Abstract:
This invention relates to arrangements for eliminating loop-around trunks for operational calls. Such trunks are used when a single switch performs two distinct functions, such as local service and operator assistant service. In order to simplify software, the software for each of these functions is designed separately; in the prior art, if both functions are needed, two separate connections are established and are joined by the use of a loop-around trunk. In accordance with Applicant&#39;s invention, the loop-around trunk is eliminated by initially establishing a connection from a real time-slot to a virtual time-slot for the first function and from a virtual time-slot to a real time-slot for the second function; the real time-slots for receiving the call and for transmitting the call to an inter-office trunk are then connected in the switch without requiring the use of a separate loop-around trunk.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a Continuation-in-Part Application of application Ser. No. 08/868,391 filed on Jun. 3, 1997, now abandoned. 
    
    
     TECHNICAL FIELD 
     This invention relates telecommunications trunk circuits and their relation to telecommunications switching systems. 
     Problem 
     Many modern switching systems carry out a plurality of functions such as local, toll, and local operator assistance. At the same time, the software for supporting each of these functions is maintained separately in order to allow features for each of these types of systems to be developed without requiring detailed studies of feature interactions among features of the different types of systems. Under these circumstances, it is frequently necessary for some types of calls, for example, calls between a local switch function and an operator service position system function to provide loop-around trunks in order to have a clean interface between the two types of calls. Under these circumstances an incoming call connection is established between an incoming trunk and one end of such a loop-around trunk, and a separate connection is established between the other end of the loop-around trunk and an outgoing trunk. The existence of a loop-around trunk ensures that the connection can be established within a switching system and the fact that the two connections are separate ensures that the features of one connection do not interfere with the features of the other connection. A problem of the prior art is that such loop-around trunks are expensive and must be generously engineered. 
     Solution 
     The above problem is solved and an advance is made over the prior art in accordance with Applicant&#39;s invention wherein a first “connection” is established from the incoming trunk to a virtual loop-around trunk, i.e., a “trunk” that exists only in memory, but has no physical appearance on the network, and a second “connection” is established from the other end of the virtual loop-around trunk to the outgoing trunk. After these “connections” have been established a real connection is established directly from the incoming trunk to the outgoing trunk. Advantageously, this arrangement avoids the cost of a separate hardware loop-around trunk while retaining the independence of the software for the two “connections.” 
     In accordance with one specific embodiment of Applicant&#39;s invention, each connection is controlled by a pair of program processes (processes), one process for controlling each end of the connection. Four processes are involved in the type of connection discussed above. The processes associated with the virtual loop-around trunks communicate with the processes associated with the real trunk and return to these processes the same types of messages as would be returned if the connection were to a real loop-around trunk. As a last step, these two processes communicate with the processes for controlling the real trunks to establish the connection between the two real trunks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a block diagram illustrating the prior art; 
     FIG. 2 is a block diagram illustrating Applicant&#39;s invention; and 
     FIG. 3 is a flow diagram illustrating the establishment of a call in accordance with Applicant&#39;s invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates the prior art. A switch  1  includes subsections  3  and  4  each for controlling a different feature set of the calls established in switch  1 . A common processor complex  2  controls path segments  5  and  6  in both subsections  3  and  4 . The processor complex may include message paths to transmit messages between individual processors of the processor complex, the individual processors controlling separate modules of the switch. In accordance with the prior art, a connection between trunk  11  connected to subsection  3  and trunk  14  connected to subsection  4  uses a loop-around trunk shown as two separate elements, B 12  and C 13 . A connection is established between trunk A 11  and trunk B 12  and a separate connection is established between trunk C 13  and trunk D 14 . Trunks B 12  and C 13  are inherently connected since a loop-around trunk is an arrangement for connecting the two paths. The switch in Applicant&#39;s preferred embodiment is a digital switch and a connection  5  is established by establishing a connection between a time-slot T 1   21  associated with trunk A and a time-slot T 2   22  associated with loop-around trunk segment B 12 . Another connection  6  is established by having a separate connection from loop-around trunk segment C 13  to time-slot T 3   23 , thence to time-slot T 4   24  which is then connected to trunk D. Four processes control this connection. Process P 1   31  controls trunk A and controls the selection of time-slot T 1   21 , process P 2   32  controls the selection of time-slot T 2   22  and the selection of loop-around trunk segment B 12 , process P 3   33  control the association between loop-around trunk segment C 13  and time-slot T 3   23 , while process P 4   34  controls the selection of time-slot T 4  and its connection T 4   24  and its connection to trunk D 14 . 
     A Time-Slot Interchange, (TSI) contains two types of memories: a signal memory, and a control memory. Incoming time-slots are stored in an incoming signal memory from which they are transmitted under the control of the contents of a control memory to an output signal memory for feeding a next stage of TSI, or for feeding a trunk facility. The contents of the control memory are used to steer the contents of individual time-slots of the input signal memory to the appropriate locations in the output signal memory. When a request to establish a connection is made, this request leads to setting up a path by inserting appropriate addressing information into the control memory so that the appropriate input time-slots stored in the input signal memory are sent to the appropriate output time-slots of the output signal memory. The control memory is the interface between the processor and the TSI so that the processor software deals only with the control memory. A virtual time-slot is one which does not have a location in the signal memory, or which has a location in signal memory that is unconnected to transmission facilities. However, the control memory can point to such a virtual time-slot, and the processor can request connections to, and between, virtual time-slots. The request for such connections will not lead to any signals being sent between the virtual time-slots, but if such a connection is not required as in the case described herein, the software of the processor can operate as if it were establishing real paths by establishing such paths between virtual time-slots that are capable of being referred to by real addresses generated by the software of the processor. Again, there is no need to transmit signals over such virtual trunks in the system described herein, but to avoid complications in the software, it is desirable to permit the path establishment and path disconnection software to generate addresses of such virtual trunks. 
     In accordance with Applicant&#39;s invention as shown in FIG. 2, process P 1   31  is similarly associated with time-slot T 1   21  and trunk All, but process P 2   32 , instead of being associated with a real time-slot T 2   22  and a real segment of a loop-around trunk B 12 , is instead associated with a virtual (non-existent) time-slot T 2   25  and a virtual loop-around trunk segment B 15 . Process P 2   32  responds to process P 1   31  in the same way that it would if these virtual time-slots and loop-around trunk segments were real, i.e., sends the same types of messages that it would if these units were real. Similarly, process P 3   33 , instead of controlling loop-around segment C 13 , controls virtual loop-around segment C 16  and virtual time-slot T 3   26 . P 3   33  communicates with P 4   34  in the same way as in the prior art and P 4   34  selects a real time-slot T 4   24  and controls real trunk D 14 . In the final stage of the connection processes P 2   32  and P 3   33  signal to their respective counterparts P 1   31  and P 4   34  to establish the connection between time-slots T 1   21  and T 4   24 . 
     In essence, the virtual loop-around trunk receives the same voice or data that the real loop-around trunk would receive and sends the same voice or data that the real loop-around trunk would send. The only difference is that instead of exiting the switch and being converted back and forth to different forms of signaling information, the voice or data is transmitted and received to and from a single time-slot in the switch. Further, the processes controlling this time-slot behave and are programmed exactly as though they were controlling a piece of hardware whose interface to these processes is merely the transmission and receiving of this voice or data and the successful acknowledgments of each request to receive and transmit voice or data. The voice or data, however, is not being sent out of the switch, but merely left inside the switch for the other corresponding process to retrieve. 
     For example, in the prior art, a unit of voice or data would be deposited in a digital register in the interface unit which connects to the real trunk, B 12  to C 13 , transmitted over this physical link, and then written to a digital register in the interface unit which connects to C 13  for retrieval by process P 3  in time-slot T 3   23 . In the invention, the time-slots T 2   22  and T 3   23  are replaced in the referencing processes, P 1   31  and P 4   34 , by the endpoint time-slots, T 1   21  and T 4   24 , respectively. The path, therefore, between the two time-slots, T 1   21  and T 4   24 , becomes a direct path as the time-slots are communicating directly without the need for intermediate hardware, the loop-around trunk, yet the controlling processes, P 1  with P 4  and P 2  with P 3 , treat these time-slots as though they are distinct hardware time-slots, exchanging control messages and receiving them. Each of these control messages are received and acknowledged by software that responds as though a successful completion of the requested action has taken place. Voice and data digital information need not be moved or copied to other registers than the two endpoints, and controlling software in processes P 1   31 , P 2   22 , P 3   34 , and P 3   34  need not change. Ideally, the only software that would need to be modified would be that which interfaces directly with the new, virtual trunk hardware, and it would be responsible for using the existing endpoint time-slots on the far ends of the path, T 1   21  and T 4   24 , in place of the time-slots T 2   22  and T 3   23  that they would have required in the absence of the invention so that the voice and data is transmitted between T 1   21  and T 4   24 . 
     In this invention, the high-level controlling software in P 1 , P 2 , P 3 , and P 4  need not know that the loop-around trunk is a virtual one. Only the software that communicates with and operates on the hardware that would be needed in the absence of this invention would have to ensure that voice or data were transmitted to and from the time-slots at the far ends of the path as though the hardware did in fact exist, thus behaving like a “virtual trunk”, and ensuring that the requests made to it and the responses back properly emulate a real, operational hardware trunk interface. 
     FIG. 3 is a flow diagram illustrating the operation of Applicant&#39;s invention. Process P 1  receives a loop-around (LA) type request from the real incoming trunk (trunk A) and assigns a real time-slot T 1  (Action Block  301 ). P 1  recognizes that this is a request which requires a loop-around type trunk or equivalent facility in accordance with Applicant&#39;s invention. P 1  then activates a process P 2  (Action Block  303 ). P 2 , upon receiving the activation message, knows that this is a loop-around type request (Action Block  305 ). P 2  seizes a virtual time-slot (time-slot T 2   25 ) and seizes a virtual loop-around trunk ( 15 ,  16 ) (Action Block  307 ). P 2  then tells P 1  that it has completed the path and indicates that a virtual time-slot (T 2 ) has been assigned (Action Block  309 ). P 1  proceeds as if the connection between T 1  and virtual time-slot T 2  had been established. P 2  then routes the call from the virtual trunk  15 ,  16  to P 3  and signals for the second part of the connection from its virtual trunk. The signals are essentially the same as the signals which are used in connection with the prior art arrangement (Action Block  311 ). P 3  recognizes that this is a loop-around type request and seizes its own virtual time-slot T 3  and activates process P 4  (Action Block  313 ). P 4  also knows that it is a loop-around type request and connects real time-slots T 4  to real outgoing trunk (trunk B) and tells P 3  that it has completed the path from virtual time-slot T 3  (Action Block  315 ). P 2  and P 3  then complete the connection between real time-slots T 1  and T 4  (Action Block  317 ). 
     Other embodiments of this invention can readily be derived by those of ordinary skill in the art. The invention is limited only by the Claims.