Transcript 02_intro-to-internet

Introduction to the
Internet
• Internet service concepts ...
•
•
•
•
•
•
•
•
•
Introduction to information services
Finger-, Inetd-, and Telnet-based services
FTP
WAIS
Gopher
World-Wide Web
Email services
Security
Future topics and research opportunities
I VPR
Institute for Visualization and Perception Research
© Copyright 1998 Haim Levkowitz
1
Internet service concepts
…
•
•
•
•
What is the Internet? ...
Internet services structure ...
TCP/IP ...
Info-clients info-servers comm.
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© Copyright 1998 Haim Levkowitz
2
What is the Internet? …
• Federation of computer networks ...
• Three roles ...
• What does it mean to be on the
Internet? ...
• What is on the Internet? ...
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3
Federation of computer
networks ...
• Speak same protocols
• Computer network protocols
• TCP/IP
• Connected with high-speed telephone
circuits
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4
Three roles ...
• Information providers
• Users (customers)
• Connection providers
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5
What does it mean to be
on the Internet? ...
• “Really” on the Internet
• On-demand; no Internet protocols
• Hybrid
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Full-time IP connection ...
• IP protocol
TCP/IP over
data phone line
(leased)
LAN
Internet
Connection
Provider
Router
Modem
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7
Dial-up access
• terminal emulation
Characters over
voice phone
line
Terminal
Internet
Modem
Modem
(or ISDN
interface)
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(or ISDN
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Computer
8
Hybrid ...
• SLIP: Serial Line Internet Protocol
• PPP: Point-to-Point Protocol
• ISDN: Integrated Services Digital
Network ...
• Running Internet protocols over dialup ...
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9
ISDN: Integrated Services
Digital Network ...
• Voice, data, both
• On-demand, full-time
• Speed comparable to leased-line
connection
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10
Running Internet
protocols over dial-up ...
• Dial-up hybrid
• Dial-up hybrid
TCP/IP over
voice phone
line
Terminal
Modem
(or ISDN
interface)
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Modem
Internet
Connection
Provider
(or ISDN
interface)
Institute for Visualization and Perception Research
© Copyright 1998 Haim Levkowitz
11
What is on the Internet? ...
• Computers: all kinds
• People: large number, variety
• Places
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12
Internet services structure
…
• Client/server architecture ...
• Information service client/server ...
• Any computer can be a service
provider
• Compare: commercial networks ...
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13
Client/server architecture
...
• Client: interact with user
• Server: perform tasks as directed by
user
• Same/different computers
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Information service
client/server …
• Client ...
• Server ...
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Client ...
• Accept queries/other input from users
• Send queries/data to server
• Manage display of results
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Server ...
• Receive queries/other data from clients
• Process
• Send results/status
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17
Compare: commercial
networks ...
• E.g., CompuServe
• All services from computers run by
network
• No information by users (except email)
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TCP/IP ...
• Packets: data; acknowledge data
received
• Layered protocols ...
• inetd superserver ...
• Stand-alone servers ...
• Naming ...
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Layered protocols …
• IP ...
• TCP
(connectio
n-oriented)
...
• UDP
(connectio
nless) ...
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Application
Application
TCP
UDP
IP
Device
Driver
Application
Device
Driver
Institute for Visualization and Perception Research
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ICMP
Device
Driver
20
IP ...
•
•
•
•
•
Internet Protocol
IP packet
Addresses: 32-bit numbers ...
No guaranteed delivery
No guaranteed serialization
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Addresses: 32-bit
numbers ...
• 0 to ~4.3 billion
• Dotted-octet notation ...
• Net, subnet hierarchy
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Dotted-octet notation ...
• 4 sets of 8 bits
• Convert to
decimal
• Concatenate,
separated by
dots
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Binary
00001111000100011110100000011000
Dotted Octet
15
Net
Institute for Visualization and Perception Research
© Copyright 1998 Haim Levkowitz
.
17
.
Subnet
232
.
24
Computer
23
TCP (connection-oriented)
...
• Transmission Control Protocol
• Two services IP doesn't
• Guaranteed delivery
• Serialization of data
• How? ...
• ==> Mimic stream over dedicated line
• Also, port numbers ...
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How? ...
• Sequence numbers for IP packets
• Check arriving packets for
completeness, order
• Get missing packets resent
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25
Also, port numbers ...
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•
•
•
Layer below IP address (computer)
Identify services within computer
16-bit
“Well known,” e.g., ...
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“Well known,” e.g., ...
• 25: Simple Mail Transfer Protocol
(SMTP) mailer
• 23: Telnet
• “Privileged” ports (UNIX)
• Numbers < 1024
• Only root can start
• Security
• Prevent “listening”
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UDP (connectionless) ...
• User Datagram Protocol
• Two additional features to IP
• Port #s (16-bit, not same as TCP)
• Checksumming (optional)
• Detect modifications
• Avoid TCP for 1-packet q's / responses
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inetd superserver ...
• Many servers, idle periods ==> waste
• inetd: Internet Superserver
• Listen to ports
• Start requested server
• Server talks directly to client
• inetd.conf ...
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inetd.conf ...
• Determine servers at start-up
• E.g.,: ...
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E.g., ...
telnet stream tcp nowait root /etc/telnetd telnetd
New
Pathname
Service Connection server User
(alt.: dgram for ea ID to
client
UDP)
run
(alt.:
server
start
single
server
and
wait)
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Argument
vector:
commandline
options to
pass
31
To find ...
• % grep telnet /etc/services
• telnet 23/tcp
• Connection request ==> transaction in
syslog
Jul 25 22:53:33 ohbear inetd[349] :
telnet/tcpL Connection from babs.nsr.hp.com
(15.17.232.24) at Mon Jul 25 22:53:33 1994
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Stand-alone servers ...
• inetd restarts servers whenever
needed
• Auto handle of config change
• Inefficient for busy service
• Takes time for inetd to start server
• ==> Run server stand-alone
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Daemon ...
• Listen to assigned port
• Spawn copy of self to handle ea.
request
• + Fast
• – Crash unnoticed; explicit reread of
config files when changed
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Naming ...
• Domain names ...
• Aliases ...
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Domain names ...
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•
•
•
•
cs.uml.edu (from specific to general)
.edu, .com, .gov, .org, .mil
2-letter country codes (ISO 3166)
Servers: Domain Name Server (DNS)
Clients: resolvers
• Send queries to DNS for IP addr. <-->
name
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Aliases ...
• Pointers to other domain names
• Easier to remember
• E.g., ftp.uml.edu, www.cs.uml.edu
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Info-clients info-servers
comm.
• Gopher ...
• Web ...
• FTP ...
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Gopher ...
• User request resource on Gopher
server
• Client query ...
• Gopher server response ...
• Client stores file
• TCP connection torn down
• TCP up and down for each request
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39
Client query ...
• Accept input & translate into query
• Send query to Gopher server
• Look in /etc/services to find port
number
• gopher 70/tcp
• Query --> TCP packet(s) --> server
(port 70)
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Gopher server response ...
• Listen on port 70 / inetd listen
• inetd check destination
• /etc/services to find port number
• Map to service name
• Gopher
• Start server, gopherd
• Gopher interpret query
• Open, read file, send to client
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© Copyright 1998 Haim Levkowitz
41
Web ...
• Similar to Gopher
• Ea. doc. new TCP connection
• Ea. inline graphics ==> separate TCP
connection
• With approp. server where graphics
is
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42
FTP ...
• Different from Gopher, Web
• 2 connections server <--> client
• Control: up through time user
logged in
• Data: up when needed
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43
Introduction to
information services
• Overview of Internet information
services ...
• What to do with Internet Services, e.g.,
...
• System and network requirements ...
• Human requirements ...
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© Copyright 1998 Haim Levkowitz
44
Overview of Internet
information services …
•
•
•
•
•
Mail-based ...
FTP: file transfer protocol ...
Telnet & finger ...
Gopher ...
WAIS: Wide Area Information Servers
...
• WWW: The World-Wide Web ...
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Mail-based ...
• Reach largest population
• Get quickest response
• Grab attention
• Compare: Gopher, WWW
• User has to check
• Two types ...
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Two types …
• Mailing lists ...
• Archive servers ...
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Mailing lists ...
• List of e-mail addresses
• Reach all with one address
• E-mail list server programs
• Majordomo
• Listserv
• listproc, e.g., ...
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listproc, e.g., ...
• To: [email protected]
• -------• subscribe ora-news John Q. User of
Some Organization
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Archive servers ...
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•
•
•
•
•
•
Send out files by e-mail
Response to users' e-mail requests
Also on-the-fly
First index, then file name
Archive: encodes, splits to pieces, sends
User: reassembles, decodes
ftpmail: xfer files from other hosts & deliver
by e-mail
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50
FTP: file transfer protocol
...
• Restricted login
• Limited set of commands (all)
• Limited set of files
• Anonymous ...
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51
Anonymous ...
• Public access
• User: anonymous
• Password: user's e-mail address (convention)
• Supports almost all platforms, all file formats
• Can define privileged access, limit # of users
• – Slow to browse, no file description
• Read README while logged in: get README -
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52
Telnet & finger ...
• On most OSs
• Fairly primitive
• Telnet: login over net
• E.g., DUATS: weather briefing for pilots
• duats.gtefsd.com (student),
duat.gtefsd.com
• Finger: info on users of remote system
• Also other short info, e.g., stock quotes,
weather report
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53
Gopher ...
• Text-labeled menus
• Can be cascaded
• Advantages ...
Internet Gopher Information Client v2.0.16
• Limitations ...
Home Gopher server: wildlife.ora.com
--> 1. Introduction and Cover
2. Foreword
3. Country Accounts/
4. Search Country Data <?>
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Advantages ...
• Easy navigation
• Simple, powerful, easy to administer
• Organize directory where server
runs
• Subdirectories become menu items
• Files in directories become available
• Text oriented ==> good for slow links,
dial-ups
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55
Limitations ...
• Text only display
• Can xfer binary
• Display with other software
• Link only from menu
• Compare WWW: from within
document
• Links to FTP, WAIS, Telnet
• But not same variety as WWW
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© Copyright 1998 Haim Levkowitz
56
WAIS: Wide Area
Information Servers ...
• Search data ...
• Minimal support for browsing
• Gopher, WWW assume user knows where to
look
• WAIS doesn't
• ==> Good complement to WWW, Gopher
• Requires graphical browser, IP connectivity
...
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57
Search data ...
•
•
•
•
•
Start at Directory of Servers
Index of all servers ...
Real search in most approp. servers
Search documents for keywords
Similar (but not sufficient) documents:
add entire document to keyword list
• Relevance feedback: match & similar
documents
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© Copyright 1998 Haim Levkowitz
58
Index of all servers ...
• Indexing beforehand ==> quick search
• Support many data types
• ASCII, LaTeX, PostScript, GIF, TIFF,
mail digests, NetNews archives
• Easy to add data types
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59
Requires graphical browser,
IP connectivity ...
• Text-based, pretty difficult
• Most WAIS clients provide viewers for basic
formats
• Allow specify external programs to
process & present more types
• Works best with formats w / lots of words
• Big database indexes ==> need lots of disk
space
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60
WWW: The World-Wide
Web ...
• Most powerful, many features of its own
• Integrates most other info services
• ==> Simple to use & understand
• Web browser: GUI-based access to
• FTP, WAIS, Gopher, etc.
• Format: HyperText Markup Language (HTML) ...
• Protocol: HyperText Transfer Protocol (HTTP) ...
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Format: HyperText
Markup Language (HTML)
•...
Commands to format document,
specify hyperlinks
• Browser formats, marks hyperlinks
• Follow links, format according to
type
• Fire off other programs (e.g., xv to
view images)
• Must have IP connectivity
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Protocol: HyperText
Transfer Protocol (HTTP)
...
• http://<server>/<other>
• ftp://, gopher://
• Local: file://
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What to do with Internet
Services, e.g., ...
• Internal ...
• External ...
• Commercial transactions; charging
money ...
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64
Internal ...
•
•
•
•
•
•
•
Corporate info
Forms, logos, style sheets
Timecards
Home-grown software archives
Employee directory
Workgroup mailing lists
“Intranet”
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External ...
•
•
•
•
•
•
•
Electronic magazine / newsletter
Manual pages (e.g., BSDI)
Product, support, price info
Press releases
Software product distribution
Bug reports
Contributed public domain software
archives
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66
Commercial transactions;
charging money ...
• Billing
• Authentication and secure
transactions
• Unauthorized “sharing”
• “Eavesdropping”
• Free to use but not to resell
• Future versions at a price
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67
System and network
requirements ...
•
•
•
•
Network connection type ...
Network load ...
Computational load ...
Disk space ...
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Network connection type
...
• Full-time IP connection
• Limited Gopher, Telnet, Finger, WAIS
• Minimum 28.8 Kbaud PPP connection
• Standard modem, phone line
• Most services
• Minimum 56 Kbaud
• Serious service
• ISDN or T1
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69
Network load ...
• Queries (usually small) ...
• Responses (bulk of traffic) ...
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70
Queries (usually small) ...
•
•
•
•
•
Mailing lists: short modification messages
Mail archive: request index / file
FTP: download short; upload can be long
Gopher: short menu item / document name
WAIS: long if doc’s added for relevance
feedback, but use IDs
• WWW: short strings identifying doc’s
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Responses (bulk of
traffic) ...
• Estimate size of avg. reply
• Size of files; likelihood of retrieval
• If know frequency of files / menu items ==> better
prediction
• For WWW: inline images increase avg. size
• Network tracing, monitoring
• Monitoring devices
• Usage logs: well-known ports ...
• Mailing-lists, mail archives ...
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Usage logs: well-known
ports ...
•
•
•
•
•
FTP (data connection): 20
FTP (control connection): 21
Gopher: 70
Z39.50 (WAIS protocol): 210
HTTP (WWW protocol): 80
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73
Mailing-lists, mail
archives ...
• Hard to predict size
• No dedicated out port: unreserved, > 1023
• Hard to monitor
• Hard to separate
• In port 25, but can't separate types
• Best way: syslog file
• Mailing-lists ...
• Archives ...
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74
Mailing-lists ...
• Very little reply traffic
• Other traffic can be substantial
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75
Archives ...
• Huge amounts of reply
• No effective limit
• No good way to predict avg. response
size
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76
Computational load ...
• More guessing game
• Monitor trend in peak load average
• As service grows in popularity
• Predict need for faster machine early
• Mailing-list ...
• Mail-based archive ...
• FTP, Gopher, WWW ...
• WAIS ...
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77
Mailing-list ...
• Servers don’t require much CPU
• Simple op’s on aliases file
• Not much network traffic
• Lists can be CPU intensive, depending
on size of list and message
• sendmail: no efficient sending of
thousands of messages at same
time
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78
Mail-based archive ...
• Lots of CPU time in
• File transfers
• Processing of files transferred
• Mailing those files
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FTP, Gopher, WWW ...
• CPU consumption proportional to
• Number of queries received
• Size of files processed
• FTP bogging down processors
• Wash U. FTP: special features to
limit access, set of number users
• WWW demanding because of inline
images
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80
WAIS ...
• Most demanding
• Search
• Open index files
• Compute scores (match search criteria)
• Other non-trivial tasks
• ==> Per-query load high
• No way to control access based on sys load
• Need fast processor to save large WAIS
db
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81
Disk space ...
•
•
•
•
•
•
At least enough for all files offered
Extra overhead
WAIS ...
Mail server ...
Other services requirements insignificant
But if multiple, might need as many copies
of data as number of services
• FTP copy, Gopher copy, WWW copy, etc.
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82
WAIS ...
• Index files as large as data files
• ==> Consume 2 x data
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83
Mail server ...
• Header + bodies in mail queue
directory
• ==> Lots of space
• More significant with mail-based
archive servers
• Large mail messages
• E.g., uuencoded split binaries
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Human requirements ...
• Understand material offered
• How to structure intuitively and effectively
• Constantly update, add new, check integrity
of links
• “System guru” not necessarily same as
“contents guru” (librarian)
• Librarian’s duties ...
• Librarian’s desirable qualifications ...
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Librarian’s duties ...
• Author & format info
• Meta-info: FTP README, Gopher menus,
...
• Collect & distribute info from other sources
• Keep up-to-date
• Provide & maintain links to other info
resources
• Respond to user requests for help
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Librarian’s desirable
qualifications ...
• User-interface experience
• Familiarity with subject & audience
• Ability to navigate the Internet
• Find new info resources to point to
• Check integrity of links
• Good people skills for customer
service
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Finger-, Inetd-, and Telnetbased services
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FTP
• Setting up an FTP archive
• The WU archive FTP daemon
• Maintaining and FTP archive
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WAIS
• Creating and Internet database server
with WAIS
• Creating WAIS sources with waisindex
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Gopher
•
•
•
•
•
•
•
•
Introduction
Compiling the server
Managing the server
Preparing Information
Linking services together
Incorporating databases
Veronica and jughead
Gopher+ forms and other new features
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91
World-Wide Web
•
•
•
•
•
Introduction to the World-Wide Web
Setting up a Web server
Authoring for the Web
Gateways and forms
Access control and security
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92
Email services
• Introduction
• Simple mailing lists
• Automating mailing list with
majordomo
• The majordomo list owner and
moderator
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Security
•
•
•
•
Firewalls and information services
xinetd
Legal issues
Protecting intellectual property
I VPR
Institute for Visualization and Perception Research
© Copyright 1998 Haim Levkowitz
94
Future topics and
research opportunities
• New & improved
• Authentication, verification, and other security schemes
• Information encryption/decryption
• Secure fund transfers
• Etc.
• Contents quality visualization and assessment
• New and improved information search and exploration
schemes
• Image and other high bandwidth transfer
• New interaction paradigms
• Automatic contents control
• E.g., parents' control of children's access
95
Visualization
and Perception
Research simplistic ``hit'' counts).
IV
R Institute
• PWeb
site for
traffic
assessment
(beyond
• Other topics
© Copyright 1998 Haim Levkowitz