Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1997-12-18
2001-10-30
Kizou, Hassan (Department: 2662)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S473000, C370S490000
Reexamination Certificate
active
06310891
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of scheduling a plurality of cells in a temporal frame, and more particularly, to a method of scheduling a plurality of time division multiplex (TDM) cells in a synchronous optical network (SONET) frame.
2. Background
The telecommunications industry has developed schemes for transmitting telephony signals, which are usually in the form of time division multiplex (TDM) signals that have been formatted into asynchronous transfer mode (ATM) cells over a physical layer interface, such as a synchronous optical network (SONET) interface. The SONET uses an industry-standard framed transmission format in which signals are transmitted in SONET superframes each having a duration of 1 ms. Each SONET superframe is divided into 8 SONET frames each having a duration of 125 &mgr;s. Each SONET frame includes a plurality of cells each adapted to carry data in the ATM format. Digital video signals and computer data signals are usually carried in the ATM format whereas telephony signals are usually carried in the TDM format. Systems and methods have been developed to carry both telephony and digital video signals over the same communications network. Methods have been developed to convert the TDM format into the ATM format such that both telephony and digital video signals can be transmitted over a single physical layer interface.
However, when the SONET frames are received by a SONET octal bus over a plurality of ports, address collisions may occur between cells of different SONET frames. For example, if a TDM cell in a frame overlaps with another TDM cell in an adjacent frame when received by a receive interface such as a SONET octal bus, an address collision occurs which causes jitters that are undesirable for the demultiplexing of the TDM signals. Therefore, there is a need for a method of scheduling the TDM cells in the SONET frames to avoid an address collision between the TDM cells of different frames even if the frames are received by the receive interface with some overlap.
SUMMARY OF THE INVENTION
In view of the above problem, the present invention provides a method of scheduling a plurality of time multiplexed cells and a plurality of asynchronous cells within a temporal frame such that an address collision between the time multiplexed cells in adjacent frames may be avoided. The method of scheduling a plurality of cells in a temporal sequence in a frame divided into a first subframe and a second subframe roughly comprises the steps of:
(a) assigning a plurality of time multiplexed cells and a first plurality of asynchronous cells to the first subframe, the time multiplexed cells temporally interspersed from each other by at least one asynchronous cell in the first plurality of asynchronous cells; and
(b) assigning a second plurality of asynchronous cells to the second subframe.
In a further embodiment, the duration of the first subframe is no more than three times the duration of the second subframe. The time multiplexed cells may be formatted in an unpacked mode or a packed mode. The time multiplexed cells may be time division multiplexed (TDM) cells while the asynchronous cells may be asynchronous transfer mode (ATM) cells.
Advantageously, the method according to the present invention satisfies the need for avoiding jitters at the receive interface caused by an address collision between the time multiplexed cells in the different frames even if they are received with some temporal overlap by the receive interface. A further advantage of the present invention is that it allows the asynchronous cells, which may carry wideband signals such as video signals, to retain a relatively wide bandwidth when they are scheduled with the time multiplexed cells in the same frame.
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Dove Jason W.
Semple Brian
Witel Rodney
Alcatel USA Sourcing L.P.
Kizou Hassan
Smith ,Danamraj & Youst, P.C.
Tsegaye Saba
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