Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – With blocking of normal usage
Reexamination Certificate
1997-11-07
2002-01-22
Chan, Wing F. (Department: 2743)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
With blocking of normal usage
C379S008000, C379S022000, C379S015050, C379S009000
Reexamination Certificate
active
06341158
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of checking the integrity of a communications network and, more particularly, to a method of detecting a loopback condition in the communications network.
A communication network may be populated by a number of switches, as shown in FIG.
1
. The switches are typically interconnected by optical or electrical cables (“facilities”) that carry communication traffic. In a time division multiplexed (TDM) scheme, facilities carry communication data for one call in a time slot (“trunk”) multiplexed with data for other calls in other time slots. For two way communication, a call is assigned two trunks. A forward trunk on a first facility
10
carries data in a forward direction, such as from an originating switch
100
to a terminating switch
200
; a return trunk on a second facility
20
carries data in a reverse direction, such as from the terminating switch
200
to the originating switch
100
. By convention, the same trunks of the two facilities are assigned to the same call. For example, if trunk no. 2 of facility
10
is assigned as the forward trunk, trunk no. 2 of an associated facility
20
is assigned for the return trunk.
Control signals typically are used for call setup and tear down in communication networks (i.e., to establish call paths through the network during call setup and termination). Although communication traffic from an originating switch
100
is transmitted to a terminating switch
200
over trunks, the trunks do not carry control signals. To setup and terminate calls, an originating switch sends call setup information over an A LINK
30
to a signal transfer point (“STP”)
300
. The STP
300
communicates the call setup information to the terminating switch over a second A LINK
40
. Through this out-of-band signaling, the originating switch
100
and terminating switch
200
confirm that each is operating and establish trunk assignments for the new call.
Out-of-band signaling does not permit the originating switch
100
or the terminating switch
200
to confirm the integrity of the facilities that interconnect them. Although the originating switch
100
and terminating switch
200
communicate over the A LINK, they would not be able to determine whether one or more of the facilities that interconnect them are damaged. If facility
50
is severed, for example, communications data placed on the facility
50
by the originating switch
100
would be lost; it would never reach the terminating switch
200
. Although the terminating switch
200
would expect to receive communication traffic over the facility
50
, the absence of communication traffic on the facility would not normally generate an alarm condition and/or a report.
To detect facility failures, it is known to conduct a continuity test in which, before carrying communication traffic, the originating switch
100
instructs the terminating switch
200
via the A LINK to switch all the data that it receives on the forward trunk to the return trunk. The originating switch
100
generates a test tone on the forward trunk and monitors the return trunk to detect the tone. The originating switch
100
determines that the facilities are operable when it detects the test tone on the return trunk. When it confirms that the facilities are operating properly, the originating switch
100
completes the call setup process.
The continuity test, while it is useful to detect certain facility failures such as open conditions, is vulnerable to other network failures, such as loopback conditions. A loopback condition occurs when a facility originates and terminates at the same switch, shown as
60
and
70
in FIG.
1
. Most often, loopback conditions are caused by human error during facility installation or maintenance. The facilities are configured incorrectly. When a continuity test is run on a facility
60
that loops from a switch back to the same switch, the continuity test generates a “false positive;” the originating switch
100
detects the test tone on the “return trunk” even though the forward trunk failed to reach the terminating switch.
Although a loopback facility
60
cannot carry data between the originating switch
100
and the terminating switch
200
, the continuity test cannot identify this type of equipment failure. The limitations of the continuity test result in unsuccessful calls and customer dissatisfaction.
Accordingly, there is a need in the art for a test protocol in communications networks that detect the presence of loopback conditions. Further, there is a need in the art for a continuity test protocol that tests for loopback conditions and maintains the viability of the continuity test protocol.
SUMMARY OF THE INVENTION
The disadvantages of the prior art are alleviated to a great extent by a test protocol that tests for loopback conditions according to the following method: An originating switch engages a normal call setup operation to communicate with and confirm the operation of the terminating switch. The originating switch generates a test tone on the forward trunk. Unlike the continuity test, the originating switch does not instruct the terminating switch to switch the forward trunk to the return trunk. If the originating switch monitors the return trunk and detects the test tone, the originating switch fails the facility due to the presence of a loopback condition.
The loopback test protocol complements and works with the continuity test. The tests may be run in succession to detect facility integrity and the absence of loopback errors. For example, while setting up on a first call, the continuity test may confirm the viability of the facility through the known continuity test. Then, on a subsequent call, the loopback test procedure may be run. By alternating the continuity and loopback tests, the present invention detects both error conditions.
REFERENCES:
patent: 3912882 (1975-10-01), Beerbaum
patent: 4270030 (1981-05-01), Brolin et al.
patent: 4309105 (1982-01-01), Lebduska
patent: 4558188 (1985-12-01), Stuparits et al.
patent: 4630268 (1986-12-01), Rodenbaugh
patent: 4908819 (1990-03-01), Casady et al.
patent: 5224149 (1993-06-01), Garcia
patent: 5274692 (1993-12-01), Lechner et al.
patent: 5343461 (1994-08-01), Barton et al.
patent: 5353326 (1994-10-01), Jung
Corso, III Martin
De Trana Nicholas D.
DeCaluwe Craig L.
Demmert Robert G.
AT&T Corporation
Chan Wing F.
Kenyon & Kenyon
Nguyen Duc
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