Shell VS. PPP

Excerpt from University of Alabama Roadmap 

Level One connectivity ("access through a gateway") is access to the Internet from a network that really isn't "on" the Internet. Picture two circles that touch each other at only one point. One of the circles is the Internet, the other circle is a non-Internet network, and the point where the two networks touch is called a gateway. The gateway allows the two networks to "talk" to each other, but users of the non-Internet network are limited in their ability to fully access all of the tools of the Internet. With Level One connectivity, you are limited to what you can access on the Internet by what your service provider allows you to access. 

A good example of networks with Level One connectivity is America On-Line (AOL), Compuserve, Prodigy, and many of the other commercial on-line services. AOL is, in effect, its own little network. It has a great number of different programs that its subscribers can use, but ALL of these programs only run on the AOL network. 

AOL subscribers, and the subscribers to most of the other commercial on-line services, are lucky in the fact that they can still access SOME of the tools ofthe Internet through their gateway. A lot of people with Level One connectivity only have e-mail access (by the way, if you have Level One connectivity, do not worry -- I'll show you how to access a lot of the Internet's tools using e-mail (it's not easy, but you can do it)). 

Level Two Internet access ("remote modem access") is access through a dial-up terminal connection. This is where, through the use of a modem, you access a "host" and your computer acts like it is a terminal on that mainframe. You may type the commands on your own computer, but it is the host that carries out your commands. 

Level Two connectivity is the most "popular" (in the sense that more people have Level Two connectivity than any other level) and the most misunderstood level of connectivity. 

To begin with, Level Two connectivity limits you to using the programs (also known as "clients") that are running on the host. If, for example, you hear of this hot new client called "Mosaic" and you want to try it out, if your host does not have a Mosaic client on it you are out of luck! Putting a copy of the Mosaic client software on your own computer won't do ANYTHING for you -- remember that the only programs that you can use when you have Level Two connectivity are the programs that the host has! 

Also, with Level Two connectivity you must always remember that everything you are doing is through the host, NOT through your own computer. If you download a file from somewhere (like we did last Friday with the GET command) that file will go to the host, NOT to your own personal computer. You'll need to download the file one more time -- this time from the host to your computer -- if you want the file to be on YOUR computer. (Your local Internet provider can tell you more about this). 

Level Three connectivity ("Direct Internet Access") is the highest, and most expensive, level of connectivity there is. With Level Three connectivity, you are directly wired into the Internet using high-speed telephone lines, and you are "on-line" twenty-four hours a day, seven days a week. Level Three connectivity is great if you are a mainframe or a major site with hundreds of users, but is not too advantageous if you are a sole user with a beat-up PC. 

Besides, Level Three Internet access is so incredibly expensive (1) (the University of Alabama pays $29,000.00 (US) each and every year just to connect to the Internet, and that doesn't include the software, hardware, facility, and staff expenses) that, until recently, Level Three connectivity was limited to large corporations and Universities. Also, because Level Three connectivity is limited mostly to mainframes, you as a user are still limited to using the programs that are already loaded on the mainframe. 

Thanks to some recent breakthroughs in modems and telephone lines, there is a new branch of Level Three connectivity which is called "On-Demand Direct Connectivity." Since you probably aren't going to spend twenty-four hours a day on the Internet, there are some sites out there that will let you connect to the Internet whenever you want using a high speed modem and something called "Point to Point Protocol (PPP)" or "Serial Line Internet Protocol (SLIP)" connection. 

There are two cool things about PPP and SLIP connections. First, because you aren't connected to the Internet all day long, it doesn't cost as much as regular Level Three connectivity (you can find sites that will only charge you about $40 or $50 US (that's about $29,547,952.00 Canadian -- I'm kidding :) -- month for a PPP or SLIP connection). The second cool thing about PPP and SLIP connections is that the client software is stored on YOUR computer. Want to play with Mosaic? Load it onto your computer and play with it (you can't do this with any of the other levels of connectivity). 

The one bad thing about PPP and SLIP connections is that they are a relatively scarce commodity. Not many Internet service providers offer PPP and SLIP connections, but the number of providers offering PPP and SLIP connections will certainly increase over time :) 

In review, there are three levels of Internet connectivity:

One Access through a Gateway Limited Internet access
Two Remote modem access Most "popular"
Commands executed by host
All programs on host
Can only run client software already on the host
All files on host unless you download to your computer
Three Direct Access EXPENSIVE!
24 hour connection
All software on mainframe
..... PPP/SLIP Not all that expensive
Connect when you want
Client software on YOUR computer


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