The Internet is a world-wide computer network accessed by millions of people each day. The Internet can be used as a:
to access remote systems
to communicate with colleagues
to obtain information on world-wide bulletin board and other information server systems and databases
to publish your own work to the Internet community such as research papers, promotional material, and other information of interest to others
The goal of this course is to define what the Internet is and how to connect to it, to introduce several common Internetworking tools, and to provide pointers to other related material.
The Internet is a world-wide "network of networks" linking millions of systems on thousands of local, regional, and national networks, including NICEnet (NRL's local area network).
Communication across the Internet is possible as all systems speak the same "language," the networking protocol TCP/IP.
Fig. 1 Internet
Internet management and administration is highly decentralized, although organizations such as ANS (Advanced Network Systems) and the InterNIC provide some measure of authority. TCP/IP and its related protocols are specified by the Internet Engineering Task Force (IETF) which is part of the non-profit Internet Society.
Three are three levels of Internet connectivity:
Corporations, universities, and government sites typically have their own local area networks with Internet connectivity. Systems may be connected directly to the local area network or indirectly through a subnetwork.
Modem connections can be established using the Point to Point Protocol (PPP) or the Serial Line Internet Protocol (SLIP) allowing you to operate as if physically connected.
Normal modem connections to a host system. Internet access limited by connectivity of host. Provides indirect access to the Internet. All programs run on the host. Downloading files is a two step process---first to host, then to your system.
Access through a commercial service provider via an Internet gateway. Types of Internet access may be limited---some providers allow only email access, others provide full Internet access.
Each machine on the Internet must have a unique address, known as an IP address. This address is a 32-bit number commonly represented as a set of four numbers (8 bits each with values 0-255) separated by periods. For example:
132.250.110.121
Host names are associated with a machine's numeric address and have the format "host.domain" where domain is a multi-level hierarchy reflecting the organization of the Internet. For example:
amp.nrl.navy.mil
Each domain is served by a computer within that domain (known as a name server) that maps Internet host names to IP addresses.
Host names can be abbreviated within a domain. The above system can be referred to as "amp" from other machines in the "nrl.navy.mil" domain. However, Fully Qualified Domain Names (FQDNs) are more portable as there may be many hosts with the same name in different domains.
Domain level names and addresses are assigned by the Network Information Center (NIC). Local network administrators assign host names and addresses within their domain.
TCP/IP (Transmission Control Protocol/Internet Protocol) is not one but a whole suite of standardized protocols each serving a specific purpose, such as:
TCP/IP provides three basic services:
Numerous other services have been developed on top of TCP/IP, including:
What is needed:
The physical network connection between your system and the Internet may either be an Ethernet card or a connection to a local area network which itself is connected to the Internet.
Two types of software are needed:
Communications software is available both commercially and public domain from a number of sources.
NICEnet is managed by the CCS's Operational Networks Section, Code 5592, (202)767-3903. Connections can be set up for almost any type of system, including UNIX workstations, Macintosh and IBM personal computers, and mainframe systems.
Internet host registration forms are available via anonymous FTP from "net.nrl.navy.mil" in the public/forms directory. Example forms are provided for many types of connections. This system also provides a variety of other network-related information, including:
To register a host, complete the appropriate form and return it via electronic mail to "hostmaster@net.nrl.navy.mil". The hostmaster will then notify you of your host name and address and other necessary configuration information.
NICEnet information, including registration forms, is also available on the World Wide Web at:
http://www-opnet.nrl.navy.mil/
Questions concerning host registration should be sent to "hostmaster@net.nrl.navy.mil". Other network related questions can be sent to "netgroup@net.nrl.navy.mil".
Electronic mail, or "email," is the most prevalent networking application.
Internet email addresses have the following format:
user@host.domain
where "user" is the recipient's username and "host.domain" is their Internet address.
The most difficult part about using electronic mail is finding someone's email address. The following address lookup utilities are available:
% whois -h mailserv.nrl.navy.mil name
Mail utilities are available on most systems. Some common mail utilities include:
The telnet utility can be used to access remote systems.
-------------------------------------
% telnet amp.nrl.navy.mil
Trying 132.250.110.121...
Connected to amp.nrl.navy.mil
Escape character is '^]'
UNIX(r) System V Release 4.0 (amp)
login: stu01
Password:
% logout
%
-------------------------------------
Example 1 Telnet
6. File Transfer Protocol (FTP)
FTP is the primary means of transferring files over the Internet. Using FTP, it is possible to transfer files around the world at very high speed.
FTP can be used in one of two ways:
This last method is referred to as using "anonymous" FTP. Some sites have dedicated entire systems to maintaining extensive archives of source code and other information.
FTP is invoked from the command line as follows:
% ftp host-name
You will be prompted for a login name and password. Anonymous FTP sites accept "anonymous" as the login name and expect an email address at the password prompt.
For example, to connect to the FTP archive at NCSA, use:
% ftp ftp.ncsa.uiuc.edu Name (ftp.ncsa.uiuc.edu:stu01): anonymous Password: stu01@amp.nrl.navy.mil ftp>
There are two file transfer modes:
Standard format for transmitting textual data. ASCII files appear the same on every system, regardless of manufacturer or operating system. In ASCII mode transfers, certain characters are translated to make files readable.
Binary
Binary files have no standard format. A particular binary file may only be readable on certain systems or by certain programs. In binary mode transfers, no translation is performed.
You can typically determine a files type by its extension. Filenames ending in ".txt" or ".doc" are generally ASCII files. Files with other extension are generally binary files.
Commonly used FTP commands include:
-----------------------------------------------------asciiset transfer mode to ASCIIbinarysets transfer mode to binarylslists remote filesdirlists remote files (long listing)cdchanges remote directorylcdchanges local directoryget filenamegets file from remote systemput filenameputs file to remote systempromptturns off (on) prompting during multi ple file operationsmget file-specgets multiple files using wildcardsmput file-specputs multiple files using wildcards?displays help informationquitquit ftp -----------------------------------------------------
------------------------------------------
% ftp ccfsun.nrl.navy.mil
Name (ccfsun.nrl.navy.mil:stu01): stu01
Password: stu01@amp.nrl.navy.mil
ftp> dir
.
.
.
ftp> cd pub/popmail/mac
ftp> get 00README
.
.
.
ftp> quit
%
------------------------------------------
Example 2 FTP Session
Files can be previewed before retrieving using one of the following methods:
ftp> get filename - ftp> get filename |more
Files are commonly stored in compressed, archived format. File compression typically saves 50-75% on disk space. Archiving files, in which entire directory structures are saved in a single file (or saveset), eases the transfer of multiple files. De-archiving the saveset reproduces the original directory structure.
There are no standard methods for compressing and archiving files---hundreds of methods are used. To decompress and de-archive files on a particular system, you must know which archival and compression utilities were used. This can be done by looking at the:
Many FTP sites have files explaining how to install and/or use the programs they have archived
File extension
Common utilities use their own file extensions
In UNIX, files have the following extensions:
.Z compressed file (UNIX compress command)
.tar saveset (UNIX tar command)
The following commands uncompress and untar files:
% uncompress xxx.tar.Z % tar -xf xxx.tar
The tar utility will recreate the original directory structure from the tar dataset.
The Archie program developed at McGill University can be used to locate software available via anonymous FTP. By maintaining one central database for all known archive sites, Archie greatly speeds task of finding specific programs. Currently there are over 3500 public domain packages available at over 600 archive sites.
Archie is actually a pair of software tools:
Information returned as a result of an Archie query includes:
Archie can be queried by telnetting to one of several Archie servers using "archie" as the login name. Archie servers include:
archie.ans.net archie.unl.edu archie.sura.net archie.rutgers.edu
For example:
% telnet archie.rutgers.edu login: archie
Commonly used Archie commands include:
------------------------------------------------------------------------
list [expression] lists sites in database and time at which they were
last updated
help display help information
prog expression search database for file
site site-name list files at specified site
whatis substring search for keyword in software description data
base
set variable-name set variable
show variable-name show value of variable
quit quit Archie
------------------------------------------------------------------------
The following is an example Archie session:
-------------------------------
% telnet archie.rutgers.edu
login: archie
.
.
.
archie> set pager
archie> set term vt100 24 80
archie> whatis popmail
.
.
.
archie> prog popmail
.
.
.
archie> quit
%
-------------------------------
Example 3 Archie Session
In addition to telnet access, Archie can also be queried via email or using a command line or X window client.
Usenet is an electronic "bulletin board"-like system where users can read and post messages on a wide variety of topics.
Fig. 2 Usenet
Usenet can be accessed through any of several common news reader programs, including:
Using a news reader involves the following steps:
Messages are categorized in newsgroups organized hierarchically by areas of interest. Newsgroups may be local, regional, or world-wide. Major world-wide categories include:
comp computer related
sci scientific
soc socially oriented
talk serious discussions
news information about Usenet
rec recreational activities
misc miscellaneous
Local and regional categories include:
nrl NRL local information
dc Washington, DC area information
Newsgroups may be either:
There are three main levels within rn:
Each level has its own set of commands and help menu. At any level, you can type "h" to display its help menu. Typing space at any prompt performs the default action.
rn uses a file named ".newsrc" in your home directory to keep track of which newsgroups you are subscribed to and which articles in each newsgroup you have read.
If any new newsgroups have been created since the previous time you invoked rn, you will be prompted as to whether or not you wish to subscribe to them.
At the newsgroup selection level you specify which newsgroup you want to read next or read them in the default order, which is the order they appear in the .newsrc file. The newsgroup selection prompt is as follows:
******** 17 unread articles in nrl.seminars--read now? [ynq]
Newsgroup selection commands include:
--------------------------------------------------
l string list unsubscribed newsgroups contain
ing string
g newsgroup go to newsgroup (if not currently sub
scribed, you will be prompted as to
whether or not you wish to)
u newsgroup unsubscribe from newsgroup
y read this newsgroup now (default)
n go to next newsgroup
q quit rn
--------------------------------------------------
At the article selection level you specify which article you want next or read them in the default order (either numeric order or by subject). The article selection prompt is as follows:
End of article 248 (of 257)--what next? [npq]
Article selection commands include:
-----------------------------------------------------=list subjects of unread articlesnumberdisplay article numberngo to next unread article (default)pgo to previous unread articleqreturn to newsgroup selection levelmmark current article as unreadccatchup (mark all articles as read) this newsgrouprreply via emailfsubmit followup articleFsubmit followup article (include current article)s filenamesave current article to filename -----------------------------------------------------
The paging level works similar to the UNIX "more" utility allowing you to page through articles screen be screen. The paging level prompt is as follows:
--More--(17%)
Paging level commands include:
-------------------------------------------<space>display next page<return>display next linebbackup one pageqreturn to article selection level -------------------------------------------
There are three ways to post messages:
Messages can be posted at any of several distribution levels---local, regional, or world-wide. There are also newsgroups specifically set up for testing message posting (alt.test).
Many users have "signature" files which are automatically appended to each message posted. Signature files are named ".signature" and are placed in your main directory.
Several newsgroups contain introductory information on the use of Usenet:
Series of articles that explain various aspects of Usenet
Where you can ask question about how Usenet works
Contains information about new and proposed newsgroups
Contains lists of Frequently Asked Questions (FAQs) and their answers and is a good place to "browse the wealth of Usenet"
The World Wide Web (also known simply as "the Web") is a distributed hypermedia (combining the concepts of hypertext and multimedia) information server system. Web documents are multimedia, containing:
Web documents contain hypertext links (highlighted phrases or images) to other Web documents or information sources on the Internet, and are designed to be read in a non-linear fashion.
Web clients (or "browsers") communicate with Web servers using the HyperText Transfer Protocol (HTTP). Web clients can also communicate directly with other Internet information server systems, including:
In addition, Web servers can provide gateways to other programs and databases, including whois and archie. With the ability to access other types of servers, this almost makes using a Web browser a single interface to the Internet.
Public domain Web browsers include NCSA Mosaic (with versions for X Windows, Macintoshes, and PCs) and Lynx (for line-mode terminals). Many commercial browsers are also available (including Netscape). Depending on which browser you are using, various features may not be implemented or may work slightly differently.
When first invoked, the browser program displays the default, or "home," page of information. To follow a link in Mosaic, click on the highlighted text or image. (Lynx links are followed by typing their number.) A connection will be made transparently to the Web server containing the requested information.
In addition to simply following links or using menu options, Web documents can be referenced by their Uniform Resource Locators (URLs) which define the type of resource accessed and its location. The format of a URL is:
scheme://host.domain[:port]/path/filename
where scheme is one of:
http a file on a Web server
ftp a file on an anonymous FTP server
file a file on your local system
news pointer to a Usenet newsgroup
gopher a file on a Gopher server
wais a file on a WAIS server
URLs can be opened via the "Open URL" menu option.
For example, the URLs for the NRL and CCS home pages are, respectively:
http://www.nrl.navy.mil/ http://www.nrl.navy.mil/ccs.html
The URL for CCS Training is:
http://amp.nrl.navy.mil/code5595/
ccs-training
The hotlist feature (under the "Navigate" menu) allows you to remember URLs of interest and to easily return to them. URLs can be added to your hotlist by selecting the "Add Current to Hotlist" menu item.
Mosaic can display certain types of images (GIF and bitmap image formats) inline. Other multimedia document types, including images, animations, sound files, and PostScript documents, are handled by external programs, known as "viewers."
These external programs must be installed on your system in addition to the browser software itself.
Providing information on the Web involves running your own Web server and writing documents using the HyperText Markup Language (HTML).
The CCS also offers a class, "Publishing on the Web," which provides instruction on setting up your own Web server.
In today's information society, researchers and scientists must know how to make effective use of the Internet in order to keep up with the latest technology.
Suggestions for working on the Internet:
Check file sizes before transferring files
Remember time differences
Use utilities after normal business hours
A companion page for this class, containing examples and pointers to related information, can be found at:
http://amp.nrl.navy.mil/code5595/
ccs-training/internetworking