Network evolution

Network evolution
The methods for sending and transmitting data across telephone lines have changed over the past few decades. Data networks have evolved over a series of generations. Some of the more significant data network milestones are the mainframe computer, the personal computer, LANs, WANs, the Internet, intranets, and extranets. Many companies incorporate all of these technologies in their corporate data networks. IBM calls this combination of an organization’s networks its “enterprise network.”

Mainframe computer networking
In the beginning, mainframe computers handled all data processing. “Dumb” terminals displayed the results of the mainframe computer’s work. Remote dumb terminals connected with the mainframe across expensive leased telephone lines.

For example, a national hotel chain used a mainframe at its home office to handle reservations. The dumb terminals at each hotel property connected to the mainframe for data processing and to access reservation records. The connection took place across telephone company leased lines. The phone companies “dedicated” the leased lines for the hotel chain’s use only, so they were very costly, but there was no other way for the hotel to do business. It was too expensive to purchase a mainframe for each hotel to do data processing, and each hotel still needed access to the home office’s reservation records.

Personal computers
The greatest distinction between mainframes and PCs is that PCs allow individuals to process their own data without the need to be connected to a mainframe computer. Using a modem, one PC can dial up another PC and share data. So, for example, the hotel chain could scrap its mainframe and use PCs at each location for data processing, but each hotel would still need to connect to the home office to handle reservations. Depending on the amount of traffic, a dial-up modem connection may be more cost effective than dedicated lines, but it would not be as reliable.

LANs
LANs are simply two or more computers connecting to each other in one location. For example, the network used by a small law firm consisting of a server, a printer, and five personal computers is considered a LAN. Figure 1 is an example of a LAN


Figure 1: Typical LAN.

WANs, MANs, and VPNs
A WAN is two or more computing devices in separate locations connecting to each other across telephone lines. Figure 2 shows an example of a typical WAN. WANs connect with dedicated private lines, circuit switching, packet switching, or a combination of these services


Figure 2: WAN.

Most WANs can also be called VPNs. A truly private network means that in addition to owning the computing equipment, the user also owns the phone lines that connect the computers. Some universities and corporate campuses have private networks. Building a physical telecommunications network is very difficult and very expensive; few organizations use private networks. Instead, they have private communications over lines owned by the phone company. This is not a private network; it is a “virtual” private network.

When telecommunications professionals use the term VPN, they are usually referring to large businesses that transmit voice and data across a data network. A metropolitan-area network (MAN) simply refers to a WAN that is contained within one metropolitan area.