Introduction to the Internet

Institute for Visualization and Perception ResearchI VP R 1

© Copyright 1998 Haim Levkowitz

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



Internet service concepts …

• What is the Internet? ...

• Internet services structure ...

• TCP/IP ...

• Info-clients info-servers comm.



What is the Internet? …

• Federation of computer networks ...

• Three roles ...

• What does it mean to be on the Internet? ...

• What is on the Internet? ...



Federation of computer networks ...

• Speak same protocols

• Computer network protocols

• TCP/IP

• Connected with high-speed telephone circuits



Three roles ...

• Information providers

• Users (customers)

• Connection providers



What does it mean to be on the Internet? ...

• “Really” on the Internet

• On-demand; no Internet protocols

• Hybrid



Full-time IP connection ...

• IP protocol

LAN

Router

Modem

Internet ConnectionProvider

TCP/IP over data phone line

(leased)



Dial-up access

• terminal emulation

Internet

Characters over voice phone

line

Modem(or ISDN interface)


Terminal

Computer



Hybrid ...

• SLIP: Serial Line Internet Protocol

• PPP: Point-to-Point Protocol

• ISDN: Integrated Services Digital Network ...

• Running Internet protocols over dial-up ...



ISDN: Integrated Services Digital Network ...

• Voice, data, both

• On-demand, full-time

• Speed comparable to leased-line connection



Running Internet protocols over dial-up ...

• Dial-up hybrid

• Dial-up hybrid

Internet Connection Provider

TCP/IP over voice phone

line



Terminal



What is on the Internet? ...

• Computers: all kinds

• People: large number, variety

• Places



Internet services structure …

• Client/server architecture ...

• Information service client/server ...

• Any computer can be a service provider

• Compare: commercial networks ...



Client/server architecture ...

• Client: interact with user

• Server: perform tasks as directed by user

• Same/different computers



Information service client/server …

• Client ...

• Server ...



Client ...

• Accept queries/other input from users

• Send queries/data to server

• Manage display of results



Server ...

• Receive queries/other data from clients

• Process

• Send results/status



Compare: commercial networks ...

• E.g., CompuServe

• All services from computers run by network

• No information by users (except e-mail)



TCP/IP ...

• Packets: data; acknowledge data received

• Layered protocols ...

• inetd superserver ...

• Stand-alone servers ...

• Naming ...



Layered protocols …

• IP ...• TCP

(connection-oriented) ...

• UDP (connectionless) ...

Application Application Application

TCP

ICMPIP

UDP

Device Driver

Device Driver

Device Driver



IP ...

• Internet Protocol

• IP packet

• Addresses: 32-bit numbers ...

• No guaranteed delivery

• No guaranteed serialization



Addresses: 32-bit numbers ...

• 0 to ~4.3 billion

• Dotted-octet notation ...

• Net, subnet hierarchy



Dotted-octet notation ...

• 4 sets of 8 bits• Convert to

decimal• Concatenate,

separated by dots

Binary

Dotted Octet

00001111000100011110100000011000

15 17 232 24.. .

Net Subnet Computer



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 ...



How? ...

• Sequence numbers for IP packets

• Check arriving packets for completeness, order

• Get missing packets resent



Also, port numbers ...

• Layer below IP address (computer)

• Identify services within computer

• 16-bit

• “Well known,” e.g., ...



“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”



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



inetd superserver ...

• Many servers, idle periods ==> waste

• inetd: Internet Superserver

• Listen to ports

• Start requested server

• Server talks directly to client

• inetd.conf ...



inetd.conf ...

• Determine servers at start-up

• E.g.,: ...



E.g., ... telnet stream tcp nowait root /etc/telnetd telnetd

Service Connection (alt.: dgram UDP)

New server for ea client (alt.: start single server and wait)

User ID to run server

Pathname Argument vector: command-line options to pass



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



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



Daemon ...

• Listen to assigned port

• Spawn copy of self to handle ea. request

• + Fast

• – Crash unnoticed; explicit reread of config files when changed



Naming ...

• Domain names ...

• Aliases ...



Domain names ...

• 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



Aliases ...

• Pointers to other domain names

• Easier to remember

• E.g., ftp.uml.edu, www.cs.uml.edu



Info-clients info-servers comm.

• Gopher ...

• Web ...

• FTP ...



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



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)



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



Web ...

• Similar to Gopher

• Ea. doc. new TCP connection

• Ea. inline graphics ==> separate TCP connection

• With approp. server where graphics is



FTP ...

• Different from Gopher, Web

• 2 connections server <--> client

• Control: up through time user logged in

• Data: up when needed



Introduction to information services

• Overview of Internet information services ...

• What to do with Internet Services, e.g., ...

• System and network requirements ...

• Human requirements ...



Overview of Internet information services …

• Mail-based ...• FTP: file transfer protocol ...• Telnet & finger ...• Gopher ...• WAIS: Wide Area Information Servers ...• WWW: The World-Wide Web ...



Mail-based ...

• Reach largest population

• Get quickest response

• Grab attention

• Compare: Gopher, WWW

• User has to check

• Two types ...



Two types …

• Mailing lists ...

• Archive servers ...



Mailing lists ...

• List of e-mail addresses

• Reach all with one address

• E-mail list server programs

• Majordomo

• Listserv

• listproc, e.g., ...



listproc, e.g., ...

• To: [email protected]

• --------

• subscribe ora-news John Q. User of Some Organization



Archive servers ...• 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



FTP: file transfer protocol ...

• Restricted login

• Limited set of commands (all)

• Limited set of files

• Anonymous ...



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 -



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



Gopher ...

• Text-labeled menus

• Can be cascaded

• Advantages ...

• Limitations ...Internet Gopher Information Client v2.0.16

Home Gopher server: wildlife.ora.com

--> 1. Introduction and Cover

2. Foreword

3. Country Accounts/

4. Search Country Data <?>



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



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



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 ...



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



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



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



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) ...



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



Protocol: HyperText Transfer Protocol (HTTP) ...• http://<server>/<other>

• ftp://, gopher://

• Local: file://



What to do with Internet Services, e.g., ...

• Internal ...

• External ...

• Commercial transactions; charging money ...



Internal ...

• Corporate info

• Forms, logos, style sheets

• Timecards

• Home-grown software archives

• Employee directory

• Workgroup mailing lists

• “Intranet”



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



Commercial transactions; charging money ...

• Billing• Authentication and secure transactions• Unauthorized “sharing”• “Eavesdropping”• Free to use but not to resell• Future versions at a price



System and network requirements ...

• Network connection type ...

• Network load ...

• Computational load ...

• Disk space ...



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



Network load ...

• Queries (usually small) ...

• Responses (bulk of traffic) ...



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



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 ...



Usage logs: well-known ports ...

• FTP (data connection): 20

• FTP (control connection): 21

• Gopher: 70

• Z39.50 (WAIS protocol): 210

• HTTP (WWW protocol): 80



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 ...



Mailing-lists ...

• Very little reply traffic

• Other traffic can be substantial



Archives ...

• Huge amounts of reply

• No effective limit

• No good way to predict avg. response size



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 ...



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



Mail-based archive ...

• Lots of CPU time in

• File transfers

• Processing of files transferred

• Mailing those files



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



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



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.



WAIS ...

• Index files as large as data files

• ==> Consume 2 x data



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



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 ...



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



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



Finger-, Inetd-, and Telnet-based services



FTP

• Setting up an FTP archive

• The WU archive FTP daemon

• Maintaining and FTP archive



WAIS

• Creating and Internet database server with WAIS

• Creating WAIS sources with waisindex



Gopher• Introduction• Compiling the server• Managing the server• Preparing Information• Linking services together• Incorporating databases• Veronica and jughead• Gopher+ forms and other new features



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



Email services

• Introduction

• Simple mailing lists

• Automating mailing list with majordomo

• The majordomo list owner and moderator



Security

• Firewalls and information services

• xinetd

• Legal issues

• Protecting intellectual property



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• Web site traffic assessment (beyond simplistic ``hit'' counts).• Other topics

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Introduction to the Internet

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