Many companies and other organizations run networks that are deliberately firewalled so that their users can get to servers like those at ripe.net, but nobody outside the company network can get to company hosts. A user of such a network can thus use WWW, Gopher, FTP, and TELNET, but cannot supply resources through these protocols to people outside the company. Since a network that is owned and operated by a company in support of its own operations is called an enterprise network, let's call these networks enterprise IP networks, since they typically use the Internet Protocol (IP) to support these services. Some companies integrate their enterprise IP networks into the Internet without firewalls, but most do use firewalls, and those are the ones that are of interest here, since they're the ones with one-way access to these Internet services. Another name for an enterprise IP network, with or without firewall, is an enterprise Internet.

For purposes of this distinction between suppliers and consumers, it doesn't matter whether the hosts behind the firewall access servers beyond the firewall by direct IP and TCP connections from their own IP addresses, or whether they use proxy application gateways (such as SOCKS) at the firewall. In either case, they can use outside services, but cannot supply them.

So for services such as WWW, Gopher, FTP, and TELNET, we can draw a useful distinction between supplier or distributor computers such as those at ripe.net and consumer computers such as those inside firewalled enterprise IP networks. It might seem more obvious to say producer computers and consumer computers, since those would be more clearly paired terms. However, the information distributed by a supplier computer isn't necessarily produced on that computer or within its parent organization. In fact, most of the information on the bigger FTP archive servers is produced elsewhere. So we choose to say distributors and consumers. Stores and shoppers would work about as well, if you prefer.

Let's call the non-firewalled computers the core Internet, and the core plus the consumer-capable computers the consumer Internet. Some people have referred to these two categories as the Backbone Internet and the Internet Web. We find the already existing connotations of "Backbone" and "Web" confusing, so we prefer core Internet and consumer Internet.

It's true that many companies with firewalls have one or two computers carefully placed at the firewall so that they can serve resources. Company employees may be able to place resources on these servers, but they can't serve resources directly from their own computers. It's rather like having to reserve space on a single company delivery truck, instead of owning one yourself. If you're talking about companies, yes, the company is thus fully on the core Internet, yet its users aren't as fully on the Internet as users not behind a firewall.

If you're just interested in computers that can distribute information (maybe you're selling server software), that's a much smaller Internet than if you're interested in all the computers that can retrieve such information for their users (maybe you have information you want to distribute). A few years ago it probably wouldn't have been hard to get agreement that firewalled company networks were a different kind of thing than the Internet itself. Nowadays, firewalls have become so popular that it's hard to find an enterprise IP network that is not firewalled, and the total number of hosts on such consumer-capable networks is probably almost as large as the number on the supplier-capable core of the Internet. So many people now like to include these consumer-capable networks along with the supplier-capable core when discussing the Internet.

But what about mail, lists, and news? We carefully left those out of the discussion of firewalls, because almost all the firewalled networks do let these communications services in and out, so there's little useful distinction between firewalled and non-firewalled networks on the basis of these services. That's because there's a big difference between these communications services and the resource sharing (TELNET, FTP) and resource discovery (Gopher, WWW) services that firewalls usually filter. The communications services are normally batch, asynchronous, or store-and-forward. These characterizations mean more or less the same thing, so pick the one you like best. The point is that when you send mail, you compose a message and queue it for delivery. The actual delivery is a separate process; it may take seconds or hours, but it is done after you finish composing the message, and you normally do not have to wait for the message to be delivered before doing something else. It is not uncommon for a mail system to batch up several messages to go through a single network link or to the same destination and then deliver them all at once. And mail doesn't even necessarily go to its final destination in one hop; repeated storing at an intermediate destination followed by forwarding to another computer is common; thus the term store-and-forward. Mailing lists are built on top of the same delivery mechanisms as regular electronic mail. USENET news uses somewhat different delivery mechanisms, but ones that are also typically batch, asynchronous, and store-and-forward. Because it is delivered in this manner, a mail message or a news article is much less likely to be a security problem than a TELNET, FTP, Gopher, or WWW connection. This is why firewalls usually pass mail, lists, and news in both directions, but usually stop incoming connections of those interactive protocols.

Because WWW, Gopher, TELNET, and FTP are basically interactive, you need IP or something like it to support them. Because mail, lists, and news are asynchronous, you can support them with protocols that are not interactive, such as UUCP and FidoNet. In fact, there are whole networks that do just that, called UUCP and FidoNet, among others. These networks carry mail and news, but are not capable of supporting TELNET, FTP, Gopher, or WWW. We don't consider them part of the Internet, since they lack the most distinctive and characteristic services of the Internet.

Some people argue that anything that uses RFC-822 mail is therefore using Internet mail and must be part of the Internet. We find this about as plausible as arguing that anybody who flies in a Boeing 737 is using American equipment and is thus within the United States. Besides, there are plenty of systems out there that use mail but not RFC-822. So what to call systems that can exchange mail, but aren't on the Internet? We say they are part of the Matrix, which is all computer systems worldwide that can exchange electronic mail. This term is borrowed (with permission) from Bill Gibson, the science fiction writer.

Other people refer to the Matrix as global E-mail. That's accurate, but is a description, rather than a name. Some even call it the e- mail Internet. We find that term misleading, since if a system can only exchange mail, we don't consider it part of the Internet. Not to mention not everything in the world defines itself in terms of the Internet, or communicates through the Internet. FidoNet and WWIVnet, for example, have gateways between themselves that have nothing to do with the Internet. Referring to the Matrix as the Internet is rather like referring to the United Kingdom as England. You may call it convenient shorthand; the Scots may disagree.

What about news? Well, the set of all systems that exchange news already has a name: USENET. USENET is presumably a subset of the Matrix, since it's hard to imagine a USENET node without mail, even though USENET itself is news, not mail. USENET is clearly not the same thing as the Internet, since many (almost certainly most) Internet nodes do not carry USENET news, and many USENET nodes are on other networks, especially UUCP, FidoNet, and BITNET.



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