Cell flow control in square-grid expanded ATM switch

Details Cell flow control in square-grid expanded ATM switch Cell flow control in square-grid expanded ATM switch

2001-05-22

2004-07-20

Gaffin, Jeffrey (Department: 2182)

Electrical computers and digital data processing systems: input/

Input/output data processing

Input/output data buffering

C710S007000, C710S029000, C710S053000, C710S056000, C710S057000, C710S310000, C370S395430, C370S392000

Reexamination Certificate

active

06766387

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to cell flow control techniques employing a backpressure control scheme in an ATM (Asynchronous Transfer Mode) switch, and in particular to a cell flow control method and system in a square-grid expanded ATM switch.
2. Description of Related Art
In some ATM switches having input and output buffers therein, a backpressure controller is provided to perform backpressure control to prevent call overflow in output buffers. Such a backpressure control has been disclosed in many publications. For example, see Japanese Patent Application Unexamined Publication Nos. 10-276206 and P2000-22716A.
There has been proposed a square-grid expanded ATM switch. Hereafter, taking a 2×2 square-grid expanded ATM switch as an example, a conventional cell flow control method applied to the square-grid expanded ATM switch and its disadvantages will be described with reference to
FIGS. 1 and 2
.
Referring to
FIG. 1
, the square-grid expanded ATM switch is provided with 2n input ports
901
-
1
to
901
-
2
n
, an input section
911
, an output section
921
,
2
n
output ports
931
-
1
to
931
-
2
n.
The input section
911
has 2n input modules
912
-
1
to
912
-
2
n
therein. Each of the input modules
912
-
1
to
912
-
2
n
, which will be hereafter denoted by reference numeral
912
-i (i=1, 2, . . ,
2
n
), includes input buffers
913
-i-
1
to
913
-i-
2
n
corresponding to respective ones of the 2n output ports
931
-i to
931
-
2
n.
Here, the 2n input ports
901
-
1
to
901
-
2
n
are divided into two input port lines: first input port line (or group) composed of n input ports
901
-
1
to
901
-n; and second input port line (or group) composed of n input ports
901
-(n/
1
) to
901
-
2
n
. Similarly, the 2n output ports
931
-
1
to
931
-
2
n
are divided into two output port lines; first output port line (or group) composed of n output ports
931
-
1
to
931
-n; and second output port line (or group) composed of n output ports
931
-(n+1) to
931
-
2
n.
The output section
921
has 2×2 output modules
922
-(
1
,
1
)
922
-(
1
,
2
),
922
-(
2
,
1
), and
922
-(
2
,
2
) arrayed like a square grid. Each of the output modules will be hereafter denoted by reference numeral
922
-(k, h), where k=1, 2 and h=1, 2. In other words, k indicates one of the first and second input port lines and h indicates one of the first and second output port lines. The output section
921
further has two output cell controllers
925
-
1
and
925
-
2
, each of which will be denoted by reference numeral
925
-h. Each output module
922
-(k, h) includes n output buffers
923
-(k, h)-
1
to
923
-(k, h)-n and a backpressure controller
924
-(k, h).
Each input port
901
-i receives a stream of ATM cells from a corresponding incoming line. The input port
901
-i checks the header information of a received ATM cell to determine an output port.
931
-j (j=1, 2, . . . , 2
n
) to which the ATM cell is forwarded and then outputs the ATM cell to an input buffer
913
-i-j corresponding to the determined output port
931
-j.
Each input buffer
913
-i-j (i-1 to n, j-1 to n) outputs an ATM cell to an output buffer
923
-(
1
,
1
)-j. Each input buffer
913
-i-(n+j) (i=1 to n, j=1 to n) outputs an ATM cell to an output buffer
923
-(
1
,
2
)-j. Each input buffer
913
-(n+i)-j (i=1 to n, j=1 to n) outputs an ATM cell to an output buffer
923
-(2, 1)-j. Each input buffer
913
-(n+i)-(n+j) (i=1 to n, j=1 to n) outputs an ATM cell to an output buffer
923
-(
2
,
2
)-j.
Accordingly, output modules
922
-(k, h) on the same row handle ATM cells received at the same input port line and output modules
922
-(k, h) on the same column handle ATM cells to be forwarded to the same output port line. In other words, the output modules
922
-(k, h) are arrayed in a row for each input port line and in a column for each output port line.
In this example, the output modules
922
-(
1
, h) on the first row belong to the first input port line and the output modules
922
-(
2
, h) on the second row belong to the second input port line. The output modules
922
-(k,
1
) on the first column belong to the first output port line and the output modules
922
-(k,
2
) on the second column belong to the second output port line.
In association with this, the first input port line includes the input ports
901
-
1
to
901
-n, input modules
912
-
1
to
912
-n, input buffers
913
-
1
-
1
to
913
-
1
-
2
n
, . . . ,
913
-n-
1
to
913
-n-
2
n
, and output buffers
923
-(
1
,
1
)-
1
to
923
-(
1
,
1
)-n,
923
-(
1
,
2
)-
1
to
923
-(
1
,
2
)-n. The second input port line includes the input ports
901
-(n+1) to
901
-
2
n
, input modules
912
-(n+1) to
912
-
2
n
, input buffers
913
-(n+1)-
1
to
913
-(n+1)-
2
n
, . . .
913
-
2
n
-
1
to
913
-
2
n
-
2
n
, and output buffers
923
-(
2
,
1
)-
1
to
923
-(
2
,
1
)-n,
923
-(
2
,
2
)-
1
to
923
-(
2
,
2
)-n.
Further, the first output port line includes the output ports
931
-
1
to
931
-n, output cell controller
925
-
1
, output buffers
923
-(
1
,
1
)-
1
to
923
-(
1
,
1
)-n,
923
-(
2
,
1
)-
1
to
913
-(
2
,
1
)-n, and input buffers
913
-
1
-
1
to
913
-
1
-n, . . . ,
913
-
2
n
-
1
to
913
-
2
n
-n. The second output port line includes the output ports
931
-(n+1) to
931
-
2
n
, output cell controller
925
-
2
, output buffers
923
-(
1
,
2
)-
1
to
923
-(
1
,
2
)-n,
923
-(
2
,
2
)-
1
to
913
(
2
,
2
)-n, and input buffers
913
-
1
-(n+1) to
913
-
1
-
2
n
, . . . ,
913
-
2
n
-(n+1) to
913
-
2
n
-
2
n.
ATM cells read out from the output buffer
923
-(
1
,
1
)-j (j=1 to n) are forwarded to a corresponding outgoing line through the output cell controller
925
-
1
and the output port
931
-j. ATM cells read out from the output buffer
923
-(
1
,
2
)-j (j=1 to n) are forwarded to a corresponding outgoing line through the output cell controller
925
-
2
and the output port
931
-(n+1). ATM cells read out from the output buffer
923
-(
2
,
1
)-j (j=1 to n) are forwarded to a corresponding outgoing line through the output cell controller
925
-
1
and the output port
931
-j. ATM cells read out from the output buffer
923
-(
2
,
2
)-j (n=1 to n) are forwarded to a corresponding outgoing line through the output cell controller
925
-
2
and the output port
931
-(n/j).
The output cell controller
925
-
1
performs arbitration of forwarding ATM cells from the output buffer
923
-(
1
,
1
)-(j−1 to n) to the output port
931
-j and ATM cells from the output buffer
923
-(
2
,
1
)-j (i=1 to n) to the output port
931
-j so as to avoid contention for the output port
931
-j. The output cell controller
925
-
2
performs arbitration of forwarding ATM cells from the output buffer
923
-(
1
,
2
)j (j=1 to n) to the output port
931
-(n+j) and ATM cells from the output buffer
923
-(
2
,
2
)-j (j−1 to n) to the output port
931
-(n+j) so as to avoid contention for the output port
931
-(n+j),
In the above ATM switch of
FIG. 1
, a conventional backpressure-type cell flow control system will be described hereafter.
Referring to
FIG. 2
, the backpressure controller
924
-(
1
,
1
) determines whether an occupation rate of ATM cells in the output buffer
923
-(
1
,
1
)-j (j−1 to n) exceeds a threshold and, if the occupation rate exceeds the threshold, then outputs a backpressure control signal
951
-(
1
,
1
)-j to the input buffer
913
-i-j (i=1 to n). The backpressure controller
924
-(
1
,
2
) determines whether an occupation rate of ATM cells in the output buffer
923
-(
1
,
2
)-j (j−1 to n) exceeds a threshold and, if the occupation rate exceeds the threshold, then outputs a backpressure control signal
951
-(
1
,
2
)-j to the input buffer
913
-i-(n+j) (i=1 to n). The backpressure controller
924
-(
2
,
1
) determines whether an occupation rate of ATM cells in the out

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