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1 Section 1: Internet Technologies
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1
Section 1:Internet Technologies
2
Internet Overview
3
What is the Internet?
Collection of computers networked together
Uses standards based on TCP/IP Data broken down into packets Allows for differing computer platforms to
communicate Based on globally unique address for
each node Network is global
4
Computer
Computer
Computer
ComputerComputer
Internet
The Internet Network
Data
Data
Data
Data
Data
Data
5
Using the Internet
Computer
Internet
Application
TCP/IP
Internet
User
Data
DataInternetConnection
6
Computer to Access Internet: Three Requirements
Application - many available E-Mail, Web Browser, Server, File Transfer,
Video Conferencing, + Others TCP/IP
Standard in computer operating systems Interfaces to Internet
Internet Connection
7
Application
TCP/IP
Internet
UserE-MailWeb Browser, ServerFile Transfer ProtocolVideo Conferencing+ Others
Included with Computer Operating System (usually)
InternetConnectionData
8
Application
TCP/IP
Internet
User
•Plain Phone Line (POTS)•Higher Speed Phone Line:
ISDN, DSL•Cable Modem•Ethernet etc.
Internet Connection
9
100 500 150 250 10 300
Example:What is the throughput capacity of this system?
Throughput in MB/Sec
Note: real Internet is very large scale and dynamic
10
What is the World Wide Web? Client: browser connected to Internet. Uses hypertext and graphics to display information Server: server software connected to Internet Client-Server based - no platform incompatibilities (?) Any WWW browser can connect to any WWW server (if
both follow standards) Rapid growth in capabilities of servers and clients
(browsers). Note use of standards.
11
The World Wide Web
Computer
Computer
Internet
Data
Request SentData Received
Browser
TCP/IP
Server
TCP/IPRequest ReceivedData Sent
Client clicks on hyperlink.Data received
Data resides on server
12
WWW and Hyperlinks
Use embedded codes to allow for hyperlinks (Hypertext Markup Language).
When viewed in browser, user does not see embedded codes.
Allows for simple point and click navigation.
13
Browsers
Hyperlinked text Graphics Plug-ins (e.g. sound, video) Active elements (Java, ActiveX) Operating Environment
IncreasingSophistication
14
Web Pages and HTML
Hypertext Markup Language (HTML) Uses tags that allow browser to change the
format Tools to help write HTML (Word, FrontPage
etc.) See refs on web site
15
HTML Element An HTML element may include a name,
some attributes and some text or hypertext
<tag_name> text </tag_name> or
<tag_name attribute_name=argument> text </tag_name> or
<tag_name>
16
HTML Text Elements <h1> . . . </h1> Heading 1 to heading 6 <h6> . . .
</h6> <b> . . . </b> Bold; <i> . . . </i> Italic; <u> . . .
</u> Underline Unordered List ul <ul> <li> First item in the list <li> Next item in the list </ul>
17
HTML Hyperlink
<a href="URL"> . . . </a> Links to another file or resource
Also need <html> <head> and <TITLE> Examples Other elements are also defined – will be
using HTML Forms later
18
<html> <head> <TITLE>HTML Example</TITLE> </head> <body> <H1>HTML is Pretty Easy To Learn</H1> <P>Welcome to HTML. This is a paragraph.</P><IMG SRC=http://www.engineering.uiowa.edu/~pjogrady/Internet/ImagesSounds/
JACKSGLOBE.gif> <P> <A HREF =
"http://www.engineering.uiowa.edu/~pjogrady/Internet/Default.htm"> This is a hyperlink</A></P> </body> </html>
1. Put the above text in a file named *.htm or *.html (use Notepad or similar text editor.)
2. Open using browser3. Browser interprets tags to display contents
19
20
Growth in Number of Web Sites
1992 50 web sites in world.
Now 65,000 web sites added per hour.
21
Thoughts on the Issue of Internet Overload.
The first suggests that the internet capacity is a finite resource but that users are not charged for each use. Hence Internet will be overused.
The second school of thought more optimistically suggests that the Internet can continue to grow and response time can remain reasonable. Seems to be the most accurate.
22
Internet Traffic Routers on the Internet continually collate
the return time for test packets and this is called the ping delay (next slide)
Used as part of routing for packets
23
Technology Change
Processor (Moore’s Law) Communications Capacity (Gilder's Law)
(infrastructure and bandwidth) More complex to forecast than processor Estimate to be growing by factor of three per year
(doubtful)
“Technology will develop in response to customer demand”
Peter O’Grady
24
From http://www.physics.udel.edu/wwwusers/watson/scen103/intel.html.
25From: The Economist, 2003
26
Computer Processing Power: Moore's Law
MIPs
0.3 0.9 5 20100
300
500
1000
0
200
400
600
800
1000
1200
8088 8286 8386 8486 Pentium PentiumPro
PentiumII
886
Compaq Microsoft Dell
27
Name Date Transistors MicronsClock speed
MIPS
8080 1974 6,000 6 2 MHz 0.64
8088 1979 29,000 3 5 MHz 0.33
80286 1982 134,000 1.5 6 MHz 1
80386 1985 275,000 1.5 16 MHz 5
80486 1989 1,200,000 1 25 MHz 20
Pentium 1993 3,100,000 0.8 60 MHz 100
Pentium II 1997 7,500,000 0.35 233 MHz ~300
Pentium III 1999 9,500,000 0.25 450 MHz ~510
Pentium 4 2000 42,000,000 0.18 1.5 GHz ~1,700
Pentium 4 "Prescott"
2004 125,000,000 0.09 3.6 GHz ~7,000
From: http://computer.howstuffworks.com/microprocessor2.htm
28
Communications (2002 = 1)
0
1000
2000
3000
4000
5000
6000
7000
2002 2003 2004 2005 2006 2007 2008 2009 2010
Investment in new fiber has slumpedEstimated 95% of fiber is “dark”Potential increase in efficiency of existing fiber.
29
Trans-Oceanic Fiber-Optic Cable
020406080
100120140
Year
Ca
pa
cit
y, G
iga
bit
s/s
ec
AtlanticPacific
30From: The Economist, 2003
31
What are the implications of this growth in bandwidth?
Potential for increasing speed of information flow and ideas. This could increaseProductivityEconomic growthWorld peace?Outsourcing (why?)
32
Old and New Economies
A BLittle Trade
A BLarge Trade
OLD
NEW
Tariffs, Regulations, Poor Communications
Ricardo - Theory of Comparative Advantage 1817Increased economic growth
33
Manufacturing Output per Hour 1995-2000 Average Annual Change %
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
%
Source: Bureau of Labour Statistics
34
World Trade Volumes
From: The Economist
35
36
37
38
39
From: The Economist
40
Impact of E-Commerce Impact of Business to Consumer
5% reduction in aggregate distribution costs 0.5 - 0.7% reduction in costs in overall
economy 63-88% of annual increase in total factor
productivity in G-7 countries Impact of Business to Business E-
Commerce “orders of magnitude higher”
Source: OECD: “The Economic and Social Impacts of E-Commerce”
41
Internet Fundamentals
42
How do standards happen? Standards organizations (e.g. ISO)
Usually international Often slow Non-proprietary
Industry Groups (e.g. bar codes) De Facto (e.g. TCP/IP)
Result of widespread use Can be quick to develop Can be quick to change, proprietary, no
international body to maintain standard
43
ISO Model
The International Standards Organization, based in Geneva Switzerland
Composed of groups from various countries that set standards working towards the establishment of world-wide standards for communication and data exchange.
44
ISO Model Developed a Reference Model that
contains specifications for a network architecture for connecting dissimilar computers.
A main goal being that of producing an open and non-proprietary method of data communication.
45
ISO Model
This reference model, called the Open Systems Interconnect Reference Model (OSI RM), was developed in 1981 and revised in 1984.
46
The OSI RM
Uses 7 layers, each independent of each other, to allow computers to exchange data.
To transfer a message from user A to user B, the data has to pass through the 7 layers on user's A machine, before being transmitted through the selected medium.
47
The OSI RM
At the receiving computer of user B, the data must then pass through the 7 layers again, this time in reverse sequence before being received by user B.
For data to be transferred, it must pass through all 7 layers on both computers.
48
The OSI RM
Each layer follows a relatively strict specification and this allows the differing layers to be produced and implemented by different concerns.
Each layer can then interface with its neighboring layers even though they may have been developed by different groups.
49
The OSI RM
The Layers Are Arranged in Order As Follows: Layer 7, Application Layer. Layer 6, Presentation Layer. Layer 5, Session Layer. Layer 4, Transport Layer. Layer 3, Network Layer. Layer 2, Data Link Layer. Layer 1, Physical Layer.
50
The OSI RM
In spite of enormous amount of work, little of the OSI RM is in use.
This is probably due to the rise of TCP/IP
51
Internet Network Structure The Internet grew out of the 1960s Cold
War. Response to the issue of making sure that
computer networks could survive a nuclear weapons attack.
Problem: Nuclear war could destroy much of the military communications networks - military control then lost.
52
Internet Network Structure Approach needed whereby the networks
could operate even when substantive portions had been destroyed.
One proposal formed the basis of the Internet
Based on a simple and elegant digital model of a very decentralized network.
53
Internet Network Structure
Such a network is digital in nature and was therefore dependent on readily available computing power.
Such power was becoming available only in the 1970s.
54
Internet Network Structure
The University of California at Berkeley received a contract from the United States Department of Defense to develop a computer network that would: Operate on a wide variety of computer
hardware with differing communications media Reconfigure itself if portions of the network
failed.
55
The TCP/IP Model, and Hence the Internet
Based on two structures: Data being transmitted Computer routers that make up the core of the
network.
56
Data is broken down into smaller packets. Each packet includes address of the
destination computer as well as other information such as the transmitting computer.
The packets are reassembled into the data file at the destination computer.
The TCP/IP Model: Data
57
Packets
Data broken into packets Each packet sent separately with address
(note need for unique address) Passes through routers in network Similar to sending letter via multiple
postcards Packet switching technology required Unique address IMPORTANT
58
The network is essentially composed of a number of routing computers (or routers)
Route the packets towards their destination computer by passing them to the next router that is available in the general direction of the destination computer.
The TCP/IP Model: Routing
59
Analogy: Sending Postcards
Break a message into smaller parts and send each on a postcard
each packet (or postcard) may follow a completely different route and each may arrive at different times.
For the digital Internet network we can improve performance by e.g. replicating packets.
60
The Internet Network Model The model is essentially non-hierarchical
in character with each router being at the same level of control.
The model is highly decentralized with each router operating quasi-independently.
The model is also self-managing to some extent.
61
The Internet Network Model
The model is also scaleable in that we can continue to add (or subtract) routers and computers to the network without changing its essentially characteristics.
The Internet model is an open standard with the specifications being openly and freely available.
62
TCP/IP TCP/IP consists of a whole series of
protocols applications and services. Can be thought of as containing five layers
(cf. OSI RM with seven layers).
63
TCP/IP
The application layer containing such protocols and applications as Simple Mail Transfer Protocol (SMPT), File Transfer Protocol (FTP), Hypertext Transfer Protocol (HTTP) and Telnet.
The transport layer contains such protocols as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
64
TCP/IP
The Internet layer contains such protocols as Internet Protocol (IP), Internet Control Message Protocol (ICMP), Address Resolution Protocol (ARP), and Reverse Address Resolution Protocol (RARP)
The data link layer and The physical layer handle the hardware
connections. A wide variety of hardware network connections are possible ranging from token ring to Ethernet and from twisted pair cables to fiber optic cables.
65
TCP/IP
Upper layer: application Mid-layers (transport and Internet)
Core of Internet Allows for applications to communicate with
other computers Lower Layer (data link and physical layers)
Hardware Ethernet, token ring, fiber optic
66
TCP/IP
Modular approach Allows for wide variety of configurations Need to have at least one from each layer.
Often called the “stack”
67
TCP/IP Protocols
See course ref chapter 2. Note wide variety possible. Modular architecture also allows new
protocols and applications to be developed
68
Internet Addressing
The Internet Protocol (IP) Uses Numbers to Identify Host Computers and Uses These Address Numbers to Route Data Between Them.
The IP Addresses Are 32 Bit (or 4 Byte) Binary Values, for Example: 10000000.11111111. 00010111.10111100
69
Internet Addressing
These Are Usually Expressed in Decimal With a Period Between the Bytes for Convenience.
The Above IP Address Would Therefore Be Expressed in Decimal As Follows:
128.255.23.188 (server in instructors office)
Note: IP address often allocated dynamically to individual computers
70
Example IP Specification
in Windows
71
Note address in xx.xx.xx.xx form
72
Internet Addressing Each site connected to the Internet has it's
own IP Address and messages can be addressed using this number. The routers on the Internet then pass the message through to its address.
The numbering scheme was thought to be somewhat difficult to use and early in the development of the Internet a parallel naming scheme was begun.
73
Internet Addressing
Uses descriptive words for the site address, so that telegraph.co.uk for example could be used instead of it's IP address of 193.130.188.19
The system that operates this is called the Domain Name System (DNS).
DNS servers scattered around Internet
74
Example DNS Specification
in Windows
75
Internet Addressing Lookup tables are incorporated into the
Internet to convert from the more descriptive form, the DNS name, to the IP number address.
These are used in DNS servers In the DNS, domain types are allocated to
particular categories.
76
DNS Categories
For example, in U.S. then the categories are allocated as follows: .com Commercial (E.G. intel.com) .edu Education (E.G. uiowa.edu) .org Organization (E.G. ims.org) .gov Government (E.G. nsf.gov) .mil Military (E.G. navy.mil)
77
DNS Categories
The countries are also identified. For example: .jp Japan .kr Korea .uk United Kingdom. .de Germany .nl Netherlands
78
DNS
The DNS Name Is Usually Cascaded. For example,www.eng.cam.ac.uk refers to
the WWW site in the Engineering Department (eng) at Cambridge University (cam) which is an academic institution (ac) in the United Kingdom (uk).
79
IP Packet or Datagram
Version IHL TOS Total Length Identification Flags Fragment Offset
TTL Protocol Header Checksum Source IP Address
Destination IP Address Options Padding
Payload (TCP/UDP/ICMP etc.) From http://www.inetdaemon.com/tutorials/internet/ip/datagrams.html
See http://www.inetdaemon.com/tutorials/internet/ip/datagrams.html
80
Ports and IPv6
81
Ports
Generally speaking, a computer has a single physical connection to the network. All data destined for a particular computer arrives through that connection. However, the data may be intended for different applications running on the computer. So how does the computer know to which application to forward the data?
Through the use of ports. Data transmitted over the Internet is accompanied by addressing information that identifies the computer and the port for which it is destined. The computer is identified by its 32-bit IP address, which IP uses to deliver data to the right computer on the network. Ports are identified by a 16-bit number, which TCP and UDP use to deliver the data to the right application.
[From sun.com]
82
Ports Port numbers range from 0 to 65,535 because
ports are represented by 16-bit numbers. The port numbers ranging from 0 - 1023 are restricted; they are reserved for use by well-known services such as HTTP and FTP and other system services. These ports are called well-known ports.
There are 65,535 port numbers available for application processes that use Transmission Control Protocol (TCP). The same number of ports are available for application processes that use User Datagram Protocol (UDP).
[from sun.com] [see http://www.iana.org/assignments/port-numbers ]
83
PortsDefault TCP Port
Number I nternet Service
20 File Transfer Protocol (FTP) Data Channel
21 File Transfer Protocol (FTP) Control Channel
23 Telnet (enabled on some intranet or Internet servers)
25 Simple Mail Transfer Protocol (SMTP)
80 Hypertext Transfer Protocol (HTTP) used for World Wide Web
119 Network News Transfer Protocol (NNTP)
443 Hypertext Transfer Protocol over TLS/SSL (HTTPS) for secure World Wide Web
563 Network News Transfer Protocol over TLS/SSL (NNTPS)
From Microsoft.com
UPD Port Number Service
53 Domain Name System (DNS) name queries (supports some Internet services)
161 Simple Network Management Protocol (SNMP)
84
IPv6
Present IPv4 is used This is 32 bits, and has about 4,300,000,000
address spaces (2^32 – 1) IPv6 is started to be implemented. IPv6 is 128 bits giving 3.4 x 10^38 addresses Allows for an (almost) inexhaustible supply of
addresses.
85
Internet History
Started with design of network to survive nuclear attack
Highly distributed design Mainly used by researchers and
academics up to about 1993-1995
86
History of WWW
1989 CERN started development to allow physicists to communicate
August 1991 first WWW software publicly released
February 1993 NCSA published Mosaic Exponential growth in WWW servers
87
The World Wide Web
While the Internet provided powerful capabilities in such utilities as telnet and FTP, it was not particularly easy to use.
88
The World Wide Web
This began to change in 1993 when researcher at CERN in Switzerland developed a means of sharing data using hypertext, where codes in the document being examined allowed users to jump to another document merely by clicking on a hyperlink.
89
The World Wide Web
ftp and telnet capability were added so that they could also be invoked merely by clicking on a hyperlink.
This type of program became known as a browser
CERN browser was limited to text documents.
90
The World Wide Web A team at University of Illinois at Urbana-
Champaign (specifically the National Center for Supercomputer Applications - NCSA) developed a more powerful browser called Mosaic which allowed for the inclusion of graphics.
Mosaic was freely available and led to a huge increase in the use of the Internet and WWW.
91
The World Wide Web
Some of those involved in the development of Mosaic helped form Netscape Corporation, which has developed commercial versions of both browsers and servers.
92
WWW Clients and Servers
The WWW, in it's early form, is a very large collection of clients and servers that support the Hypertext Transfer Protocol (HTTP) on the Internet.
This is an open standard and is implemented on a wide variety of platforms.
93
WWW Developments The interaction between WWW servers and clients
can be classified as follows: The web server sends a static file to the client as a
result of a Hypertext Transmission Protocol (HTTP) request from the client.
The WWW Server Can Process Data in Response to Input From Client Browser. Such process can include, for example, extracting the information from the corporate databases in response to the client browser requests. SERVER SIDE PROGRAMMING
A program can be downloaded from the WWW server to a client which can then carry out the programmed actions on the client. CLIENT SIDE PROGRAMMING
94
Server Side Programming
Common Gateway Interface (CGI) CGI Is a standard for interfacing external
applications with WWW servers (Common Gateway Interface, 1995).
Application Programming Interface (API)
95
Common Gateway Interface (CGI)
CGI is just a set of commonly-named variables and agreed-upon conventions for passing information back and forth between the client (the user's WWW browser) and the server (the computer that sends web pages to the client).
96
Web Browser HTTP Sever
CGI Program
DatabaseDatabaseInterface
Information Query
Database Query
Information Query
Query Results
HTML page Formatted Results
Query Results
Common Gateway Interface
Query Results
97
Use of APIs
Each time a new CGI program is started a new process is begun and this is notoriously inefficient.
For a server with multiple CGIs executing simultaneously, the result can be very slow response times.
98
Use of APIs Recently, therefore, much attention has
begun to be focussed on more efficient methods of executing programs on the server.
Much of the developments has been on Application Program Interfaces (API) that, in their pure form, is a set of functions in the operating system that programmers can use.
99
Use of APIs
However the APIs tend to be proprietary and therefore are particular to server/operating system combinations.
An example Is the Internet Services Application Programming Interface (ISAPI) that Is proprietary to Microsoft.
100
Use of APIs
ISAPI Allows for Programs to Be Dynamic Link Libraries (DLLs) for Use on a Windows Server and Only One Copy of the DLL Need Be Loaded No Matter How Many Programs Use It.
Active Server Pages (Microsoft) Java Server Pages (Sun/Netscape) have program on server.
101
Use of APIs
Results would indicate that servers that use APIs have substantially shorter response time than those that use CGIs and we can therefore expect that CGIs will tend to fall in relative disuse.
102
Server Side Programming CGI API ASP (Microsoft only) JSP can include executable
and/or scripts
Client Side Programming Java applet Java Script VB Script (Microsoft
only)
Important application is interfacing to databases.
Course homework addresses many of these.
