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Some protocols can’t dial out of the neighborhood. Have they been bad? Are they being punished? No, they’re just not very bright and are largely based on the network card’s capability to talk to the local network. These protocols can speak only to other MAC addresses and are known as DLC (data link control) protocols. They are not routable, which means they can talk only to other stations on the same network. You can think of DLC as the “four-digit dialing” you might find in some hotel telephones (without the ability to press 9 to dial out).
Microsoft’s NetBEUI is an example of a DLC protocol. NetBEUI stands for NetBIOS Extended User Interface, which tells you nothing unless you know what NetBIOS is—Network Basic Input Output System. In a nutshell, NetBEUI is simply an improvement of NetBIOS. NetBIOS is a simple networking protocol that was used by IBM and Microsoft in early DOS-based file sharing products; NetBEUI is an improvement now used in Windows 95.
Windows 95/98 users always ask me, “Why can’t I see other people’s workgroups on the network?” Usually, this is because they’re asking Windows 9x to use NetBEUI for file sharing, but they’re trying to see workgroups on the other side of a router. You can add a routable protocol such as IPX/SPX to solve this problem. (TCP/IP can be used, too, but is more complex to configure.)
IPX/SPX, in addition to being a routable protocol, is also a very easy protocol to work with from a user’s perspective. Instead of having to deal with network masks and figuring out network numbers, you need only look at the server (or router) on a network to get the network number, which is an arbitrary and unique hexadecimal number. The node address is simply the MAC address of the network card. The full address, “area code” and all, looks something like this:
0000001D: 000093552899
This translates to network number 1D, node number 93552899 and involves no figuring at all. Even better, workstations need no address configuration whatsoever, because the address is simply lifted from the network card’s MAC address. Unfortunately, because IPX/SPX (invented by Novell, the makers of NetWare) used to be a somewhat proprietary protocol, it never got the market presence that TCP/IP has. Even though Microsoft has adopted IPX/SPX as a routable protocol for file and print sharing under Windows NT and 95, the juggernaut-like momentum of the Internet (and as a result, TCP/IP) probably means that IPX/SPX will remain the less dominant player. It isn’t going away too soon, though. If you have IPX/SPX in your shop, it’s definitely worth being familiar with. See Hour 13, “NetWare Networking Basics” for details.
Another important building block of a network (as important to networking as the red blood cells in your veins are to you) is the packet (sometimes called a frame). It’s the smallest whole unit of communication on the network, much like a sentence is the smallest whole unit of communication in a conversation. (Although words themselves are even smaller units, they’re not complete units of communication. For example, just saying “dinner” to someone doesn’t tell him whether you want to invite him to dinner, eat him for dinner, or skip dinner altogether.)
Only one packet can be on the wire at a time, which makes it tough when multiple users are on the network attempting to complete multiple tasks. For example, suppose the following chunks of conversations traveled the wire in this order:
Tough to follow, huh? Luckily, networks use packet switching. The idea of packet switching is simple. Because conversations need to appear to be seamless, each chunk of the conversation contains information to keep track of who is talking and to whom. Suddenly, what once appeared to be one confused conversation becomes two logical ones:
Because each packet actually has the address (or “phone number”) of the person you need to talk to, and because one computer might have more than one program that wants to talk, there’s an additional concept called known as a socket, which acts very much like a telephone extension. Therefore, just like you might call Frobozz Magic Gadgets and ask to speak to the Wizard at extension 412, when your computer makes a network call, it calls a network address and asks for a socket number.
A socket number is frequently represented by a colon (:) after the address. For example, when you fire up your Web browser to http://www.co.chatham.ga.us, you’re actually referring to 167.195.160.9:80 (or socket 80 of the TCP/IP address 167.195.160.9). Socket 80 is the standard socket for Web services, called HTTP (Hypertext Transfer Protocol).
HTTP is the name of the service that is usually offered at socket 80 by the program that lives there. However, HTTP also refers to the set of rules that allow for Web transactions that Web servers and browsers attempt to follow. It’s important to understand that there are two definitions of HTTP here: the socket name (as in “socket 80 is the socket typically used for HTTP”) and the protocol, itself (as in “All Web servers need to follow the HTTP protocol to ensure error-free operation”). Many other protocols and services have this dual reference as well—for example, SMTP, which refers both to socket number 25 (typically used for mail services) as well as the Simple Mail Transfer Protocol’s rules of engagement.
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