Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B3/00—Line transmission systems
  • H04B3/02—Details
  • H04B3/20—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other
  • H04B3/23—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers

Definitions

• the present lm ention relates genei aily to echo control in netw orks and. more particularly . to pro ⁇ idmg echo control for e: packet itched netw orks.
• circuit sw itched netw orks such as the public switched telephone network (PSTN)
• PSTN public switched telephone network
• IP Internet Protocol
• the PSTN typically uses both 2-wire circuits and 4-w ⁇ re circuits for carrying full duplex voice traffic.
• the 2-wire circuits are typically used in the local loop portion of the PSTN, such as the connection from the end user to a local switch or a local central office.
• a ⁇ oice call from a typical telephone may be routed to a sw itch over the PSTN as an analog signal on a standard tw o-w ire circuit.
• a hy brid circuit may convert the 2-w ire circuit connection to a 4-wire circuit connection.
• the switch may also forward the ⁇ oice call to one or more conventional gateways that provide various services associated with transmitting information over an IP network.
• the gate ay may convert analog voice signals in pulse code modulation ( PCM) format into packets for transmission over the IP netw ork.
• PCM pulse code modulation
• the packetized signal may be converted back to an analog signal.
• Another switch located in relath e proximity t ⁇ the called party may include a b ⁇ d ciicuit that ens a 4-w ire cn cuii to a 2-w ire circuit for connection to the called party's telephone.
• the tone disabler function refers to a 2100 Hz tone with phase reversal that is generated by a data modem. This tone is typically used to disable echo cancellers since echo cancellers often interfere ith voiceband data traffic. Since the gateways do not support the tone disabler function, voiceband data traffic cannot be supported over the network.
• a system that includes a first echo canceller, a first gateway, a second gateway and a second echo canceller is provided.
• the first echo canceller is coupled to a first switch in a circuit switched network and is configured to cancel echo associated with voice calls transmitted over a circuit sw itched netw ork and a packet switched network.
• the first gate ay is coupled to the first echo canceller and is configured to forward a first voice call over the packet sw itched network.
• the second gateway is coupled to the first gateway via the packet switched network and is configured to receive the first voice call from the first gateway via the packet switched network and forward the first voice call to a second switch in the circuit switched network.
• the second echo canceller is coupled to the second gateway and the second sw itch and is configured to cancel echo associated with voice calls transmitted over the circuit switched network and the packet switched network.
• the second echo canceller is configured to cancel echo associated with the first voice call when a time associated with transmitting a first voice signal is greater than or equal to a predetermined threshold.
• Another aspect of the present invention provides a method for cancelling echo in a voice call from a first party to a second party, where the voice call is routed from the first party to the second party over circuit switched and packet switched networks.
• the method includes fo ⁇ v arding the voice call from the first party to a first switch included in a first circuit switched network, where the first switch includes a hybrid circuit that conv erts a tw o- ire circuit to a four-w ire circuit.
• the method also includes transmitting the voice call ov er the four-wire circuit to a first gateway, converting, at the first gateway , the voice call to a formal compatible with the packet sw itched network, and transmuting the voice call over the packet switched network to a second gateway.
• the method further includes converting, at the second gateway, the v oice call to a format compatible w ith a second circuit switched network and transmitting the voice call to a second sw itch included in the second circuit switched network.
• the second switch includes a hybrid .circuit that converts the four-wire circuit to a two-w ire circuit.
• the method also includes forw arding the voice call to the second party, where a portion of the voice call reflects back at the second switch toward the first party, and cancelling the reflected portion of the v oice call using an echo canceller.
• the echo canceller is located externally from each of the first switch, the second switch, the first gateway and the second gateway and is not controlled by any of the first switch, the second switch, the first gateway and the second gateway.
• a method for providing echo control in a system that routes voice calls over a circuit switched network and a packet switched network includes identifying echo sources in the system. The method also includes determining whether a first time associated with transmitting a first signal from a first one of the echo sources over a voice path that traverses both the circuit switched and packet switched networks and receiving a reflected portion of the first signal at the first echo source is greater than or equal to 35 milliseconds. The method further includes determining whether a second time associated with transmitting a second signal from a second one of the echo sources over the v oice path and receiving a reflected portion of the second signal at the second echo source is greater than or equal to 35 milliseconds. The method also includes inserting first and second stand-alone echo cancellers on the v oice path w hen the first and second times are both greater than or equal to 35 milliseconds.
• FIG. 1 is a block diagram of an exemplary system in which methods and systems consistent w ith the present invention may be implemented.
• Fig. 2 is an exemplary flow diagram, consistent with the present invention, illustrating processing for determining whether external echo cancellers are needed in the system of Fig. 1.
• FIG. 3 is a block diagram of an exemplary system, consistent with the present invention, w hich illustrates the insertion of external echo cancellers in the system of Fig.
• FIG. 4 is a block diagram of another exemplary sy tem in hich methods and systems consistent with the present invention may be implemented.
• Fig. 5 is an exemplary flow diagram, consistent w ith the present inv ention. illustrating processing for determining whether external echo cancellers are needed in the system of Fig. 4.
• Fig. 6 is a block diagram of an exemplary system, consistent w ith the present invention, which illustrates the insertion of external echo cancellers in the system of Fig.
• FIG. 7 is a block diagram of another exemplary system in w hich methods and systems consistent with the present invention may be implemented.
• Fig. 8 is a block diagram of an exemplary system, consistent w ith the present invention, which illustrates the insertion of external echo cancellers in the system of Fig.
• Fig. 1 is a block diagram of an exemplary sy stem 100 in which methods and systems consistent with the present invention may be implemented.
• the system 100 includes telephones 1 10 and 120, switches 130 and 140, gateways 150 and 160 and netw ork 170.
• the exemplary configuration lllusti ated m Fig. 1 is lor simplicity It should be understood that other dev ices may be included m system 100 in implementations consistent w ith the present mv ention.
• the telephones 1 10 and 1 0 may include conventional telephones, such as those that interface ith the PSTN (not show n) to place and receiv e telephone calls, in an exemplary implementation of the present inv ention, the connection betw een telephone 1 10 and switch 130, labeled 1 12 in Fig. 1 , may be a two-wire analog circuit. Similarly, the connection between telephone 120 and switch 140. labeled 122 in Fig 1. may be a t o-w ire analog circuit.
• Each of sw itches 130 and 140 may represent a conv entional sw itch, such as a private branch exchange (PBX) that may be located at a customer ' s premises. Alternatively, switches 130 and 140 may be located at a telephone service pro ider's premises.
• the connection between switch 130 and gateway 150, labeled 1 14 in Fig. 1. may be a four-w ire circuit.
• the switch 130 includes a hybrid circuit that con erts the two- wire circuit 1 12 from the telephone 1 10 into the four-w ire circuit 1 14. as illustrated in Fig. 1.
• Switch 140 may similarly include a hybrid circuit that conv erts two-w ire circuit, labeled 122, to four-wire circuit 124, and vice versa, as illustrated in Fig. 1. As discussed prev iously, these two-wire to four-wire hybrid circuits at s itches 130 and 140 may cause echo problems as a result of impedance mismatch.
• Gatew ay s (GVV ) 1 0 and 160 may include '.onv enti ⁇ nal gatew ay s used to conv ert input channels from a circuit sw itched netw ork into the format needed foi a packet s itched netw ork, such as netw ork 170.
• gatew y 15'.' and 160 may be enterprise gatew a s that interface w ith a particu ' .u ⁇ isiomerN equipment, such as the respective sw itches 130 and 140.
• Gate y s 1 0 and 160 may be located at the customer ' s premises For example, w hen sw itches 1 0 and i 40 are customer PBXs. enterprise gateways 150 and 160 may be located at a customer's premises to interface with PBXs 130 and 140. respectiv ely.
• Network 170 may be a con entional packet s itched netw ork, such as an IP network.
• Network 170 may include the Internet, an intranet, a W AN. a LAN oi a similar netw ork that transmits data packets, such as IP data packets.
• a telephone service provider determines whether system 100 requires external echo cancellers, as described in more detail below. When external echo cancellers are needed, the echo cancellers are strategically located to eliminate or reduce echo and to improve v oice quality.
• Fig. 2 is an exemplary flow diagram, consistent with the present invention, illustrating processing for determining whether external echo cancellers are needed in system 100 of Fig. 1.
• Processing begins by a telephone service provider identifying potential echo sources in the service provider's system (act 210).
• the 2-wire to 4-wire hybrid circuits included at sw itches 130 and 140 are potential sources of echo caused by impedance mismatch. Therefore, in s stem 100, the telephone service pro ider may identify switches 130 and 140 as potential echo sources.
• the telephone serv ice prov ider determines w hethei the round trip delay intioduced by any oice, echo ath in system 100 is greater than a predetermined amount of time (act 220). For example, if the round trip delay introduced by the v oice echo path betw een sw itches 130 and 140 labeled D in Fig 1. is greater than approximately 25 milliseconds (ms). then echo may be perceiv able by the human ear and may ultimately reduce v oice quality.
• ms milliseconds
• Fig. 3 is a block diagram of an exemplary,' system 300, consistent w ith the present invention, which illustrates the insertion of external echo cancellers in system 100 to combat echo problems.
• echo canceller 310 may be located in system 300 between sw itch 130 and gateway 150. Echo canceller 310 may then cancel echo associated with caller 120. That is, echo canceller 310 cancels the echo caused by a leflection in the signal that occurs at the hybrid circuit at switch 1 ?0 and propagates back tow ard sw itch 140.
• echo canceller 310 is preferably located as close to the source of the echo as possible, w hich in this example is the hy brid circuit at switch 130.
• echo canceller 3 10 may be located near switch 1 30.
• Echo canceller 320 may be located in system 300 betw een s itch 140 and gatew ay 160. Echo canceller 320 may then cancel echo associated with caller 1 10. That is. echo canceller 320 cancels the echo caused by a reflection in the signal that occurs at the hybrid circuit at switch 140 and propagates back toward switch 130. Similar to echo canceller 310. Echo canceller 320 is preferably located near the source of the echo, w hich in this case, is the hybrid circuit in switch 140. Therefore, echo canceller 320 may be located near switch 140.
• a voice call when placed from telephone 1 10. it is transmitted to switch 130 over a two-wire analog circuit 1 12, converted at switch 130 into a four wire circuit and passed on through echo canceller 310 to gateway 150.
• echo cancellers such as echo cancellers 310 and 320, cancel echo traveling in a single direction and do not affect the voice signal traveling on its intended voice path.
• Gateway 150 may packetize the v oice call into an appropriate protocol for network 170 and forward the voice call over network 170.
• Gateway 160 receives the voice call and forwards the voice call through echo canceller 320 to switch 140. It should be understood that switches 130 and 140 may be included in the same or different circuit switched networks.
• the voice call is converted back to a two-wire analog circuit at sw itch 140 for transmission to telephone 120.
• the voice call is being forwarded through switch 140 to telephone 120.
• a portion of the voice call may reflect or echo back toward switch 130.
• Echo canceller 320 receives this echo and ""cancels " the echo ( i.e.. prevents the echo from being transmuted back ov er the oice path to telephone 1 10).
• echo canceller 3 10 prev ents the echo associated w ith a voice call made from telephone 120 from echoing back to telephone
• stand-alone echo cancellers 310 and 320 are strategically located to prev ent echo from reducing voice quality.
• one or both of the gateways 150 and 160 include integrated echo cancellers, these integrated echo cancellers may be disabled.
• echo cancellers 310 and 320 may be conventional devices, such as Quad-Tl echo cancellers manufactured by Ditech Communications Corporation. Alternati ely, other conventional echo cancellers may be used in implementations consistent w ith the present invention.
• echo cancellers 310 and 320 are located externally from the switches and gateways of system 300.
• echo canceller 310 is coupled beuv een switch 130 and gateway 150.
• Echo canceller 310 is located externally from these devices.
• echo canceller 320 is located externally from switch 140 and gateway 160.
• the stand-alone echo cancellers 310 and 320 are not controlled by either the sw itches or gateways of system 300.
• echo canceller 310 is not controlled by any particular control logic, such as conventional Q. l 1 5 echo control logic. being executed at switch 130, switch 140 ; gateway 150 or gatew ay 160.
• Echo canceller 10 is also not tied to w orking in conjunction w ith any particular protocol, such as conventional Q.55 echo control protocol, that may be included in sw itch 1 0. s itch 140. gateway 1 50 or gatew ay 160.
• echo canceller 310 operates independently from the switches and gateways in system 300 and may be used in any mixed PSTN'IP network in which echo may be a problem.
• Echo canceller 320 operates in a similar manner. That is. Echo canceller 320 is not controlled by any of the switches and gateways in system 300 and is not tied to orking in conjunction w ith any particular control protocol.
• Echo cancellers 310 and 320 may also introduce "'comfort noise" onto the voice path between telephones 1 10 and 120. That is, echo cancellers 310 and 320 may introduce noise onto the voice path to prevent a listener from perceiv ing loss of connectivity with the other party.
• echo cancellers 310 and 320 may be configured to support the tone disabler function. That is. when a 2100 hertz tone with phase reversal from a data modem is received, echo cancellers 310 and 320 may disable themselves. This allows system 300 to support voiceband data traffic.
• Fig. 4 is a block diagram of another exemplary system 400 in which methods and systems consistent with the present invention may be implemented.
• the system 400 includes telephones 410A, 410B and 4 IOC. switches 420, 430 and 440. gatew ays 450 and 460. network 470. switches 480 and 485 and echo cancellers 490 and 495.
• the exemplary configuration illustrated in Fig. 4 is for simplicity. It should be understood that other devices may be included in sy stem 400 in implementations consistent w ith the present invention
• the telephones 410A-C may include conv entional telephones, such as those that interface ith the PSTN (not shown i to make and receiv c telephone calls.
• the connection betw een telephone 410A and switch 420 may be a two-wire analog circuit.
• the respectiv e connections between telephones 410B and 410C and switches 430 and 440 may be two- w ire analog circuits.
• Each of s itches 420, 430 and 440 may represent a conv entional switch.
• switches 420-440 may be PBXs that are located at various customers ' premises or at a telephone service provider's premises.
• switches 420-440 each include hybrid circuits that convert two-wire circuits from telephones 410A-C into four wire circuits and vice versa. As discussed previously, these hybrid circuits may cause echo problems.
• Gateway 450 may include a conventional gateway used to con ert input channels from a circuit switched network into the format needed for a packet switched netw ork, such as network 470.
• gateway 450 may include an ente ⁇ rise gateway that interfaces with a particular customer's equipment, such as sw itch 420. and may be located at the customer's premises. For example, when switch 420 is a customer PBX, ente ⁇ rise gateway 450 may be located at the customer's premises to interface with PBX 420. Alternatively, gateway 450 may be located at a telephone service provider's central office.
• Gatew ay 460 may include a direct access line ( DAL ) gatew ay .
• a D L gatew ay may be a specialized gateway used to allow customers to communicate w ith each other over a v irtual priv ate network (VPN ).
• DAL direct access line
• a D L gatew ay may be a specialized gateway used to allow customers to
• S itches 4S0 and 4S5 may include conventional class 3 (C3 ) sw itches used to perform arious switching functions for voice calls in a netw ork.
• the connection between switches 4S0 and 485 may represent an inter-machine trunk (IMT).
• IMT inter-machine trunk
• Network 470 may be a conventional packet switched network, such as an IP network.
• Network 470 may include the Internet, an intranet, a WAN. a LAN or a similar network that transmits data packets, such as IP data packets.
• Echo cancellers 490 and 495 may each be conv entional echo cancellers located on the IMT between class 3 switches 480 and 485. Echo cancellers 490 and 495 may be used to cancel echo in the IMT between class 3 switches 480 and 485.
• a telephone service provider determines whether system 400 requires external echo cancellers, as described in more detail below. When external echo cancellers are needed. the echo cancellers are strategically located to eliminate or reduce echo and to improve voice quality.
• Fig. 5 is a flow diagram, consistent with the present invention, illustrating processing for determining whether external echo cancellers are needed for system 400 of
• Fig. 4. Processing begins by a telephone service provider identifying potential echo sources in the service provider's system (act 510). For example, in system 400. the 2- wire to 4-vvire hybrid circuits included at switches 420. 430 and 440 are potential sources of echo caused by impedance mismatch. Therefore, in sy stem 400. the telephone serv ice prov ider may identify sw itches 420-440 as potential echo sources. (0057) Next, the telephone serv ice prov ider determines w hether the round trip delay introduced by any voice/echo path m system 400 is greater than a predetermined threshold. For example, similar to the discussion abov e w uh respect to Fig 2. in an exemplary implementation of the present invention, if the sound trip delay introduced by a particular voice/echo path is 35 ms or more, then echo problems may ultimately reduce v oice quality.
• a predetermined threshold For example, similar to the discussion abov e w uh respect to Fig 2.
• the telephone serv ice prov ider detemiines whether the round trip delay for a signal on voice/echo path D ⁇ B , for example, is greater than or equal to 35 ms (act 520). That is, if the time it takes for a signal to travel from switch 420 to switch 430 and echo back to switch 420 is at least 35 ms. then the quality of voice signals received via telephones 410A and 410B w ill by degraded due to the echo.
• Fig. 6 is a block diagram of an exemplary system 600, consistent with the present inv ention, which illustrates the insertion of external echo cancellers in system 400 to combat echo problems. Referring to Fig. 6.
• echo canceller 610 may be located in system 600 between switch 420 and gateway 450. Echo canceller 610 may then cancel echo associated w ith a caller at telephone J 10B. That is. echo canceller 61 cancels the echo caused by a reflection in the signal thru occurs at the hybrid circuit at s itch 420 and propagates back tow ard sw itch 430 In an exemplary implementation, echo canceller 610 is preferably located near the source of the echo, w Inch in this case :s sw itch 420. [00611 Echo canceller 620 may be Ocaied in sy stem 600 between class 3 sw itch 480 and gateway 460. Echo canceller 620 may then cancel echo associated w ith a caller at telephone 410A.
• echo canceller 620 cancels the echo caused by a reflection in the signal that occurs at the hybrid circuit at s itch 430 and propagates back tow ard switch 420.
• echo canceller 620 is located between gateway 460 and class 3 sw itch 480.
• echo canceller 620 could be located between class 3 switch 480 and switch 430.
• the telephone service provider may then identify whether system 400 includes any other voice/echo paths that do not include external echo cancellers (act 560).
• each of the paths D,.,; and D BC include external echo cancellers along the potential echo paths.
• echo cancellers 490 and 495 may cancel echo on the path between telephones 410B and 4 I OC.
• These echo cancellers 490 and 495 may similarly cancel echo associated with calls between telephones 410A and 410C.
• echo cancellers 610 and 620 (Fig. 6) may be used to cancel echo on voice calls between telephones 4 I 0A and 4 IOC. In either case, no additional external echo cancellers are needed.
• processing returns to act 520 to determine whether the round trip delay on any identified voice/echo paths is 35 ms or more. If any such path existed, the telephone service prov ider w ould determine the appropriate location* s i for the external echo cancellers to reduce the echo on this particular voice path.
• stand-alone echo cancellers 610 and 620 are strategically located to prev ent echo from reducing v oice quality
• these integrated echo cancellers may be disabled.
• echo cancellers 610 and 620 may be conventional devices, such as Quad-T l echo cancellers described prev lousiy or other conventional echo cancellers. Similar to the discussion w ith regard to Fig. 3. the external echo cancellers 610 and 620 are located externally from the s itches and gateways of system 600.
• the standalone echo cancellers 610 and 620 are not controlled by any particular control logic executed by the switches or gateways of system 600, such as conventional Q.1 15 echo control logic. Echo cancellers 610 and 620 are also not tied to working in conjunction with any particular echo control protocol, such as com entiona! Q.55 echo control protocol, that may be included in the switches or gateways of s stem 600. In other words, echo cancellers 610 and 620 operate independently from the sw itches and gateways in system 600 and may be used in any mixed PSTN, IP network in which echo may be a problem.
• Echo cancellers 610 and 620 may also introduce comfort noise onto the voice path betw een telephones 410A and 410B to prevent a listener from perceiving loss of connectiv ity with the other party.
• echo cancellers 610 and 620 may also be configui ed to support the tone disabler function. This allows sy tem 600 to support v iceband data traffic.
• Fig. ⁇ is a block diagram of another exemplary sy stem " 00 ;n w hich methods and systems consistent w ith the present inv ention may be implemented
• the s tem " 00 includes telephones 710A. 710B and 7 I OC. switch 720. networks " 30. 740 and 770. gatew ays 50 and 760. sw itches 780 and 7S5 and echo cancellers " 90 and 795.
• the exemplary configuration illustrated in Fig. 7 is for simplicity. It should be understood that other dev ices may be included in system 700 in implementations consistent w ith the present invention
• the telephones 710A-C may include conventional telephones, such as those that interface with the PSTN (not shown) to make and receive telephone calls.
• the connection between telephone 710A and switch 720 may be a two-wire analog circuit.
• the respective connections between telephones 710B and 710C and networks 730 and 740 may be two- wire analog circuits.
• Sw itch 720 may represent a conventional switch.
• sw itches 720 may ⁇ be a PBX located at a customer's premises or at a telephone service prov ider's premises.
• switch " 20 includes a hybrid circuit that converts a two-wire circuit from telephone 710A into a four-w ire circuit and vice versa. As discussed previously, these hybrid circuits may cause echo problems.
• Gateway 750 may include a conventional gateway used to conv ert input channels from a circuit switched network into the format needed for a packet sw itched netw ork, such as network 770.
• gateway " 50 may include an entciprise gateway that interfaces w ith a particular customer ' s equipment, such as sw itch
• w hen sw itch ⁇ 20 is a customer PBX.
• enterprise gateway " 50 may be located at the customer ' s pi cmiscs to interface ith PBX 720.
• gatew ay 750 may be located at a telephone serv ice prov ider ' s central office.
• Gate ay 760 may include a network gateway.
• Netw ork gatew ay 60 may be a conventional gateway used to interface with a class 3 (C3) switch, such as switch 780.
• C3 class 3
• Netw ork gateway 760 may be located at the telephone service provider ' s central office.
• S itches 780 and 785 may include conventional class 3 sw itches used to perform v arious sw itching functions for voice calls in a netw ork.
• the connection betw een switches 780 and 785 may represent an inter-machine trunk (IMT).
• Network 770 may be a conventional packet switched network, such as an IP network.
• Network 770 may include the Internet, an intranet, a WAN, a LAN or a similar network that transmits data packets, such as IP data packets.
• Networks 730 and 740 may include a circuit switched network, such as the PSTN.
• Networks 730 and 740 may be associated with a local exchange carrier (LEC) and may include hybrid circuits that convert the 2-wire local loop circuits to 4-vvire circuits and vice v ersa for interfacing with class 3 switches 780 and 785. respecti ely.
• LEC local exchange carrier
• Echo cancellers 790 and 795 may each be conventional echo cancellers located on the IMT between class 3 switches 780 and 785. Echo cancellers 790 and 795 may be used to cancel echo in the IMT between class 3 s itches 780 and 785.
• a telephone service provider determines w hether system 700 needs external echo cancellers, in a similar manner as that described with respect to Fig. 5. [0078] That is. the telephone service provider identifies potential echo sources system 700. As describe above, in system 700.
• the 2-wire to 4-w ire hy b ⁇ d circuits included at switch 720 and LEC networks 730 and 740 are potential sources of echo caused by- impedance mismatch.
• the telephone sen-ice provider determines w hether the round trip delay introduced by any voice/echo path in system 700 is greater than a predetermined threshold. For example, similar to the discussion abov e w ith respect to Fig. 5, in an exemplary implementation of the present inv ention, if the round trip delay- introduced by a particular voice/echo path is greater than or equal to 35 ms. then external echo cancellers may be needed.
• the telephone service provider checks whether the round trip delay time for a signal on v oice/echo path D AB , for example, is greater than or equal to 35 ms. That is. if the time that it takes for a signal to trav el from switch 720 to LEC 730 and echo back to s itch 720 is 35 ms or more, external echo cancellers are needed on that path. If the round trip delay is less than 35 ms, no external echo cancellers are needed on voice/echo path D A3 . [0080] Assume that the round trip delay on voice/echo path D ⁇ is greater than 35 ms. In this case, the telephone service provider determines the appropriate location(s) for the external echo cancellers.
• Fig. 8 is a block diagram of an exemplary system 800. consistent w ith the present invention, which illustrates the insertion of external echo cancellers in svstem 700 to combat echo problems.
• echo canceller 10 may be located in sy tem 800 betw een sw itch 720 and gatew ay 750. Echo canceller 810 may then cancel echo associated w ith a caller at telephone ⁇ 10B or 7 IOC. That is. echo cancellei MO may cancel the echo caused by a reflection in the signal that occurs ai the hy brid circuit at switch 720 and propagates back tow ard LEC 730 or LEC 740.
• echo canceller 8 10 is preferably located near the source of the echo, which in this case is switch 720.
• Echo canceller S20 may be located in system 800 between class 3 sw itch 7S0 and gatew ay 760.
• echo canceller 820 may be located in system S00 betw een class 3 switch 780 and LEC 730. In either case, echo canceller 820 may cancel echo associated w ith a caller at telephone 710A. That is. echo canceller 820 cancels the echo caused by a reflection in the signal that occurs at the hybrid circuit at LEC 730 and propagates back toward switch 720.
• the telephone service provider may then determine whether system 700 includes any other voice/echo paths that do not include external echo cancellers.
• each of the paths D c and D B c includes external echo cancellers along the potential echo paths. Therefore, no additional external echo cancellers are needed. If, however, additional paths existed in which no external echo cancellers are provided the telephone service provider would determine whether the round trip time for transmitting a signal and receiving a reflected portion of the signal is greater than or equal to 35 ms. If any such paths existed, the telephone service prov ider would identify the appropriate location(s) for the external echo cancellers on that v oice path.
• these integrated echo cancellers may be disabled.
• echo cancellers 810 and 820 may be conventional dev ices, such as Quad-Tl echo c ⁇ mcelle ⁇ described previously or other conventional echo cancellers. Similar to the discussion w ith regard to Fig. 3, the external echo cancellers 810 and 820 aie located externally from the switches and gateways of system S00.
• the standalone echo cancellers 810 and 820 are not controlled by any particular control logic executed by the switches or gateways of system 800, such as conventional Q. l 15 echo control logic. Echo cancellers 810 and 820 are also not tied to w orking in conjunction with any particular echo control protocol, such as conventional Q.55 echo control protocol, that may be included in the switches or gateways of system 800. In other ⁇ words, echo cancellers 810 and S20 operate independently from the sw itches and gateways in system 800 and may be used in any mixed PSTN/IP netw ork in hich echo may be a problem.
• Echo cancellers 810 and 820 may also introduce comfort noise onto the voice path between telephones 710A and 710B to prevent a listener from perceiv ing loss of connectivity w ith the other party.
• echo cancellers 810 and 820 may also be configured to support the tone disabler function to allow system 800 to support voiceband data traffic.
• ⁇ n adv antage of the inv ention is that the echo cancellers are independent of ihe v nous devices m the networks and may be used in networks that operate in accordance w ith any protocol.
• Another advantage of the inv ention is that the echo cancel lei s may cancel objectionable echo w hile introducing comfort noise into a v oice path This results in more reliable and accurate conversations between parties and prev ents parties from perceiv ing a loss of connectiv ity.
• a further advantage of the present in ention is the system is flexible and can be easily modified. That is. the echo cancellers may be easily inserted 01 removed from a v oice path in w hich echo control is needed or in w hich echo control is no longer needed.
• the present invention has been described mainly in relation to mixe ⁇ network that includes the PSTN and an IP network.
• the present inv ention may also be used in other mixed circuit switched/packet switched netw orks.
• the present invention may be used in conjunction ith a circuit switched network that includes an integrated services digital network (ISDN).
• ISDN integrated services digital network
• the present invention may also be used in a non-mixed network, such as a separate circuit s itched network or a separate packet switched network.
• a non-mixed network such as a separate circuit s itched network or a separate packet switched network.
• the present in ention has also been described as determining whether the round trip delay introduced by a voice/echo path is greater than a predetermined amount of lime, such as 35 ms.
• a predetermined amount of lime such as 35 ms.
• conventional reflecto etr ⁇ ma ⁇ be used to measure the actual time associated with the round trip delay.
• the round trip delay may be estimated based on a distance.
• the round trip delay introduced by such a voice ' echo path may be estimated to be 35 ms or more.
• the measured distance may be the distance between two telephones, i.e., a calling party and a called party.
• these components may add throughput/signal processing delay on a voice path and may also reduce general noise on a voice path, making echo more noticeable.
• the predetermined distance may be less, such as 300 miles.
• an external echo canceller may be dynamically activated deactivated based on the network conditions. For example, the round trip delay introduced by a voice/echo path may be monitored continuously or periodically over time. When the dynamically measured delay in the voice'echo path is greater than a predetermined period, such as 35 ms.
• the external echo canceller may be activated.
• the external echo canceller may ⁇ be deactiv-ated.
• the activation/deactivalion may be accomplished using control circuitry in either or both the timing device and the external echo canceller to automatically activate/deactivate the echo canceller based on the measured delay.
• control circuitry in either or both the timing device and the external echo canceller to automatically activate/deactivate the echo canceller based on the measured delay.
• the round trip delay associated with a voice/echo path has been described as corresponding to the time associated with transmitting a signal from a switch to an echo source and back to the switch. It should be understood, however, that the round trip delay also includes the time associated with transmitting the signal from/to a caller.
• the round trip delay may be the time associated with transmitting a signal from telephone 1 10 to switch 140 and back to telephone 110.
• the voice/echo path may include the portion of the path labeled 1 12 in Fig. 1.
• the time associated with transmitting the signal from the caller, i.e.. telephone 1 10 in Fig.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Telephonic Communication Services (AREA)
• Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

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• 2002
  • 2002-11-25 EP EP02794022A patent/EP1464123A1/de not_active Withdrawn
  • 2002-11-25 AU AU2002359480A patent/AU2002359480A1/en not_active Abandoned
  • 2002-11-25 WO PCT/US2002/037825 patent/WO2003052959A1/en not_active Application Discontinuation
  • 2002-11-25 CA CA002470097A patent/CA2470097A1/en not_active Abandoned

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