Networks for the transfer of data between computers, both public and private, are ubiquitous in today’s business world. A public network is one that is publicly available to subscribers (Stallings, 2001). It provides service to multiple subscribers and is built and maintained by a public network provider. Internationally, the term “public network” is often applied to networks that are under government control or are a national monopoly. However, a network can also be a privately owned network whose services are sold to the public. Whether the network is under government control or is a privately owned network whose services are sold to the public, businesses access the network by installing an access device at each site and using an access line to the nearest point of presence (POP) of the public network provider
Overview of public network concepts and services
Traditionally, companies desiring to connect business computers in different geographic locations have used private networks. That is, they have used point-to-point leased lines between business sites to create their own circuit-switching or packet-switching networks for their data communication requirements (Panko, 2001). Unlike telephone calls, which set up the required capacity as needed, leased lines provide dedicated transmission capacity between sites.
The structure of the public switched telephone network system
The public switched telephone network system is often used to provide the technology that a business uses to access a public network or is the technology of the public or private lines. The structure of the PSTN in the U.S. has evolved from one that was almost entirely controlled by a single company to one that allows competition in a free market. Before January 1, 1984, AT&T (also known as the Bell System) controlled 80% of the PSTN in the U.S. (Bellamy, 2000). A Justice Department antitrust suit filed in 1974 and a private antitrust case by MCI resulted in the breakup of AT&T (Noam, 2001). The suit argued that AT&T used its control of the local operation as an unfair advantage against competing for long-distance carriers.
A modem is the most inexpensive and easiest to use access technology. The use of modems for data transmission will be substantial for many years to come (Stallings, 2001). Voice-grade modems use a 4-kHz bandwidth on an ordinary telephone line, the same bandwidth that is used for voice signals. Modems can be packaged inside an information product, such as a personal computer. Companies often have modem banks that allow employees to dial in directly to the company intranet or to access a large computer system.
Access and public network technologies
To use a public network for data services, a user must access the public network through some network service from the user’s computing equipment to the nearest public network node. Factors in selecting a particular service include the cost of the service that is provided and the features, including the transmission speed, that is provided by the technology. Generally, the higher the transmission speed that technology can support, the more costly the service becomes. Transmission speeds for networks are described in bits per second.
Digital Subscriber Lines
Faster service than voice-grade modems that are beginning to be offered by telephone companies is the digital subscriber line (DSL). A widely publicized version of this is asymmetric digital subscriber line (ADSL). ADSL offers high-speed downstream access to the customer site and a lower-speed upstream access from the customer.
Synchronous Optical Network
A synchronous optical network defines a hierarchy of standardized digital data rates. A compatible version, Synchronous digital hierarchy has been published by the ITU-T. SONET is intended to provide a specification for high-speed digital transmission over optical fiber.
Strategic control of a network is designing and implementing a network to satisfy the organization’s unique requirements. If the organization operates its own private network then it can determine the configuration of the network. But, if the organization uses a public network the organization does not have strategic control over the configuration of the network. The public network provider designs the network for the average subscriber