MXPA98004517A - Signal processing system to achieve control by-call - Google Patents

Abstract

The present invention relates to a telecommunications network (10) that includes an Origin Switching System (12-1) and a Termination Switching System (12-2) linked by a plurality of trunks (20-1 / 20) -4). For an incoming call that receives, the Origin Switching System establishes a Circuit Selection Capability Indicator (CSCI) that determines what improvement, if any, will provide the Origin Switching System to the call. The Origin Switching System also uses the CSCI to select an appropriate trunk, which is compatible with the type of call enhancement, if any, to direct the call to the Termination Switching System that also improves the call according to the CSCI . The concept of signal processing system with control by call (SPCC) allows different types of calls that are directed in the same trunk to obtain different call quality improvements (such as True Voice-r and Control of Echo), depending on the type of call. SPCC allows a call quality improvement to be applied to an individual call on a per-call basis, and these improvements may be different in the OSS and TSS, which can give different types of enhancements to the calling party and the called party. SPCC allows new "sound flavors" of signal processing to be developed in the SPS, and these new sound flavors will be offered as a new service feature through CSCI Table updates on the switch, without software development. The SPCC concept provides an evolution path for current overlay networks implemented for specialized signal processing requirements, in particular the dedicated disconnected TV network to avoid True Voice-r enhancement and the dedicated disconnected EC network to avoid echo cancellation for example for SDS services. The SPCC capability of SPCC trunks allows control of TV Enhancement and Echo Cancellation on a per-call basis, thus allowing SPCC trunks to be used in a shared way for calls that require TV enhancement, calls that require avoid TV enhancement, and for data calls that do not require echo cancellation. The benefits are a) very flexible call control capacity within a simple integrated network, b) cost effectiveness, c) robustness to overloads and d) network efficiency improvement

Description

SIGNAL PROCESSING SYSTEM FOR ACQUIRING CALL CONTROL Field Technical This invention relates to a technique for providing different types of phone call enhancements on a call-by-call basis. Previous Technique To meet the needs of its customers and differentiate their products and services, AT &T improves the quality of select voice calls that are transported through its inter-core network. One such enhancement currently available is the AT &T True VoiceR service, which amplifies selected frequencies of a voice call, to provide a more pleasant telephone conversation. The manner in which said frequencies are amplified is described and claimed in US Patents. Nos. 5,195,132 and 5,333,195, both entitled "Telephone Network Speech Signal Enhancement", filed on behalf of Dune Bowker and collaborators, and both assigned to AT &T (here incorporated by reference) . Another available enhancement of AT & T is compensation for background interference described in US Patents. Nos. 5,524,148 and 5,485,515, both entitled "Background Noise Compensation in a Telephone Network" (Noise Compensation REF: 27276 from Pondo in a Telephone Network) presented in the name of Jonathan B. Alien and collaborators and arabas assigned to AT &T; (here incorporated by reference). Still another improvement that is provided by AT &T is echo cancellation obtained by directing calls through a canceled echo of a type known in the art. While the improvements described above are useful, they can inter-act with existing technology, and in some cases, in fact impede transmission quality. Currently, calls that require that the enhancement and / or echo cancellation be disabled are directed over separate "overlay" networks. Figure 1 illustrates the use of dedicated "superposition" networks to provide specific transmission signal processing, where dedicated linkage and tandem switching is implemented, to provide specific transmission capabilities. Typically, voice calls are provided with echo cancellation and True VoiceR enhancement where the associated transmission signal processing provides denoted trunks as switched TV trunks. However, for calls that do not require the processing of the on-line TV signal, the dedicated overlay networks illustrated in the Figure require it to be used. For example, as illustrated in Figure 1, calls of type Digital Switched Service Data (SDS) are routed through the switching systems within the AT & T network, which deactivate the improvement and cancellation of echo. Similarly, those voice and voiceband calls that require echo cancellation, but which also require voice enhancement to be disabled, typically target dedicated path switching systems that provide echo cancellation but have voice enhancements turned off , both for entry and exit trunks. While providing a specialized network for transporting calls without enhancement and / or echo cancellation overcomes the problems of undesirable interactions, this approach achieves little flexibility in terms of improvement and / or perform echo cancellation in select calls within a common network and leads to inefficiencies in network capacity, due to the need to provide separate dedicated networks for different types of calls, instead of using a simple integrated network with a signal processing system (SPS) capability to provide the required transmission processing on a per-call-control basis (PCC = per-call-control). In this way, there is a need for a technique to direct calls to allow improvement and / or cancellation of calls echo in a select base.

BRIEF COMPENDIUM OF THE INVENTION Briefly, according to the invention, there is provided a method for directing at least one call in a telecommunications network from an Originating Switching System (OSS) where the call originates in the network to a Switching System Termination (TSS = Terminating Switching System) where the call ends, so that the call is selectively improved. As illustrated in Figure lb, dedicated overlay networks can be replaced by an integrated network capability, consisting of trunks that are provided with a signal processing system (SPS) capability in the source switching system (OSS) ), by the switching system (VSS), and termination switching system (TSS), to provide the desired transmission signal processing on a per-call-control (PCC) basis. These trunks are denoted as SPS trunks by call-control (SPCC = SPS per-cali-control). SPCC trunks can be used to provide, on a per-call basis, the required transmission signal processing, such as (a) echo cancellation with the enhanced True VoiceR enabled, denoted as TV on (TV on), which can used for normal voice calls, (b) echo cancellation with the True VoiceR off, denoted as TV deactivates (TV off), which may be used for example for some voiceband data calls, or (c) without cancellation of echo, denoted as disconnected EC(EC off) that can be used for example for digital switched services (SDS) calls. The method of the invention is initiated upon receipt of an incoming call in the OSS. For each incoming call, the OSS establishes a Circuit Selection Capability Indicator (CSCI) that specifies the type of improvement, if any, to provide for the call. For example, the call can be improved by echo cancellation. Instead of this echo cancellation (or in addition to it), the call can be improved by amplifying certain frequencies. Additionally, the call can be improved by compensating for background noise. Using the CSCI, the OSS chooses one of a plurality of trunks that interconnect the OSS and TSS to direct the call to the TSS which may already be a trunk direct to the TSS or on a path through a VSS to the TSS. Based on the CSCI, the OSS performs the selected improvement, if required. In this way, for example, if the CSCI established by the OSS specifies that there is no echo cancellation and there is no selective frequency improvement, then the selected trunk may be a SPCC trunk, which may be used to provide, on a control basis. per-call, the required transmission signal processing, which in this case is without echo cancellation, denoted as EC off (EC off). Conversely, if the CSCI established by the OSS specifies call enhancement, then a trunk having the capacity to carry such enhanced calls may be an SPCC trunk, which may be used to provide, on a per-call basis, processing of the required transmission signal, which in this case is echo cancellation with the enhanced True VoiceR enabled, denoted as TV activated (TV on). If this SPCC trunk is not available, the call can be addressed as a second selection option on the TV on trunks illustrated in Figure lb, which are provided with echo cancellation and with the True VoiceR enhancement enabled. Once the trunk is chosen, the call is routed through a selected trunk to direct the TSS where the call is improved according to the established CSCI. Therefore, the SPCC concept allows different types of calls that are routed on the same trunk to obtain different call quality enhancements (such as True VoiceR and Eco Control), depending on the type of call. SPCC allows an improvement in call quality to be applied to an individual call on a per-call basis. SPCC allows up to 16 different types of enhancements to be applied in a call, and these improvements may be different in OSS and TSS, which can give different types of improvements to the calling party and the called party. With this structure, new "sound flavors" of signal processing (improvements) can be developed in the SPS for example, and these new sound flavors can be offered as a new service feature through table updates in the switching system without software development. Furthermore, SPCC allows the ability to change the current improvement for any type of call to any desired improvement through the provision of a CSCI Table, without the development of a new switching system. The SPCC concept provides an evolutionary trajectory for current overlay networks implemented for specialized signal processing requirements, in particular the dedicated disconnected TV network to avoid True VoiceR enhancement, and the dedicated disconnected EC network to avoid echo cancellation for example for SDS services. This is achieved for these services by replacing dedicated disconnected TV (disconnected TV) and EC (ECoff) trunks that terminate at the switch with the SPCC trunks that have control capability per SPS call. The PCC capacity of the SPCC trunks allows control of TV enhancement and echo cancellation on a per-call basis, thus allowing the SPCC trunks to be used in a shared form for calls that require TV enhancement, calls that require avoiding TV enhancement and for data calls that do not require echo cancellation. The benefits are a) very flexible call control capacity within a single integrated network, b) cost effectiveness, c) robustness to overloads and d) improved network efficiency. The method described above advantageously provides improvement of calls on a select basis, while also allowing unimproved calls to be routed between switching systems in a simple, integrated network with SPCC capacity instead of requiring the use of separate networks. BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a schematic block diagram of a telecommunications network before and after the application of the invention; and FIGURE 2 is a schematic block diagram of a telecommunication network according to the invention. DETAILED DESCRIPTION The Figure illustrates the use of dedicated "overlay" networks to provide specific transmission signal processing, where dedicated linkage and tandem switching is implemented to provide specific transmission capabilities. Typically, voice calls are provided with echo cancellation and True Voice enhancement, where the associated transmission signal processing is provided on denoted trunks as activated TV trunks (TV on). However, for calls that do not require activated TV signal processing, the dedicated overlay networks illustrated in the Figure require it to be used. For example, as illustrated in FIG. 1, SDS data type calls are routed from OSS 121 to TSS 122, through a partially dedicated VSS switching system 125, where trunks 206 are provided with disconnected EC. Similarly, calls that require avoiding True VoiceR enhancement such as some voiceband data type calls, are routed from OSS 12x to TSS 122 via a dedicated VSS 124 path switching system, where the trunks 205 are provided. with TV disconnected. Figure lb illustrates the use of the call control network with signal processing system SPS 24, to provide transmission signal processing on a call demand basis according to the invention. Here, trunks for call control SPS 204 can provide TV on, TV off and ECC disconnected on a per-call basis. For example, as illustrated in Figure lb, SDS data type calls are routed from OSS 12x to TSS 122, either on a direct SPCC trunk 204, or via a VSS 123 path switching system, where the trunk SPCC 204 conforms to EC disconnected. Similarly, calls that require avoiding True VoiceR enhancement such as some voiceband data type calls, are routed from OSS 12x to TSS 122, either on a direct SPCC trunk 204, or through a VSS path switching system 123, where SPCC 204 trunks are set to disconnected TV. Normal voice calls are provided with echo cancellation and True VoiceR enhancement and are routed from OSS 12x to TSS 122 either on a direct SPCC trunk 204 or through a VSS 123 path switching system, where SPCC trunks 204 they adjust to TV on. If SPCC trunks are not available, these normal voice calls can be routed on the 20x trunks that are supplied with the TV on. Figure 2 illustrates a schematic block diagram of a Carrier Network In re-Centrals 10, such as the type of network maintained by AT &T. In its simplest form, network 10 includes a first quota switching system 121 # typically a 4ESS Model Rate Switch, formerly manufactured by AT &T. For discussion purposes, the switching system 121 # which will be referred to below as the "Source Switching System" (OSS) because the calls are assumed to originate (ie enter the network 10) at this station switching. These calls can be received on one of a set of trunks in a group of 13x trunks from a Local Carrier Central switching system (LEC = Local Exchange Carrier) 141 serving a calling party 1 X. In practice, the LEC 14x exchange switching system may comprise a 5ESS model switch formerly manufactured by AT &T. Calls may also be received in the 12x quota switching system on one or more trunks in a trunk group 17x from a client served directly by the switching system such as PBX 1B1. Calls that originate in the OSS 12 x terminate in a second Quota Switching System (TSS) 122 coupled to the OSS by a plurality of 20 ^ 204 trunks. The OSS 12x is also linked to the TSS 122 by a signaling system 22, such as the AT &; T 7 as it is well known in the telephony technique. Calls ending in the quota switching system 122 are finally supplied in a group of trunks 132 to a switching system of the LEC 142 exchange, for reception by a call party 162 or in a group of trunks 172 to a customer attended to directly by TSS, such as PBX 182. While network 10 has been illustrated to include a single OSS 12- ^ and a single TSS 122, a typical IXC network such as that maintained by AT &T includes a plurality of security systems. interconnected quota switching, including those that originate and terminate calls, as well as through switching systems that interconnect these source and termination switching systems. Both of the switching systems 12-L and 122 have a Signal Processing System (SPS) 24 associated with a time slot exchanger (not shown) within each of the switching systems 12x and 122. The SPS 24 within each switching system may have echo cancellation capability, the ability to amplify selected frequencies as described in the US patents Nos. 5,195,132 and 5,333,195 to Bowker et al. (Here incorporated by reference) (enhancement of True Voice ™ of AT & T), and / or the ability to compensate for background noise as described in US Pat. Nos. 5,524,148. and 5,485,515 to Alien et al., incorporated herein by reference. The ability of SPS 24 to improve voice calls is very advantageous. However, for certain types of calls, such as data calls, for example, improvement by echo cancellation, frequency amplification and / or background noise compensation, is undesirable. In order to avoid improvements of certain calls which may be undesirable, the present invention provides selective enhancement on a call-by-call basis as well as call routing from OSS 12x to TSS 122 by one of the selected 20 ^ 204 trunks in accordance with its ability to carry improved or unimproved calls as the case may be. To provide selective enhancement on a call-by-call basis, the OSS 12x, upon receiving an incoming call, establishes a Circuit Selection Capability Indicator (CSCI) for the call. The CSCI specifies if the call will be improved and if so, what kind of improvement should be made. For certain calls, such as data calls, for example, no improvement should be made while for most voice calls, echo cancellation, frequency amplification and / or background noise cancellation may be desirable. The OSS 12x establishes the CSCI to activate the time slot exchanger, to activate or deactivate the SPS 24 that provides the desired improvement based on certain "triggers", that is, certain conditions. In general, the triggers or triggers that dictate the CSCI for a particular revenue call are determined from one or more of the following: (1) the call number (ie the digits associated with the call), (2) ) the ANI of the calling party, (3) the nature of the trunk in which the call reaches the OSS 121 # (4) call processing information retransmitted to the OSS 12x from a Network Control Point (NCP = Network Control Point) (ie a database) by means of the signaling system 22, and / or (5) the Service Indicator (SI = Service Indicator) established for the call by the OSS 12x based on the nature of the class -of-call service. Table I lists an exemplary set of different improvements for different CSCI values. TABLE I CSCI OSS 12 TSS 12- 0 TV ON, EC ON TV ON, EC ON 1 TV OFF, EC OFF TV OFF, EC OFF 2 TV OFF, EC ON TV OFF, EC ON 3 TV OFF, EC ON TV OFF, EC ON Table I supposes TV improvements (Service True VoiceR from AT & that provides select frequency amplification) and EC (echo cancellation). (Other types of improvements are possible and different CSCI values will be associated). It should be noted that two different CSCI values (2,3) seem to be associated with the same two improvement states. TV disconnected (TV OFF) and EC on (EC ON). In fact, a CSCI value of 2 reflects a condition where an improvement without TV is required, while a CSCI value of 3 reflects the condition where it is desired although an improvement without TV is not required. The nature of the improvement dictated by the CSCI value established in the OSS 12j ^ also dictates the selection of the particular trunk 20- ^ 204 connecting the OSS 12j_ and the TSS 122. In the embodiment illustrated in Figure 2, each one of the 20 ^ 204 trunks have different characteristics. The 20 ^ 202 trunks are designed to handle enhanced calls by the AT &T True VoiceR service, as discussed above, while the 203 and 204 trunks comprise a new trunk type then designated as an SPCC trunk, whose characteristics are they are adjusted by the SPS associated with the time slot exchangers of the SPCC trunk within the OSS 12x and the TSS 122. Physically, the trunks 203 and 204 are the same as the other trunks. What differentiates trunks 203 and 204 are trunk characteristics, in terms of their ability to carry calls controlled by enhanced, unimproved or non-echo controlled echoes, as determined by OSS 12-L and TSS 122 in a call-by-call basis, depending on the CSCI for the call where the SPS 24 associated with the SPCC trunk is controlled accordingly. The manner in which the 20 ^ 204 trunks are chosen is determined by mapping the CSCI values set forth in Table 1 to a Circuit Selection Capability (CSC) preference, as illustrated below in Table II, denoted as the CSCI table. Table II - Table CSCI £££ Treatment PCC Treatment FITR _O = 5_ TSS 0 Preset Preset Allowed 1 Preset Preset Prohibited 2 TV off TV off Prohibited EC on EC on 3 TV off TV off Forbidden EC on EC on Table II - Table CSCI (continued) SC Preference CSC CSCI overflow without TV SPCC Other 0 Abs PF1 Pres PF1 D / C 1 D / C Pres PF1 D / C 2 Pres Req Pres PF1 D / C 3 3 Pres PF2 Pres PF1 D / C The terms "Abs" represent absence, "Pres" present, "Req" required , "PFl" for preferred first, "PF2" for second preferred and "D / C" for no matter. The term "predefined" under the Control-by-Call (PCC) treatment indicates that echo cancellation and selective frequency amplification (True VoiceR service from AT & T) must be activated for voice calls and deactivated for SDS calls (data ). As can be seen from Table II, a CSCI value of 2 indicates that the selective frequency amplification should be disabled and the echo cancellation should be activated in both the OSS 12x and the TSS 122. As illustrated in Table II, there is an option of Inter-Fee Forced Addressing, whereby an intra-commutation system call can receive the treatment for forced inter-quota addressing, depending on the CSCI value. A CSC preference rule set is used by OSS 12l7 when selecting the particular of 20 ^ 204 trunks, in which calls are routed. The degree to which the trunks are chosen is based on the following order of preferences: Required > First Preferred (PFl) > Second Preferred (PF2) > No Matter (D / C) For example, a call with a CSCI value of 2 requires an address without TV, "Presence Required" and "SPCC, First Preferred Presence". In other words, a call that has a CSCI value of 2 requires addressing on a trunk for which no TV = yes, and a first preference for the SPCC backbone (which is adjusted using a control per SPS call for disconnected TV and connected EC). In terms of trunk preference, the OSS 12x will look for a trunk in the following order: 1. no TV = yes and SPCC = yes 2. no TV = yes and SPCC = no If OSS 12] ^ takes a trunk at rest and the trunk is controllable by TV, with control capacity per SPS call, then the SPCC is ready for the call, and under these circumstances the call will be improved by echo cancellation, but not by selective frequency amplification (ie TV disconnected). If routing is necessary (ie the call must be routed from OSS 12x to TSS 122, via a track or intermediate switch, (as illustrated in Figure lb), then the VSS uses the CSCI flag to select the trunk in which the call is routed from the VSS to the TSS as the first selection of an SPCC trunk, and if the SPS function is chosen, it is used to disconnect the True Voice enhancement of the SPCC trunk If an SPCC trunk is not available, the VSS chooses as a second selection a trunk that has the supplied improvement True Voice disconnected (trunk TV disconnected), if that trunk is available, in case that route address fails, then the call overflows, with the CSCI value it becomes 3. Once the call does not reach the TS 121; the call is treated as if the CSCI was 2 and the appropriate improvements are made. The foregoing describes a technique for directing calls between a 12x Source Switching System and a Terminating Switching System 122, thereby selectively improving calls on a call-by-call basis according to a Selection Capability Indicator Circuit established by the Origin Switching System. The CSCI value is also used by the Source Switching System to select a trunk to the Termination switching system that is compatible with the selected type of improvement. It will be understood that the embodiments described above are merely illustrative of the principles of the invention. Various modifications and changes can be practiced by those with skill in the specialty that incorporate the principles of the invention and fall within the spirit and scope of the same.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (29)

1. CLAIMS 1. A method for directing calls in a telecommunications network from an Origin Switching System (OSS) to a Termination Switching System (TSS) through a plurality of trunks, thereby selectively improving calls in a call-by-call basis, characterized in that it comprises the steps of: receiving in the OSS, an incoming call from a calling party in a trunk of entry; establish in the OSS a Circuit Selection Capability Indicator (CSCI) indicative of the desired improvement, if any, that is provided to the call; selecting in accordance with the CSCI, one of the plurality of trunks to direct the call received in the OSS to the TSS; provide in the OSS, the desired improvement, if any, to the call; provide the TSS with the desired improvement of the call in accordance with the CSCI. The method according to claim 1, characterized in that the call is improved according to the CSCI when amplifying selected frequencies. 3. The method according to claim 1, characterized in that the call is improved according to the CSCI by echo cancellation. 4. The method according to claim 3, characterized in that the call is further improved according to the CSCI when amplifying selected frequencies. 5. The method according to claim 1, characterized in that the incoming call is a data call and where improvement is not provided. The method according to claim 2, characterized in that the trunk is chosen to carry calls that have been improved by amplification of selected frequencies. The method according to claim 3, characterized in that the trunk is chosen to carry calls that have been improved by echo cancellation. The method according to claim 4, characterized in that the trunk is chosen to carry calls that are improved by both echo cancellation and selective frequency amplification. The method according to claim 5, characterized in that the trunk is chosen to carry calls that are not improved. The method according to claim 1, characterized in that at least one of the plurality of trunks can be configured to carry improved and unimproved calls and wherein the truncal selection stage includes the step of configuring the trunk to transport an of the improved and unimproved trunks according to the CSCI established for the call. 11. The method according to claim 1, characterized in that the OSS establishes the CSCI according to the originating telephone number of the calling party. 12. The method according to claim 1, characterized in that the OSS establishes the CSCI value according to the entry trunk in which the call was received. The method according to claim 1, characterized in that the OSS sets the CSCI value according to a set of dialed digits associated with the incoming call. The method according to claim 1, characterized in that the OSS establishes the CSCI in accordance with call processing information that is supplied to the OSS from a Network Control Point. 15. The method according to claim 1, characterized in that the OSS establishes the CSCI according to the Service Identity (SI) of the call. 16. A method for directing calls in a telecommunications network from an Origin Switching System (OSS) in which calls are selectively enhanced on a call-by-call basis to a Termination Switching System (TSS) in which calls are selectively enhanced on a call-by-call basis through one of a plurality of trunks, at least one has the ability to carry enhanced calls and another has the ability to carry unimproved calls, characterized in that it comprises the stages of: receiving, in the OSS, an incoming call from a calling party in an entry trunk, - establishing, in the OSS, a Circuit Selection Capability Indicator (CSCI) indicative of the desired improvement, of have, which is provided for the call; selecting, in accordance with the CSCI, one of the plurality of trunks to direct the call received in the OSS to the TSS, such that the selected trunk is compatible with the call enhancement that is provided by the OSS; provide, in the OSS, the desired improvement of having, to the call; and provide in the TSS, the desired improvement of the call in accordance with the CSCI. The method according to claim 16, characterized in that the call is improved according to the CSCI when amplifying selected frequencies and where the trunk selected to carry calls is improved by amplifying selected frequencies. 18. The method according to claim 16, characterized in that the call is improved according to the CSCI by echo cancellation and where the trunk selected to carry calls is improved by echo cancellation. The method according to claim 16, characterized in that the call is improved according to the CSCI by amplifying selected frequencies and by echo cancellation, and where the trunk chosen to carry calls is improved by amplifying selected frequencies and echo cancellation. The method according to claim 16, characterized in that the incoming call is a data call for which no improvement is provided and wherein the selected trunk to direct the call is compatible with unimproved calls. The method according to claim 16, characterized in that at least one of the plurality of trunks can be configured to carry improved and unimproved calls and wherein the step of selecting the trunk includes the step of configuring the trunk to transport one of the trunk improved and not improved, according to the CSCI established for the call. 22. The method according to claim 16, characterized in that the OSS establishes the CSCI according to the originating telephone number of the calling party. 23. The method according to claim 16, characterized in that the OSS establishes the CSCI value according to the entry trunk in which the call is received. 24. The method according to claim 16, characterized in that the OSS sets the CSCI value according to sets of dialed digits that are associated with the incoming call. The method according to claim 16, characterized in that the OSS establishes the CSCI in accordance with call processing information that is supplied to the OSS from a Network Control Point. 26. The method according to claim 16, characterized in that individual signal processing characteristics are provided in a base per call in a selected trunk, depending on an individual service type. 27. The method according to claim 26, characterized in that provisionable selection of signal processing characteristics of transmission, is achieved in the individual service type by providing new CSCI values. The method according to claim 27, characterized in that provisionable selection of additional transmission signal processing characteristics to add new sound enhancements is achieved in the individual service type by providing new CSCI values. 29. The method according to claim 16, characterized in that signal-by-call processing control capability is achieved to achieve separate signal processing characteristics, in a single integrated network that achieves separate overlay network capabilities on a base of per-call control. The method according to claim 16, characterized in that the OSS and the TSS provide different improvements. SUMMARY OF THE INVENTION The present invention relates to a telecommunications network (10) that includes an Origin Switching System (12x) and a Termination Switching System (122) linked by a plurality of trunks (20 ^ 204). For an incoming call that receives, the Origin Switching System establishes a Circuit Selection Capability Indicator (CSCI) that determines what improvement, if any, will provide the Call Origin Switching System. The Origin Switching System also uses the CSCI to select an appropriate trunk, which is compatible with the type of call enhancement, if any, to direct the call to the Termination Switching System that also improves the call according to the CSCI . The concept of signal processing system with control by call (SPCC) allows different types of calls that are directed in the same trunk to obtain different call quality improvements (such as True VoiceR and Eco Control), depending on the type of call. SPCC allows a call quality improvement to be applied to an individual call on a per-call basis, and these improvements may be different in the OSS and TSS, which can give different types of enhancements to the calling party and the called party. SPCC allows new "sound flavors" of signal processing to be developed in the SPS, and these new sound flavors will be offered as a new service feature through CSCI Table updates on the switch, without software development. The SPCC concept provides an evolution path for current overlay networks implemented for specialized signal processing requirements, in particular the dedicated disconnected TV network to avoid True VoiceR enhancement and the dedicated disconnected EC network to avoid echo cancellation for example for SDS services . The SPCC capability of SPCC trunks allows control of TV Enhancement and Echo Cancellation on a per-call basis, thus allowing SPCC trunks to be used in a shared way for calls that require TV enhancement, calls that require avoid TV enhancement, and for data calls that do not require echo cancellation. The benefits are a) very flexible call control capacity within a simple integrated network, b) cost effectiveness, c) robustness to overloads and d) improved network efficiency.