Web servers and the Internet

1
Web servers and the Internet
2
Web server functions

• Receive requests for resources
• Send responses containing specified resource
• Resource identified by URL
• Uniform Resource Locator
• URL maps on to
• files (usually) send file
• programs (often in dynamic sites) run program
  and send output

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Recap action of HTTP

• Suppose you enterhttp//www.port.ac.uk/index.html
  
• The URL has three componentsltmethodgt//lthostgt/ltp
  athgt
• The browser would interpret this as a request
• To use the http ltmethodgt, i.e. use the hypertext
  transfer protocol to
• Communicate with lthostgt www.port.ac.uk
• To access the file index.html

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Browser actions

• Browser would parse the information
• To send the following message
• To host www.port.ac.uk

GET index.html HTTP/1.0 ltCRgtltLFgt ltCRgtltLFgt
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Server actions

• The request would arrive at port 80 (the default
  HTTP port) on the host www.port.ac.uk
• The message in three parts
• A method (an HTTP method not a URL method) that
  in this case is GET
• The Uniform Resource Identifier (URI)
  index.html
• The version of the protocol used in the message
  (HTTP v1.0 in this case).

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Other web server features

• Run fast
• Be multitasking so
• Can handle more than one request at a time
• Maintain the data it serves
• Authenticate enquirers
• Respond to errors in the messages

• Negotiate a style and language
• Offer different file formats, e.g.
• JPEG
• GIF
• TIFF
• Run as a proxy server
• Be secure!

7
Web server hardware

• The question to resolve is
• For how many simultaneous hits?
• For how long without failing?
• For how many different types of data just text
  or multimedia?

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Web server software

• The most popular two web servers are
• Apache
• Microsoft Internet Information Server (IIS)
• For an analysis of the situation, see
  http//serverwatch.internet.com/webservers.html
• Apache Web server choices
• Unix based systems (including Linux)
• Windows

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Client Software

• Web Clients
• Microsoft Internet Explorer
• Mozilla Firefox
• Netscape Navigator
• Opera
• Lynx text only

• Plug-ins
• For multimedia, e.g.
• Flash
• QuickTime
• RealPlayer, etc.
• For executing programs, e.g.
• JavaScript
• VB script
• For presenting data
• XML

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Related servers - databases

• Expensive Ones
• Oracle
• Microsoft SQL Server
• IBM DB2
• Informix

• Cheap/Free Ones
• MySQL
• PostgreSQL
• Microsoft Access

11
Glue code (web applications)

• What programming language?
• Java
• PHP
• ASP
• Perl
• C/C
• PL/SQL

• What application development environment?
• Oracle WebDB
• NetBeans
• Eclipse
• iPortal
• IBM WebSphere
• Microsoft Studio

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Management issues

• Content management
• Structure and architecture
• Security questions
• Monitoring and evaluation
• Recovery and backup
• Legal issues
• Scalability and the future

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Networking recap
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Recap of TCP/IP

• Transmission Control Protocol/Internet Protocol
• Each computer on a TCP/IP network needs an IP
  address
• e.g. 192.168.27.58
• Four parts to the address, separated by dots
• Each of these parts is a byte in the 4-byte IP
  address

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IP address components

• IP Address divided into two logical components
• The host number
• The network number
• Default divide uses first few bits to give three
  basic classes of network
• Class A
• Class B
• Class C

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TCP/IP Ports

• Different services use a different port or
  logical channel number, e.g.
• NNTP port 119 (for the Network News Transfer
  Protocol news services)
• SMTP port 25 (for the Simple Mail Transfer
  Protocol email services)
• DNS port 53 (for the Domain Name Service name
  services)
• HTTP port 80 (for the HyperText Transport
  Protocol for web services)

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Web server names

• As with the IP addresses, the IP names are
  divided into parts with dots
• No fixed relationship between dotted decimal
  addresses and dotted Internet names
• The mapping is done using some kind of lookup
  table.
• A HOSTS file on each machine
• A Name Service to manage the lookup for you, e.g.
  the DNS system

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HOSTS file
127.0.0.1 localhost Network using private
addresses 192.168.27.52 RanaEnorma.Home 192.168.
27.53 Frogtum.Home 192.168.27.56
Iceline.Home 192.168.27.55 WebbedFrog.Home 192.1
68.27.58 MeshedFrog.Home
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Network classes

• Class A.
• 0 -127 (i.e. 0xxxxxxx binary)
• Divide after first byte.
• 125 networks, each can support up to 16,777,214
  hosts.
• Class B.
• 128 -191 (i.e. 10xxxxxx binary)
• Divide after second byte
• 16,382 networks, each can support up to 65,534
  hosts.

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Network classes

• Class C.
• 192 - 223 (i.e. 110xxxxx binary)
• Divide after third byte.
• 2,097,150 networks each can support 254 hosts.
• Other special IP addresses.
• Localhost 127.0.0.1
• A loopback to yourself important for testing.

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Subnets

• A network can be divided into smaller parts,
  called subnets
• subnet mask used to identify which bits used for
  subnet and which for host
• Some of the bits notionally reserved for hosts
  are used to identify the subnet
• Take the default is usually safe for your
  experiments

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Host communications

• Both hosts on same physical network
• If same IP network number
• And different IP host number
• Then just send packets
• Hosts on different physical networks
• Router finds a connection path
• Using the network number part of IP

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Types of packet

• There are two main styles of packet that can be
  sent by two computers using IP
• UDP (User Datagram Protocol) like posting a
  letter to your friend
• TCP (Transmission Control Protocol) like
  telephoning your friend
• Web servers use TCP for most transactions