy.
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Introduction to
Web Technologies
Advantages of Three-Tier Architectures
• It isolates the database technology used to implement the
final layer.
• It removes a large amount of code from the clients and
places it on the server.
• It fits in with modern object-oriented ideas as the
processing code is associated with objects.
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Introduction to
Web Technologies
Closing
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Questions???
Remarks???
Comments!!!
Evaluation!
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