MXPA00004087A - Atm-based distributed virtual tandem switching system - Google Patents

Abstract

An Asynchronous Transfer Mode (ATM)-based distributed virtual tandem switching system is provided in which a network of ATM-based devices is combined to create a distributed virtual tandem switch. The system includes an ATM switching network that dynamically sets up individual switched virtual connections. The system also includes a trunk interworking function (T-IWF) device and a centralized control and signaling interworking function (CS-IWF) device. The trunk interworking function device converts end office voice trunks from TDM channels to ATM cells by employing a structured circuit emulation service. The centralized control and signaling interworking function device performs call control functions and interfaces narrowband signaling and broadband signaling for call processing and control within the ATM switching network. Consequently, the ATM based distributed virtual tandem switching system replaces a standard tandem switch in the PSTN.

Description

TANDEM VIRTUAL SWITCHING SYSTEM, DISTRIBUTED BASED ON THE ASYNCHRONOUS TRANSFER MODE CROSS REFERENCE TO RELATED APPLICATION This application claims the benefit of Provisional Patent Application of E.U.A .:, No. 60 / 083,640, filed on April 30, 1998,. entitled "Tandem Virtual Switch System, Distributed Based on the Synchronous Transfer Mode [" ATM "], of ALLEN et al., the description of which is expressly incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telecommunications architecture. More particularly, the present invention relates to tandem switch systems, for use within a public switched telephone network ("PSTN"). This invention enables the connection of voice lines over a network in the asynchronous transfer mode ("ATM"), replacing the tandem switches with a distributed tandem virtual switch system, which includes a high speed ATM network. The replacement is virtual because, as regards the terminal offices, the tandem virtual switching system, distributed on the basis of the ATM, is functionally equivalent to the traditional tandem switching system, multi-channelized in the division of time. ("TDM"). 2. Background Information Within public switched telephone networks (PSTN), an originating caller communicates with a destination, establishing a connection between a terminal office, which serves the caller of origin, and a terminal office, which serves the destination. Figure 1 shows the architecture of the current PSTN. In this current PSTN, the switches 10 of the terminal office are connected to each other by means of groups 12 of tandem trunks, groups 14 of direct trunks or both in groups of trunks in tandem as groups of direct trunks, 12 and 14. Each trunk within a group of trunks is typically a communication line of a digital service level 0 (DSO) (ie 64 kilobits per second), which transmits between the terminal offices 10 in a multi-channelized manner in time division ( TDM). When a terminal office uses a group 14 of direct trunks, the connection between the 10 terminal offices is without any intermediary. When a terminal / central office 1 uses a group 12 of tandem logs, the connection between the terminal offices 10 is via a tandem switch 16. The tandem switch or office 16 is a switch or intermediate connection, between a location of the originating telephone call and the final destination of the call, which passes the call along the same. The tandem switches are often used to handle calls that exceed their capacity. That is, when all the trajectories are occupied in a primary rut, for example, trunk group 14 between direct office between the 10 terminal offices of. destination source, alternative routes through switch 16 e taidem handle the volume of overflow calls. The tandem 16 switch can also function as a physical path to directly connected offices in addition to operating as an overflow path for directly connected offices. If the overflow route through the tandem switch 16 becomes saturated, an alternative final route may be provided. The alternative fine route is through another terminal office 10, using two trunk groups 14 between offices.

The signaling is necessary within the PSTN, to establish a connection (ie the establishment of a telephone call) between the calling party and a destination. This signaling enables the line acquisition and establishes the call route, in addition to performing other functions. The signaling can be transmitted through a common channel with the voice data (signaling in band) or it can be transmitted to a dedicated channel (signaling out of band). The dominant signaling protocol currently in use is transmitted through the dedicated channel and is called the Signaling System 7 (SS7). A conventional establishment of connection between two terminal offices 20, 22, in a tandem network, will now be described with reference to Figures 2 and 3. When a calling party 19 (for example 235-1111) dials a telephone number (for example 676-2222), the the central office 20 interprets the dialed digits and guides the call to any of a trunk group 14 between direct offices, between the terminal offices 20, 22, or a pair of 12 trunk groups of tandem offices, and the switch 16 in tandem between the end offices, 20, 22. Assuming that the pair of groups 12 of office trunks and the corresponding tandem switch 16 are used, a trunk of each group 12 of trunks needs to be selected and reserved by the signaling within the SS7 network. Thus, the necessary information is transmitted from the originating terminal office 20 to its associated point 18"of signal transfer.Although only a single signal transfer point is shown in the figures, a network typically includes many signal transfer points. Thus, each signaling transfer point 18 transfers signals from one signaling link to another, in the SS7 network, which carries the SS7 messages.The information transmitted is in the form of an ISUP message (part of the ISDN user). It contains a unique point code, which uniquely identifies each end office, which corresponds to the originating terminal office (source point code (OPC)) and destination (target point code (DPC)). Since the message must first go to office 16 in tandem, the ISUP message contains the code of the destination point of the tandem office.The message also contains an identification code. circuit circuit (CIC), which corresponds to the physical circuit that will be used by the dog to transport the data. Thus, trunks between offices are identified by the code of the point of origin (OPC), the code of the destination point (DPC), and the circuit identification code (CIC). As shown in the example illustrated in Figure 3, initially an ISUP message is sent, which contains a signal from the DPC to 246 1 2, an OPC signal equal to 246 1 1, and a CIC equal to 22. Consequently, A circuit will be established between the terminal office 20 of origin and the office 16 in tandem. The tandem switch 16 receives the SS7 message and determines the called number, which is embedded in the protocol, where the call is routed, ie the appropriate destination terminal office 22. Then, through the SS7 network, the call is established between the tandem switch 16 and the appropriate terminating office 22, in a similar manner. Thus, because the tandem office 16 needs to transport the data to the destination terminal 22, the tandem office 16 sends an ISUP message to the signal transfer point 18, which includes the code of the destination point of the destination end offices, ie 246 1-3, the code of the office's point of origin, ie 246 1 2, and the circuit identification code, which corresponds to the circuit between office 16 in tandem and the destination office 20, for example circuit 7. After this ISUP message is sent to signal transfer point 18, this signal transfer point 18 forwards the ISUP message to the destination terminal office 22, with the In order to establish the connection between the office 16 in tandem and the office 22 of destination, reserving the circuit. The switch 22 of the terminating central office receives the SS7 message and determines where the call ends, interpreting the called number embedded in the protocol. A call flow scenario will now be described with reference to Figure 2. A caller 29 dials the telephone number of a destination 23. The first terminal office 20 (terminal office A) collects the digits of the called number and verifies the tables of route to determine - which terminal office 22 the dialed telephone number belongs to. Then the terminal office 20 of origin finds a group 14 of direct trunks between itself and the terminal office owned by the dialed telephone number. Subsequently, the originating terminal office finds an inactive trunk within group 14 of logs. The terminal office 20 of origin selects and reserves. the inactive trunk of group 14 of logs and initiates an SS7 IAM message (initial address message), which contains the following: route direction of the signaling transfer point of the destination terminal office; the number of the calling telephone; the phone number called and trunk ID (CIC) of the trunk selected from the group of these trunks. The signal transfer point 18 receives the IAM message and sends it forward to the destination terminal 22. The destination terminal office 22 receives the IAM message and uses the CIC information to reserve the selected trunk within group 24 of_ logs. The destination terminal office 20 (terminal B office) then checks whether the 23 number of the called telephone is hung and the characteristic support and hold the line, assuming that the dialed telephone number is hung. The destination terminal 22 then applies a ring to the line and a ring tone to the selected trunk in group 14 of logs. Next, the destination terminal office 22 connects the line of the dialed telephone number to the selected trunk in the trunk group 14, initiates a message of SS7 ACM (Full Address Message.) And sends it forward to the 18th transfer point of the trunk. signs The signal transfer point receives the ACM message and sends it ahead to the originating terminal office 20, which receives the ACM message. The originating terminal office 20 then connects the line of the telephone number which calls the selected trunk. Consequently, the caller's call hears a ringing tone and if the party called on the called telephone number picks up the telephone The destination terminal office 22 detects the off-hook e the telephone number '23 called and suspends the tone d ringing . The destination terminal office 22 then initiates an SS / ANM message (response) to the signal transfer point 1. This signal transfer point 18 receives this ANM message and sends it forward to the originating office 20. This terminal office 20 receives the ANM message and initiates the necessary measurement for the invoice. Another call flow scenario, according to the prior art, will now be described with reference to Figure 2. Initially, a caller, for example e 235-1111, marks a destination, for example 676-2222. office terminal 20 of origin (office terminal A) collects the digits of the called number and checks the route tables d to determine which terminal office manages * the 676. L terminal office 20 of origin finds that 676 belongs a 22 office of destination end ( terminal office B) The terminal office A then places a group 14 of trunks directly to the terminal B office. It is assumed in this example that no inactive trunk exists within group 14 of direct trunks. terminal A chooses and reserves a first group 12 of tandem trunks, and a trunk selected from the first group 12 of reserved trunks. Next, the terminal office A initiates an SS7 IAM message, which contains the following: the route address of the tandem signal transfer point; the calling phone number; the phone number called; and trunk identification (CIC) for the trunk selected from the first group 12 of reserved trunks. The signal transfer point 18 receives an IAM message and sends it forward to the tandem switch 16. The tandem office 16 receives the IAM message and. uses the information of the CIC to reserve the selected number of the first group 12 of reserved logs. The tandem office 16 checks a route table, to determine the destination and receives a trunk selected from a second group 12 of logs, which connects to the destination. Subsequently, the tandem 16 initiates an SS7 IAM message to the signal transfer point ol8 with the following information: the route address of the signal transfer point 18 of the terminal B office; the calling phone number; the phone number called; and trunk identification (CIC) for the trunk selected from the second group 12 of logs. The signal transfer point 18 receives the IAM message and sends it forward to the terminal office B. This terminal office B receives the IAM message and uses the information of the CIC to reserve the selected trunk of the second group 12 of logs. The terminal office B checks whether the called telephone number is hung and retains the line, assuming that the 676-222 is hung. The terminal office B applies a ring to the line and a ring tone to the selected trunk of the second group 12 of trunks The terminal office B lueg connects the line to the trunk selected from the second group 1 of logs and initiates a message from SS7 AM to point 18 d signal transfer. This signal transfer point 18 receives the ACM message and sends it forward to the tandem switch 16 e. This tandem switch 16 receives the message ACM from the signal transfer point 18 accordingly, the tandem switch initiates an ACM message to the signal transfer point 18.

The signal transfer point 18 receives the message from ACM and sends it forward to the terminal office A. This terminal office A receives the message from ACM and connects 235-1111 to the selected trunk of the first reserved trunk group 12. Next, the caller at 235-1111 hears a ring tone and the called party at 676-2222 picks up the telephone. As a result, the B terminal office detects the unhooked or 676-2222. Therefore, the terminal office B suspends the ringing tone and initiates an ANM message to point 18 of signal transfer. This signal transfer point 18 receives the message ANM and sends it forward to the switch 16 in tandem. This tandem switch 16 receives the ANM message from the signal transfer point 18 and the tandem switch 16 initiates an ANM message to the signal transfer point 18. The signal transfer point 18 receives the ANM message from the tandem switch and sends it to the terminal office A. This terminal office A receives the message from the signal transfer point 18 and initiates the measurement necessary for billing. Finally, the calling party at 235-111 speaks to the called party at 676-2222.

The current system has disadvantages. In order to minimize call volume overflow, the size of a group of logs needs to be predicted so that the logs group can handle the volume of expected calls. Then, groups of logs of appropriate size are previously provided each with a dedicated band width. The process of forecasting and forecasting is expensive. Likewise, the current architecture of logs requires a large number of small groups of logs to be linked to the terminal offices, due to the large number of terminal offices that each terminal office must connect. This form of logs leads to inefficiencies due to the relatively small size of a significant number of groups of logs. That is, the small size reduces the capacity of trunk calls and, therefore, requires a higher percentage of overflow trunks. In addition, the increased number of logs requires high investments in hardware and software so that systems keep track of individual logs between offices. In addition, log forecasting and provisioning are necessary for thousands of individual log groups.

The VTOA Group of ATM Forum has tried to solve the problems associated with voice trunks over ATM. E Grupo VTOA developed a specification to take voice over ATM in a private network environment. For example, see ATM Forum Technical Committée, in "Version 2.0 of Interoperability Specification of the Circuit Emulation Service" (January 1997). The specification allows private businesses to make use of an AT network to establish voice channels through the ATM network, using a protocol, such as the private network-network interface ("PNNI"), which facilitates moving calls from one point in the ATM network to another point in this ATM network. However, the specification is limited to the application within a private environment, which is not appropriate for the amplifications in the PSTN. That is, the interaction is not supported with systems that include out-of-band signals, for example, the Signal System 7 (SS7), which is essential to support the capabilities, such as an advanced intelligent network (AIN). Within these private networks, signaling is typically in band. Thus, no interface with an out-of-band signaling network will be required. Likewise, if a calling party within the private network would like to make contact with someone outside the private network, the calling party must communicate about the normal PSTN, thus leaving the scope of the VTOA Group system. U.S. Patent No. 5,483,527 is directed to voice trunks within the PSTN. This patent describes a system that interposes an ATM network between two central offices. The signaling is sent from the central office by means of a signal transfer point (STP) to the ATM switch. Within each ATM switch, a process system is provided for the interface of the ATM switch with the STP. Thus ATM switches are modified to be able to communicate with the signal transfer point, which is a very expensive process. Also, due to the interface provided within each ATM switch, the path through the ATM network is established relatively slowly. Finally, the distributed placement of the interface between the signal transfer points and the ATM network has its own disadvantages.

Glossary of Acronyms AAL Adaptation layer of ATM ACM ADPCM Complete Address Message Modulation of Adaptive Differential Pulse Code ADSL Asymmetric Digital Subscriber Line AIN Intelligent Advanced Network ANM Response Message ANSI Institute of American National Standards ATM Asynchronous Transfer Mode B-ISUP User Part of Broadband ISDN CAS Associated Signaling of CBR Channel Constant Bit Regime - CCS Signaling of Common Channel CES Circuit Emulation Service CIC Circuit Identification Code CS-IWF Internal Control and Signaling Work Function DPC Destiny Point Code DSO Digital Signal Level 0 (64 Kbps digital signal format) DS1 Digital Signal Level 1 (1.544 Mbps IAM digital signal format Initial IP Address Message ISDN Internet Protocol Integrated Service Digital Network ISUP User Part of the ITU-T ISDN International Telecommunications Union IF Internal Work Function IXC Internal Exchange Bearer OAM &P Operations, Administration, Maintenance Provisioning 0C12 level 12 optical Carrier signal (622 Mbps) 0C3 Optical Carrier level 3 signal (155 Mbps) OPC Point of Origin Code PCM Pulse Code Modulation PNNI Private Network Interface-POTS Network Old Plan Phone Service PSTN Public Switched Phone Network SS7 Signaling System 7 SSP Service Switch Point STP Signal Transfer Point SVC Switched Virtual Connection TDM Multiplexer (Multicanalizador) Division of the Time T- F Internal Work Function of Trunk UNI User Interface to the VTOA Network Voice and Telephony over ATM SUMMARY OF THE INVENTION In view of the foregoing, the present invention is directed to providing a replacement for a current trunking system, operating between the terminal offices, as well as between the terminal offices and an internal exchange carrier network. Therefore, a tandem virtual switching system is provided, based on the Asynchronous Transfer Mode (ATM). This system comprises an ATM switching network, a trunks internal work function device (T7I F), and a centralized internal control and signaling work function device (CS-I F). The internal log work function device (T-IWF) is adapted to receive voice trunks from terminal offices from the multichannel time division (TDM) channels and convert the trunks into ATM cells. The centralized control and signaling internal work device (CS-I F) performs call control functions and is adapted for the signaling interface of narrow bands and broad bands for the process and control of calls within the switching network of ATM. Thus, the tandem virtual switching system, distributed on the basis of ATM, replaces a standard tandem switching. According to a preferred embodiment, the T-IWF includes a circuit emulation service. In addition, the T-IWF may include an ATM adaptation layer 1 (AAL1). Alternatively, the T-IWF adapts the circuit traffic to the ATM cells, which use the ATM adaptation layer 2 (AAL2). If AAL2 is used, silence suppression and / or "voice compression can be backed up. According to a preferred embodiment, each voice trunk is dynamically established as a single switched virtual connection in the ATM switching network. the T-IWF and the terminal office switch are placed in the same place. In accordance with a preferred embodiment, the narrowband signaling is the signaling of SS7.

In addition, the wide banking signaling is preferably PNNI, B-ISUP and / or UNÍ. A method is provided to transport the voice from a source location to a destination through the Asynchronous Transfer Mode (ATM) network. The method includes transmitting the voice from the source location to a source trunk that leaves a terminal office switch; convert the trunk of origin to ATM cells; and to interface between narrowband and broadband signaling, for the process and control of calls within the ATM network. Also, the method includes transmitting the voice within the ATM cells through the ATM network, which uses broadband signaling; convert ATM cells to a destination trunk; and transmit the voice from the destination trunk to this destination. - _ According to a preferred embodiment, transport is enabled by emulating a circuit using a circuit emulation service. In addition, the voice can be converted into ATM cells using the ATM adaptation layer 1 (AAL1). Alternatively, the voice can be converted to ATM cells using an ATM adaptation layer 2 (AAL2). If AAL2 is selected, mute suppression and / or voice compression is used. According to a preferred embodiment, each speech trunk is dynamically established as a virtual switched connection to the individual in the ATM network. Likewise, the conversion of the trunk of origin to the cells of the ATM occurs in the T-IWF within a terminal office of origin and the conversion of the cells of the ATM to a trunk of destination occurs in the TI F inside a terminal office d destination . According to a preferred embodiment, narrowband signaling is the signaling of SS7. In addition, broadband signaling is preferable PNNI, B-ISUP and / or UNÍ. According to a preferred embodiment, s provides a tandem virtual switching system, distributed based on the Asynchronous Transfer Mode (ATM), in which a network of ATM devices combines to create a distributed virtual tandem switch. . The system includes a dynamically established ATM switching network with individual switched circuits. The system also includes an internal trunk work function device and a centralized control and signaling internal work device. The internal trunk work function converts the trunk of the terminal office of the TDM channels into ATM cells, using a circuit emulation service. The internal work function function of the centralized control signaling function performs call control functions and interfaces the narrowband signals with the broadband signals for the process and call control within the ATM switching network.

Consequently, the distributed tandem virtual switching system based on the ATM replaces a standard tandem switch.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is further described in the detailed description that follows, with reference to the drawings illustrated in the form of non-limiting examples of the preferred embodiments of the present invention, in which like reference numbers represent similar parts to through the various views of the drawings, and in which: Figure 1 shows a prior art system, for communications between terminal offices; Figure 2 shows an architecture of a group of trunks or connections known; Figure 3 shows a dedicated, well-known out-of-band signaling network associated with a tandem network and exemplary ISUP messages; Figure 4 shows an exemplary architecture of a tandem virtual switching system, distributed based on the ATM, according to an aspect of the present invention; Figure 5 shows an exemplary architecture of a tandem virtual switching system, distributed based on the ATM, which includes an out-of-band signaling network, in accordance with an aspect of the present invention; Figure 6 shows an exemplary architecture of the trunk group, in accordance with an aspect of the present invention; and Figure 7 shows an alternative architecture for a tandem virtual switching system, based on the ATM.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES A tandem virtual switching system, distributed based on the ATM, is supplied to replace the standard tandem switches and facilitate the reduction of the groups of logs or necessary connections, without reducing the volume of the process. calls. Referring now to Figure 4, the tandem virtual switching system, distributed based on the ATM, is described in accordance with the present invention. The terminal office 20 of origin and the terminal office 22 of destination are similar to the headquarters 10, shown in Figure 1. Terminal offices 10 are typically Class 5 switches, such as the 5ESS, available from Lucent Technology, Inc., of Murray Hill, New Jersey, or the DMS100, available from Northern Telecom Ltd (Nortel Networks) of Canada. However, any other switch in the Class 5 terminal office can replace the Nortel and Lucent switches. Also shown is the signal transfer point (STP) 18. This signal transfer point 18 is well known in the art and may be provided, for example, by Alcatel of France. The signal transfer point 18 'communicates with the terminal offices 20, 22 by means of the signaling of SS7, as described above.An asynchronous transfer mode (ATM) switching network 26 is also provided. within the network may be provided by vendors, such as, but not limited to, Lucent, Cisco, Systems, Inc., San Jose, California, or Nortel - An internal work function device 28 is also provided. trunk (TI F) Although described as a device, the TI F may be of multiple devices or any combination of hardware and software The T-IWF 28 converts the voice trunks of the terminal offices 20, 22, of the TDM channels in ATM cells More particularly, the T-IWF 28 segments channels carrying 64 Kbps in ATM cells in one direction reassemble the ATM cells in the 64 Kbps channels in the other direction, preferably the TI F 28 s distribute through the PSTN with a T-I F 28 that corresponds to each terminal office 20, 22. An exemplary T-IWF 28 is a Multiple Succession Gateway (SMG) 4000, provided by Nortel. However, any other T-I F 28 may be employed. The distributed ATM-based network also requires centralized control and an internal work function function device 30 (CS-IWF). Although described as a device, the CS-I F 30 can be of multiple devices or any combination of hardware and software. The CS-I F 30 performs the necessary call control functions as well as the conversion between the narrowband signaling, for example the Signaling System 7 (SS7), protocol and a broadband signaling protocol for the signaling process. calls and control within the ATM network. Preferably, a CS-IWF 30 serves for all T-I F 28 in a metropolitan area. An exemplary CS-I F 30 is a Server of Successful Calls (SCS), provided by Nortel. However, any other CS-IWF 30 can be employed. The T-IWF 28, the CS-IWF 30, the "ATM switching network 26, and the interconnection links together comprise the tandem virtual switching system, distributed based on the ATM." The system was distributed because the tandem functions are carried out in part by the IT F 28, which is located near the terminal offices 20, 22, in a distributed way, the system is virtual because, as regards the terminal offices 20 , 22, the tandem virtual switching system, distributed on the basis of ATM, is functionally equivalent to the traditional multi-channel tandem switchover system (TDM) 16. Thus the terminal offices 20, 22 require only slight changes in the configuration in order to use the present invention. " The virtual aspect also refers to the fact that the individual trunks are no longer DS0 time slots that need to be statistically provisioned. Rather, the trunks are made through virtual connections switched with the ATM, established dynamically.

The deployment of the tandem virtual switching system, distributed based on the ATM, allows a terminal office 20, 22 to handle normal call volumes, while having only one or a small group of logs connecting the ATM switching network. , thus eliminating the need for the provision of separate trunk groups to different destination terminal offices. In addition, the total trunk bandwidth is shared by traffic to all destinations, because ATM virtual connections are provided on demand by signaling. Consequently, the bandwidth is not dedicated to any TDM voice channel between predetermined locations, but rather is dynamically shared. According to a preferred embodiment, the terminal offices 20, 22 have a single large trunk group that connects to the virtual switch in tandem, although exceptions may exist where more than one trunk group is necessary, for example, if a terminal office limits the number of members in a group of logs connected to the terminal office. Consequently, the trunks 14 of direct internal offices between the terminal offices 10 (shown in Figure 1) are eliminated.

Thus, the present invention reduces the total number of logs needed in a terminal office 20, 22, improves the utilization of logs and reduces or eliminates the task of forecasting and stocking of logs, likewise, the growth in the needs of the logs for the logs. switches of the terminal offices 20, 22, can be more easily accomplished, because the tandem virtual switching system of the present invention allows the scalable form supported by the ATM networks. This scalable form is achieved due to the increased bandwidth of the ATM network and the statistical multichannelization of the ATM network, which more efficiently utilize the existing bandwidth. The internal work function of logs TI F 28 is a device that is preferably located in the same structure or building that houses each terminal office switch 20, 22. More particularly, the T-IWF 28 is made with one or more physical devices which are external to the switch 20, 22, but within the same terminal office that hosts one or more corresponding switches, 20, 22. The reason for the relocation is that the sooner the TDM trunks are converted to the ATM, the earlier the they will enjoy the benefits of statistical multichannel gains. Because the T-IWF 28 is physically located in the central office 20, 22, the T-I F must comply with the environmental requirements of the central office. In a preferred embodiment, level 3 of the network equipment building standards (NEBS) is satisfied. Because the ATM is a oriented package rather than a circuit oriented technology, this ATM must emulate the characteristics of the circuit in order to carry a constant bitrate (CBR) traffic such as a voice. This emulation is referred to as a circuit emulation service (CES). The T-IWF 28 -converts between the 64 Kbps trunks and the ATM cells, employing a well-known circuit emulation method, which is described in "Version 2.0 of the Circuit Emulation Service Interoperability Specification", by The ATM Forum Technical Committee (January 1997), which is expressly incorporated herein by reference in its entirety. Preferably, Structured Digital Service Level 1 (DSl), nx64 Kbps service, described in the CES interoperability specification, is used to connect the DSl equipment, through the emulated circuits carried in an ATM network. The DSL nx64 Kbps structured circuit emulation system efficiently carries TDM trunks through the ATM trunks network. The structured CES DSl requires that the ATM switches treat one or more DSOs in an IT circuit, such as individual virtual ATM connections. According to the DSl CES service, each internal work function is connected to an ATM network 26 by means of physical interfaces. These physical interfaces are from the user's network interface (UNI) of the ATM, which have two characteristics or requirements. The first requirement is that the ATM interface provide adequate bandwidth to carry nx64 traffic after segmentation. The second requirement is that the ATM interface must be capable of transporting synchrony that can be traced to a first reference source from the ATM network to the internal work function, when the external connection to the network synchrony is not supported. The internal work functions are also connected to standard constant-bit-rate (CBR) circuits, such as terminal offices 20, 22. Connected in this manner, the internal work functions extend the constant bit-rate (CBR) circuit, through the ATM network 26, in a transparent manner to the switches 20, 22. An important function of the operation of the circuit emulation service within the TI F 28 is the adaptation of the circuit traffic to the cells of the ATM . This function is named ATM adaptation. As described above, when the multi-channel time division trunks are converted to ATM cells, the ATM adaptation process occurs. More generally, ATM adaptation refers to converting non-ATM format information into the size and format of ATM cells. For circuit traffic, such as the voice, to be converted to the ATM format, two adaptation layers that can be used appropriately are ATM adaptation layer 1 (AAL1) and adaptation layer 2 of the ATM. ATM (AAL2) However, the present invention is not limited to AAL1 and AAL2 and other layers that can be satisfactorily converted into ATM cell traffic, such as AAL5, can be employed In accordance with a preferred embodiment, The emulation service of the structured nx64 Kbps DSL circuit uses AAL1 so that the circuit traffic is treated as a constant bit rate traffic (CBR) within the ATM tandem switching system, however, the system does not it is limited to the AAL1 and other protocols, such as that of the AAL2, can be adopted to incorporate band-width saving features, such as voice compression and mute suppression, which can further improve the efficiency of the band. The AAL1 has been standardized at the Internationa Telecommunications Union - Telecommunication (ITU-T) and the American National Standards Institute (ANSI) since 1993 and is preferred for the use of circuit emulation services due to its simplicity. The AAL1 is designed to support constant bit rate services and allows the specification of the peak cell rate, cell loss rate and cell delay variation. Depending on the embodiment, the bandwidth of the peak cell regime can be dedicated or guaranteed. There is a difference between the dedicated and guaranteed bandwidth. When the bandwidth of the peak cell regime is to be dedicated to the constant bit rate service, no other service can use any of the bandwidth of the constant bit rate, even if it is not used by the service regime itself of constant bits. However, if the peak cell rate bandwidth is guaranteed to the constant bit rate service, the unused portion of the dedicated bandwidth of the constant bit rate can be used by other services ^, while these other services have the bandwidth return when the constant bit rate service needs it. The AAL1 introduces an additional delay because the ATM AAL1 connection carries information for only a single user. With speech input at 64 Kbps, it takes 5-875 milliseconds or approximately six milliseconds to fill a payload from the AAL1 of an ATM cell. An alternative to AAL1 is AAL2. The AAL2 begins as a contribution to the TlS1.5m committee a subcommittee of standards ANSÍThe AAL2 was then introduced in Group 13 of the ITU-T Study in May 1996, under the temporary name of AAL-CU, where CU remains for the composite user. The AAL2 has now been defined in ITU-T Recommendation 1363.2. This AAL2 enables the voice to be carried as variable bit rate (VBR) data, while maintaining its sensitive nature of delay. The AAL2 support for the variable bit rate (VNR) traffic allows saving characteristics of many bandwidths, such as voice compression and silence suppression that will be used. These characteristics are discussed in May detail below. The AAL2 enables multiple users to share a single ATM connection, while allowing each user to select a potentially different number of service parameters. The structure of the AAL2 also allows the packing of short length packets in one or more ATM cells. In contrast to the AAL1, which has a fixed payload size, the AAL2 offers a variable payload inside the cells and through the cells. This variable payload provides a drastic improvement in the bandwidth efficiency of the structured circuit emulation over the AAL1. An important aspect of the AAL2 is the packet fill delay parameter. This packet fill delay parameter allows the network operator to set a period of time during which the AAL2 protocol data units are assembled and then segmented into the ATM cells. Adjusting this parameter allows the network operator to control the cell construction delay. This allows the operator to exchange the delay and the efficiency of the bandwidth in order to meet the delay requirements of some voice connections. For example, the 64 Kbps pulse code modulation (PCM) voice to fill an ATM cell takes six milliseconds. The AAL2 can reduce this delay by half by adjusting the packet fill delay of 3 milliseconds, which will result in each payload in the ATM cell being half filled. Thus, the 50% loss of bandwidth is changed by 50% lower delay. Essentially, when the AAL1 or AAL2 allow the selection to carry the voice trunks through the ATM network as a constant bit rate traffic or variable bit rate traffic. If the voice is sent as constant bitrate traffic, then the DSL circulation emulation service of nx64 Kbps, structured from the ATM Forum, using the AALl is used. If the voice is sent as a real-time variable bit-rate traffic, then the AAL2 as the adaptation layer of the ATM is employed, taking advantage of the many characteristics of efficiency and performance improvement, supported by the AAL2. ATM network 26 will now be discussed. From the point of view of the physical connection, the trunks of the ATM between the switching offices can be established with direct fibers from point to point, or by means of the ringing of a synchronous optical network (SONET). However, logically the ATM allows the internal office trunks to be established in many different ways. Thus, within the ATM switching network 26, the originating and terminating logs are preferably connected through the establishment of virtual connections in one of three ways. "• According to a preferred embodiment of the invention, individual switched virtual connections (SVC) are provided where the ATM virtual switched connection is established for each call of nx64 Kbps. When using individual switched virtual connections, _ .ellas they are provided dynamically by means of signaling and a peak cell regime is set equal to nx64 Kbps. The available ATM network bandwidth that would otherwise be dedicated to carrying voice traffic, can be used by other data applications On a dynamic basis, the individual switched virtual connections have the advantage that they are established automatically and on demand the provisioning results in trunk bandwidth efficiency.

According to another modality, a permanent virtual trajectory of (PVP) mesh is provided. This permanent virtual trajectory of mesh establishes a permanent virtual trajectory of the ATM through the ATM tandem network, between each two end offices. Thus, the permanent virtual trajectories are provided manually with a ridge cell regime equal to the size of the trunk group existing between the two terminal offices. As with individual switched virtual connections, the bandwidth of the otherwise available ATM network will be dedicated to carrying voice traffic: and can be used by other data applications on a dynamic basis. Among the advantages of the permanent virtual trajectory of mesh are that little or no signaling is required-, depending on how many virtual connections are used within the permanent virtual trajectories. That is, all that is required is to achieve the assignment within a trajectory; no adjustment is required. In addition, each terminal office receives direct logs with each of the terminal offices. However, the permanent virtual mesh trajectory requires manual provisioning and the bandwidth of the constant, preassigned and guaranteed bit rate reduced the efficiency of the trunk bandwidth. According to yet another modality, a permanent virtual trajectory in star is provided. With a permanent virtual trajectory in star, a simple permanent virtual path of the ATM between each terminal office and the ATM tandem network is established. This permanent virtual path is manually provisioned so that only one permanent virtual path is provided and a peak cell rate equal to the sum of all trunks of the terminal office is established. As with the other two systems, the bandwidth of the available ATM network that would otherwise be dedicated to carrying voice traffic, can be used by other data applications on a dynamic basis. Similar to the permanent virtual trajectory of mesh, the permanent virtual trajectory in star has the advantage of little or no signaling, depending on whether and how virtual connections are used in the permanent virtual path. Likewise, each terminal office perceives a single trunk in tandem. In addition to the switching translation is easy because it seems that a single trunk leaves each terminal office. Thus, all traffic is directed to the group of logs. However, the permanent virtual path in star has the disadvantage of manual provisioning and that the band width of the constant bit rate, preassigned guaranteed, reduces the efficiency of the bandwidth of the trunk. The permanent virtual path in star and the permanent virtual trajectory of mesh remove most of the established load of calls from the switch, using permanent virtual paths manually provisioned. Using the individual switched virtual connection increases the established call load due to the elimination of direct trunks. That is, calls that previously use the direct trunks will not cross over to the ATM tandem switch. The function of the CS-IWF 30 is the bridge between the narrow band signaling in the PSTN and the broadband signaling within the ATM network 26. Two types of inter-office signaling methods are used in current networks, common channel signaling (CCS) (ie, narrow-band signaling) and channel-associated signaling (CAS): This CAS is an old class of signaling in which the information of the signal is carried on the same bearer channel as the user information and is of little interest in the present invention. ~ ^ Because the dominant inter-office signaling protocol currently in use is the Signaling System 7 (SS7), the CS-IWF 30 is provided to interact with SS7 and enable SS7 support within the ATM network 26. SS7 is a protocol of a common channel signal (CCS) for call control information. This protocol is transported by physically separate networks from those of the channels that carry the voice. With reference to Figure 5, an explanation is provided as to how the present invention supports the signaling of the SS7 within the ATM network 26, preserving the existing signaling process of the SS7, and the integrity of the ISUP message. The originating terminal office 20 sends its ISUP message to signal transfer point 18, as described above. Subsequently, the signal transfer point 18 sends forward the message of the CS-IWF 30, which translates the ISUP messages that enter the ATM signaling messages. For example, the codes of the single point are transferred to ATM addresses. An ATM connection is then established between the two TI F 28 by means of the ATM signal protocol, such as the broadband ISDN user part (B-ISUP) defined by the ITU-T, PNNI defined by the ATM Forum, or UNI 3.0, 3.1, 4.0 defined by the Forum. of the ATM. On the destination side, the T-IWF-28 is composed of an ISUP message and sends it to the signal transfer point 18, which then completes the connection establishment with the ISUP messages to the destination final office 22 . An exemplary call flow, according to the present invention, will now be described with reference to Figure 5. After the originating terminal office creates an ISUP message, the originating terminal office sends the ISUP message to the 18th point of signal transfer. This signal transfer point 18 guides the ISUP message to CS-I F 30 by means of a set of A links (connections between the terminal office and the STP). In the CS-IWF 30, the ISUP message is processed and the call control information is distributed to the T-I F 28 via the ATM network 26. The CS-I F 30 also formulates an ISUP message relative to the receiver trunk and sends it back to the signal transfer point 18. This point 18 of signal transfer guides the ISUP message to the destination terminal office 22. This office then reserves the corresponding trunk. At this point, an ATM virtual connection can be established between the T-IWF 28 to carry the voice traffic. Thus, the CS-I F 30 converts between the narrow band and the ATM signal to establish connections. ATM virtual connections are dynamically established by the system through signaling, as described above with reference to SVCs. Although the signaling protocols must be based on standards, such as ATM UNI or PNNI, the exact protocol can * vary between the embodiments. The transport of the ISUP messages from the terminal offices, 20, 22, can be accompanied in two ways. The ISUP messages can be carried in the SS7 network without change or the ISUP messages can be carried in the ATM network in a special ATM connection. According to a preferred embodiment, the ISUP messages are carried in the SS7 network because they simplify the liability and I F and preserve the external form of the band nature of the SS7 signaling network. The CS-IWF 30 must have a unique point code.

For a system with a redundant CS-I F pair, two point codes can be assigned. Two sets of IT interfaces to a corresponding pair of signal transfer points must also be provided. In addition, an OC-3 ATM user to the network interface (UNI) to the ATM network must be provided. Preferably, the CS-I F 30 currently supports a log network of at least 500,000 logs and is capable of connecting 3,000,000 calls in one hour of occupancy. As new processors develop, capacity will increase. Preferably, the T-I F 28 scales from less than 100 to 16,000 logs. Similar to CS-IWF 307 as new processors develop, capacity will increase. According to a preferred embodiment, the interface is TI, T3 and OC-3 compatible at the TDM end and DS-3, OC-3 and OC-12 on the ATM side. Preferably, the ATM signals are UNI 3.1 UNI 4.0 or PNNI 1.0 on the ATM side. Each "call" is carried by the ATM virtual switching connection established by means of signaling.The TI F 28 is a multi-changer as opposed to a switch, that is, the switching function is not within TI F 28 for cost considerations. From the point of view of the realization IT F 28 and the CS-IWF 30 can be separated (as previously described in the preferred embodiment) or integrated. If they are performed as separate entities, a CS-I F 30 can serve a T-IWF 29, or the CS-IWF can centrally serve multiple T-IWF 28. Multiple embodiments are possible for the T-IWF 28. to be integrated in the switch, 20, 22, can be integrated into the ATM edge switch or it can be provided as a special-purpose device alone, which has no switching capability. The provision of the T-IWF 28 within the ATM edge switch or as a device only requires a minimum or no change of the existing switches 20, 22. Preferably, the TI F 28 is closely relocated with the switch 20, 22 therein. terminal office, in order to maximize the efficiency of the trunks or connections. The CS-I F 30 can be integrated into the switch 2-0, 22 or an ATM edge switch, or it can be a special-purpose device placed alone, which has no switching capability. The CS-IWF 30 can also be integrated into the signal transfer point 18. As shown in Figure 7, if "CS-IWF 30 is art of the ATM edge switch, this ATM edge switch preferably operates as an integrated IWF 40, ie it contains both the T-IWF 28 and the CS -IWF 30. In this case, because the CS-IWF 30 and the T-IWF 28 are physically integrated in the ATM edge switch, they maintain the one-to-one relationship, preferably the ATM edge switch it is then recollected with the switch in the terminal office According to this embodiment, the CS-I F 30 are seen as distributed in each terminal office In accordance with one embodiment of the present invention, silence suppression is employed. Silence suppression is a mechanism that saves extra network bandwidth by not transmitting pauses in a voice conversation on the network Silence suppression can be used at the end of the sender for not generating voice samples when the level * conversation is below a threshold With modulation of adaptive differential pulse code (ADPCM) silence suppression results in smaller bits per sample during speech inactivity. Silence suppression can be performed in an ATM trunk network, for example, by a voice module in an ATM edge switch. The voice module detects silence and stops the transmission of these silence intervals in the ATM network. Silence suppression also suffers from side effects. For example, because silence suppression removes background noise, a listener may think that the line has been disconnected when a pause in the conversation occurs. The suppression of silence also increases the delay of the construction of the ATM cell and adds variability to the delay. This mute suppression should always be disabled when fax or modem tones are detected. For ATM trunks, the silence suppression feature is not required, however, the availability of silence suppression improves the efficiency of the network. Voice compression is another way to save network bandwidth. Voice compression uses algorithms, such as ADPCM to reduce the 64 Kbps voice tone of standard PCM, to 32 Kbps, 24 Kbps, 16 Kbps or even 8 Kbps. However, the side effects of voice compression degrade the Voice quality and delay of the increased ATM cell construction. As with the suppression of silence, voice compression is not required, but may be employed in the embodiment of the present invention. The trunks of the ATM for narrowband services introduce additional delays to that caused by transport over the ATM network. The additional delay is primarily associated with the buffer to accommodate the variation of the cell delay introduced by the ATM network and the cell construction delay. Thus, the three types of voice traffic delay can be experienced when they are carried by the ATM network and are: ATM switching delay and network transit, delay d regulation in the ATM switching to accommodate the delay variation of the ATM. cell, and the delay of the ATM cell construction. While the first types of delay are dependent on the design of the switch, the physical medium, distance and traffic condition, etc., and the ATM cell construction delay, when the AALl circuit emulation service is used, it is fixed. As mentioned before, for a pulse code modulated voice (64 Kbps PCM, it takes six milliseconds to fill an ATM cell with a simple voice channel.) The total time of the echo path is thus 12 milliseconds plus additional traffic and regulation delays For the compressed voice, for example 32 Kbps, using -the DPCM, the delay will be doubled to 24 milliseconds, because it takes twice as much to fill an ATM cell with the data speaks of a simple voice channel.

In order to counteract the excessive delay, appropriate echo control measures are employed in voice connections, where the final delay is significant. According to a preferred embodiment, an active echo control device is used in all connections exceeding the total one-way conversation or the echo transmission path of 25 milliseconds. A call flow scenario, according to the present invention, will now be described with reference to Figure 6. Initially, the calling party 19, for example 235-1111, marks a destination 23, for example 676-2222 . The terminal office 20 of the calling party (terminal office A) collects the dialed digits corresponding to the called number and checks the route tables to determine the terminal office that connects to the marked destination. After determining the destination terminal office 22 (terminal office B), the terminal office A finds a trunk (for example trunk 6) that connects to the terminal office A = sT-IWF 28. Assuming the trunk is inactive, the terminal office A reserve the trunk 6. The terminal office A then initiates an SS / IAM message containing, among other information, the following: route direction of the signaling transfer point of CS-IWF 30; calling phone number; phone number called; and trunk identification (CIC) for the trunk 6. After the signaling transfer point 18 receives the IAM message, point 18 d signaling transfer sends forward to CS-I F 30. This CS-I F 30, Based on the calling phone number, it identifies the originating T-IWF (TI FA) with its ATM address or other identifier. This CS-IWF 30 then sends the CÍ to the TI FA via an ATM message through the ATM re (ie, the in-band signal)., The CS-IWF 30, co based on the telephone number called, identifies the destination T-IW 28 (T-IWF B) with its ATM address or other identifier. This CS-IWF 30 then sends a request to T-I F B for an inactive trunk, by means of an ATM connection (i.e., in-band signaling) in the ATM network 26 d. The T-I F A receives the message from the CS-I F 30 based on the received CID, determines the corresponding DSO channel in its line interfaces. The TI F also receives a request from the CS-IWF 30. Therefore, the TI FB finds an inactive DSO channel in its line interfaces and reserves it, for example trunk 36. The T-IWF B determines the CIC for this DSO and send the CIC to CS-I F 3 by means of an ATM message. The CS-I F 30 receives the message from the T-IWF B and sends an IAM message to the signal transfer point 18, which contains, among other information, the following: address d of the signal transfer point of the signal terminal B office; calling phone number; phone number called; and identification of the trunk (CIC). The point 18 d signal transfer receives the IAM message and is sent by the terminal office B. This terminal B receives the IAM message uses the CIC received to reserve the corresponding trunk, trunk 35. Each terminal B office checks the number d phone called in its hung state and active calling features. Terminal B maintains the line, applies a ring to the line and a ring tone to trunk 35 (assuming 676-2222 is "hung") Terminal B then connects line to trunk 35 and initiates an SS7 message ACM to signal transfer point 18. This signal transfer point 18 receives the message from ACM and sends it forward to CS-1WF 30. When this CS-I F 30 receives the message from ACM, the CS-IWF 30 sends the message to T-IWF A, which requests that this IFA establish an ATM connection with the T-IWF B or vice versa, ie the TI FB can establish a connection with the T-IWFA. T-IWF A establishes a 64 Kbps CBR connection with T-IWF B. TI FA also forms the appropriate DSO map to the switched virtual output connection., the T-IWF B is associated with the input switched virtual connection to the corresponding DSO. After establishing the connection, the T-IWF A sends an ATM message to the CS-TWF 30, which indicates the establishment of the ATM connection. The CS-IWF 30 receives the message from T-IWF A and the CS IWF 30 sends an ACM message to the signal transfer point 18. This signal transfer point 18 receives the ACM message and sends it to the terminal office A. E "this terminal office A receives the ACM message from point 18 of signal transfer and connects 235-1111 to trunk 6. Consequently, the calling party at 235-1111 hears the ringing tone. "When - destination 23 at 676-2222 picks up the telephone, terminal B detects the unhooked and removes the ringing tone. The B-end office then initiates an ANM message to point 18 of signal transfer. This signal transfer point 18 receives the ANM message and sends it forward to the CS-IW 30. This CS-I F 30 receives the ANM message from the point 18 of signal transfer and initiates an ANM message to point 18 of signal transfer. This signal transfer point 18 receives the message from the ANM from the CS-IWF 30, and sends it to the terminal office A. This terminal office A receives the message AN from the signal transfer point 18"and initiates the measurement. necessary for billing. Finally, the part 19 who calls at 235-1111 speaks to fate 23 at e 676-2222. The present invention thus allows savings in three broad categories: the reduction in the termination of the trunk of the terminal office and / or the displacements d growth, the reduction of the bandwidth in the transport facilities associated with the reduction d the termination of the trunk of the terminal office, and the administrative savings associated with the trunk forecast and trunk record maintenance. The use of large trunk groups according to the present invention creates an increased carrying capacity which results in a reduction in the requirements of the trunk unit of the terminal office. The reduction allows for a decrease in capital outlay for the trunk units and / or allows the quickest response to the growing trunk requirements brought about new traffic, such as Internet access traffic. The reduction of the bandwidth in the transport facilities also occurs because the current internal office trunks use a width d band when or not the trunk is used. The present invention allows trunks to utilize bandwidth in transport facilities only when this trunk is used. When the trunk is inactive, no bandwidth in the transport facility is required. During the low traffic period, such as late afternoon or early morning, the bandwidth available in the transportation facilities may increase by more than 50%. As a result, bandwidth is available for other applications, such as to transfer data files. Administrative savings are made in two areas, the trunk forecast and trunk record maintenance. The nature of the current trunks requires huge investments in hardware and software for the systems in order to keep track of the trunks between individual offices. The present invention does not need the maintenance of detailed records, by the individual trunk, because the trunks are virtual. Therefore, these individual trunks that extend into the network exist only when the calls are in progress. Consequently, the maintenance of records in the individual trunks between offices can be drastically reduced. The forecast and supply of logs for thousands of individual groups of logs, can be reduced just to a few groups of logs per terminal office. The call charges for the terminal office can be used to forecast log requirements rather than for trunk and trunk measurements. The data collection can also be simplified due to the reduction in the amount of data needed to accurately measure the capacity loads the office carries. According to another embodiment, the establishment of the Class 5 characteristic may reside within the CS-IWF 30. In addition, a switch management system may be provided to handle all the peripheral switching circuits and make all the OAM & P (operations administration, maintenance and provisioning) for the switch. The switch management system makes private line establishments point by point. The present invention has utility in many environments in addition to tandem switching systems, such as wireless environments and digital environments subscriber lines. For wireless services, an IWF T can be placed in the mobile switching center to convert log traffic to ATM traffic send it to the virtual tandem switch based on the ATM. The T-IWF can operate with asymmetric digital subscriber lines (ADSL) by subscriber digital line access multichannel (DSLAM) function. The present invention also applies to the service providers of the Internet. The present invention facilitates a more efficient way of carrying Internet connections to dial. Currently, an Internet user typically has access to the Internet by connecting the Internet service provider via a dial-up modem. This type of connection consumes resources in the PSTN network as a regular vo connection. However, unlike a voice connection, a modem connection carries burst data with Internet Protocol (IP) packets. It is wasteful that the burst data is carried by TDM circuits. Thus, the T-I provides an ideal place to perform a modem pool that terminates dial-up connections and converts them into ATM connections. These ATM connections can be carried by the ATM network to the respective Internet service providers. Depending on the ability of the Internet service provider to receive the ATM connections, these connections can be delivered to the Internet service provider as ATM, or converted back to IP packets. The ability to terminate the modem in the T-IWF helps to make more efficient use of network resources by carrying internet traffic as data traffic using ATM connections. The present invention also applies to broadband intelligent advanced networks (AIN). The CS-IWF is an ideal place for the residence of advanced broadband smart network capabilities. Maintaining the CS I F as a central intelligence point with an open interface that allows new services and capabilities to be developed and deployed throughout the network very quickly.

The present invention also has applicability in provisioning private leased lines (ie High Cap circuit). The provisioning of private lines rented in the current network is a complicated process prone to errors. Using the proposed ATM network, much of the complexity and provisioning can be eliminated, due to the ATM's ability to automatically establish connections through signaling. Only final circuits at the end points need to be provisioned and maintained manually. The exchange carrier networks may also take advantage of the present invention. For the terminal bureaus that have trunks to an exchange carrier network (IXC), the IXC trunks remain multichannel in the division of time and not change. The final offices that do not have direct trunks to the exchange bearer's re can choose to use either the multichannel tandem network in the time division or the ATM band system to bring the exchange bearers to traffic. If the internal exchange bearer trunks are carried by the ATM tandem network, a T-IWF will need to be placed on the interface between the local exchange bearer and the internal exchange bearer networks to act as a gate. For an ATM-based system, a T-IWF is provided at the interface between the local exchange bearer and the internal exchange bearer network, to act as a gate. In addition, the T-IWF can be provided with the ability to terminate logs from an internal exchange carrier. The T-IWF also ensures that billing is done correctly. This arrangement applies not only to switches of the internal exchange carrier, but also to switches owned and operated by independent local telephone service providers or competitive carriers of local exchange. Although the invention has been described with reference to several exemplary embodiments, it will be understood that the words that have been used are words of description and illustration, rather than words of limitation. Changes can be made within the point of view of the appended claims, as they are currently indicated and as amended, without departing from the scope and spirit of the invention in its aspects. Although the invention has been described with reference to particular elements, materials and embodiments, the invention does not intend to be limited to the particular forms disclosed; rather, the invention extends to all functionally equivalent structures, methods and uses, which are within the scope of the appended claims.

Claims (25)

1. R E I V I N D I C T I O N S 1. A tandem virtual switching system, distributed based on the Asynchronous Transfer Mode (ATM), this system comprises: an ATM switching network; an internal trunk work function device (T-I F), which is adapted to receive the voice trunks of the terminal office from the TDM channels and convert these trunks into ATM cells; and an internal work function of centralized signaling control (CS-I F), which performs call control functions and adapts to narrow-band signaling and broadband interface, to process and control calls within the network of ATM switching.
2. 2. A tandem virtual switching system, distributed based on the ATM, according to claim 1, in which this tandem virtual switching system, distributed based on the ATM, is adapted to comprise a virtual switch in a PSTN.
3. 3. A tandem virtual switching system, distributed based on the ATM, according to claim 1, wherein the TI device F comprises a circuit emulation service.
4. 4. A tandem virtual switching system, distributed based on the ATM, according to claim 3, wherein the T-IWF device comprises an ATM adaptation layer 1.
5. 5. A tandem virtual switching system, distributed based on the ATM, according to claim 3, in which the T-IWF device comprises an adaptation layer 2 of the ATM.
6. 6. A tandem virtual switching system, distributed based on the ATM, according to claim 5, wherein at least silence suppression and speech compression are employed. -
7. 7. A tandem virtual switching system, distributed based on the ATM, according to claim 1, in which the T-IWF device and the terminal office switch are placed in the same place.
8. 8. A tandem virtual switching system, distributed based on the ATM, according to claim 1, wherein each T-IWF device has its own CS-I F device.
9. 9. A tandem virtual switching system, distributed based on the ATM, according to claim 1, wherein the narrow band signaling is a SS7 signal.
10. 10. A tandem virtual switching system, distributed based on the ATM, according to claim 9, in which the broadband signaling is PNNI.
11. 11. A tandem virtual switching system, distributed based on the ATM, according to claim 9, wherein the broadband signaling is the B-TSUP.
12. 12. A tandem virtual switching system, distributed based on the ATM, according to claim 9, in which the broad band signaling is the UNI.
13. 13. A tandem virtual switching system, distributed based on the ATM, according to claim 1, wherein each trunk is dynamically established as an individual switched virtual connection in the ATM switching network.
14. 14. A method to transport the voice from a location of origin to a destiny, through a network with Asynchronous Transfer Mode (ATM), this method includes: transmit the voice from the origin location to a trunk of origin, which leaves a terminal office switch; convert the trunk of origin into ATM cells; interface between narrowband and broadband signaling, to process and control calls within the ATM network; transmit the voice within the ATM cells, through the ATM network, using the broadband signaling; convert the ATM cells to a destination trunk; and transmit the voice from the destination trunk to this destination.
15. 15. A method for transporting the voice, according to claim 14, in which the transport is enabled by emulating a circuit by the use of a circuit emulation circuit.
16. 16. A method for transporting the voice, according to claim 15, wherein the voice is converted into cells of the ATM, using an ATM adaptation layer 1.
17. 17. A method for transporting the voice, according to claim 15, wherein the voice is converted into cells of the ATM, using an ATM adaptation layer 2.
18. 18. A method for transporting speech, according to claim 17, wherein at least one suppression of silence and one voice compression is employed.
19. 19. A method for transporting the voice, according to claim 14, wherein each voice trunk is dynamically established as a single switched virtual connection in the ATM network. '
20. 20. A method for transporting the voice, according to claim 14, in which the conversion of the trunk of origin to the ATM cells occurs in the T-IWF device, within a terminal office of origin and the conversion of the cells from the ATM to a destination trunk occurs in the IT device F within a destination terminal office.
21. 21. A method for transporting the voice, according to claim 14, in which the narrow band signaling is an SS7 signaling.
22. 22. A method for transporting the voice, according to claim 21, wherein the broadband signaling is PNNI.
23. 23. A method for transporting the voice, according to claim 21, wherein the broadband signaling is the B-ISUP. __
24. 24. A method for transporting the voice, according to claim 21, in which the broadband signaling is the UNI.
25. 25. A virtual switching system in tandem, distributed based on the Asynchronous Transfer Mode. { ATM), in which a network of ATM-based devices is combined to create a distributed tandem virtual switch, this system comprises: an ATM switching network, which dynamically establishes individual switched virtual connections; internal trunk work, which converts the voice trunks of the terminal office from the TDM channels into ATM cells, employing a circuit emulation service; and a centralized control device and internal work function of signaling, which performed call control functions and interfaces narrowband signals and broadband signals, for the process and control of calls within the network d ATM switching; in which the tandem virtual switching system, distributed based on the ATM, is adapted to include a virtual switch in a Public Switched Telephone Network (PSTN). SUMMARY OF THE INVENTION A virtual tandem switching system is disclosed, distributed based on the Asynchronous Transfer Mode (ATM), in which a network of ATM-based devices is combined to create a virtual switch in tandem distributed. The system includes an ATM switching network that dynamically establishes switched individual virtual connections. The system also includes a network internal work function device (T-IWF) and a centralized control function and internal signaling function (CS-IWF). This internal trunk work function device converts the voice trunks of the terminal office from the TDM channels to the ATM cells, employing a structured circuit emulation service. _E1 centralized control device and internal work function of signaling performs call control functions and makes narrowband signaling and broadband signaling interface, for the process and control of calls, within the ATM switching network . Consequently, the tandem virtual switching system, distributed based on the ATM, replaces a standard tandem switch in the Public Switched Telephone Network (PSTN).