Mini Tutorial

Internet for You

Katarzyna J. Macura, M.D., Ph.D.

The Russell H. Morgan Department of Radiology and Radiological Science •  Johns Hopkins Medical Institutions

Part 3 — Communicating on the Internet
by Katarzyna J. Macura, M.D., Ph.D.

The most important feature of the Internet is making it easier for people to communicate with one another using computers. The most popular way of communication on the Internet is electronic mail (e-mail). The oldest electronic message programs date back to the early 1960s. They only worked locally, allowing the exchange of messages between users who shared the same machine. Such users could create a text file and deliver it to a designated "mailbox". The first e-mail message was sent in 1971 by an engineer named Ray Tomlinson, who had been working on an experimental file transfer protocol (FTP), CYPNET, for transferring files among linked computers at remote sites within ARPANET, the precursor to the Internet. Using the CYPNET protocol, he was able to send messages to remote mailboxes on the network.

Tomlinson chose the @ symbol to distinguish between messages addressed to mailboxes in the local machine and messages that were headed out to the network. An Internet e-mail address contains a combination of a user name @ a domain name (text version of an IP address – Internet protocol address representing a numeric address for each computer location on the Internet). The e-mail message can be simple text or can be enhanced by attachment of other binary files, such as images, videos, sounds and executable files.

When the mail is delivered to a user’s mailbox, the user needs a way to read the mail, compose new mail and respond to mail. E-mail software called mailer or reader is used for this purpose. Most e-mail software has a mail notification alert that informs the user via a message or sound about the arrival of new mail. The message files are first encoded using one of the encoding schemes, such as MIME or UUencode, and subsequently decoded when they reach the recipient using the same scheme. Many e-mail software packages encode and decode automatically.

When someone sends an e-mail message, the message usually is not delivered directly to a recipient’s computer. Instead, it gets sent to a mail server. Two different servers are running on a mail server machine. One is called the SMTP Server, where SMTP stands for Simple Mail Transfer Protocol. The SMTP server handles outgoing mail. The other is a POP3 Server, where POP stands for Post Office Protocol. The POP3 server handles incoming mail. Recipient’s e-mail software logs into the mail server and checks whether there is any new mail. The new mail messages will be displayed as a list when the user logs in to the server using the login name and password.

When the user wants to read a message, he/she selects the message and it is downloaded to the user’s computer. E-mail software lets the user create folders for storing mail, allows the user to search through messages, keeps an address book, creates group mailing lists, creates and adds signature file, etc. The newest generation of e-mail software reads HTML-based pages allowing the user to receive in the mailbox fully formatted Web pages. The browser will launch and visit the pages that are linked to the mail messages.

E-mail messages are sent the same way as other Internet data. The TCP protocol breaks the messages into packets, each packet bears the address of the destination, the IP protocol delivers the packets to the proper location, and then the TCP reassembles the message on the receiving end so that it can be read. If the mail is sent to someone on the same network, an internal router delivers the mail directly to the addressee over the same network. If the mail is addressed to someone outside the network, it is sent to the Internet router. Routers on the Internet look at the addresses in each packet and send them on the best path to get to the destination. When all the packets have been received at the receiving address, they are recombined into a complete e-mail message.

Mailing list

A mailing list connects a group of people who are interested in the same topic. When one person sends e-mail to the mailing list, that message is automatically sent to everyone on the list. Mailing lists can be moderated or unmoderated. A moderated mailing list is screened by the list administrator, who may kill duplicate messages or messages that are not related to the list’s theme. An unmoderated mailing list is wide open; all mail sent to it is automatically transferred to everyone on the list. The mailing list itself is a database of the e-mail addresses of people who have subscribed to it. When the user wants to subscribe to a mailing list, he/she sends a message to the mailing list administrator, asking to join the list or sends a message to a list server that automatically subscribes the requestor to the list, by adding the requestor’s e-mail address to the database. To cancel a subscription, a cancellation request needs to be sent to the list administrator.

Usenet Newsgroups

Usenet is a global bulletin board and electronic discussion forum. It collects messages about different topics forming thematic newsgroups in which anyone can participate. To participate, people send and read messages that are posted to the newsgroup. Newsgroups and all their messages are stored on a Usenet server. Usenet servers communicate with one another so that all messages posted on one server are duplicated on the other servers. System administrators decide which newsgroups they want to carry at their sites. Newsgroup reader software, which is included with most browsers, allows for reading messages and responding to newsgroups. The user can read newsgroups without subscribing to them by manually asking to read specific newsgroups instead of having it done automatically. Many newsgroups have a list of Frequently Asked Questions (FAQ). These FAQs answer common questions about the newsgroup. Thousands of Usenet newsgroups are divided into hierarchies of topics to make it easier for users to find the particular newsgroups they want to participate in. In the hierarchy of newsgroups, the major topic is followed by a subtopic and that subtopic can be further subdivided. The user can often identify the newsgroup by its name, e.g. "rec" for discussions of recreational topics, or "sci" for discussions of scientific topics. Newsgroup members frequently post articles as a reply to another article. These replies may cause the author of the original article, or others, to post additional articles related to the original one. The original article and all subsequent articles are called a thread or threaded discussion. In moderated newsgroups, each message goes first to a human moderator for verification and then is posted. In the unmoderated newsgroup messages are posted automatically. Usenet evolves constantly, new newsgroups are being created and old ones are being eliminated.

Internet Relay Chat

One of the most immediate ways to communicate with others via the Internet is to participate in live "chat". Internet Relay Chat (IRC) means that user holds "live keyboard conversations" with other Internet users who are online at the same time. A chat room refers to the communications channel that permits users to chat on a particular topic. Some chat rooms support graphical, voice and video chats. IRC follows a client-server model, which means that both client and server software are required to use it. Most of today’s browsers include a chat client. To chat, the user makes a connection to the Internet and starts client software. Next, the user logs into the IRC server. IRC servers are connected together in a network so that they can send messages to one another. After selection of a specific "channel," the user chooses a user name to identify himself/herself during the chat. By joining a channel, the user is able to see the conversations that are taking place. To join a conversation, the user just types a message on the keyboard. This message is sent from the client software to the IRC server to which the user is connected. The message is then sent from one server to another. Each server distributes the message to the client software of users connected to the same channel that can read and respond to the message.

Internet Telephony

The Internet can be also used for traditional telephone-like communication. The most exciting part of using the Internet to make phone calls is the price. Users pay for the Internet connection, as if they were browsing the Web or sending e-mail anywhere in the world. Special software is required (e.g. Net2Phone, DigiPhone) for computer-to-computer or computer-to-phone communication. Also, a microphone, a sound card and speakers are needed. In the computer-to-computer communication, both users need access to multimedia PC. To send and receive calls over the Internet, the user connects directly using an e-mail address or connects to the directory that contains a list of people who can connect using the same software. The directory allows for matching the name with the Internet IP address. The call is then routed to the recipient’s computer, and the conversation can take place by using the sound cards, microphones and speakers. The voice is converted into the binary data and also compressed for efficient transfer over the Internet. The speed of the transfer of the sound depends on the speed of the connection; higher the speed, better the quality of the sound. The sound of the caller and recipient voice is broken into packets that are delivered, like any other type of data, using the Internet’s TCP/IP protocols. On the receiving computer, software decompresses the packets so they can be played and heard. Sometimes, packets arrive out of order and some might be missing. For high quality communication, it is best to use the highest possible connection speed during low traffic hours.

Another way of using an Internet connection for a phone-like communication is through a computer-to-phone connection. Net2Phone enables Internet users to place domestic and international calls from a personal computer to any telephone in the world at significantly reduced rates. This type of connection enables the user to carry on real-time, two-way conversations, using a sound-equipped PC on one end and a regular phone on the other end. The call is being transferred from a caller’s computer over the Internet to Net2Phones’s telephone switches that automatically relay the call to its final destination. Because the call is carried over the Internet until it reaches Net2Phone’s switches, rates are not dependent upon the country of origin.

Wireless Communication

Today, many users connect to the Internet wirelessly using cellular or satellite services. Web-enabled devices include handheld devices, such as Personal Digital Assistants (PDAs), smart phones, smart pagers and hand-free (voice activated) Internet devices found in automobiles. A smart phone is a cellular phone that, in addition to other features, allows the user to send and receive messages over the Internet and browse Web sites specifically configured for display on a phone. A smart pager is a two-way pager whose features include sending and receiving e-mail and receiving news alerts from the Web. To connect to the Internet using wireless technology, an Internet service provider that can communicate with the device is needed. Once the user subscribes to the service, the wireless provider communicates with an antenna on the Web-enabled device. The user can access the Web directly using the Web-enabled device or can connect the smart phone to the laptop computer, providing wireless access from the laptop computer. Since the download times of many Web sites would be too slow for efficient use of the wireless device, two schemes have been introduced for improving the wireless communication over the Internet, the wireless portal and Web clipping.

The wireless portal is a single Web site that attempts to provide all information a wireless user might require and offers services such as search engines, news, e-mail, etc. Web clipping applications were developed for some of the most popular sites on the Web targeted specifically for display on a Web-enabled device. When the user needs information from one of those sites, he/she makes a query and the information is "clipped" from the site, transmitted across the airwaves and downloaded onto the device.

The future of wireless Web communications continues to grow rapidly.

The mobile Internet access market will cater to 136 million people by the end of 2007, thanks to the increased mobility of the workforce and the introduction of mobile-specific applications, according to Frost & Sullivan (an international marketing consulting and training company). That's an increase from 2.9 million active subscribers in 2000. The development of the Bluetooth wireless technology is set to revolutionize the personal connectivity market by providing freedom from wired connections. Bluetooth provides short-range radio links for point-to-point and point-to-multi-point voice and data transfer. A Bluetooth chip is designed to replace cables by taking the information normally carried by the cable and transmitting it at a special frequency to a receiver Bluetooth chip.

Bluetooth will enable users to connect to a wide range of computing and telecommunications devices without the need for proprietary cables with the gross data transfer rate at 432 Kbps for full duplex transmission, 721/56 Kbps for asymmetric transmission. Bluetooth products will provide links between mobile computers, mobile phones and other portable handheld devices, and connectivity to the Internet. The wireless connectivity will support Wireless Personal Area Networking (WPAN), Wireless Local Area Networking (WLAN) and Wireless Wide Area Networking (WWAN). This cable-replacement technology is named after a Danish Viking and King, Harald Blåtand (Bluetooth in English), who lived in the late 10th century. Harald Blåtand united and controlled Denmark and Norway; hence the inspiration on the name: uniting devices through Bluetooth. Old Harald had an inclination towards eating blueberries, thus his teeth became stained with the blue color. It is predicted that Bluetooth is likely to become a standard for mobile phones, PCs, laptops and a whole range of other electronic devices. Bluetooth is set to become the fastest adopted communication technology in history.

www.aawr.org Editor's Note: The original Mini-Tutorial on the Internet by Katarzyna J. Macura, M.D., Ph.D., was published in the AAWR Newsletter Focus. Dr. Macura updated her series for RSNA News.