Download Getting Started

Internet / Intranet
CIS-536
Getting Started
Introduction to Internet Technologies
Class 1 Agenda
• Introduction
– Syllabus
– Homework
• Introduction to Internet Technologies
– Internet History and Protocols
– Networking Principles: TCP/IP
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Web Hierarchy
TECHNOLOGY
Key Components
Web Applications
Web Forms
World Wide Web
Core Internet Protocols
Scripting
CGI
HTML, Browsers, Web Servers
SMTP (Mail), FTP, Telnet
The Internet
Networking
OSI Model, Ethernet, LANs
Operating Systems
UNIX, Windows, Other O/S
Computers
Mainframes, Minis, PC’s
TCP/IP, DNS, Backbone
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Networking Roots
• Why? A Need to Transfer Data Between Computers
• Issue: Computers Vary Widely
– Multiple Manufacturers, Types
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Variations: Speed, Disk Space, Peripherals, Technology
Operating System (O/S):
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Mainframes: IBM, BUNCH
Minis: Same + DEC, DG, HP, etc.
PC’s: IBM, Apple
Now: Unix, Windows, Mac, Other
Before: IBM, BUNCH, Unix, VMS
User Interface: Text-Based, Graphical, Hand-Held
• The Need:
– File Transfer Between Computers
– Data Transfer Between Computers
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Session-Based
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Networking Options
• Basic: (One Sender / One Recipient at a Time)
– “Print and ReKey”
– “SneakerNet”
– Direct “Dumb” Connection
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E.g. Parallel Port
Modem
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Protocols:
File Transfer Protocols
– E.g. XMODEM, ZMODEM
• Advanced: Non-Dedicated
– Shared Connection
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Broadcast
– Filters
Routing
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Physical Networking Issues
• Distance Between Machines
– Local – LAN
– Metropolitan (MAN)
– National / International (WAN)
• Public vs. Private Networks
• Cable Type: (e.g. UTP, Coax, Fiber)
• Wiring Topology
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Network Topologies
DIRECT
STAR
RING
BUS
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Communication Issues
• Connection Type
– Circuit vs. Packet
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Packet Details
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Size
Format
Routing
Bandwidth Sharing
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Circuit: Session Based
Packet: Package Based
Load Balancing
Routing
Error Handling
Security
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The OSI Networking Model
• An Attempt to Separate Physical Issues,
Communication Issues, etc.
• The Concept:
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Each Layer Is Independent
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“Black Box Approach”
A Layer Has No Knowledge of Other Layer’s Internal
Structure
Allows Layers to Be Swapped In and Out Easily
• The Reality:
– Pure OSI is Too Slow
– Most Implementations Cross Layers
– Nevertheless: Useful Conceptual Model to
Understand Networking
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OSI Networking Model
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Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
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OSI Layers (1)
• 1. Physical Layer
– The physical cable that connects the computer to
the network (e.g. RS-232C, UTP)
• 2. Data-Link Layer
– Moves data from the computer to the cable
– Physical addressing
– Packages the data according to pre-determined rules
• 3. Network Layer
– Addressing
• 4. Transport Layer
– Reliability
– Error Handling / Quality Control
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OSI Layers(2)
• 5. Session Layer
– Connection Management
– Interfaces between O/S and the lower layers.
• 6. Presentation Layer
– The Operating System / GUI
• 7. Application Layer
– The Application Doing the Communication
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TCP / IP
• The Basic Protocol of the Internet
• Covers Layers 3-4 of the OSI Model ( Network /
Transport Layers)
• Multiple Layer 1-2 (Physical / Data Transport)
Protocols Are Supported
Ethernet – Direct Connection
– Token Ring
– Modems / Dial-Up
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Why Is the OSI Model Important?
• Great Lesson in Practical Software Engineering and the Role
of Standards:
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1. The Goal Of Independent Layers Was Proper and Valuable
2. The Model Turned Out to Be Impractical In Its Details
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Only Implementation Could Expose All of the Impracticalities
Some of It Was Probably Wrong Anyways
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3. Implementer’s Violated The Model to Achieve Market
Success
4. Yet, The Goal Survived
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Question: Is the OSI Model a Success or a Failure?
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No: In Practice Nobody Actually Follows It
Yes: Without It, We Wouldn’t Have As Many Choices For
Connecting to the Internet
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Web Hierarchy
TECHNOLOGY
Key Components
Web Applications
Web Forms
World Wide Web
Core Internet Protocols
Scripting
CGI
HTML, Browsers, Web Servers
SMTP (Mail), FTP, Telnet
The Internet
Networking
OSI Model, Ethernet, LANs
Operating Systems
UNIX, Windows, Other O/S
Computers
Mainframes, Minis, PC’s
TCP/IP, DNS, Backbone
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Internet Enabling Technologies
• TCP/IP
– A Method to Assign a Unique Address to Computers
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IP Address: 32 bit Address
A Method to Create and Address Packages of Data
A Method to Route Data Between Computers
A Method to Share the Network Bandwidth
Error Handling and Other Advanced Networking
Features
• DNS
– A Method to Link Names to 32 Bit IP Addresses
– Lookup the Name in a DNS Database
– Efficient Method to Maintain DNS Databases
Worldwide
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TCP / IP
• IP : Internet Protocol
– Addressing
– Routing
– Packaging
• TCP : Transmission Control Protocol
– Advanced Traffic Management
– Error Detection / Correction
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IP Addressing
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Each Machine (“Host”) Has Its Own Unique Address
Related Machines Are Grouped Into “Networks”
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The Address Identifies the Network as Well as the Node
32 Bit Address
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Broken into four 8-bit chunks:
– Written as: xxx.xxx.xxx.xxx
Higher Order Bits Identify the Network
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IP Addressing (2)
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Different Classes of Networks:
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Subnetting
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Class A (Very Large Networks)
– IP addresses: 1.0.0.0 to 127.0.0.0
Class B (Large Networks)
– IP addresses: 128.0.0.0 to 191.254.254.254
Class C (Small/Medium Networks)
– IP addresses: 192.0.0.0 to 223.254.254.254
Breaking Up a “Network” Into Smaller Networks
– Subnet Mask: Logical And with IP Address to Define the
Network
Special Reserved Addresses
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0,1,2, 255 – Reserved
– Define Network, Broadcast, etc.
127.xxx.xxx.xxx – Loopback
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IP Routing
• Typical WAN Challenges
– How to Balance the Load Across the Network?
– Must Localize Traffic to Conserve Bandwidth
Analogy: Postal Service
Get a Package From Point A to B
– Minimize the Number of Miles a Package Travels
– Optimize Use of “Bandwidth”
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e.g. Jeeps/ Semi-Trailers / Airplanes
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“Postal” Routing Example
• Solution : Create a “Distribution Center” Hierarchy
Boston
Los Angeles
UCLA
Waltham
Cambridge
Chicago
Brandeis
J. Smith
MIT
Polaroid
Feldberg 123
W3C
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IP Routing Example
• Solution : Emulate a “Distribution Center” Hierarchy
NOTE: For Demonstration Only. Not Real IP Addresses or Structure
Boston
129.0.0.0
Los Angeles
164.67.0.0
UCLA
164.67.80.0
J. Smith
164.67.80.123
Chicago
198.23.0.0
Polaroid
129.64.95.0
Waltham
129.64.0.0
Brandeis
129.64.99.0
Feldberg 123
129.64.99.128
Cambridge
129.70.0.0
MIT
129.70.53.0
Lab 1
129.70.53.41
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IP Routing Details
• IP Specifics
– Routers (Gateways) Serve as Distribution Centers
– Routers Responsible for Where Package Goes Next
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Nodes Within A Network Can Communicate Without
Going Through the Router
Each Node Must Know the Name Of Its Router
(Network)
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“Store and Forward”
Multiple Paths From Sender to Recipient
Subnet Mask Used to Identify Routers (Networks)
IP Address is Used For Routing
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Hierarchical
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IP Packets
• The Challenge:
– How to Share the Bandwidth Evenly?
– How to Recover From Data Errors?
• The Solution
– Packet Based, not Circuit Based
– Packet Size Limits
– Large Packages broken-up into Smaller Packets
– Each Packet Can Travel A Different Route
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Packets May Arrive at Different Times
Total Package Must Be Reassembled at Destination
If an Error Occurs, Only the Damaged Packet Must
Be Retransmitted
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IP Packaging
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Sender
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Recipient
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The IP Packet
• Byte 1:
– Version (4 bits)
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Packet Header Length (4 bits)
Type of Service (8 bits)
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Version 4 is Common
Version 6 is Latest
Priority – Ignored by Most Routers
Length (8 bits)
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Total Length of Packet
Min: 576 bytes, Max: 65,525 bytes
• Byte 2:
– ID, Fragmentation Info
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Unique ID for Packet and Fragmentation Info
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The IP Packet (2)
• Byte 3:
– Time To Live (8 bits)
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Protocol ID (8 bits)
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Helps Identify When a Package is Undeliverable
6 is TCP
Checksum (16 bits)
• Byte 4:
– Source IP Address
• Byte 5:
– Destination IP Address
• Next Byte(s):
– Optional Header Information
• Next Bytes:
– The Data Itself
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The Future of IP
• Current Version: IPv4
– 4 Billion Theoretical IP Addresses
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“Smart Devices” Will Want IP Addresses
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In Practice, Many Less Available
e.g. Refrigerators!
Routing Tables Getting Less Efficient
• IPng – IP Next Generation (IPv6)
– 128 Bit Addresses
– Faster Routing
– Security Mechanisms
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The TCP in TCP / IP
• Ports
– IP Address Is Not Enough
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A Computer May Have Multiple Applications Running
Allows Applications to Distinguish Communications Meant
For Them
• TCP – Transmission Control Protocol
– Manages the Traffic More Efficiently
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e.g. Makes Sure That A Connection Exists Before Sending
Full Package
Advanced Error Detection / Correction
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Breaks Up and Reassembles Packets
• UDP – In Between IP and TCP
– Less Error Detection – Therefore Faster
– Sometimes Used Locally
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The TCP Packet
• Carried Within the IP Data
• Byte 1:
– Source Port (16 bits)
– Destination Port (16 bits)
• Byte 2:
– Sequence Number
• Byte 3:
– Acknowledgment Number
• Next Bytes:
– Header Length, Flags, Options
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DNS Naming Conventions
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(Host).(SubOrganization..).(Organization).Domain
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Common Domains
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Edu, Org, Com, Net
Country: e.g. UK, NL
“Right to Left” Hierarchy
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Find the Name Server for the Domain (e.g. edu)
Find the Name Server for The Organization
Then Suborganization(s), Host
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Internet Enabling Technologies
• Core Communications Backbone
– Others Connect to the Backbone via Established
Node
• New Connectivity Options
– Dedicated (T1, T3)
– Dial-Up Over Standard Telephone Lines
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Advanced Modem Technologies (e.g. 56 KB)
Other Substitutes
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CableModems
xDSL
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In Class Exercise: IP Addresses
• Feldberg Accounts
• IP Exercises
– ipconfig
– tracert
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Web Hierarchy
TECHNOLOGY
Key Components
Web Applications
Web Forms
World Wide Web
Core Internet Protocols
Scripting
CGI
HTML, Browsers, Web Servers
SMTP (Mail), FTP, Telnet
The Internet
Networking
OSI Model, Ethernet, LANs
Operating Systems
UNIX, Windows, Other O/S
Computers
Mainframes, Minis, PC’s
TCP/IP, DNS, Backbone
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Core Internet Protocols
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Enable Computers to Share Data Using Non-Proprietary Standards
Built on TCP/IP
– Telnet
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FTP – File Transfer Protocol
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Download/Upload Files From One Computer to Another
Basic File-Type Conversion
– ASCII / EBCDIC
» Binary Format of Characters
– UNIX, MS-DOS/Windows
» Line Termination Characters
Electonic Mail – SMTP/POP
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Remote Login
Mail Servers Established to Act as Post Offices
Multiple Users Have Accounts at Post Office
News Groups - NNTP
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Electronic Bulletin Boards
Users Can Share Information
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The Internet – In The Beginning
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Late 1960’s
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1969 – 4 nodes
1971 – 15 nodes
1972 – BBN Wins Bid to Build a Packet Switched Protocol
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The Result: TCP/IP
1973 – International. Added London, Sweden.
1979 – Usenet Created
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Limited to Military and Academic Researchers
Military wanted a system that would continue to function when
parts of network were disabled
ARPA Net – Advanced Research Projects Agency (DOD)
Newsgroups
1983 – Split into 2 nets:
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MILNET – military only
NSFNET – (National Science Foundation)
– Supercomputers linked for distributed processing
Universities added on to allow their students access to
supercomputers.
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Internet: Pre-Commercialization
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NSF’s Acceptable Use Policy:
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Independent Bulletin Board Systems (BBS) Begin to
Convert to Usenet
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1985 – The WELL (Whole Earth Electronic Link)
New Protocols Join email, telnet, usenet
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For Research and Education Only.
Commercial / For-Profit Activity Excluded
Gopher – Campus Information System
WAIS – Document Retrieval
1987 – Over 10,000 nodes
1990 – 100,000 nodes. 9 countries
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Before the Web
• Information Shared Publicly via FTP
– Relevant Documents Listed in a Directory
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Must Be Organized By Directory
User Must Know That Directory Exists
File Names Only – No Descriptive Information
• Clearly a Need to Organize Information
– Archie
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Gopher
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Catalog of FTP Servers
Menu Based Organization of Files
WAIS
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Library of Files With Search Capabilities
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Archie
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The First Search Engine?
Maintains a Catalog of Anonymous FTP Servers
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Users Login to an Archie Server
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Can Search by Keyword
Lists FTP Servers Where File Can Be Found
Descriptive Index
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Client Contacts Each Server Monthly
– Lists All of the Files Available via Anonymous FTP
– Maintains This List Locally
– Based on FTP: No Special Process Needed on Server
Administrator’s Keep Index of Available Files
– Add Comments – No Standard Format
Comments Become Searchable
Email Interface
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Submit Search via email, Get Results Back as an email
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Gopher
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A Desire to Distribute Campus Information Online
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Session Based
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Requires a Client and Server
TCP/IP Communication via Port 70
Menu Based System
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Originated at University of Minnesota
List of Menu Choices
Can “Drill Down” a Menu
Text-Based
– Most Terminals Support 25 Lines of Text
Allows Links to Other Gopher Sites
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Allows Different Groups to Maintain Their Own Files
CSO – Text Based Forms / Processing
Allows FTP Through Same Interface
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WAIS – Wide Area Information Service
• Improved Search Engine
• Full-Text Search and Retrieval
• Session Based
– TCP/IP Communication via Port 210
• Requires a “Librarian” to Maintain an Index
• Servers Can Ask Another to Perform a Search
• XWAIS – X-Windows GUI to WAIS
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Internet – Pre-Commercialization
• Non-Commercial Culture Develops
• Lots of Public Domain Software
– UNIX
– The Free Software Foundation
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Richard Stallman
General Public License
• Spirit of Cooperation
– Newsgroups
• “Netiquette”
– Self-Policing Rules
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Web Hierarchy
TECHNOLOGY
Key Components
Web Applications
Web Forms
World Wide Web
Core Internet Protocols
Scripting
CGI
HTML, Browsers, Web Servers
SMTP (Mail), FTP, Telnet
The Internet
Networking
OSI Model, Ethernet, LANs
Operating Systems
UNIX, Windows, Other O/S
Computers
Mainframes, Minis, PC’s
TCP/IP, DNS, Backbone
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Web Beginnings
• 1991 - Internet Commericalization
– NSF lifts restriction forbidding commercial traffic
• 1990 – Tim Berners-Lee Proposes Web Structure to
CERN (Center for European Research)
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Goal: To Distribute Research Across CERN’s Many
Laboratories and Affiliates
• New Protocol: HTTP
– Encapsulates Multiple Internet Protocols
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FTP, Gopher, etc.
Files Identified by URL – Uniform Resource Locator
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Web Beginnings (2)
• Hypertext Markup Language (HTML)
– Modification of SGML – Standard Generalized Markup
Language
– Hypertext
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Includes “Links” to Other Places Within the Document
Includes Links to Other Documents
Why Hypertext?
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Allows Distributed Documents
Maintainability - Documents More Current
Storage Doesn’t Need to Be Duplicated
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The Need For HTML
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Need For Portable Method to Distribute Technical Documents
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Options
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GUI’s Not Prevalent
– Most Used “Dumb Terminals”
» Fonts, Characters Per Line, Lines Per Screen Varied
Many Different Operating Systems – Hardware Limitations
No Standard Word Processing Applications
Plain Text
– No Formatting
Print-Based
– Postscript, GIF
– Large Files, No Searching
Text-Based
– TeX, RTF, nroff
– Describe How to Print Document
» Display Capabilities Vary
Solution: HTML
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Describes Document’s Content, Not its Format
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Web Client (Browser) Development
• HTML Requires an Application to Display it
• First Browser: www (1991)
– Text Based
• GUI’s Becoming More Prevalent
– Apple Macintosh
– MS-Windows
– X/Motif (UNIX)
• First Graphical Browsers
– 1993 - Mosaic (NCSA – National Center for Supercomputing
Applications)
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Available on all Platforms
Public Domain
• Netscape Communications Corporation (1994)
– Private Corporation. Founded By Mosaic’s Creators
• Microsoft Internet Explorer
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Browser Wars
• Netscape
– Extended HTML With “Custom” Extensions
– “Plug-Ins” – Allow Local Applications to Run Within Browser
• Microsoft Internet Explorer
– Based on Spyglass’ Mosaic
– Custom Extensions to HTML
– Active X – Microsoft Equivalent of Plug-Ins
• Other Browsers Left Behind
– Custom Extensions Make it Difficult to Keep Up
– Changes the Web Significantly
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Universal Accessibility is Sacrificed
– Requires GUI
– Requires Current Hardware
HTML Standards Expand Rapidly
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Goal: To Create a Single Standard Used by Both Browsers
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Who’s Managing the Web?
• Web Commercialization/Competition Changes Culture
– Internet Experiences Exponential Growth
• 1994 - CERN/MIT Found the World Wide Web Consortium
(W3C)
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Attempt to Manage/Control Standards
Member Organizations Only
IETF – Internet Engineering Task Force
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Protocol Engineering and Development
– Open to Individuals
• CERN Drops Out
– INRIA Takes Over for CERN (Funded by EC)
• New Extensions to Web Usage
– Two-Way Communications (e.g. Forms)
– Advanced UI Functionality (Scripting, Java)
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Web Hierarchy
TECHNOLOGY
Web Applications
Web Forms
World Wide Web
Core Internet Protocols
Key Components
Scripting, Applets
CGI
HTML, Browsers, Web Servers
SMTP (Mail), FTP, Telnet
The Internet
Networking
OSI Model, Ethernet, LANs
Operating Systems
UNIX, Windows, Other O/S
Computers
Mainframes, Minis, PC’s
TCP/IP, DNS, Backbone
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For More Information
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Portal
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Internet History
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Hobbes Internet Timeline
– http://info.isoc.org/guest/zakon/Internet/History/HIT.html
Free Software Foundation /GNU
– http://www.gnu.org
Networking
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http://www.internet.com
Brandeis: Computer Networks and Data Communications
TCP/IP, FTP, etc.
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Brandeis: TCP/IP
Winsock Programming
– Windows Sockets Network Programming by Bob Quinn
and Dave Shute. Addison-Wesley
Brandeis University Internet/Intranet Spring 2000
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