Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1999-12-17
2004-04-27
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S463000, C370S353000, C370S355000, C370S356000
Reexamination Certificate
active
06728238
ABSTRACT:
BACKGROUND OF THE INVENTION
B. Field of Invention
The present invention pertains generally to telecommunications and more specifically to time domain multiplexed channels on a single twisted pair.
C. Description of the Background
Telecommunications have grown rapidly over the past few years due to the increasing availability and ease of use of the Internet. Telecommunications companies, particularly local exchange carriers (LECs), i.e., local telephone companies, have experienced growing pains due to the substantial increase in demand for new services. This demand for new services has been created in large part by small customers that obtain data services by attaching to the Internet through analog modems. When a user is attached to the Internet via an analog modem, the local telephone company switch (voice switch) has to allocate a channel for the duration of the call. The analog modem uses tone signals that are generated over a twisted pair that are digitized by the telephone switch at the central office. The use and allocation of voice switches has been based on a model of typical calling patterns for voice calls during peak calling hours before the advent of the Internet. While the average phone call only runs approximately 3 minutes on average, the average Internet connection runs 20 minutes, with the average Internet user being connected to the Internet for 23 hours per month. As more users tie up telephone switches with analog modem data traffic, the number of available channels for voice calls diminishes drastically. This has forced the Telecos to add a great deal of switch capacity in order to meet the required grade of service as defined by the Public Utilities Commission, which is approximately 99.8% availability. Not only have the Telecos been required to outlay significant sums for capital improvement by adding switch capacity, the problem is further exacerbated by the fact that the cost of the new switching equipment is not offset by increased revenue because Internet users are tying up the switches for analog modem data traffic by making local calls which fall under the basic monthly fee for the telephone line. As a result, the profit of Telecos is stagnant or falling with respect to these services.
The voice switch systems used by the local exchange carriers (Telecos or LECs) digitize the tone data emanating from the voice of a speaker, or a modem, to produce a digital signal that can be transmitted through the public switch telephone network (PSTN). These voice switches are designed to maintain a constant connection between the talking parties. This is because it is difficult to carry on a conversation when a voice is not continuous. People perceive subtleties in the nuances of speech. If the voice channel deletes segments of this information, the users have difficulty in carrying on conversations.
Data networks operate in a completely different fashion. A constant open channel is not required to transmit data. Data is bursty by nature and it is relatively insignificant if small delays occur in the transmission of data packets in that the overall data transmission rate is not reduced by packetizing the data transmissions. Data networks are designed to make maximum use of the network by sending data on any available path it can find to a destination and receiving that data in any order and reorganizing it in the proper order. In other words, a portion of a file can be routed through one network path while another portion is routed through a totally different path, with different pieces arriving in an order that is different from the way the data was sent. When the data is received at the other end of the network, the network equipment reassembles the data into the original order. Clearly, voice data cannot be transmitted in this fashion.
The public switch telephone network (PSTN) has used T-1 data services for many years. T-1 is a digital transmission system that was developed to carry digitized voice signals and was later adapted to also carry pure data signals. The T-1 methodology of using clear channels, i.e., dedicated open channels, to carry digitized voice signals is necessary, as indicated above, for carrying these voice signals, but is extremely wasteful of bandwidth when used to carry data. T-1 services were initially offered with full T-1 bandwidth, i.e., 24 channels. As a result, only large corporations could afford the cost of T-1 systems. New services, such as fractional T-1 and frame relay, take advantage of the bursty nature of data to provide lower cost data services over the T-1 infrastructure. These services have brought the cost of T-1 systems down to a level where much smaller companies can afford to link their internal corporate data network with the outside world.
Data networks, such as local area networks (LANs) are typically based on Ethernet, which is a data packet protocol that was designed to transfer data between computers. These networks were not designed to provide voice services as pointed out above. Ethernet has become a de facto corporate network standard because of its low cost and its backwards compatibility with slower predecessors. A need therefore arose to interface these data networks with the PSTN to allow the seamless transmission of data from a local network over the telecommunications system. To meet these needs, bridges and routers were developed that provide the interconnection between the data networks and the PSTN. The bridges and routers perform the data conversions necessary to communicate and transfer data over these incompatible systems.
Although T-1 systems have been modified to provide less expensive services that are affordable for small corporations, a need has existed for even less expensive digital services that are affordable for small businesses and homeowners. ISDN has attempted to fill that need. However, ISDN services have been expensive to implement because these services have required the installation of ISDN digital line cards at the central office (CO) and expensive digital telephones for special terminal adapters at the customer's premises. As a result, ISDN services have been slow to be deployed in the U.S. In less developed countries where the national telecommunications infrastructure was not fully developed, a significant capital investment was made in ISDN and it has been adopted to a large extent. However, in the U.S., few customers were willing to pay the high cost to change their existing telephone systems for ISDN systems. The cost factor has been exacerbated by the lack of services which the Telecos were providing for ISDN. The high cost factor associated with implementing ISDN, plus the fact that the Internet was not in common use at the time ISDN was first implemented, rendered ISDN a solution to a problem that had not yet been created in the U.S. ISDN is capable of providing 144 Kbps. In the 1970s, 1980s, and early 1990s, this high bandwidth digital service (144 Kbps) was not needed by most customers and their data needs were satisfied by inexpensive standard analog modems which were used to transmit documents via fax. One benefit that has accrued from development of ISDN services is that it has employed 2B1Q coding which is compatible with AMI line coding format that is used in T-1 services. Both of these services can be run in the same wire bundles without causing interference. This is not the case with newer coding formats such as CAP and DMT that are being proposed for the higher speed ADSL systems that run in excess of 8 Mbps.
Due to the lack of widespread adoption of ISDN, the telecommunications industry is leapfrogging this technology to adopt a much faster technology known as Digital Subscriber Line service (DSL). Typical DSL technologies are able to provide data services at data rates ranging from 768 Kbps (HDSL) to rates in excess of 8 Mbps (ADSL, SDSL, and MDSL). The 56 k analog modems (which actually run at 33 Kbps) are woefully inadequate in transferring data at rates required for the graphic intensive presentations that are typically provided on the Internet, or
DeLangis Eric M.
Long Gary E.
Hsu Alpus H.
Molinari Michael J
Remote Switch Systems, Inc.
The Law Offices of William W. Cochran, LLC
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