Multiplex communications – Channel assignment techniques – Using time slots
Reexamination Certificate
1999-11-24
2002-06-18
Ton, Dang (Department: 2661)
Multiplex communications
Channel assignment techniques
Using time slots
C370S489000
Reexamination Certificate
active
06408008
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of telephone systems and in particular to telephone systems in which multiple stations may be operated on a single shared telephone line.
2. Description of the Prior Art
The System
Home and small office telephone systems are typically purchased and operated by the telephone user. In addition, the telephone user or the owner of the building in which the telephone system is installed, is similarly responsible for the installation and maintenance of the internal telephone lines beginning at the telephone company line terminal at the entry point to the building. Very commonly, the internal telephone wiring which is available in a home or small office is a single line system. In other words, while there may be multiple telephone jacks, each of the jacks are coupled in parallel to a single telephone line within the structure. Therefore, only one telephone conversation at a time may be carried on the line and if two handsets are picked up, the power on the line is distributed between the two activated handsets with a consequent loss of audible volume. Additionally, the communication as well as the central office link must be generally held in common between the two participants.
A number of schemes have been attempted for expanding the communication capability of a single internal telephone line network, most of which involved various voice band multiplexing schemes. As the features and complexity of the telephone network increases, greater demand is placed upon the multiplexing system. The complexity of the multiplexing scheme can become prohibitive when the system must be full featured. For example, when the system must provide an automated operator to provide voice message answering of incoming calls, special handling of fax, phone, modem and answering machines at the telephone stations, extension dialing, a host of separate business phone features and fax features, and accommodate a large number of phone stations all incorporated in an economical package which easily lends itself to expansion and modification, the prior art has failed to provide practical solutions. The difficulty arises from many reasons including the following: (1) The expense and labor involved in wiring or rewiring the facility if a star wire system is used (a separate wire to each phone); and (2) the complexity and technical difficulty in implementing a digital or frequency band (AM, FM, etc.) form of sharing a single common line. Finally, the high communication and computer overhead time which is required in a multiplexing system to handle multiple features and stations with complete flexibility and adaptability. The amount of digital communication which must be carried on often becomes prohibitive and the system fails during peak periods or unusual demand scenarios.
Many multiple wire (star wire) as well as some two-wire small phone systems utilizing a master controller and multiple station controllers are known in the art. The multitude of star wire systems suffer from both the inherent wiring complexity as well as the following problem. One typical two wire system is the Model 8002 MCD base key telephone system unsuccessfully offered by Rockwell. In such systems, a sophisticated processor is not only required in the master controller, but also at each station which adds to the cost and complexity of the system. An architecture which is built upon multiprocessing makes changes in the system difficult since modifications must be made in both the controller program and in the station programs. Communication between these multiprocessors is complex and when the number of stations increases, overall communication can become very slow during busy periods. Only a few features can be changed remotely since again most of the features require changes in both station and controller programs.
In the Rockwell system, a mix of voice channels, digital channels and a reference signal on a twisted pair telephone line, using double side band suppressed carrier with amplitude modulated signals was employed. However, the Rockwell system did not define the structure of digital data communication, nor did it remove the requirement for a separate control processor in every station. Therefore, although it did allow multiple signals on a single twisted pair telephone line, it did not provide any simplification to the complexities of multiprocessing nor solve the inflexibilities inherent in multiprocessing architectures. Additionally, this product suffered from severe noise, phase lock, and synchronization problems which eventually doomed it to failure.
Therefore, what is needed is a single twisted pair, multichannel telephone system which can be economically and easily adapted to a home or small business and which has the power and flexibility to perform the functions discussed above without undue complexity, expense or susceptibility to failure under heavy demand or unusual use scenarios. Additionally, it needs to solve the critical noise and synchronization problems inherent in such a system without resort to a full digital (and very expensive) solution.
Simplified Processor
Conventional general purpose processors typically operate on a program stored in a read only memory by means of an instruction counter in order to read the stored instructions in sequence or according to a sequence with programmed jumps. This architecture is relatively complex, requires large numbers of transistors to implement and will therefore use a large area of a chip when integrating this function, and is time consuming of real time communication cycle time. The disadvantages of such a processor are particularly burdensome in an application where general programmability is not required.
What is needed is an architecture and method of operation for a processor which is more usable for applications that require only a limited number of operations and that avoids the overhead and timing disadvantages of a general purpose processor.
Communication Signaling Scheme
In a typical prior art small telephone system, a separate pair of wires is coupled from a control unit or master phone to each remote station or telephone handset. This type of system is commonly referred to as a “star wire” system. The control unit determines where the message is coming from and where it will be going according to which pair of wires is selected. This system has the disadvantage that there is a need to provide a separate wire pair for each remote station connected to the control unit and thus eliminates the use of standard house telephone wiring since conventional home wiring typically connects to all the extensions or telephone stations in parallel on a single pair of wires.
The prior art has also devised a scheme in which a single pair of wires is shared between multiple remote stations connected to a control unit. The control unit or master phone manages the telephone network by using a message based protocol. Whenever a phone call or message is to be sent, the transmitting unit, regardless of whether it is a remote station or control unit, will initiate a message in the network by sending an initial data protocol which will define the transmitter and recipient of the message. This type of message based protocol is subject to slow downs or lock up as the number of remote units and systems activity increases.
What is needed is a communication protocol for a small telephone system which is not subject to the limitations of the prior art. In particular, the protocol should eliminate the need in the system to establish a handshake protocol every time a message is sent in either direction to avoid slow downs during active communication periods between a plurality of units. Such a protocol should also allow serial digital data to be transmitted over the same line in burst format without affecting signaling speed so that components such as a display can be serviced quickly without affecting signaling response time. Additionally, a good error correction scheme must be implemented without affect
Komarek James A.
Lewis Harold F.
Minney Jack L.
Nordine Stephen P.
Stockman John F.
Creative Integrated Systems, Inc.
Dawes Daniel L.
Myers Dawes & Andras LLP
Ton Dang
LandOfFree
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