internet

THE INTERNET PRIMER

A. Preconditions for using the Internet:

1. computer--can be PC, Mac, multiuser system (e.g., UNIX-

based) which necessitates logging in

2. online connection (via cable), modem

3. protocols--divvy up physical network into discreet

locations and enable one location to send messages

to another

B. Physical components of the Internet:

1. network host--computer connected to network

2. commercial Internet access provider

3. speed of information exchange within network limited by

a. telephone line

b. your modem speed

4. your computer and the Internet usually separated by LAN

a. privately owned LANs affiliated with businesses and

campuses everywhere

b. common physical medium is Ethernet--connection either

a small, metal "T" with a cable running through it

to back of computer or a small plastic box (with

transceiver) attached to computer by modular cable

5. router

a. a computer bridging gap between whatever medium is

used for LAN and a long-distance line accessing the

Internet at large

b. insulates the two from each other

--LAN doesn't have to process outside site work

--Internet not affected by LAN crashes

6. long distance portions of network consists of dedicated

phone lines

a. differ from voice traffic phone lines in 2 key ways:

--greater capacity for carrying data

--tend to be point-to-point lines (circuit always

open between the 2 points connected by line)

b. information transfer speed comparison

--Ethernet-based LANs: 10 million bits per second

(10 Mbps); 600 screenfuls of information per

second; 19.2 kilobits per second

--voice-grade phone lines: 19,200 bps; 1 screenful

of data

--"leased" lines (dedicated phone lines between 2

points): 56-64 kbps; 3.5 screens per second

--T1 lines: widely used as major data arteries;

capacity of 1.5 Mbps; 94 screens

--T3 lines: introduced to the Internet in 1991 and

now used throughout its North American backbone

(funded by NSF); transmit data at 30x T1 rate

C. the Internet relatively free of network-wide regulation

1. all parts (individual networks) owned by someone; each

sets its own policies

2. largest player, NSF, has dev. an Acceptable Use Policy

a. applies to traffic using NSFNET facilities

b. advocates the following:

--communication between researchers

--collecting information about and applying for

grants and research contracts

--administration of research programs and academic

professional societies

c. some commercial activity unacceptable:

--advertising

--consulting for pay

--general use by "for-profit" institutions

3. commercial sector the fastest growing portion of the

Internet user community

a. many of large regional networks less restrictive

regarding commercial activities

b. an infrastructure for commercial use currently

being built alongside the academic community structure

D. Finger

1. easiest command to use

2. displays information about a user: name, home directory,

file named .plan contents

3. e.g.: finger quake@geophy.washington.edu

4. problems which might arise in trying to execute command:

a. finger can't find user (...mistyped user name)

b. finger can't find computer

--unknown host:...

--ask system administrator for help

c. your computer can't find finger

--finger: Command not found.

--telnet with computer name and no. 79

(1) if telnet connects successfully, type user name

and press Return

(2) e.g.: Login name: aurora

--if you still get "command not found" message,

confirm with computer's administrator that there

is a connection to the Internet

E. Protocols on the Internet

1. definition: mutually agreed-upon format or set of

conventions, defined for a specific purpose

2. functions:

a. choreograph the movement of messages; network protocol

b. check integrity of what was sent; transport protocol

c. "massage" data from one format into another;

application protocol

3. Internet Protocol (IP)

a. a network protocal; manages logistics of getting a

message from sending machine to receiving machine

b. packets the base message unit delivered by IP

--smaller than many of messages and files transferred

over the Internet

--transmission often requires multiple packets

4. Transmission Control Protocol (TCP); User Datagram

Protocol

a. transport protocols

b. collect related packets, order them, and verify that

none are garbled

5. there are as many application protocols as there are

applications on the Internet; e.g., Mail, telnet, ftp,

archie, gopher, WAIS, World Wide Web

6. TCP/IP frequently paired

a. protocol of choice with UNIX vendors; also available

for mac, PC, other multiuser computers

b. TCP/IP-based LAN a miniature version of the Internet

c. many of tools available on the Internet (e.g., mail,

telnet, ftp) packaged with basic networking software

of UNIX systems

7. for IP to work, there must be a means of identifying

sites that will exchange messages

a. points of attachment are arbitrary and changeable

b. under IP, each network and each computer has a fixed

address allowing another computer to reach it

--a 32 bit-number; 4 numbers separated by periods

(none of the 4 numbers can be larger than 255)

--address has 2 components:

(1) one identifies the individual computer

(2) the other identifies the network of which the

computer is a member

--assigned when LAN registers for Internet con-

nection with the Internet Network Informtion

Center (the NIC, or InterNIC)

--the NIC also gives LAN administrator a range

of addresses to be assigned to indiv. hosts

c. although many information resources are available on

the Internet via menu systems, many others identified

only by IP address

8. Domain Name System (DNS)

a. definition: conventions for naming network computer

and directory service for looking up names

b. domain a named group of network hosts

c. domain-style names a series of names separated by

periods

--Fully Qualified Domain Name (FQDN): name of a

computer and hierarchy of domains in which it is

nested (in order of increasing generality)

--can be used in place of an IP address;

e.g., caticsuf.csufresno.edu

--2 main types:

(1) organizational

--tells organizational affiliation of computer

--top-level domains:

com commercial

edu educational

gov U.S. government

int international

mil U.S. military

net Network Backbone Systems &

Information Centers

org nonprofit organizations

(2) geographical

--2-letter names representing country (lower

level domains a mixture of geographical and

non-geographical names)

(a) codes unique only within fields, not

across them

(b) e.g., well.sf.ca.us (computer named

"well" in the San Francisco area

--top-level domains include:

au Australia

at Austria

ca Canada

uk UK/Ireland

as United States

d. unlike IP address

--more user friendly

--more versatile; names can be reassigned or reused

9. Serial Line Internet Protocol (SLIP) & Point-to-Point

Protocol (PPP) make it possible for anyone with computer/

modem/phone line to connect to the Internet

a. your computer becomes an Internet host with a unique

IP address (whereas, if dialing Internet host and

logging in your account to work with the Internet,

your computer is completely unknown to the Internet)

b. SLIP is not very sophisticated; it exchanges IP

packets over a serial line with minimal error

checking and additional encoding

--little overhead

--there are problems, however, in coping with line

noise and other interruptions common on serial lines

c. PPP more versatile; in the long run, it should render

SLIP obsolete

--more robust message control

--designed to handle protocols other than IP

--however, it imposes more overhead

d. both make it possible to run applications that use the

Internet on computers that don't have a permanent

network connection; e.g., via commercial access

providers

--advantage: greater convenience than with UNIX

command line interface common for dial-up users

--disadvantages:

(1) commercial access providers charge more for

such access

(2) you'll have to find and install Internet

applications on your own

F. Software Applications

1. def.: tools enabling us to communicate with others and

access data throughout the Internet

2. some are practically universal because they are bundled

with the network portion of the UNIX operating system

a. they are likely to be included with the networking

packages of other operating systems as well

b. e.g., mail, telnet, ftp

3. other Internet tools aren't part of any operating system

a. developed within the Internet community to simplify

access to worldwide resources

b. e.g., gopher, WAIS, WWW, archie

4. conventional, stand-alone computer programs able to get

all the resources they need from local sources

a. i.e., usually 1 or more files located on a disk in the

computer where the program is run

b. there are limits, however, when they are shared among

a group of users:

--data must either be replicated on many machines, or

everyone must use same machine

--copying same data everywhere wastes disk space

--using same computer creates performance problems

and interpersonal conflicts

5. to overcome these limits network applications are built

on client/server model

a. i.e., tools distribute the work of one application

across 2 programs, a client and a server, that carry

on a dialog with each other

b. this model makes it possible for anyone with Internet

access to use most available data anonymously

c. when information needed, do following:

--start up a program (a client) and supply detail

about what you need

--client program opens a connection to a server

program that controls the information requested

--dialog between the client & server uses application

protocols which format the message for transmission

across the network

--server receives client's request, evaluates it,

finds desired information, formats the result in

application protocol and passes response to the

appropriate protocol handler

--when client receives the requested information, it

provides an interface through which you can either

view information or direct it elsewhere

d. guidelines regarding these applications:

--client programs run ad hoc, but server programs

run continuously

--client and server programs can run on same computer

--clients can maintain multiple, simultaneous

connections to a server

--clients can connect to more than one server at a

time

--servers can open connections to other servers

--clients and servers can support multiple network

protocols

6. interfacing

a. the ASCII version of a client possesses the least

extravagant hardware requirement

--particularly helpful for users

(1) without access to workstations with graphical

user interfaces (GUIs)

(2) whose only access to Internet in indirect

(through telnet or dial-up connection)

--also versions for different GUIs; e.g., Xwindows,

Macintosh, MS-Windows

b. the client program may also deliver messages when

things go wrong during the client/server dialog

--the client program isn't necessarily the source of

errors it reports; e.g., messages originating in

the server or the path between the client and server

--knowing the general structure of client/server

interaction can be helpful in figuring the next move

G. Network Discovery Tools

1. tools checking your Internet connection are utilities

packaged with software that implements the TCP/IP

protocol suite

a. all tools available if accessing via UNIX computer

b. regarding personal computers where TCP/IP an add-on

product, there are more vendors and packaging of the

utilities is less uniform

2. ping

a. queries hosts on an IP network to verify they're up

and capable of sending and receiving network packets

b. standard component of UNIX TCP/IP installations;

also widely available in commercial TCP/IP

implementations for DOS & Windows systems

c. e.g.: ping optimism

optimism is alive.

--since a Fully Qualified Domain Name not used, only

local network computer named optimism being queried

--response says optimism capable of receiving and

sending packets with IP

d. if your version issues queries continuously, don't

let it run on needlessly

--potentially wasteful of Internet resources

--can be interrupted with Ctrl-C in most cases

e. problems which might be encountered:

--ping: Command not found

Execute the command again again specifying its

full path name.

--ping: rs.internic.net:host unknown

Ping couldn't resolve computer name you provided

into an Internet address

(1) ask whether computer accessible from any

Internet host

(2) your computer may not be connected to Internet

(3) you may achieve a connection to some Internet

facilities via e mail

--ping: no answer from rs.internic.net
Ping received no response to its query

(1) usually means computer being pinged is down

(2) repeat later

3. basic facts about your home computer stored in a file

named hosts

a. configuration file for TCP/IP protocol created when

software to manage the TCP/IP protocol is installed

b. plain text file containing IP addresses and host names

c. in /etc directory on UNIX systems

--DOS systems include it in directory containing

TCP/IP software

--Mac in System Folder

d. commands for display of file

--UNIX: cat /etc/hosts

--DOS: type /etc/hosts

e. check size before display

--UNIX: ls

--DOS: dir

f. response to display command: IP address followed by

the host's name and any aliases

--e.g., 103.214.50.59 optimism loghost

--could have information about different computers

--lines in hosts file beginning with # are comments

g. it you can't tell from the hosts file what the name &

IP address are, use hostname on UNIX computers with IP

--some Internet hosts will return a Fully Qualified

Domain Name

--if you know local comupter's name, easy to look up

its IP address in hosts file

4. also advisable to inventory network applications available

a. easiest way to see if application is available is to

try starting it

b. it commands fail, they'll do so in predictable ways:

--command not found

(1) 1st check that command is typed properly

(2) try executing command by full pathname;

e.g., /usr/ucb/telnet

(3) consult system administrator

--host unknown

--connection refused

--connection timed out

H. ftp

1. generic file transfer program

2. the Internet offers the following ways of locating files

for downloading:

a. the listing of Internet services

b. USENET newsgroups

c. archie

3. information needed to use ftp effectively:

a. name and location of file

b. type of file (must know how to interpret file names)

c. size of file (use "dir" command)

4. files for all sorts of computers available

a. plain text or binary the 2 file types which matter

most to ftp

b. some compressed to conserve space

--a table summarizing file compression software and

naming conventions by platforms is available

--file /doc/penet/compression at ftp.cso.uiuc.edu

5. naming conventions most frequently encountered on the

Internet

Category Extension Meaning _______________________

ASCII .c C Programming Language Source Code

.h C Programming Language Header File

.txt Text (ASCII) file

.uu ASCII file produced by uuencode

.bat DOS Batch file

.shar UNIX Shell Archive

.ps Post Script file

.hqx Mac Bin Hexed file thru release 4.0

Binary .EXE Executable binary file (DOS, VAX/VMS)

.COM Executable binary file (DOS)

.z Binary file created by compress

.sit Stuff it file for Macintosh

.gz file compressed with GNU gzip

.hqx Mac. Bin Hexed file release 5.0+

________________________________________________________________

6. most Internet users don't have accounts on all machines

from which they want to copy a file

a. no administrator wants to be bogged down by adding

indiv. accounts for all network users

b. sites publishing files to be copied via ftp usually

offer a special login name

--anonymous

--frequently asked to supply information; e.g., e mail

address, password

7. connecting via ftp like logging in to a remote computer

a. ftp session generally starts from the login account's

home directory

b. you can work directly with the files there or move to

another directory

c. when connecting to another system anonymously, ftp

also provides a working directory

8. once connected, you receive an ftp> prompt

a. you can then issue commands to move files between

computers

b. 5 key commands: ascii, binary, get, put, quit

c. meaning of some important commands:

--ascii assume transferred files are text (default)

--binary assume transferred files are binary (image)

--cr toggle stripping of carriage returns from

ASCII files (to preserve carriage returns,

toggle cr off

--hash print hash marks to controlling terminal

during transfer

(1) monitors ftp's progress during file

transfer

(2) # printed on your screen with each block

of data transferred

(3) during long file transfer, keeps the

Internet from automatically discon-

necting user deemed inactive too long

--prompt toggle prompting on or off during multiple

file transfer

(1) on: asked to confirm each file transfer

(2) off: transfer of multiple files without

interruption

--status display current status of all settable

options

--user set login name and password; permits

recovery from failed logins

--verbose toggle verbose messages on/off; can suppress

unwanted messages as needed

--help; ? both provide a list of all available

commands:

| cr ls prompt runique

$ delete macdef proxy send

account debug mdelete sendport status

append dir mdir put struct

ascii disconnect mget pwd sunique

bell form mkdir quit tenex

binary get mls quote trace

bye glob mode recv type

case hash mput remotehelp user

cd help mmop rename verbose

cdup image ntrans reset

close lcd open rmdir

d. choice of ascii or binary depends on file's content

and intended use

--if downloaded file will ultimately be used on a

computer with different architecture or operating

system, use binary representation

--if reading file with local machine's generic program

for displaying files (e.g., DOS type, UNIX cat), use

ascii type of transfer

9. ftp provides commands for moving around directories on a

remote computer

a. these commands are similar to directory navigation

commands for UNIX

b. notable examples:

--pwd print working (current) directory for remote

system

--cd change directory on remote system (requires

directory name)

--cdup change directory on remote system to parent

of current directory

--dir list contents of a directory on a remote

system including name, permissions, owner

and size

--ls list contents of a directory on a remote

system by name only

--mls list contents of multiple directories on a

remote system by name only

--lcd change working directory on local system

(requires directory name)

10. mls, mdir and get assume local file will hold the

command's output

a. therefore, it may be prudentto review output on

the screen rather than store it in a file

b. 2 ways to do this:

--hyphen (-): sends ftp output to screen in an

uninterrrupted stream

--| more or | pg: allows for viewing file a page at

a time

11. commands for copying files:

get move a file from remote to local

--must include name of file to be copied (source

file)

--may include a name for the destination file

--e.g.: get inet.services.txt

recv synonym for get

put move a file from local to remote

send synonym for put

mget move several files from remote to local

mput move several files from local to remote

12. on UNIX system, /tmp is directory in which any user can

create files

a. useful if you have problems with directory permissions

& ftp

b. include both path and file name (/tmp/filename) when

specifying destination file

c. avoid using it for:

--large files

--permanent storage

d. delete such files or move them to your own directory

as soon as possible

13. asterisk

a. a wildcard character

b. matches any string of characters in the file name

c. e.g.: mget README Makefile *.c *.h (*.c matches all

filenames ending in .c)

14. archie

a. its heart is a database containing directory listings

of what is available through anonymous ftp at several

hundred Internet sites

--database compiled by a program that surveys each

site monthly via ftp connection

--database then publishes on various archie servers

& is made available to query

b. example, archie server: archie.unl.edu (USA)

c. example, search: archie factbook

d. to determine whether your computer has this client,

type archie at UNIX prompt

--if you have it, prompt becomes archie>

--if not, message to that effect

I. telnet

1. used to log in to one computer on the Internet from

another

2. can navigate manually

3. differs from ftp (which is geared to transferring files)

in that its connections are general-purpose

4. many databases on the Internet are only accessible

through telnet

5. used with login name & password for the remote computer

J. Electronic Mail

1. makes possible:

a. communication with other Internet users

b. use of Internet applications possessing a mail

interface

c. communication with users on networks that are

connected to the Internet but use protocols other

than IP

d. use of some Internet services without having an

account on the Internet itself

2. the standard mailer on UNIX systems named mail

a. contents: address, subject, note proper, cc: notation

b. minimal editing capabilities:

--erase character (either Backspace or Delete) to

back up a character at a time

--use short lines; mailer won't wrap lines

--Ctrl-C to throw text away

c. Ctrl-D or . on line by itself sends message

d. to read mail, type mail & Return

--you'll see infomation regarding your version of

mail & messages in your system mailbox

--> means current message

--N means new message; number which follows is the

sequence of the message in mailbox

--these items followed by: sender's name; time message

sent; size of message; subject

--& (ampersnad) means mail command prompt

--to read current message press Return

--read any other message by typing sequence number

e. respond to current message by typing r at mailer

prompt

f. d means delete message

g. header makes message more difficult to read and

increases the space it takes up in your mailbox

--create .malrc file to make local configuration

changes in mailer's behavior

--mail arriving will include full header, but fields

suppressed with ignore command won't be displayed

when reading

--fields suppressed also won't be saved with message

if moved to a local mailbox

h. system mailbox should be kept small

--there is a risk of running out of space for new

messages

--the more messages, the harder the mailer works when

you read mail (the software usually works slower)

i. most systems automatically move mail messages from the

system mailbox to local mailbox after the message is

read

--UNIX places them in file named mbox in your home