Network Services
File Transfer Protocol
FTP stands for file transfer protocol. It is a means of transferring files
between computers of different types on the Internet.
Standard commands are used to connect to computers, which hold files.
These computers are called ftp servers.
When you logon to an ftp server, you need to supply a username and
password.
Most ftp servers allow users to use an account called anonymous, which
allow users to logon using this account with limited access.
When users logon to an ftp server using the account anonymous, it is
usual for them to use their email address as the password.
The features of ftp are,
ftp servers exist to provide a storage place for useful files and
programs
users can logon to these servers and download the files to their local
computer
you have to know the server name and whereabouts the file is located
(subdirectory and filename)
it is command driven using commands like open, bye, get
it is hard to see the general structure or layout of any ftp server [would
be nice to have a roadmap or hierarchical diagram of the directory
tree]
Telnet
Telnet is a service that allows a user to login and run programs on a
remote server on the Internet.
This requires a user account (name and password) on the telnet server.
On the user computer, a telnet client application is run, similar to the ftp
command interface discussed earlier.
The general features of telnet are
you must logon using a specific account and password
you run programs on the host computer
program output is seen on your own computer
it is interactive
you must know the commands and what programs are available
All commands you type are sent to the host computer you are connected
to and executed there. You see the programs output on your local
computer.
In this way, it is possible for a user to run programs on a much more
powerful computer than their own, or run software which may not be
present on their own local computer.
E-mail
Electronic mail is a way of sending messages between users over the
Internet.
As outlined in chapter one, each user must have an email address.
An email program allows users to create messages and send them to other
users.
There are five essential parts to an email message.
Email uses the protocol SMTP (Simple Mail Transport Protocol) to
forward email messages around the Internet.
When you create an email message it is send to your mail server and held
in an outgoing folder.
At regular intervals, your mail server will attempt to send the messages in
its outgoing folder by contacting the destination mail servers and
transferring the messages to them.
This principle is called store and forward. If the destination mail server
cannot be found, the messages are eventually discarded.
Bounced email occurs when an email message is sent to a mail server,
but there is no valid recipient for that message.
For example, the address postmistress@mail.cit.ac.nz would be returned
(by deliberately misspelling) with no such user.
Usenet News
Usenet news is a large discussion type service that allows users to post
and reply to messages in certain categories.
It is a great way to ask questions and communicate with people of similar
interests.
News is held on a news server. This server is connected to the Internet
and regularly gets news articles from other news servers.
Any new messages that local users write are forwarded from the local
news server to the next level up, and so on, until the message propagates
to all other news servers in the world.
As you might expect, this can generate a large amount of information
traffic.
To help with the organization of news, articles are placed into groups.
There is a hierarchy of groups, illustrated below,
alt alternate lifestyles
biz business companies
comp computers
misc miscellaneous
rec recreational
soc social issues
In addition, there are also country specific and organization specific news
groups. For instance, New Zealand has some news groups which begin
with nz.
To read news you require a news-reader client and access to a news
server. News uses the NNTP protocol that runs on top of TCP/IP.
Gopher
It was not long before people using the Internet realised that finding
information on the Internet was a hard task.
Gopher consisted of two parts, a Gopher server and a Gopher client.
A Gopher server was a means of providing documents and programs (in
fact any type of file) to users.
Whereas archie and ftp where purely command type interfaces (where
users had to type commands and the responses were given back as text),
Gopher implemented a means of displaying the information graphically
for the client.
This made navigation of the documents available on Gopher servers
much easier.
Another advantage was the ability of Gopher servers to link to other
Gopher servers.
If you could not find the information you were looking for on one
Gopher server, you could try the next one and so on till you located the
desired information.
The Gopher client was a primitive form of web browser, and displayed
the information available on the Gopher server in graphical format using
small easily recognisable icons.
This meant you could readily identify the information as a text document
or a program.
Clicking on the associated icon downloaded the file to your computer,
where you could save it on disk for later viewing or use.
In the picture on the
left, it displays a
typical Gopher list of
the information
available on the
Gopher server.
Note the use of
different icons to
represent different file
types.
Gopher is seldom used
today, with the WWW
and web browsers
offering much more
functionality