Multiplex communications – Communication techniques for information carried in plural... – Assembly or disassembly of messages having address headers
Utility Patent
1997-12-18
2001-01-02
Pham, Chi H. (Department: 2731)
Multiplex communications
Communication techniques for information carried in plural...
Assembly or disassembly of messages having address headers
C370S471000, C370S473000, C370S476000
Utility Patent
active
06169749
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of sequencing a plurality of cells in a temporal frame, and more particularly, to a method of sequencing 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 sequencing the TDM cells in the SONET frames to avoid an address collision between the TDM cells of different frames.
SUMMARY OF THE INVENTION
In view of the above problem, the present invention provides a method of sequencing a plurality of time multiplexed cells in temporal frames by assigning a marker frame and a marker cell within the marker frame coded with header data. The method according to the present invention is able to avoid an address collision between the time multiplexed cells in adjacent frames. The method of sequencing a plurality of cells in a superframe consisting of a plurality of frames in a temporal sequence roughly comprises the steps of:
(a) assigning one of the frames as a marker frame, the marker frame including a plurality of time multiplexed cells and a plurality of asynchronous cells;
(b) assigning one of the time multiplexed cells in the marker frame as a marker cell, the marker cell including a plurality of header bytes and a plurality of payload bytes; and
(c) coding the plurality of header bytes with header data.
In a further embodiment, the last frame in the superframe is assigned as the marker frame, and the first time multiplexed cell in the marker frame is assigned as the marker cell. The marker cell, which includes a plurality of header bytes and payload bytes, is coded with a frame number for referencing the order of the marker frame within the superframe, a cell number for referencing the order of the marker cell within the marker frame, a frame frequency marker, a time multiplexed cell indicator and a packed mode indicator.
In another embodiment, a marker cell is not necessary to designate a particular cell sequence. An encoded sequence of header bits is used instead to identify any of the TDM cells in the cell slot sequence. Moreover, the header bits may include upstream and downstream identifier bits to signify the direction in which the TDM cell is conveyed, thus allowing cross connections to occur between transmit and receive physical layer interfaces.
Advantageously, the method according to the present invention satisfies the need for designating a particular frame in a superframe and a particular time multiplexed cell in the marker frame as a marker cell, such that when the superframes are received by a receive interface such as a SONET octal bus, the marker frame within each SONET superframe and the marker cell within each marker frame can be identified to maintain a proper temporal sequence of the SONET frames and the cells within the frames. A further advantage of the present invention is that the header data identifying the marker cell, the marker frame, and the format of the marker cell can be coded into the existing header bits of the marker cell without requiring the provision of additional header bits or otherwise displacing some of the payload bits that are used for carrying information.
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Dove Jason W.
Semple Brian
Witel Rodney
Alcatel USA Sourcing L.P.
Fliesler Dubb Meyer & Lovejoy LLP
Pham Brenda H.
Pham Chi H.
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