WXET1143 Lecture7: , Chat and Messaging

Introduction  Electronic mail is everywhere.  Now many people in business, government, and education use more than the telephone to communicate with their colleagues.  has been around since the Internet was formed but was first popular only on LAN.

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

Multipurpose Internet Mail Extension (MIME)  Body of 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 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 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 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  Using an 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 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 to locate the recipient’s 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 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 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 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 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.