Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Testing of subscriber loop or terminal
Reexamination Certificate
2000-05-31
2004-09-14
Tran, Quoc (Department: 2743)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Testing of subscriber loop or terminal
C379S001010, C379S022000, C379S022010, C379S022040, C379S026010, C379S029010
Reexamination Certificate
active
06792080
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to signaling for enhanced 911 systems, and more specifically, to testing such signaling over digital loop carrier arrangements.
2. Description of the Related Art
Enhanced 911 (E911) service refers to establishing communication between customer telephones and the nearest Public Safety Answering Point (PSAP), which is an answering location for 911 calls originating in a given geographic area.
The operation of this E911 service will now be described with reference to the prior art E911 system
100
shown in FIG.
1
. All communication paths in this system
100
are conventional two-wire paths, which use a “tip” wire and a “ring” wire to define a loop (also known as a channel) used for communication. In this system, one of the customer telephones
110
goes “off-hook” to report an emergency by dialing 911. In response to the dialed digits, the associated Private Branch Exchange (PBX)
120
senses this off-hook condition, which is a low resistance tip-to-ring path. The PBX
120
is typically large, with many telephones
110
widely dispersed, to merit the deployment of a dedicated analog E911 trunk
155
. Such an E911 trunk is typically dedicated solely for E911 service, and is configured for outward (i.e., PBX-originated) communication. After sensing the off-hook condition, the PBX
120
seizes the trunk
155
(i.e., wires between the PBX
120
and the local central office (CO)
160
) by closing the loop defined by the tip/ring pair of wires in the trunk
155
. A trunk seizure condition in E911 signaling is defined as a call state initiated by the PBX
120
in response to a customer telephone
110
in which the CO
160
prepares to receive signals.
After the CO
160
acknowledges seizure of the trunk
155
by reversing the battery polarity applied to the trunk
155
, the PBX
120
sends two separate data messages: one identifying the E911 switch (
170
) to handle the call during the emergency, and the second identifying the telephone
110
. An E911 switch
170
may be a central office switch which has been programmed to handle E911 signaling and switching. As used herein, the term “E911 switch” refers to either the above-described E911 CO simulator, or a dedicated E911 switching unit. When the E911 switch
170
receives the messages identifying the closest PSAP
130
and the calling telephone
110
, the E911 switch
170
makes a connection to the closest PSAP
130
. In some implementations a separate box
150
interfaces the PBX
120
to the trunk
155
, to provide E911 compatibility to a legacy PBX. The data messages between the PBX
120
and the CO
160
are sent using a multi-frequency (MF) protocol, which uses pairs of tones with frequencies contained within the voice bandwidth of the respective channel units (not shown, but defined as those units which control communication along one or more communication channels) in and between the PBX
120
and CO
160
. Thus, the DC signaling characteristics of the channel units operating the PBX/CO link are used only for supervision in initiating the E911 call and in terminating it.
The above-described E911 service, where the PBX
120
seizes the trunk
155
by closing the loop and the CO
160
terminates the trunk
155
by applying reverse battery polarity to acknowledge, is used on a conventional analog trunk
155
. Such signaling between the PBX
120
and CO
160
is generically termed “loop reverse battery” (LRB) signaling. This E911 interface at the PBX end is specified by an American National Standards Institute (ANSI) standard, ANSI T1.411-1995, “Interface between Carriers and Customer Installation—Analog Voicegrade Enhanced 911 Switched Access Using Network-Provided Reverse-Battery Signaling.”
Recently, so-called digital loop carrier (DLC) systems have been developed and implemented, where a larger number of channels may be implemented on fewer wires than in a conventional analog network. DLC channel units accomplish this greater channel density by time division multiplexing digital data for a number of channels onto two pairs of wires. For example, 24 communication channels may be implemented on two wire pairs in a DLC system, whereas the two wires only provide one channel in an analog implementation.
As shown in
FIG. 2
, DLC channel units
210
,
220
are typically located in a central office terminal (COT)
250
in the CO
160
, and in a remote terminal (RT)
200
near the PBX
120
to coordinate signaling therebetween. DLC trunks
230
and
240
are able to be seized only by an originating channel unit
210
, so in a seizure sense, the trunks arc unidirectional. However, once communication has been established between the CO and PBX, two-way traffic occurs over the DLC trunk. RT
200
includes an originating channel unit
210
connected to DLC trunk
230
, which is terminated by terminating channel unit
220
in COT
250
. Originating channel unit
210
in the RT
200
seizes the trunk
230
when a PBX originated call occurs. Similarly, DLC trunk
240
is seized by channel unit
210
in the COT
250
Telcordia (previously named Bellcore) has published three standards for DLC systems that specify signaling arrangements between a central office (CO) and a Private Branch Exchange (PBX) for direct-inward-dialing (DID) service (i.e., calls originating from the central office) using the loop reverse battery (LRB) signaling protocol. These standards are termed TR-08, TR-57, and GR-303. TR-08 and GR-303 cover “integrated” DLC systems (i.e., a digital facility terminated directly by a digital interface of a switch used to connect one channel to another in the central office). TR-57 specifies requirements for a “universal” DLC that uses a central office terminal (COT)
250
to convert the digital signal from the DLC
230
to an analog signal which is sensed by an analog switch
260
in the CO. In conventional DID service, the CO
160
seizes the DLC trunk
240
, and the PBX
120
acknowledges such seizure via a RT
200
which contains a DLC channel unit
220
. A trunk seizure condition conventional DID service is defined as a call state initiated by the CO in which the PBX prepares to receive incoming signals.
Where the telephone company employs a universal DLC system to assist in connecting the CO switch and the PBX over the loop pair, the channel units of the DLC system at the remote terminal (RT) location present the same interface to the PBX as do the channel units of a conventional analog CO. Similarly, the COT channel units present the same interface to the switch in the CO as do the channel units of a conventional analog PBX. As mentioned above, the DLC systems in use today seize the trunk at the CO to implement DID. However, E911 service mandates seizing the trunk at the PBX, and such trunk seizure is not specified by any of the existing TR-08. TR-57, or GR-303 digital loop carrier standards.
Accordingly, a manner of implementing enhanced 911 service on digital loop carrier systems is needed. Further, the above-described conventional analog enhanced 911 systems are difficult to test prior to deployment, and, once they are deployed, each channel must be tested individually. Thus, a method of testing enhanced 911 service on digital loop carrier systems prior to deployment is also needed.
SUMMARY OF THE INVENTION
The present invention provides a method and system for rapidly and automatically testing E911 systems using digital loop carrier trunks in a laboratory prior to deployment. A testbed running a testing program evaluates the functionality of a digital loop carrier trunk, a channel unit pair, and an E911 switch by measuring a delay and duration of an acknowledgement pulse from the E911 switch in response to an off-hook condition at a simulated PBX. The testbed and testing program also evaluate the functionality of the E911 switch and a simulated PSAP by measuring a delay and duration of a ring signal from the E911 switch in response to an emergency signal sent by the simulated PBX. Once connection between the simulated PBX and the simulated
Imperato Anthony
Rice David Reagan
Yueh Shan
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