Part XI - Internet Servers - Behind the scenes

TCP/IP and Ports

All Internet communications are performed using the TCP/IP protocol. TCP/IP stands for Transport Control Protocol/Interface Program.  TCP/IP is a packet oriented protocol that uses a system of ports to determine what each server process should "listen" to. A complete list of ports can be found in rfc1700 which stands for Request For Comment number 1700. All Internet Request for Comments can be found at http://www.isi.edu/  under publications. Some time when you can't sleep you can look through these archives to see what has been going on behind the scenes of Internet development.

As I explain each of the common services I will mention the port that the process listens to so you will be familiar with their usage. Why? Because many programs refer to this information from time to time (Front Page, Outlook Express, etc) and because I told you I was going to tell you about the Internet behind the scenes.

E-MAIL

Through all the hype of the World Wide Web, e-mail is still used heavily by many people and is growing rapidly. This is probably due to several reasons including a chance to communicate with friends and family that have been out of touch for any number of reasons.

So how does e-mail work? In simple terms, you use a Mail User Agent (MUA) such as Outlook Express to write your mail and send it (typically using a POP (Post Office Protocol) server over TCP/IP port 25 to a Mail Transfer Agent (MTA) such as Sendmail, which then communicates with the server of the person you are sending the mail to, who then retrieves their mail with an MUA looking at TCP/IP port 110 to read it. Did I say simple terms? Assuming you and your mail recipient are using an ISP (Internet Service Provider) there are no less than 4 computers involved in the mail process - yours, your ISP's, your recipient's and your recipient's ISP. More than likely there are many servers involved. If you are curious how many, simply follow these steps using Windows95:

Connect to your ISP

Click on Start

Select Programs

Select MS-DOS Prompt

Enter "tracert visiontm.com" (without the quotes)

Hit the enter key

The tracert (Trace Route) program shows you every route (server, router, etc) that your e-mail takes to get to the Vision Technology Management server.

WEB BROWSERS

The most common use of the Internet today (with e-mail running neck and neck) is using a Web browser (Internet Explorer, Netscape Navigator, etc) to explore the World Wide Web. We have discussed how to develop Web pages using HTML over the past 10 newsletters. What we have not discussed is how this process actually works behind the scenes.

In order to get the HTML code to work, you need to use a Web Server such as Apache, Microsoft Personal Server, Red Hat, and many others. What these servers due is monitor port 80 of the TCP/IP protocol for activity. When it finds activity, the server responds back with the requested information. The requested information is usually stored as HTML pages that your Web Browser then interprets and displays to your screen. The server's job is to determine what domain you are looking for, what file you would like, whether you are authorized to see that file, and then send it to you. Your browser is responsible for how it looks on your screen.

Autoresponders

If you have spent any time on the Web you have probably run in to an autoresponder. An autoresponder's sole job is to wait for an e-mail and then immediately send back an e-mail to the sender. Autoresponders can be used to send an e-mail stating that the recipient is on vacation, to send requested literature, or to acknowledge receipt of an e-mail before a human has had time to read the content.

In a UNIX environment, Autoresponders are typically set up by using a program called Procmail. All mail requests to a domain can be routed to Procmail, which then determines whether the mail matches the user's criteria to respond with an e-mail message. If the mail doesn't match any criteria, it is forwarded on through the normal process. Procmail can be used for many other tasks such as selective filing of e-mail messages to folders, forwarding to another e-mail address, rejecting of SPAM, etc. For a detailed example of how to set up Procmail or Autoresponders within a Vision domain please go to http://www.visiontm.com/index.php?option=com_content&task=view&id=23&Itemid=34 .

Web Statistics

Web statistical analysis programs help the webmaster of a domain determine the effectiveness of his/her Web Marketing efforts. A good analysis program will tell the webmaster how many people came to the site, where they found the site, what browser they were using, the most frequently used pages, and even what keywords were entered in a search engine to find your domain.

A very good program available to all Vision customers is Analog. Vision customers access Analog using a simple web page. After making the selections on the form (or accepting the defaults) webmasters are instantly presented with a report showing an amazing amount of information.