Abstract:
A telecommunications system has identical access terminal shelves and an intershelf bus interconnecting each shelf. Each access terminal shelf has transmission card slots constructed to accept different types of transmission cards that use different types of transmission media to communicate with remote telecommunications equipment and a processor programmed to determine whether transmissions from the remote telecommunications equipment are to be transferred to the intershelf bus for connection completion.

Description:
BACKGROUND 
     The invention is related to telecommunications systems access equipment such as digital loop carriers. 
     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&#39; 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 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 or multiple T 1  signal. A mirror DLC located at a remote terminal (RT) can decode the multiplexed T 1  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 
     In general, in one aspect, a telecommunications system has access terminal shelves and an intershelf bus interconnecting each access terminal shelf. Each access terminal shelf has transmission card slots. These slots are constructed to accept different types of transmission cards. Each different type of transmission card may use a different type of transmission medium to communicate with remote telecommunications equipment. The telecommunications system also includes a processor programmed to determine whether, to complete the connection, a transmission from the remote telecommunications equipment needs to be transferred via the intershelf bus to another shelf in the terminal. 
     In accordance with various implementations, the intershelf bus structure may be controlled by a bus controller. The intershelf bus may include two bidirectional data buses with complementary timing, a timing and synchronization bus and a control local area network. The intrashelf bus structure includes a control bus, a time division multiplexed bus and a timing bus. 
     A method of handling transmission in a telecommunications system having a plurality of identical shelves includes communicating with remote telecommunications equipment, accepting different types of transmissions from the remote telecommunications equipment over different types of transmission media and determining whether the accepted transmissions need to be transferred from a shelf that accepted them to another shelf via an intershelf bus structure to complete connection. 
     In accordance with various implementations, transferring of transmissions between shelves via the intershelf bus structure may be controlled by a bus controller. The determination of whether transmissions need to be transferred is performed by a processor residing on each shelf. 
     Advantages may includes one or more of the following. Telephone service providers will be able to construct a digital loop carrier without requiring an expensive master control shelf. Digital loop carriers constructed using the configurations described here are expandable on as-needed basis. Moreover, system efficiency will increase due to the distributed processing configuration. Other advantages and features will become apparent from the following description including the drawings and claims. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of a telecommunications system; 
     FIG. 2 is a diagram of DLC components; 
     FIG. 3 is a block diagram of components of a system controller; 
     FIGS. 4 and 5 are diagrams of an inter-shelf bus structure; 
     FIG. 6 is a flow chart of DLC operation. 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1, a telecommunications system  2  includes a digital loop carrier (DLC)  4 . DLC  4  includes a central office terminal (CT)  6  coupled to one or more remote terminals (RT)  10  via metallic, fiber or other suitable communication media  9 . DLC  4  performs call control and management signals and provides central office call processing functions. Subscriber devices, such as telephone service equipment  12   a-n ,  13   a-n , can be coupled to the central office terminal  6  and to the remote terminal  10 . The central office terminal  6  also is coupled to a local exchange carrier (LEC) network  18 , optionally through a switch  16 , such as a class  5  switch. 
     As shown in FIG. 2, an access terminal  10  contains shelves  20   a-n  that have slots  22   a-n  for accepting a variety of cards. Certain slots are dedicated to one type of card, e.g., service module slots are able to accept service module cards. Different cards perform different terminal functions. An inserted card connects to the terminal&#39;s backplane via a connector in slots  22   a-n  (not shown). The backplane contains a variety of buses including a subscriber bus (not shown) that electronically connects each inserted terminal card to every other terminal card. Many slots  22   a-n , including those that hold service module cards, have a “hot condition” capability that allows an administrator to insert and remove cards without interrupting terminal operation. 
     Several types of slots  22   a-n  exist with many slots per shelf. Service module slots can hold any type of service module. Different service modules serve different kinds of narrowband (e.g. POTS, COIN, UVG/EWG, EM 4 , U 4 W, and BRIU) and wideband (e.g. ISDN, DS 1 U, T 1 U, ADS 1 U, AT 1 U, E 1 , E 1 S, E 1 L, and E 1 Conc) subscriber lines. Many of the slots in each shelf are dedicated service module slots. Also, every shelf has a dedicated slot for each of the following cards: a System Controller (SC) card, Bank Power Supply and Ringing Generator (BPS/RG) card, and an Alarm Maintenance Unit (AMU) card. 
     In a typical configuration shown in FIG. 2, a subscriber device  12   a  is coupled to POTS card  26  which is inserted into one of the service module slots and thereby becomes associated with a channel on a transport, such as E 1  or T 1 , of one of the SC cards  24   a-n . Although POTS card  26  is shown to be connected only to a single subscriber device  12   a , in practice each service module used in the system could handle multiple connections. 
     The access terminal shelves  20   a-n  are connected through an intershelf bus  28  in a distributed processing configuration. In this configuration, each shelf  20   a-n  is able to communicate with each of the other shelves in an equal, as opposed to a master-slave, relationship. An advantage of having equality among the shelves is that each shelf can make decisions that only affect itself. For example, if a subscriber&#39;s call is handled by the terminal shelf containing the connection that the call is requesting, the subscriber will be connected without involving any of the other shelves. This distributed processing structure reduces cost by eliminating the need to purchase a costly master shelf. Another advantage of this configuration is that it increases flexibility by allowing virtually any number of these shelves to be interconnected at any time. Thus, the capacity of DLC  4  can grow or shrink as desired based on the particular needs of a telephone service provider. 
     FIG. 3 shows a diagram of the system controller which includes a transport interface  34  that manages the connection  9  to the central terminal and a control bus interface  36  that manages the connection to bus controller  52 . A data bus interface and matrix processor  38  also is included and is used to manage data buses  41  and  43 . A timing circuit  44  handles the timing and synchronization of the system through the timing and synchronization bus  39  and a system management interface  40  oversees system processes. The system controller also contains a microprocessor and switching matrix  42  programmed to determine connection locations and perform proper switching in cases that intershelf hand-off (call transfer) is unnecessary. The microprocessor and switching matrix  42  of each shelf also is responsible for accepting signals handed-off from other shelves and for performing the proper switching in those cases. 
     The intershelf bus structure  28  shown in FIG. 4 enables the interconnection of shelves  20   a-n  while the intrashelf bus structure  45  shown in FIG. 5 enables the service modules to be connected to the SC. In FIG. 4, intershelf bus structure  28  includes a pair of data buses  41  and  43  for data flow between the shelves, a timing and synchronization bus  39  and a control local area network (LAN)  37 . 
     The timing of bus  41  is 180 degrees out of phase of the timing of bus  43 . Essentially, in this configuration bus  41  and bus  43  will become available in succession which allows signals to be bused more effectively. Though one bus may be used, the provision of two bidirectional data paths between the shelves increases system efficiency and reduces system delay. It should be understood that the use of two synchronous buses with complementary timing is merely exemplary and other variations of both synchronously and asynchronously timed buses configured in different timing schemes may be used. 
     Timing and synchronization bus  39  is used to transfer signals from timing circuit  44  (FIG. 3) from one shelf to another shelf. Similarly, the control LAN  37  is used to send control signals between the shelves. 
     As shown in FIG. 5, the intrashelf bus connects service modules  54   a-n  to bus controller  52 . Each of the service modules is inserted into a dedicated service module slot of slots  20   a-n . Bus controller  52  is responsible for routing and managing the connections between the off terminal elements, such as transport interface  34  or service modules  54   a-n , and the terminal&#39;s intershelf bus  28 . Each of the shelves  20   a-n  has an intrashelf bus structure  45 . The intrashelf bus includes a control bus  46 , time division multiplexed (TDM) bus  48  and timing bus  50 , each of which has connections to service modules  54   a-n  and bus controller  52 . Control bus  46 , TDM bus  48 , and timing bus  50  are used to transfer control signals, time division multiplexed signals and timing signals respectively between service modules  54   a-n  and bus controller  52 . 
     The intrashelf bus generally always will be used when line activities occur, while the intershelf bus generally only will be used for certain activities, i.e., all calls received by a shelf will use the intrashelf bus while only calls being connected through a different shelf will use the intershelf bus. Line activities occur either on the subscriber side or the LEC network side of the terminal. 
     Subscriber line activities include events which are detected by the terminal and which may need to be reported or delivered to other system components, e.g., remote terminal  10  reporting to terminal  6  and LEC network  18 . Subscriber line activities include, for example, detecting that an off-hook detector is active or inactive, detecting a dialed pulse, acknowledging completion of an initial ring, and detection of a hookflash condition. 
     LEC network  18  line activities include events which occur away from the terminal and may need to be reported to the terminal. Such activities include, for example, the fact that a called party answered the call, that the party at the remote end terminated the call, the start and cadence of ringing, notification to start subscriber pulse metering and notification of pulsed polarity, polarity type, and the start or completion of trunk conditioning. 
     FIG. 6 illustrates a call processing path diagram. When a subscriber line activity occurs, such as seizing of a line by a subscriber (step  60 ), the particular POTS card that accepted the call signal notifies the SC responsible for the shelf in which the POTS card is inserted (step  62 ). The SC determines by communicating with the LEC network over a predetermined control channel the port to which the subscriber is to be connected (i.e., the “destination port”) (step  64 ). A destination port may be on the same shelf as the POTS card that accepted the signal or may be on another shelf. 
     The SC determines, what steps to follow to complete the connection (step  66 ). If the destination port is a connection of the originating SC, the subscriber is connected to the port by that SC (step  70 ) and a signal is sent back to the POTS card to complete the connection (step  74 ). If, however, the destination port is a connection on a different shelf, the originating SC connects the subscriber to intershelf bus  28  through bus controller  52  (step  68 ). The SC containing the connection to the destination port then connects the subscriber to the assigned port (step  72 ) and sends a signal back to the POTS card to complete the connection (step  76 ). When the originating POTS card receives the signal to complete the connection, it connects the subscriber to intrashelf bus  45  and the connection is complete. 
     Although the foregoing implementations have been described with respect to a POTS card, other types of digital or analog channel unit cards also can be used. Additionally, although the foregoing techniques have been described with respect to a digital loop carrier system having a central office terminal and a remote terminal, the techniques can be used in a stand-alone access terminal as well. 
     In some implementations, a single LEC network may include various components that allow the LEC network to handle signals or messages using more than one protocol. In that case, a single access terminal can accommodate multiple channel unit cards coupled to the LEC network even though different channel unit cards use different protocols when communicating with the LEC network. 
     Other embodiments are within the scope of the following claims.