WO1999039542A1

WO1999039542A1 - Emergency wireless backup for telecommunications terminal

Info

Publication number: WO1999039542A1
Application number: PCT/US1999/002012
Authority: WO
Inventors: Glen A. Giordano; Martin P. J. Cornes
Original assignee: Alcatel Usa Sourcing L.P.
Priority date: 1998-01-30
Filing date: 1999-01-29
Publication date: 1999-08-05
Also published as: AU2485999A

Abstract

A telecommunications terminal (24) has a digital loop carrier with subscriber line interfaces and network trunk interfaces. A processor (40) is programmed to verify that the connection to the network is available and to assert an alarm if the connection to the network is not available. Also provided are a wireless communication card (38) capable of connecting to a wireless network, a DSP (36) coupled to remote telecommunications equipment and capable of detecting emergency calls coming from the remote telecommunications equipment, and a control processor (34) programmed to receive the alarm and to route emergency calls recognized by the DSP through the wireless communication card for connection to a wireless network (31).

Description

EMERGENCY WIRELESS BACKUP FOR TELECOMMUNICATIONS TERMINAL

Background The invention is related to access terminals for telecommunications systems. Telecommunications terminals connect subscriber lines, such as POTS (Plain Old Telephone Service) and ISDN (Integrated Services Digital Network) lines, to telecommunications equipment such as a telecommunications switch, e.g., a class 5 switch. Telecommunications switches connect and route messages between different lines .

A telecommunications terminal contains channel unit card slots that accept channel unit cards. Channel unit cards convert analog and digital signals from subscriber lines into formatted digital data signals. Different types of channel unit cards service different types of subscriber lines (e.g. POTS or ISDN) . The terminal constructs one or more time division multiplexed (TDM) signals from several channel unit cards, formatted digital data signals for transmission to remote telecommunications equipment for example, another telecommunications terminal. The terminal also demultiplexes TDM signals received from remote telecommunications equipment to deliver formatted digital data back to the channel unit cards. Channel unit cards convert the formatted digital data into a form suitable for transmission over subscriber lines.

Two telecommunications terminals can be connected "back-to-back" to form a digital loop carrier (DLC) network. A DLC typically includes a remote terminal (RT) placed near a business or residence and a central terminal (CT) placed in a central exchange connected to a telecommunications switch. The RT and CT communicate over a single line or multiple lines carrying TDM signals. This configuration connects subscribers to the telecommunications switch via the DLC.

A digital loop carrier (DLC) at a central terminal (CT) includes a multiplexor which, using TDM, can multiplex multiple analog and digital signals from subscriber telephone lines into a single wideband (e.g., Tl or El) signal or multiple wideband signals. A mirror DLC located at a remote terminal (RT) can decode the multiplexed Tl signal into a form suitable for transmission over subscriber telephone lines. This data flow also occurs in the opposite direction from RT to CT.

Summary A telecommunications terminal has a digital loop carrier connected to a primary network, a processor programmed to monitor availability of the connection between the digital loop carrier and the primary network and a backup communications card for connecting emergency calls through a backup network when the connection between the digital loop carrier and the primary network is unavailable.

The backup communications card may be a wireless communications card and the backup network may be a wireless network. The processor may be a transport card programmed to verify that the connection between the digital loop carrier and the primary network is available and to assert an alarm when the connection is unavailable. The telecommunications terminal may also include a digital signal processor capable of detecting an emergency call incoming from remote telecommunications equipment and a control processor programmed to route an emergency call detected by the digital signal processor to the backup communications card based on an alarm asserted by the transport card. The remote telecommunications equipment may be a subscriber line coupled to the digital loop carrier through a subscriber line interface. The control processor may be a bandwidth allocator, processor and timing card. The wireless network may be a cellular network, a telecommunications terminal having a wireless communication card and connected to the primary network or is a satellite network.

A method of routing emergency calls in a telecommunications terminal is disclosed including detecting whether a connection to a primary network is available and asserting an alarm if the connection to the primary network is not available. Also, the method includes detecting an emergency call while the alarm is asserted and routing the emergency call through a backup network.

The backup network may be a cellular network, another terminal having a wireless communication card or a satellite network. The other terminal having a wireless communication card can be connected to the primary network or a network other than the primary network. The detection of emergency calls may be performed by a digital signal processor. The routing of the emergency calls may include transmitting the emergency call to the backup network using a wireless communication card.

A telecommunications terminal has means for verifying that a connection to a network is available for use and means for asserting an alarm if the connection is not available for use. The telecommunications terminal also has means for detecting emergency calls while the alarm is asserted and means for routing emergency calls through a wireless communication card for connection to the primary network.

Advantages may include one or more of the following. Emergency calls, for example, calls to 911 or the like, will be completed even if a remote telecommunications terminal becomes severed from its network or otherwise incapacitated. System efficiency will not be affected by the additional hardware since the wireless communication card is idle until needed.

Because the configuration is adaptable, users can specify any form for emergency calls.

Other advantages and features will become apparent from the following description including the drawings and claims.

Description of the Drawings FIGS. 1 and 2 are diagrams of a telecommunications system;

FIG. 3 is a diagram of components in a telecommunications system;

FIG. 4 is flow chart of the operation of a telecommunications system;

FIG. 5 is flow chart of the operation of a telecommunications system.

Detailed Description

As shown in FIG. 1, telecommunications system 2 includes a digital loop carrier (DLC) 4. The digital loop carrier 4 includes a central office terminal (CT) 6 coupled to one or more remote terminals (RT) 8, 10 via metallic, fiber or other suitable communication media 12. DLC 4 performs call control and management signals and provides central office call processing functions. Subscriber devices, such as telephone service equipment 14, 16, 18, can be coupled to the central office terminal 6 and to the remote terminals 8, 10, respectively. The central office terminal 6 also is coupled to a local exchange carrier (LEC) network 22. The central office terminal 6 may be coupled to the LEC network 22 through a switch 20, such as a class 5 switch.

As shown in FIG. 2, LEC network 22 also may be coupled to a cellular switch 21. The cellular switch provides access to cellular service through cellular base stations, such as base station 23.

In instances where the communication medium between the central office terminal 6 and a remote terminal 8 or 10 becomes severed or otherwise inoperative the remote terminal is isolated from the central office terminal, thereby terminating service in the area serviced by that remote terminal . This could pose a dangerous situation for subscribers who have an emergency and need to reach the police, fire department, ambulance, etc. on an urgent basis. The telecommunications system described here, inter alia, enables subscribers to make such emergency calls even when the usual primary communication channels between the remote terminal and the central terminal have broken down. In the configuration shown in FIG. 2, each terminal 24, 26 is equipped with a backup communication card (e.g., a wireless communication card) that is capable of connecting to a cellular system, for example through base station 23, to other wireless systems (e.g., directly to the central office terminal) or to a satellite for connection to the network. If the primary connection to the central office terminal became severed emergency calls can be routed through the backup (e.g., wireless communication) link. This ensures that subscribers have access to emergency lines even when the primary communications channels fail.

FIG. 3 shows a block diagram of the general components of a Litespan-120 DLC, made by DSC Communications Corporation, configured for emergency wireless service. Remote terminal 24 is connected to the central office terminal 26 by a physical transport 32, such as Tl lines, El lines, optics, etc. A wireless connection 30 exists between the remote terminal 24 and a cellular system 31 which includes base station 23. Subscribers are connected to the remote terminal 24 through subscriber ports 28a-n. Each subscriber port 28a-n may be adapted to accept different types of transmission media, i.e., POTS, ISDN, etc. by insertion of a different service module card. Also, each subscriber port 28a-n is connected to a control processor for the remote terminal, for example, a bandwidth allocator, processor and timing card (BPT) 34, via a subscriber bus (not shown) for purposes of generic call control . BPT card 34 collects formatted digital signals placed on the subscriber bus by service module cards, and multiplexes them into a TDM signal. The BPT card 34 sends the TDM signal to transport card 40 over an octal bus (not shown) for transmission to remote telecommunications equipment, such as central office terminal 26. The BPT card 34 also receives TDM signals from the transport card 40 over the octal bus. These TDM signals are sent to the transport card 40 from remote telecommunications equipment. The BPT card 34 demultiplexes the TDM signal and places the demultiplexed data on the subscriber bus for delivery to service module cards .

Transport card 40 enables the remote terminal 24 to communicate with central office terminal 26 over a physical transport 32. Transport card 40 handles the conversion between the type of signals sent over physical transport 32 and the type of signals that can be processed by the remote terminal. Transport card 40 performs other functions including data scrambling/descrambling and detecting the availability of physical transport 32.

Wireless card 38 performs similarly to transport card 40. However, instead of being connected to a physical transport 32, a transmitter, receiver are included on the wireless card 38 and an antenna connected. These components allow wireless card 38 to connect to base station 23 of wireless network 31 via wireless connection 30. The system also contains a digital signal processor (DSP) card 36. DSP card 36 includes a specialized microprocessor, e.g., DSP, memory and an application specific integrated circuit (ASIC) or an Field Programmable Gate Array (FPGA) , that provides call resources, such as dial tone generation, digit and dial plan collection, etc. DSP card 36 is responsible for detecting emergency calls when physical transport 32 is unavailable.

During normal operation as shown in FIG. 4, if a subscriber goes off-hook (step 42) , the software of a service module card detects the off-hook state and sends a signal to the LEC network (step 44) . The LEC network responds to this signal by issuing a dial tone to the subscriber (step 46) . once dial tone is issued, a subscriber is able to dial the desired number (step 48) and the call is completed through the LEC network (step 50) .

FIG. 5 describes a process that occurs if the connection 32 to the central terminal 26 becomes severed or otherwise fails. If the connection becomes severed (step 56) , or a loss of transport occurs, transport card 40 detects this condition (step 58) and an alarm is triggered (step 60) . BPT card 34 detects this alarm and routes all off-hook subscribers to DSP card 36 which will then provide dial tone and collect digits. From these digits the occurrence of emergency calls can be detected (step 62) . Emergency calls may be designated in many different forms, e.g., 911, depending on the geographic region in which the terminal is deployed. Once an alarm has been triggered, BPT card 34 routes all calls to DSP card 36 for emergency call detection (step 64) until connection 32 is restored. If an emergency call is detected, DSP 36 informs BPT 34 of the subscriber channel on which the emergency call was placed. BPT 34 then routes the call on the subscriber channel handling the emergency call from DSP 36 to wireless card 38 (step 66) . Finally, BPT 34 prompts wireless card 38 to initiate the call (step 68) and the emergency call is completed via wireless connection 30 (step 70) . This emergency backup terminal provides a means for connecting emergency calls to a network even if the primary connection to the network is unavailable. The path through which the emergency calls are routed can vary depending upon the configuration of the terminal . The emergency calls may be routed from the terminal to a cellular base station, to another terminal with wireless capabilities or to a satellite for connection to the network .

Connecting to a cellular system is accomplished by configuring the terminal with a cellular communications card and taking advantage of an existing cellular network in the area. Connection to a satellite is similar, but a digital satellite communications card must be provided and the terminal is taking advantage of an existing satellite network. Connecting to another terminal with wireless capabilities involves providing a digital radio communications card on each terminal and possibly repeaters. Repeaters may be necessary due to the fact that the remote terminal is most likely far from the terminal to which it is connecting. In either case, the digital radio signal carry the wireless signal back to the digital radio communications card of the other terminal .

Other implementations are within the scope of the following claims.

What is claimed is:

Claims

1. A telecommunications terminal comprising: a digital loop carrier connected to a primary network; a processor programmed to monitor availability of the connection between the digital loop carrier and the primary network; and a backup communications card for connecting emergency calls through a backup network when the connection between the digital loop carrier and the primary network is unavailable.

2. The telecommunications terminal of claim 1 wherein the backup communications card comprises a wireless communications card and the backup network comprises a wireless network.

3. The telecommunications terminal of claim 1 wherein the processor comprises a transport card programmed to verify that the connection between the digital loop carrier and the primary network is available and to assert an alarm when the connection is unavailable.

4. The telecommunications terminal of claim 3 further comprising a digital signal processor capable of detecting an emergency call incoming from remote telecommunications equipment.

5. The telecommunications terminal of claim 4 further comprising a control processor programmed to route an emergency call detected by the digital signal processor to the backup communications card based on an alarm asserted by the transport card.

6. The telecommunications terminal of claim 5 wherein the remote telecommunications equipment comprises a subscriber line coupled to the digital loop carrier through a subscriber line interface.

7. The telecommunications terminal of claim 5, wherein the control processor comprises a bandwidth allocator, processor and timing card.

8. The telecommunications terminal of claim 2, wherein the wireless network comprises a cellular network.

9. The telecommunications terminal of claim 2, wherein the wireless network comprises a telecommunications terminal having a wireless communication card and connected to the primary network.

10. The telecommunications terminal of claim 2, wherein the wireless network is a telecommunications terminal having a wireless communication card connected to network other than the primary network.

11. The telecommunications terminal of claim 2, wherein the wireless network is a satellite network.

12. A method of routing emergency calls in a telecommunications terminal, the method comprising: detecting whether a connection to a primary network is available; asserting an alarm if the connection to the primary network is not available; detecting an emergency call while the alarm is asserted; and routing the emergency call through a backup network.

13. The method of claim 12, wherein the backup network comprises a cellular network.

14. The method of claim 12, wherein the backup network comprises another terminal having a wireless communication card connected to the primary network.

15. The method of claim 12, wherein the backup network comprises another terminal having a wireless communication card connected to another network.

16. The method of claim 12, wherein detection of emergency calls is performed by a digital signal processor.

17. The method of claim 12 wherein routing the emergency call comprises transmitting the emergency call to the backup network using a wireless communication card.

18. The method of claim 12 wherein routing the emergency call comprises transmitting the emergency call to the backup network using a digital satellite communications card.

19. A telecommunications terminal, comprising: means for verifying that a connection to a network is available for use; means for asserting an alarm if the connection is not available for use; means for detecting emergency calls while the alarm is asserted; and means for routing emergency calls through a wireless communication card for connection to the primary network .