WO1999033280A1

WO1999033280A1 - Dial pulse collection in a digital loop carrier

Info

Publication number: WO1999033280A1
Application number: PCT/US1998/026873
Authority: WO
Inventors: Martin P. J. Cornes; Keith W. Herndon
Original assignee: Alcatel Usa Sourcing, L.P.
Priority date: 1997-12-23
Filing date: 1998-12-18
Publication date: 1999-07-01
Also published as: TW435048B; AU1924999A

Abstract

A telecommunications system includes an access terminal and multiple channel unit cards coupled to the access terminal. The channel unit cards are configured to sense on-hook/off-hook signals on subscriber lines coupled to respective ones of the channel unit cards. Each channel unit card is configured to process received on-hook/off-hook signals and to send a message-oriented signal to the access terminal. Each message-oriented signal includes a value representing a dialed digit corresponding to on-hook/off-hook signals received in the respective one of the channel unit cards.

Description

DIAL PULSE COLLECTION IN A DIGITAL LOOP CARRIER

Background The present invention relates to dial pulse collection in a digital loop carrier. Telecommunications access terminals connect subscriber lines, such as POTS (Plain Old Telephone Service) lines, to telecommunications exchanges and other telecommunications equipment . An access terminal contains channel unit card slots that accept channel unit cards. The channel unit cards, or line cards, convert analog or digital signals from subscriber lines into formatted digital data signals. Different types of channel unit cards service different types of subscriber lines . Some subscriber devices, such as telephones, use either dial pulsing or touchtone dialing to identify a dialed telephone number and to transmit it to other telecommunications equipment. In dial pulsing, also known as rotary dialing, regular momentary interruptions of a direct or alternating current at the subscriber end indicate the value of the dialed number or character. For example, three interruptions can represent the digit 3. In some systems, Dual Tone Multi-Frequency (DT F) , or touchtone, signals are generated by the subscriber device, but subsequently are converted by a Private Branch Exchange (PBX) to dial pulsing signals.

Summary In general, in one aspect, a method of handling subscriber line signals includes sensing, in a channel unit card, one or more on-hook/off-hook signals, where the on-hook/off-hook signals correspond to a dialed alphanumeric character. A message-oriented signal, which includes the value of the dialed alphanumeric character, is formed in the channel unit card. The message-oriented signal is delivered to an access terminal connected to the channel unit card.

In addition, a method of handling subscriber line signals in a telecommunications system, including multiple channel unit cards coupled to an access terminal, includes sensing on-hook/off-hook signals in the channel unit cards and processing the on-hook/off- hook signals in the channel unit cards in a distributed manner. Message-oriented signals are delivered from the channel unit cards to the access terminal . Each of the message-oriented signals includes a value representing a dialed digit corresponding to the on-hook/off-hook signals received in a respective one of the channel unit cards.

In another aspect, a channel unit card includes a hook detector circuit for sensing on-hook/off-hook signals on subscriber lines and for setting the state of a bit based on the received on-hook/off-hook signals. The channel unit card further includes a processor configured to scan the bit and to form a message-oriented signal based on the bit scanning. The message-oriented signal includes a value corresponding to the on-hook/off- hook signals. In addition, a telecommunications system can include an access terminal and multiple channel unit cards as described above. The channel unit cards are coupled to the access terminal .

In yet a further aspect, in a telecommunications system including an access terminal and multiple channel unit cards coupled to the access terminal, the channel unit cards are configured to sense on-hook/off-hook signals on subscriber lines coupled to respective ones of the channel unit cards . Each channel unit card is configured to process received on-hook/off-hook signals and to send a message-oriented signal to the access terminal. Each message-oriented signal includes a value representing a dialed digit corresponding to on-hook/off- hook signals received in the respective one of the channel unit cards. Various implementations include one or more of the following features. The channel unit card can determine whether a digit has been dialed at a subscriber device, such as a telephone, based on the bit scanning. The channel unit card also can determine the value of the digit or other alphanumeric character based on the bit scanning. In particular, the processor in the channel unit card can be configured to determine whether a digit has been dialed at a subscriber device based on the bit scanning. The processor also can be configured to determine the value represented by the on-hook/off-hook signals .

The channel unit card can include a counter, and the processor can be configured to increment a value stored in the counter based on the state of the bit set by the hook detector circuit. The processor also can be configured to form the message-oriented signal based on a value stored in the counter.

In some implementations, the access terminal and channel unit cards form part of a digital loop carrier system. The channel unit cards can be, for example, POTS or other line cards.

Various implementations may provide one or more of the following advantages. By distributing the performance of dial pulse collection among multiple channel unit cards coupled to an access terminal, the terminal can devote more time to other call control and processing functions. In addition, using message- oriented signaling for messages transmitted between the channel unit cards at the access terminal and a central processor in the access terminal can free up additional bandwidth to be used for other required messages or signals. The technique can be used to route dial pulse signals to telecommunications switches that require signaling according to either message-oriented or bit- oriented protocols.

Additionally, performing dial pulse collection in a distributed, rather than centralized, manner can reduce the amount of logic or hardware required on the channel unit cards, thereby reducing the cost of the channel unit cards. For example, the collection of dial pulses can be performed in software without the use of special hardware devices, such as digital signal processors.

Additional features and advantages will be readily apparent from the following description, drawings and claims.

Brief Description of the Drawings FIG. 1 is a block diagram of a telecommunications system.

FIG. 2 is a partial block diagram of a digital loop carrier.

FIG. 3 is a block diagram of subscriber devices coupled to remote POTS cards.

FIG. 4 is a partial block diagram of a POTS card. FIG. 5 is a flow chart showing steps of a method of collecting dial pulse signals.

FIG. 6 illustrates one format of a message- oriented signal generated by a POTS card.

Detailed Description As shown in FIG. 1, a 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. The digital loop carrier 4 acts as a delivery unit for the system 2, and delivers call control and management signals. 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 can be coupled to the LEC network 22 through a switch 20, such as a class 5 switch. As shown in FIG. 2, the central office terminal 6 and the remote terminals, such as terminal 8, have one or more channel unit acceptors, such as slots 26, 36, respectively. The slots 26, 36 accommodate channel unit cards which carry data signals to and from subscriber lines 48 and LEC network lines 46. The subscriber lines 48 are coupled to subscriber devices, such as the telephone 16, and the LEC network lines 46 are coupled to the LEC network 22. Channel unit cards convert incoming subscriber line data signals into formatted digital data and convert formatted digital data into data signals suitable for transmission over the subscriber lines.

Different channel unit cards serve different kinds of narrowband (e.g., POTS, COIN, UVG/EWG, Four-Wire E&M, Unversal Four-Wire, Basic Rate Interface Unit) and wideband (ISDN, DS1U, T1U, ADS1U, AT1U, El, El Short

Haul, El Long Haul and ElConc) subscriber lines. In one implementation, shown in FIG. 3, the channel unit card slots 36 at the remote terminal 8 are capable of accommodating up to twenty POTS cards, 50(1) through 50(20), each of which terminates up to six subscriber lines, 48(1) through 48(120) . Some of the subscriber lines, for example subscriber lines 48(1) and 48(6), may be coupled to rotary or other telephones 52, 54 capable of providing dial pulse signals. Other subscriber lines, such as subscriber line 48(120), may be coupled to a PBX 56 which converts DTMF signals received from a touchtone telephone 58 to dial pulse signals which are coupled to one of the POTS cards, such as the POTS card 50(20) .

As further shown in FIG. 2, each of the central office terminal 6 and the remote terminal 8 also includes one or more card acceptors, such as slots 30, 40, to accommodate transmission cards. Transmission cards in the slots 30, 40 enable the terminals 6, 8 to communicate over the communication media 12. Different transmission cards support different communication media. Electronic Interface Level 1 (El) cards, for example, can be used to support communications over metallic media, and optical line unit cards can be used for fiber optic communications. The transmission cards in the slots 30, 40 handle the conversion between the communication medium 12 signals and electric signals that the terminals 6, 8 can understand and process.

The central office terminal 6 and the remote terminal 8 each includes at least one Bandwidth Allocator, Processor and Timing Unit (BPT) card 28, 38. Each BPT card 28, 38 collects formatted digital signals from its respective channel unit cards in the slots 26 or 36 and multiplexes them into a time domain multiplexed (TDM) signal. The multiplexed signal then can be sent over the transmission medium 12 via the transmission cards in the slots 30 or 40, respectively. The BPT cards 28, 38 also receive TDM signals from their respective transmission cards. The BPT cards 28, 38 demultiplex the received TDM signals and route them for delivery to their respective channel unit cards in slots 26, 36.

Respective subscriber bus interfaces 32, 42 are used to send signals between the channel unit cards in the slots 26 or 36 and their corresponding BPT cards 28 or 38. Similarly, octal buses 34, 44 are used to send signals between the transmission cards 30 or 40 and their corresponding BPT cards 28 or 38. Further details of the BPT cards 28, 38 are described, for example, in a U.S. Patent Application (08/970,183) entitled "Telecommunications Terminal" and filed on November 14, 1997.

As shown in FIG. 4 card, the POTS card 50(1) includes a hook detector circuit 60 which can be implemented using a CODEC Subscriber Line Interface Circuit (SLIC) . The hook detector circuit 60 is coupled to subscriber devices, such as the telephone 52, through the subscriber line 48(1) . The pair of lines indicated by 48(1) in FIG. 4 represents a tip-ring pair. The hook detector circuit 60 also is coupled to a processor 62, such as a microcontroller or microprocessor, which includes a clock 64. A Motorola 68HC11 microcontroller is suitable as the processor 62. Although, as shown in FIG. 4, the clock 64 is part of the processor 62, in an alternative implementation, the clock 64 can be external to the processor 62. In addition, the processor 62 is coupled to a counter 66. The counter 66 can be implemented, for example, in software executed by the processor 62 which stores a value in random access memory (RAM) . The processor 62 is further coupled to the subscriber bus interface 42. As shown in FIG. 5, when a telephone number is dialed, for example on the telephone 52, one or more interruptions of the subscriber line current are generated to indicate a dialed digit (step 100) . For example, three interruptions would indicate the dialed digit 3. As indicated by step 102, the hook detector circuit 60 senses the state of the subscriber line current and sets an on-hook/off-hook bit which indicates the state of the subscriber line and which is sent to the processor 62. In one implementation, the on-hook/off- hook bit is set high when the current on the subscriber line is interrupted. The on-hook/off-hook bit is set low when the current is not interrupted.

The processor 62 is configured to scan the on- hook/off-hook bit received from the hook detector circuit 60 as indicated by step 104. Based on the duration and number of transitions in the on-hook/off-hook bit, the processor 62 is programmed to determine whether a digit has been dialed at the telephone 52, and if so, the value of the dialed digit. In one implementation, the processor 62 is programmed to scan the on-hook/off-hook bit at a rate of approximately once every 3 milliseconds (msec) . Depending on the duration of a detected transition in the on-hook/off-hook bit, the processor 62 determines which one of several possible states is indicated by the transition. A first predetermined period can be used to check that the value of the bit is valid. If the bit is set high for a first predetermined duration, for example six msecs, the processor 62 interprets the bit as indicating a stable on-hook signal. If the on-hook/off-hook bit remains high for at least a second predetermined duration that is longer than the first duration, but less than a third predetermined duration, the processor 62 interprets the bit as indicating a dialed digit. The second predetermined duration, can be, for example, approximately 100 msec. When the bit remains in a digital high state for longer durations, for example, one second or longer, the processor 62 interprets the signal as indicating other states, such as hook flash or subscriber telephone on- hook states. The durations used by the processor 62 to interpret the on-hook/off-hook bit may vary, for example, by country or LEC network.

Each time the processor 62 interprets a transition in the state of an on-hook/off-hook bit as a dial pulse, it increments the counter 66 by one, as indicated by step 106. The interpretation of the on-hook/off-hook bit by the processor 62 can be performed as part of an interrupt service software routine.

As indicated by step 108, the processor 62 also is programmed to check for the end of a sequence of one or more transitions in the state of the on-hook/off-hook bit where the sequence of transitions corresponds to a single dialed digit. In one implementation, once the value stored in the counter 66 changes, the processor 62 checks whether a predetermined period elapses without a further change in the value stored in the counter 66. If the predetermined period, which can be on the order of approximately one second, does elapse, and the value stored in the counter has not changed again, then the processor 62 uses the value stored in the counter as the value of the dialed digit. Thus, for example, if the digit 3 was dialed at the telephone 52, the value stored in the counter 66 would have been incremented to the value three. As indicated by step 110, the processor 62 formulates a message-oriented signal which includes the value of the dialed digit. One suitable format for the message-oriented signal is discussed in greater detail below with respect to FIG. 6. As indicated by step 112, the processor 62 also resets the value in the counter 66 to zero.

FIG. 6 illustrates an exemplary format for a message-oriented signal 70 which is sent from the processor 62 in the POTS card 50(1) to the BPT card 38 in the remote terminal 8 via the subscriber bus interface 42 and which serves to indicate the value of a dialed digit. The message oriented signal includes seven bytes, 71-77. Two bytes 71-72 contain high level routing information. A third byte 73 serves to identify an activity field. Specifically, the third byte 73 identifies the signal 70 as containing the value of a dialed digit. A fourth byte 74 contains information identifying the physical location of the subscriber line or channel on the POTS card 50(1) . A fifth byte 75 identifies the value of the dialed digit. The sixth and seventh bytes 76-77 contains a generic identifier corresponding to the channel or subscriber line identified by the information in the fourth byte. The information in the sixth and seventh bytes is used by the terminals 6, 8 as an internal designator for the subscriber channel . Use of the foregoing format is discussed further in a U.S. Patent Application (08/996,957) entitled "Routing Call Processing Communications in a Tele-communications System" and filed December 23, 1997.

Returning to FIG. 5, the processor 62 on the POTS card 50(1) forwards the message-oriented signal 70 to the BPT card 38 via the subscriber bus interface 42 (step 114) . Once the message-oriented signal 70 is received by the BPT card 38, the signal 70 is processed and transmitted to an appropriate channel unit card at the central office terminal 6, as indicated by step 116.

Thus, the BPT card forwards the message-oriented signal 70 as part of a TDM signal across the transmission line 12 to the central office terminal 6. Using information contained in the sixth and seventh bytes 76-77, the central office terminal 6 identifies a corresponding channel on a channel unit card in the slot 26 and passes the message-oriented signal 70 to the appropriate channel unit card. As indicated by step 118, the channel unit card to which the signal 70 is routed is programmed to translate the information contained in the fifth byte 75 (i.e., the dialed digit) of the signal 70 into an appropriate signal or series of signals and to route the dialed digit to the LEC network 22 according to the protocol specified by the LEC network. In general, the channel unit card slots 26 at the central office terminal 6 accommodate various types of channel unit cards. In one implementation, for example, the channel unit card slots 26 accommodate an El card which routes signals from the BPT card 28 to the switch 20 according to a protocol that uses message-oriented signaling, such as the International Telecommunications Union Telecommunications standard set forth in the ITU-T Recommendation G.964, "V-Interfaces at the Digital Local Exchange (LE) - V5.1-Interface (Based on 2048 Kbit/s) for the Support of Access Network (AN) . " The channel unit card slots 26 also accommodate channel unit cards, such as El cards, that route messages from the BPT card 28 to the switch 20 according to bit-oriented signaling, such as Channel Associated Signaling (CAS) .

As described above, the POTS cards 50(1) through 50(20) serve as the interface between the subscriber lines 48 and the BPT card 36 in the remote terminal 8 and allow the collection or counting of dial pulses to be performed in a distributed, rather than a centralized, manner. Such a distributed process of dial pulse collection can provide several advantages.

First, the collection of dial pulses can be a time-consuming process which, if performed by the BPT cards 28 or 38, can tie up other important central call control functions. The technique described above can alleviate this problem by distributing the performance of dial pulse collection among multiple channel unit cards at the remote terminal 6. Second, performing dial pulse collection in the manner described above allows message-oriented signaling to be used for messages sent between channel unit cards at the remote terminal 8 and the BPT card 38 in the remote terminal. The use of message-oriented signaling can free up additional bandwidth to be used for other required messages or signals.

Moreover, performing dial pulse collection as described above can reduce the amount of logic hardware required on the channel unit cards, such as digital signal processors, thereby reducing the cost of the channel unit cards .

Although the foregoing description has been in the context of a digital loop carrier with central office and remote terminals 6, 8, a POTS cards, such as the POTS card 50(1), alternatively can be used with a stand-alone access terminal. In that case, additional channel unit cards associated with the remote terminal 8 would translate the information contained in the fifth byte 75 (i.e., the dialed digit) of the signal 70 into an appropriate signal or series of signals and route the dialed digit, for example, to the switch 20 according to the protocol required by the switch.

Other implementations are within the scope of the following claims.

Claims

What is claimed is:

1. A method of handling subscriber line signals comprising: sensing, in a channel unit card, one or more on-hook/off-hook signals corresponding to a dialed alphanumeric character; forming, in the channel unit card, a message- oriented signal comprising a value of the dialed alphanumeric character; and delivering the message-oriented signal to an access terminal in a digital loop carrier connected to the channel unit card.

2. The method of claim 1 wherein the channel unit card comprises a POTS card.

3. The method of claim 1 further comprising setting a state of a bit in response to sensing the on- hook/off-hook signals.

4. The method of claim 3 further comprising scanning the bit in the channel unit card.

5. The method of claim 4 further comprising determining whether a digit has been dialed at a subscriber device based on the bit scanning.

6. The method of claim 4 further comprising determining a value of the alphanumeric character based on the bit scanning.

7. The method of claim 3 further comprising incrementing a value stored in a counter based on the state of the bit .

8. The method of claim 7 wherein the message-oriented signal is based on a value stored in the counter.

9. In a telecommunications system comprising a plurality of channel unit cards coupled to an access terminal in a digital loop carrier, a method of handling subscriber line signals comprising: receiving on-hook/off-hook signals in the channel unit cards; and processing the on-hook/off-hook signals in the channel unit cards in a distributed manner; and delivering message-oriented signals from the channel unit cards to the access terminal wherein each of the message-oriented signals comprises a value representing a dialed digit corresponding to the on- hook/off-hook signals received in a respective one of the channel unit cards.

10. The method of claim 9 wherein the channel unit cards comprise POTS cards.

11. The method of claim 9 further comprising routing the value of dialed digits to a local exchange carrier network which uses a message-oriented protocol.

12. A channel unit card comprising: a hook detector circuit for sensing on- hook/off-hook signals on subscriber lines and for setting a state of a bit based on the received on-hook/off-hook signals; a processor configured to scan the bit and to form a message-oriented signal based on the bit scanning, wherein the message-oriented signal comprises a value corresponding to the on-hook/off-hook signals.

13. The channel unit card of claim 12 wherein the channel unit card comprises a POTS card.

14. The channel unit card of claim 12 wherein the processor is configured to determine whether a digit has been dialed at a subscriber device based on the bit scanning .

15. The channel unit card of claim 12 wherein the processor is configured to determine the value represented by the on-hook/off-hook signals.

16. The channel unit card of claim 12 further comprising a counter wherein the processor is configured to increment a value stored in a counter based on the state of the bit.

17. The channel unit card of claim 16 wherein the processor is configured to form the message-oriented signal based on a value stored in the counter.

18. A telecommunications system comprising: an access terminal forming part of a digital loop carrier; a plurality of channel unit cards coupled to the access terminal, wherein the channel unit cards are configured to sense on-hook/off-hook signals on subscriber lines coupled to respective ones of the channel unit cards, wherein each channel unit card is configured to process received on-hook/off-hook signals and to send a message-oriented signal to the access terminal, and wherein each message-oriented signal comprises a value representing a dialed digit corresponding to on-hook/off-hook signals received in the respective one of the channel unit cards.

19. A telecommunications system comprising: an access terminal in a digital loop carrier; a plurality of channel unit cards coupled to the access terminal, wherein each channel unit card comprises:

(a) a hook detector circuit for sensing on- hook/off-hook signals on one or more subscriber lines and for setting a state of a bit based on the received on- hook/off-hook signals; (b) a processor configured to scan the bit and to form a message-oriented signal based on scanning the bit, wherein the message-oriented signal comprises a value represented by the on-hook/off-hook signals.