Communication systems for transmitting telephone calls have become an integral, indispensable part of everyday life. The first roots of telephony were planted in 1876 with the invention of the first practical telephone by Alexander Graham Bell. As the number of calling stations or customer lines (telephones) in the system began to grow, the wiring system interconnecting the telephones became extremely complicated and unwieldy. One solution to this problem was the introduction of switching systems. Each customer line terminated in a local switching system commonly referred to as a central office (CO). The central office then performed the task of connecting each of the telephone lines it served to a corresponding telephone line in order to complete a call. If the two parties to a call were serviced by the same central office, then the connection could be completed by the same central office without having to resort to other portions of the telecommunications network. If the call required connection to a telephone line serviced by a distant central office, then a connection between the central offices was carried out using a trunk, i.e., a connection between two central offices.
As the number of central offices increased, higher level switching was required to perform the interconnections between central offices. Essentially, each central office was treated as a line to a higher level switching system for switching traffic between the central offices. In this manner, a call from a first subscriber at one location to a second subscriber at a distant location is routed from the first subscriber to the central office servicing the first subscriber. The call is then routed from the first subscriber's central office to a higher level switching office and on to the second subscriber's central office. From the second subscriber's central office, the call is finally routed to the second subscriber.
Each switching system or central office includes equipment for providing signalling, control and switching functions. The signalling equipment monitors the activity of the various lines connected to the central office and forwards control information associated with each line to the control equipment. The control equipment receives the control information and establishes the appropriate connections by way of the switching equipment. The switching equipment is functionally a crosspoint matrix for completing connections between selected input lines and selected output lines. Prior to the introduction of digital switching systems, a number of crossbar switches were used to implement the crosspoint matrix. More recently, digital switching systems, such as the AT&T 5ESS, have been used in place of mechanical or electromechanical switching systems. The essentials of digital telephone switching systems, as well as digital telephony in general, are described in John Bellamy, Digital Telephony (John Wiley & Sons 1991), the contents of which are incorporated herein by reference.
Recently, the volume of telephone traffic between central offices has been growing more rapidly than local telephone traffic. As a result, so called "T-carriers" have evolved as a cost efficient method of transmission between central offices. T-carriers, such as T1, T1C, T1D, T2, T3 and T4, are all digital carriers which require the conversion of analog telephone signals into digital format before they are transmitted over the carrier to the remote end. The most common type of T-carrier is the T1, and as such will be used in the present specification. At the remote end, the digital signals are converted back into analog format and routed through the telephone system. The transmission of digital signals over the T1 carrier may be accomplished using time division multiplexing (TDM) wherein a high bandwidth communications link, such as a 1.544 Mbit/S T1 carrier, is divided into a number of lower bandwidth communication channels, such as 64 Kbit/S channels. Each 64 Kbit channel is assigned a time slot of the T1 carrier. In this way, the high bandwidth T1 carrier is periodically available for a restricted portion of time, enough for each channel to transmit at an effective rate of 64 Kbit/S.
Telephone customers are charged for their usage of the telephone network, with such charges typically being proportional to the amount of time used and the distance from the calling party to the called party. Thus, calls placed over long distances will usually cost more than calls placed over shorter distances. Additionally, local calls which do not involve higher level switching or routing within the system are oftentimes charged at a flat rate independent of the actual customer usage. To a lesser extent, flat rate charges may be established for long distance calls. This may be accomplished by way of a "leased line" wherein the customer leases a dedicated communications link from one location to another. For a fixed fee, the customer is able to place calls between the two locations. The number of calls the customer is able to place is then limited by the bandwidth of the leased line or communications link.
Another type of flat rate service is Wide Area Telephone Service (WATS) wherein a customer selects a certain geographic area for either receiving or transmitting calls. A flat rate is charged for this type of telephone service, depending on the size of the selected area and whether full time WATS service or measured time WATS service, i.e., a certain number of hours per month, is selected.
For the average customer, WATS service or leased line service is economically impractical, since such services are only cost effective for high volume users such as corporations and other institutions. Thus, the average customer is relegated to paying for telephone service on a per minute or per usage basis and is not able to enjoy the benefits of flat rate telephone usage.
An alternative to telephone communication is data communication using computer technology. One way of data communication between computers is by way of modem. Specifically, a modem is used to transmit information or data from one computer to another computer similarly equipped with a modem. However, the transmission medium for modem communication is again the telephone network. Thus, there is effectively no real economic benefit. More recently, as the number of computers in use has increased, computer networks have been used to interconnect large numbers of computers in order to provide data communication. Although access to the computer networks is by way of the telephone system, the access point to the computer network for most users is often a local call which is usually charged at a flat rate. The interconnection and routing of data once it has reached the computer network is typically by way of lower cost lines, such as leased lines, since there is now sufficient traffic to justify the cost associated with a leased line.
The Internet computer network in use today had its beginnings more than twenty years ago as a government project. Originally, the computer network was referred to as ARPANET (Advanced Research Projects Agency Network) and was constructed by identifying a small group of locations or cites across the United States that would function as network hubs. Each hub was directly connected to each other hub over a dedicated leased line running at 56 Kbps. In this way, all the sites were connected to each other by way of high speed carriers and locally connected using the local telephone network to other terminal sites not having a direct connection to any other site. The resulting configuration was in effect, a national computer network.
As the network expanded, there was a significant increase in the number of additional terminal sites locally connected to a network site, which site was itself interconnected to other sites. The number of major hubs remained relatively constant while the terminal sites connected to them began to function as intermediate satellites for providing network access to other sites. In effect, a "tree" type network evolved. Moreover, connections to countries other than the United States were established, thereby creating an international or world wide network. As the size of the network increased, the amount of data traffic also increased. This increase in traffic was the impetus for an increase in the bandwidth or capacity of the communications medium interconnecting the various hubs of the network. Today, in order to accommodate the increased traffic, fiber optic links are the primary communications link for most, if not all, of the interconnections among the network hubs. Satellite locations interface to the hubs primarily via fiber optic or T1 telephone link. Similarly, end users connected to the satellite locations are connected by way of modems or T1 lines. Currently, network control and operation is primarily administered by private or commercial organizations, as opposed to direct government involvement.
FIG. 1 illustrates a typical segment 100 of the Internet network topology. Each individual connection to the Internet is made through a router (not shown), such as part no. Cisco 4000 available from Cisco of Menlo Park, Calif. or part no. 8230 available from NewBridge of Herndon, Va. The router insulates local area networks (LAN) at specific sites from the numerous data packets being sent across the Internet which are of no interest to the particular LAN. For example, if a connection is established over the Internet from LAN 110 to LAN 120, any information exchanged between LAN 110 and LAN 120 is probably of no interest to LAN 130. The router thus prevents such information from reaching LAN 130. Conversely, if LAN 120 desires to transmit information to LAN 130, the router is sufficiently intelligent to allow this information to reach LAN 130 by way of the LAN 140 to which LAN 130 is connected.
The communications protocols used by computers on the Internet to communicate information include TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). TCP is a connection-oriented protocol that provides a reliable data path between two communicating entities. In contrast, UDP is a connectionless protocol that does not guarantee delivery of messages. Although messages are typically delivered successfully in UDP, this may not be the case in the event of network failure or congestion. Both the TCP and UDP protocols are built on top of a lower layer protocol known as the IP (Internet Protocol). IP is used to format and route TCP and UDP messages. TCP/IP and UDP/IP have become worldwide de facto standards for interprocess communication and provide the underlying transport mechanism in use on the Internet. A detailed description of the principles and protocol of TCP/IP communication is set forth in Douglas E. Comer, Internetworking with TCP/IP Volume 1 Principle Protocols and Architecture, (Prentice Hall 1991).
Computer networks such as the Internet, which are capable of transmitting generic data or information between locations, have been used to transmit audio information between computers. At the transmitting computer, a person's voice may be digitized using an analog to digital (A/D) converter and transmitted to the receiving location where it is passed through a digital to analog (DIA) converter and presented as audio. This type of audio connectivity is arguably similar to flat rate telephony, in that audio information may be transmitted from one location to another by way of a high bandwidth, flat rate communications medium. However, this type of computer telephony system suffers from several major disadvantages. First, the system is limited to only those customers who have access to the Internet. While Internet access has now widely proliferated, it has not reached the near universal accessibility of POTS ("Plain Old Telephone Service") service. Such a system is utterly useless if it is desired to communicate with someone who does not have access to the Internet.
Second, such systems provide only half duplex communication, viz., that information can only be transmitted in one direction at any given point in time. There is no simultaneous, two way transfer of information. Third, user access to such a system is only by way of a computer, which is still significantly more expensive than a telephone. Fourth, user access is extremely inconvenient in comparison with corded, cordless, portable, mobile or cellular telephones, in that access may only be provided at a location where a computer is physically located. Fifth, communication with a particular individual may only be made by addressing the information to their computer network address, not to their standard telephone number.
While attempts have been made to remedy some of these deficiencies, the resulting systems are still inadequate. For example, the "Internet Phone" device available from VocalTec of Northvale, N.J., is a computer-based Windows device which provides full duplex audio connectivity across the Internet. However, the system is extremely cumbersome and impractical to use and also suffers from several disadvantages. Specifically, the Internet Phone does not use standard telephone numbers to address individuals; it requires a computer at both transmitting and receiving ends; and both transmitting and receiving locations must call in to establish a connection between the two parties. More important however, the system does not allow spontaneous communication since the communication sessions must be scheduled in advance. Each potential receiving end must state their time availability and specify a computer or machine location where they may be reached.