Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output access regulation
Reexamination Certificate
1999-11-20
2003-06-03
Gaffin, Jeffrey (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output access regulation
C370S217000
Reexamination Certificate
active
06574686
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to ATMs and, more particularly to circumventing of faults in I/O modules of an ATM.
FIG. 1
presents a general block diagram of a conventional local ATM switch
100
with a connected I/O module
10
, and conventional remote ATM switch
200
with a connected I/O module
20
(that may be of the same construction as that of module
10
). Module
10
contains a line interface unit (LIU)
110
that is connected to fiber
210
, and a line interface unit
120
that is connected to fiber
220
. Fiber
210
is the “service” line, in the sense that it carries live data between I/O module
10
and I/O module
20
. Fiber
220
is the “protection” line, in the sense that it is ready to assume the active communication function of line
210
, should fiber
210
fail. Within module
10
, LIU
110
is connected to framer
111
, and framer
111
is connected to APS switch unit
130
. Similarly, LIU
120
is connected to framer
121
, and framer
121
is connected to APS switch unit
130
. APS switch
130
is connected to ATM processing unit
140
, and the output of ATM processing unit
140
forms the output of I/O module
10
. This output is connected to ATM switch fabric
100
. Elements
111
,
121
,
130
and
140
are connected to a control CPU
150
. Additionally, CPU
150
includes an ATM bus through which the CPU communicates directly with switch fabric
100
(not shown explicitly).
Under normal operating circumstances, traffic from the service fiber (
210
) passes through LIU
110
and framer
111
, and is applied to APS switch unit
130
. The switch is set to pass this traffic to ATM processing unit
140
and thence, to ATM switch fabric
100
. In the reverse direction, traffic flows from switch fabric
100
to ATM processing unit
140
, and is bridged by APS switch unit
130
to both framers
111
and
121
. That traffic is then transmitted out on both fibers
210
and
220
. From the above it can be realized that protection fiber
220
carries signals that are identical to the signals carried in service line
210
. The only difference is that APS switch
130
in I/O module
10
passes only the signal of framer
111
to switch unit
140
and, similarly, I/O module
20
at the remote destination passes only the signal of framer
123
to switch unit
145
.
When a failure occurs, for example, when fiber
210
is severed, CPU
150
gets an interrupt signal via line
151
from a detector in framer
111
. In response thereto, the CPU takes recovery action. First, the CPU checks to determine whether the protection line (
220
) is in good operating order. Upon an affirmative determination, CPU
150
orders APS switch
130
to disconnect the path from line
210
toward ATM processing unit
140
, and to connect the path from line
220
to ATM processing unit
140
. CPU
150
also creates an APS signal and casts it onto line
220
through framer
121
, toward I/O module
20
. Framer
113
at I/O module
20
provides the received APS signal to CPU
160
, and CPU
160
directs APS switch unit
135
to switch the signal arriving on fiber
220
to ATM processing unit
145
.
In may be noted that fibers
210
and
220
may each be a pair of fibers for carrying the two-directional traffic, or they may each be single fibers (with the two channels multiplexed thereon using, for example, wavelength division multiplexing).
While an ATM constructed with I/O modules as shown in
FIG. 1
, and employed in the manner described above, is able to circumvent problems that originate in the fiber or the LIU, it nevertheless had a significant weakness. Use of the APS switch within the I/O module requires one to connect the service fiber and the protection fiber to the same I/O module. Consequently, a general failure in the I/O module brings down both the service path and the protection path. On first blush, it would appear that placing the APS switch off the I/O module, in a separate circuit board that is interfaced between the I/O module and the ATM switch, would solve the problem because it would allow the service fibers and the protection fibers to be connected to different I/O modules. Alas, current design ATMs do not have the physical room for inserting the circuit board that would serve as the switches for selecting I/O modules. Moreover, such a solution is quite expensive.
SUMMARY OF THE INVENTION
An improved arrangement is realized by operating in a novel manner that allows the connection of the service fiber and the protection fiber to different I/O modules and achieving the necessary switching functions without the need of additional circuit boards. More specifically, while the service line and the protection line are connected to different I/O modules, the selection of the service line or the protection line is carried out by cooperation between the CPUs on the I/O modules of the service and the protection lines and the ATM switch fabric. The line that is selected has its framer buffer open, while the line that is in the standby mode has its framer buffer closed. In the other direction, traffic is multi-cast onto both the service and the protection lines by the ATM processing unit. In this manner, the protection fiber always contains information, ready to be switched from standby mode into active mode.
REFERENCES:
patent: 5069521 (1991-12-01), Hardwick
patent: 5870382 (1999-02-01), Tounai et al.
patent: 6466576 (2002-10-01), Sekine et al.
Koppol Pramod V. N.
Sha Yung-Ching
Lucent Technologies - Inc.
Patel Niketa
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