10. Networking and the Internet
IN THIS CHAPTER
The communications facilities linking computers are continually improving, allowing faster and more economical connections. The earliest computers were unconnected stand-alone systems. To transfer information from one system to another, you had to store it in some form (usually magnetic tape, paper tape, or punch cardscalled IBM or Hollerith cards), carry it to a compatible system, and read it back in. A notable advance occurred when computers began to exchange data over serial lines, although the transfer rate was slow (hundreds of bits per second). People quickly invented new ways to take advantage of this computing power, such as email, news retrieval, and bulletin board services. With the speed of today's networks, a piece of email can cross the country or even travel halfway around the world in a few seconds.
Today it would be difficult to find a computer facility that does not include a LAN to link its systems. Mac OS X systems are typically attached to an Ethernet (page 931) network. Wireless networks are also prevalent, especially Apple's Airport and Airport Extreme. Large computer facilities usually maintain several networks, often of different types, and almost certainly have connections to larger networks (companywide or campuswide and beyond).
The Internet is a loosely administered network of networks (an internetwork) that links computers on diverse LANs around the globe. An internet (small i) is a generic network of networks that may share some parts in common with the public Internet. It is the Internet that makes it possible to send an email message to a colleague thousands of miles away and receive a reply within minutes. A related term, intranet, refers to the networking infrastructure within a company or other institution. Intranets are usually private; access to them from external networks may be limited and carefully controlled, typically using firewalls (page 389).
Over the past decade many network services have emerged and become standardized. On Mac OS X and other UNIX and UNIX-like systems, special processes called daemons (page 929) support such services by exchanging specialized messages with other systems over the network. Several software systems have been created to allow computers to share filesystems with one another, making it appear as though remote files are stored on local disks. Sharing remote filesystems allows users to share information without knowing where the files physically reside, without making unnecessary copies, and without learning a new set of utilities to manipulate them. Because the files appear to be stored locally, you can use standard utilities (such as cat, vim, lpr, mv, or their graphical counterparts) to work with them.
Developers have been creating new tools and extending existing ones to take advantage of higher network speeds and to work within more crowded networks. The rlogin, rsh, and telnet utilities, which were designed long ago, have largely been supplanted by ssh (secure shell, page 847) in recent years. The ssh utility allows a user to log in on or execute commands securely on a remote computer. Users rely on such utilities as scp and ftp to transfer files from one system to another across the network. Communication utilities, including email utilities and chat programs (e.g., talk, Internet Relay Chat [IRC], ICQ, and instant messenger [IM] programs, such as iChat, AOL's AIM, and gaim) have become so prevalent that many people with very little computer expertise use them on a daily basis to keep in touch with friends, family, and colleagues.
An intranet is a network that connects computing resources at a school, company, or other organization but, unlike the Internet, typically restricts access to internal users. An intranet is very similar to a LAN (local area network) but is based on Internet technology. An intranet can provide database, email, and Web page access to a limited group of people, regardless of their geographic location.
The ability of an intranet to connect dissimilar machines is one of its strengths. Think of all the machines that are on the Internet: Macs, PCs running different versions of Windows, various machines running UNIX and Linux, and so on. Each of these machines can communicate via IP (page 391), a common protocol. So it is with an intranet: Different machines can all talk to one another.
Another key difference between the Internet and an intranet is that the Internet transmits only one protocol suite: IP. An intranet can be set up to use a number of protocols, such as IP, IPX, AppleTalk, DECnet, XNS, or various other protocols developed by vendors over the years. Although these protocols cannot be transmitted directly over the Internet, you can set up special gateway boxes at remote sites that tunnel or encapsulate these protocols into IP packets and then use the Internet to pass them.
You can use an extranet (also called a partner net) or a virtual private network (VPN) to improve security. These terms describe ways to connect remote sites securely to a local site, typically by using the public Internet as a carrier and using encryption as a means of protecting data in transit.
As with the Internet, the communications potential of intranets is boundless. You can set up a private chat between people at remote locations, access a company database, see what is new at school, or read about the new university president. Companies that developed products for use on the Internet are investing increasingly more time and money developing intranet software applications as the intranet market explodes.
Following are some terms you may want to become familiar with before you read the rest of this chapter. Refer to the Glossary on page 919 for their definitions.