WXET1143

Lecture7: Email, Chat and Messaging

Introduction

Electronic mail is everywhere. Now many people in business, government,

and education use email more than the telephone to communicate with their colleagues.

Email has been around since the Internet was formed but was first popular only on LAN.

Internet email

Uses two main standard: Simple Mail Transfer Protocol (SMTP)

To send messages Post Office Protocol

To receive messages These standards are universal. Can run on a variety of incompatible

computers and operating system.

AOL (American Online) doesn’t use SMTP or POP

Uses its own propriety protocols to send and receive emails

AOL users can communicate with people outside of AOL is because it uses gateway software that translates between different email protocols.

Multipurpose Internet Mail Extension (MIME) Body of email now can accommodate

graphics, sound, documents and video. You can add it either in the body or attach

it. When you enclose a file, your email

software encodes it and turns all multimedia data into ASCII.

The receiving end will then turn the ASCII into meaningful data.

MIME is one of the encoding scheme used.

Junk mail Spam or junk mail is another set of email standard

that enables communication which can also annoy the other party.

Electronic mailing lists automatically sends messages to a large number of users.

Can be done on a one-time basis or a regular schedule.

Mail reflector: A server that distributes mails to member of the

mailing list. List server:

Individuals send email messages to subscribe or unsubscribe to a mailing list.

File sharing A file sharing program user logs on to a file-sharing

server. The client software sends the server a list of files in

the user’s library. Other users can then search and download the file.

When a user searches for music, the host filters the new list to remove any song titles that match lists of copyrighted songs supplied by record companies.

Then the host posts the list in a database where other users can search it.

Another client enters a search term. This can be a song title, artist’s name or anything

else relevant to a song.

The client looks at all the library records in the server.

Displays the title that matches at least some of the search criteria.

The results include the name of the file, type of internet connection, the IP address of the client that makes the file available and so on.

The user selects one or more of the files for transfer.

His client software sends a message to the other client using its IP address.

The message asks permission to download the song.

The remote client obliges by becoming a server and sending the file to the computer that requested it.

At the same time someone is downloading a file, other users are finding songs on the person’s hardisk and downloading them.

Downloads/Uploads can be done simultaneously by taking turns sharing the Internet connection.

Sending email

Using an email client software, Jane creates a message to go to Bob.

She attaches an image of herself which is encoded using MIME.

The encoding turns the data into ASCII text. The email software might also compress

the enclosure before attaching it so that the message takes less time to send.

The client software contacts the ISP’s computer server over a modem or network connection.

The client software connects to a software called the SMTP server.

The server acknowledges that it has been contacted.

The client tells the server that it has a message to be sent to a certain address.

SMTP replies with a message either saying “Send it now” or “Too busy, send it later”

Client sends the message to the SMTP and asks for confirmation.

Server confirms that it has received the message.

SMTP server asks another software, a domain name server, how to route the message.

The server looks up the domain name (@yahoo or @fsktm) to locate the recipient’s email server.

The domain name server tells the SMTP the best path for the message.

After the SMTP sends the message, the mail travels through various Internet routers.

Routers decide which electronic pathway to send the email along based on how busy the routes are.

The message also passes through one or more gateways.

Gateways: translates data from one type of computer system such as Windows to the type of computer system that’s the next pass-through point on the route.

When email arrives at Bob’s SMTP server, the server transfers the message to another server called a POP (Post Office Protocol).

POP holds the message until Bob asks for it. Using his email client, Bob logs on to the

POP server with a username and password and then asks the server to check for mail.

The POP server retrieves Jane’s stored message and transmits it to Bob’s client software.

Some email software decodes and decompresses any enclosures.

So now Bob can read Jane’s message and see what it looks like.

Chat rooms

Chats are held in a chat room, a virtual room that’s really software running on an Internet server.

The chat software is designed to let several computer users, all online at the same time, type messages that are seen simultaneously by all the other chatters.

To join a chat, you must first run a chat client software.

The first time you use a chat program, you need to set up a screen name.

People usually pick something that reflects them or even maybe their alter-ego.

After you log in under your screen name, you choose the room you want to enter.

Rooms usually have names devoted to a particular subject of interest.

When room is selected, the chat server associates you with the path you took to it so that it will recognize any other messages from you.

It then adds your screen name to a lost of other people who are already in the room.

It then send a line of text that appears on the screen of everyone in the room to announce that you have joined them.

Then everything you type will be sent to the server.

The server adds your screen name to the words you type so other will know it’s you talking.

This message is then sent out to the computers of everyone that is logged on in the chat room.

They see everything you write and also vice-versa.

Instant messaging Chat rooms are for public use, instant

messaging are a more private way to communicate.

It lets you and a selected friend write messages that appear instantly on the screen.

To use instant messaging, you must sign up with one of the instant messaging service (AIM, MSN, Yahoo, etc…).

Then you can create a buddy list of your contacts.

Once installed, whenever you log onto the message service, the software running on your computer send both your handle (ID) and buddy list to a central computer.

This central computer (or messaging server) takes care of thousands of users simultaneously.

The message server adds your name to a list of people who are online. It also compares your buddy list with the handles of people online.

This way you will know which of your buddies are also online.