Multiplex communications – Channel assignment techniques – Using time slots
Reexamination Certificate
1998-05-29
2001-10-09
Olms, Douglas (Department: 2661)
Multiplex communications
Channel assignment techniques
Using time slots
C370S230000, C370S329000, C370S341000, C370S395430, C370S468000
Reexamination Certificate
active
06301262
ABSTRACT:
REFERENCE TO COMPUTER PROGRAM LISTING APPENDIX
Appendix 1 is a computer program listing which is submitted on one compact disc that is referenced in the following specification and incorporated herein by reference. Appendix 1 comprises a single file, SACAUTO.C, which was created in April 1994 and includes 278,338 bytes.
BACKGROUND OF THE INVENTION
The present invention generally relates to the field of communications networks, and more particularly to a method for facilitating communications between resources on a multichannel network by determining appropriate time slots and channels on which to transmit a message so that it will arrive at its destinations at a time when it may be received.
Time Domain Multiple Access (TDMA) communications systems allow multiple users to communicate through a Demand Assigned Multiple Access (DAMA) multiplexer over a network using a common communications path. A DAMA multiplexer is TDMA connection between a user baseband device (Teletype, Phone, FAX, etc.) and a communication system such as a local area network (LAN) or satellite relay system. A DAMA multiplexer retains send and receive data in a holding buffer until the specified time slot for communications occurs. The data then is burst in or out of the buffer at a much higher rate to facilitate a perceived constant communications path. Messages are sent during specific time slots which comprise a periodic time frame, or TDMA field.
The TDMA field of each time frame includes a timing mark to identify the beginning of each time frame and is followed by multiple time slots. In the past, DAMA multiplexers allowed both distributed (DC) and automatic (AC) control modes.
In the DC mode, users simply connect themselves to the communications fields (time slots) they are interested in. However, there are problems associated with this relatively unstructured method of communications. For example, unauthorized users could connect to private communications, constant key offenders jammed the time slots, and no policing of control and order existed. A request for a new circuit could take weeks to be assigned. Most users would leave circuits connected to a time slot even though they were not being used. These shortcomings resulted in the inefficient use of communications channels, particularly of the type used in UHF satellite communications systems.
AC mode provides a single point of control like a telephone system. In the AC mode, all communications must request connection to a specific group or user terminal(s) identified by address(es). This allows more flexibility for creative connections including communications amongst various different channels, and device matching (phone connected to another phone) for preventing jamming or interference from unknown sources. In that system, connections are made in less than five seconds if time slots are available. However, when operated in the original AC mode, the DAMA controller was a person-intensive system requiring the controller to be manned 24 hours a day, and was prone to failure. The AC mode DAMA channel controller was a manual system requiring a human to make intelligent decisions as to where to place requesting users on a time slot. Many requests went unconnected. Therefore, the DC mode remained as the fall back operational mode until a better DAMA Channel Controller could be built.
Determining the time in which to transmit a message presented another significant problem because the distances between communications resources on a network result in propagation delays for the messages between the time they are transmitted until they are received. Thus, even if a time slot was found in which a message could be transmitted, by the time the message reached its intended target receiver, the current time slot at the resource may already be allocated for some other message so that the target receiver would be unable to detect the first message.
Therefore, a need exists for an automatic system and method for determining the time slot in which a message may be sent so that the message reaches its intended destination at a time when it may be received.
SUMMARY OF THE INVENTION
The present invention provides a system which employs a computer implemented method for determining a message transmission time for establishing a communications link on a time domain multiple access network. The method comprises the steps of: a) receiving a request message having one of a set of communications type categories from a first communications resource, a source address which identifies the first communications resource, and a destination address which identifies a second communications resource; b) directing the request message to a message request processor for processing a message request having the communication type category; c) determining if a communications link is connectable between the first and second communication resources; d) generating a first message type if the determination in step (c) is that no communications link is connectable between the first and second communication resources; e) searching for assignable time slots within a periodic time frame comprising multiple time slots for transmitting a message so that the second communications resource is receptive to receiving the message during one of the time slots if the determination in step (d) is that a communications link is connectable between the first and second communications resources; f) generating a second message type if any assignable time slots are identified in step (e); and g) returning to step (a) if no assignable time slots are identified in step (e).
The scope of the invention further includes a time domain multiple access communication network system for determining a time slot within a periodic time frame in which to transmit a message from a first communication resource so that it will be received by a second communication resource. The system comprises multiple communication resource sets which each include at least one communication resource; a communication terminal connected to each communication resource set; a communication router operably connected to each communication terminal; and a control processor for determining a time slot within a periodic time frame in which one of the terminals transmits a message received from one of the communication resources connected to the one terminal so that the message will be received by designated communication resources at a time when the designated communication resources are disposed to receive the message. The control processor implements the method steps detailed herein above.
The invention may also be characterized as a computer readable medium which embodies a computer program executable by a computer that performs the above-described method steps.
An important advantage of the invention is that it provides a quick connect time from the time a message request is received to the time that a time slot assignment for transmitting the message is determined so that the intended receiving resource on a time domain multiple access network is disposed to receive the message.
Another important advantage of the invention is that it provides automatic connections between resources on a time domain multiple access network.
Yet another advantage of the invention is that it more efficiently allocates time slot assignments for periods appropriate for the transmit time of the message.
These and other advantages of the invention will become more apparent upon review of the accompanying drawings and specification, including the claims.
REFERENCES:
patent: 5742594 (1998-04-01), Natarajan
patent: 6130886 (2000-10-01), Ketseoglou et al.
patent: 6175860 (2001-01-01), Gaucher
Fendelman Harvey
Hom Shick
Kagan Michael A.
Lipovsky Peter A.
Olms Douglas
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