CA2470097A1 - Systems and methods for providing echo control - Google Patents
Systems and methods for providing echo control Download PDFInfo
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- CA2470097A1 CA2470097A1 CA002470097A CA2470097A CA2470097A1 CA 2470097 A1 CA2470097 A1 CA 2470097A1 CA 002470097 A CA002470097 A CA 002470097A CA 2470097 A CA2470097 A CA 2470097A CA 2470097 A1 CA2470097 A1 CA 2470097A1
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- Prior art keywords
- echo
- switch
- gateway
- voice
- switched network
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Classifications
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- 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
Abstract
A system for providing echo control for voice calls transmitted over circuit switched and packet switched networks uses stand-alone echo cancellers. A
first echo canceller (310) is coupled to a first switch (130) in the circuit switched network and a first gateway (150) on the packet switched network. The first gateway forwards a first voice call over the packet switched network(170) to a second gateway (160) . The second gateway forwards the first voice call to a second switch (140) on the circuit switched network. A second echo canceller (320) is coupled to the second gateway and the second switch.
The second echo canceller cancels echo associated with the first voice call when time associated with transmitting a first voice signal is greater than or equal to predetermined threshold.
first echo canceller (310) is coupled to a first switch (130) in the circuit switched network and a first gateway (150) on the packet switched network. The first gateway forwards a first voice call over the packet switched network(170) to a second gateway (160) . The second gateway forwards the first voice call to a second switch (140) on the circuit switched network. A second echo canceller (320) is coupled to the second gateway and the second switch.
The second echo canceller cancels echo associated with the first voice call when time associated with transmitting a first voice signal is greater than or equal to predetermined threshold.
Description
(0001( Sl'STE\'1S :ADD f~-1ET1-IUDS I~OR i'It0\~ID1\~G hCL-iO C~t~\~~I~ROL
(0002] FIL:Ln OF Tl-lE l~\'E\TIO\
(0003) The present invention relates ~~en~r;tily to echo control i,n mworks and. more har-ticularlv. to providing echo control for voice calls trammitted ow:~
packet switched networks.
packet switched networks.
(0004] BACKGRGL!\'D OF THE I~IVE'~ITIO\
(OOOS] Voice and voice-band traffic has traditionally L~e~n transport~.i by circuit switched nenworks, such a~ the public switched telephone nmwork (PST\). Tudav, an increasine amount of voice u~affic is carried over a combination of~ir~uit wwitched neavorks alld packet switched nenworks, such as Internet Protocol (IPj nm~~orks.
(U006] The PST\ typically uses both 2-wire circuits and rt-wire circuits for carrying full duplex voice traffic. The 2-wire circuits are typically used in the local loop portion of the PST's, such as the connection from the end user to a local switch or a local central office.
For example, a voice call from a typical telephone may be routed to ., switch over the PST\ as an analo'z signal on a standard two-wire circuit. .-\t the switch. a hybrid circuit may convert the ?-wire circuit connection to a 4-wire circuit connection. The switch may also forward the voice call to one or more conventional gateways that provide various services associated with transmitting information over an IP nehwork. For example, the ~atevway may convert analog voice signals in pulse code modulation (PC\t) format into packets for transmission over the IP nenwork. .At a second gateway. the packetized signal may be converted back to an analog signal. Another switch located in relative proximitw to the called pane m:lv include ~l hybrid circuit that converts :1 -l-wire ~
irmit to a. _'-w ire circuit for connection to tllr called party's l~:lephone.
~0007~ One problem with t! ansmittin~ ~,~oicc data in this manner is th;lt mho stay ucrur as a I'eslllt Of IIllped311Ce 1111~i11:11C17 ~tl lily 11', brt0 CIrCIIIIS, l.e..
llle pOllll ~~ ll~e llle ~-w 11'e circuits are converlwd to -t-wire circuits and vice versa. This echo is oaten perceivable by the hllillall ear and ultimately degrades the quality of the voice call.
Conventional gatewa}-s may include integrated echo cancellers to combat echo. That is, the gateways themselves perfoml echo cancellation.
(0008] One problem with gatwvays that include integrated echo cancellers is that they oaten do not support the tone disables function. The tone disables function reicrs to a 1 UO 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 with voiceband data traffic. Since the gateways do not support the tone disables function, voiceband data traffic cannot be supported over the network.
(0009] Another problem with gateways with integrated echo cancellers is they often fail to introduce "COIllt01't~~ noise alter echo cancellation has been perfonlled.
This results in the listener perceiving a loss of connectivity. In addition. the conventional gateways often do not adhere to the echo cancellation convergence criteria specified by the International Telecommunication Union (ITU) 6.168. As a result. the echo may be objectionable in voice calls made over an IP network.
[0010] SUW\iARI' OF THE I\'VE\T10\
(0011 ] There exists a need for systems and methods that improve problems associated with echo control in an IP network.
;0011) These and other needs arc ntet by the pre~.mt invention, where sUtnd-alone c~ho ~:,tncellcr; are strafe«icallv located to perform echo eancullation. By lomltin~ the echo ~,tnrcll~rs at particular !ovations, the echo problem ntay be eliminawd or substantially ~~c~iuced, tlterety, improvip~ the quality of \'OICe CaIlS 1r31151711t1~d over an IP nom ork.
;t1013J According to one aspect of the invention. a sysmm that includes a first echo ~anceller, a first gateway, a second v~atewav and a second echo cancell~r is provided. The first echo canceller is coupled to a first switch in a circuit switched network and is coati<aured to cancel echo associated with voice calls transmitted over a circuit switched nmvork and a packet switched network. The first gateway is coupled to the first echo canceller and is configured to forward a first voice call owr the packet switched 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 switch and is configured to cancel echo associated evith 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.
(0014( 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 fowarding 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 converts a wo-wire circuit to ~ four-wire circuit. T~I1C Illethod ,tl,o m~!tiiius tran~m:ttint~
the voii:c call over the lour-wire circuit to a first gateway. convertintT.
:~t the lirst '~~~teway.
tltc voice call to a format compatible ~.vith the packet switched nmvork, and transmutin~~
tl;e voice call over the packet switcl-~ed network to a second gateway. Tlte IllelhOd further incU.ides converting, at the second «atwvay, the voice call to a format compatible w ith a second circuit switched neavork and transmitting the voice call to a second switch included in the second circuit switched network. The second switch includes a hybrid .ciucuit that convents the four-wire circuit to a two-wire circuit. The method also includes forwarding 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 o1 the voice call using an echo canceller. The echo canccllen is located cxmrnally ti-om each of the first switch, the second switch. the first gateway and the second gateway alld is not controlled by any of the first switch, the second switch, the first gateway and the second gateway.
[OOI~J ~ccordina to a further aspect of the invention, a method for providing echo control in a system that routes voice calls over a circuit switched new~ork and a packet switched network is provided. The method 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 neW ~orks and receiving a retlected portion of the first signal at the first echo source is greater than or equal to 3~
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 voice path and receivine a reflected portion of the second signal at the mound cvho ;our~c is greater than or equal to 35 milliseconds. The method also includes inserting lirst anii aecond stand-alone echo eancellers on the voice path when the lint and second tinms are both Ur~atcr than or equal to 3~ milliseconds.
(0016] Other features and advantages of the present invention will become readily apparent to those skilled in this art from the following dmailed description.
The embodiments shown and described provide illustration of the best mode contemplated for aarryin~ out the invention. The invention is capable of modifications in various obvious raspects, all without departing from the invention. .Accordingly, the drawings are to be reUarded as illustrative in nature, and not as restrictive.
(U017] BRIEF DESCRIPT10?~ OF THE DRAB\'I\GS
[0018] Reference is made to the attached drawings, wherein elements having the same reference number designation may represent like elements throughout.
(0019] Fig. 1 is a block diagram of an exemplary system in which methods and systems consistent with the present invention may be implemented.
[0020] 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.
[0021] Fig. 3 is a block diagram of an exemplary system, consistent with the present invention, which illustrates the insertion of external echo cancellers in the system of Fib.
1.
J0022 J Fi'~. -1 i' a block dia~~ram ot~ another e~:rmplan w>tcm ~n w ill~Il nmllod> aml systems consistent with the present invention may be implemented.
[0023] Fig. ~ is an exemplary flow diagram. consistent with the present invention.
illustrating processing for determininU whether external echo c:~mellers are needed in the system~of Fig. ~.
(002] Fig. 6 is a block diagram of an exemplary system. consister;t with the present invention, which illustrates the insertion of external echo cancellers in the s~~snm of Fig.
[002] Fig. % is a block diagram of another exemplary system in which methods and systems consistent with the present invention may be Implemented.
[0026] Fig. 8 is a block diagram of an exemplan- system. consistent with the present invention, which illustrates the inset~tion of external echo cancellers in the system of Fig..
7.
[0027] DETAILED DESCRIPTIO\
[0028] Systems and methods consistent with the present invention avoid the problems associated the occurrence of echoes for a voice call transmitted over a mixed PST\; IP
network by providing echo.cancellers located externally from the various switches and gateways in the network. By strategically locating the echo cancellers, problems associated with echo may be avoided.
[0029] Fig. 1 is a block diagram of an exemplary system 100 in mhich methods and systems consistent with the present invention may be implemented. The system l00 includes telephones l 10 and 120, switches 130 and 1~0, gateways 1 ~0 and 160 and ncw~ork 1?0. The eacmplarv configuration illustrated in Fi~~. I is t~or sinnpli~iy. It should be understood that other devices may be included in system l0u in implementations consistent with the present invention.
[0030) The telephones 1 10 and 1 ?0 may include conventional tel~J,honcs. such a; tl~osc that interface with the PST\ (not showm) to place and r~ccive tel~phooc galls.
in an exetnplarv implementation of the present invention. the connection betvee;t telephone 1 10 and switch 130, labeled I 12 in Fig. 1, rnay be a two-wire analog circuit. Similarly, the connection between telephone 120 and switch 1=10, labeled 122 in Fi~~. 1.
Illa~~ be a two-wire analoe circuit.
[0031] Each of switches 130 and 140 may represent a conventional switch, 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 provider's premises. In an exemplary implementation of the present invention, the connection between switch 130 and gateway 150, labeled 1 14 in Fig. 1. may be a four-wire circuit.
In this implementation, the switch 130 includes a hybrid circuit that converts the two-wire circuit 1 12 from the telephone 1 10 into the four-wire circuit 1 1-1. as illusu~ated in Fig. I. The hybrid circuit in switch 130 similarly converts four-wire circuits from gateway 150 into two-wire circuits for routing the analog voice signals to telephone 1 10.
[0032) Switch 140 may similarly include a hybrid circuit that converts two-wire circuit.
labeled 122, to four-wire circuit 124, and vice versa, as illustrated in Fig.
1. As discussed previously, these two-wire to four=wire hybrid circuits at switches 130 and 1-10 may cause echo problems as a result of impedance mismatch.
[0033] Gatewa~.~; (G~~') I ~0 and I(s0 may inclu:lc ~_onvcntional ~~.ocwws umd to mnvrrt input channels tuom a circuit switched new~ork into the t~ormat n~Wed for a packet switched new~ork. such as new~ork 170. In an eaentplarv imple;mntatiort.
;_atewws I ~~.
and 150 may be enterprise ~~atewaw that imerface v,~ith .~ partiru::;r cuaomer' equipment. such as the respective switches 130 and 1-10. Gateways 1 ~0 alld I6U Illa~' be located at the customers premises. For eaampl~. ~.~ hen switches 1 30 and i W%
arc customer PBXs, enterprise g,atewavs 150 and 160 may be located at a customer's premises to interface with PBXs 130 and 140, respectively.
[0034] \'etwork 170 maybe a conventional packet switched newor',;, such as an nemork. \em~ork 170 may include the Internet, an intranet, a ~V.~\, a L ~,\ or a similar network that transmits data packets, such as IP data packets.
[003] In an exemplary implementation consistent with the present invention, a telephone service provider determines whether system I00 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.
[0036] 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 sen~ice provider identifying potential echo sources in the sen~ice provider's system (act 2101. For example, in system 100. the ?-wire to =I-wire hybrid circuits included at switches 130 and 110 are potential sources of echo caused by impedance mismatch. Therefore. in sv~tem 100, the telephonz sen~ice provider may identify switches 130 and 140 as potential echo sources.
a (0037] \ext, the telephone ser\.ice pro\ iWr iirtermines \\ Nether tl?~ round trip dcla~.
introduced by any \~oice;echo bath in sysmn 100 is greater than a prcdetcrmimd amount of time (art 2?0). For example. if the round trip delay introduced by the voice echo path between switches 130 and i-Iti. Inbeled D in Fi~~. I. ~s ~~r~ater than approvimatc:y ?~
milliseconds (ms), then ecl;o may be pcr~eivable by the 1?uman ear and tlla\' ultllll~itel_, reduce voice quality. In oti,er w ords, if the time it takes .~ signal to travel from sw itch 130 to switch 140 and reflect back (i.e., echo) to switch 130 takes more than 25 ms, then the quality of voice signals ~c:ceived via telephones 1 10 and 1?0 may be reduced due to the echo.
(0038) In an exemplary implementation of the present invention, : ~ ms has been set as the design criteria in \vhich echo tray be considered to be objectionable.
That is, if the round trip delay introduced by a voice/echo path is less than 35 ms, the echo may not be significant enough to be objectionable and external echo cancellers may not be needed (act 230). If, on the other hand, the round trip delay is 3~ ms or more, external echo cancellers may be needed (act ?=10). In this case, the telephone sewice provider determines the appropriate locations) for the external echo cancellers and inserts the echo cancellers at these locations (act 250).
[0039] Fig. 3 is a block diagram of an exemplary system 300, consistent with the present invention, which illustrates the insertion of external echo cancellers in system 100 to combat echo problems. Referring to Fig. 3, echo canceller 310 may be located in system 300 between switch 130 and gateway 1~0. Echo canceller 310 may then cancel echo associated with caller 120. That is, echo canceller 310 cancels the echo caused by a reflection in the signal that occurs at the hybrid circuit at switch 1.0 and propagates back toward s,vitch 1-I0. In an rvemplary imple111Cill;ltl011. CCIIO ~amcll~r 311.1 is pref~c;~ablv located as close to the source of thi: echo as possible, which in this example is the hybrid aircait at switch 1 30. Therefore, echo canceller 310 may be locamd near switch 1 ~0.
X00-IO[ Echo canceller 3'!O may be located in system 300 hmueen switch 140 anil ~~atewav 16;J. Echo canccller 3'0 may then cancel echo associated with caller 1 1U. That is, echo cat:celler 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. which in this case. is the hybrid circuit in switch 140. Therefore. echo canceller 320 may be iocatcd near switch 140.
[0041) In system 300., when a voice call is placed from telephone 1 10. it is transmitted to switch 130 over a hvo-wire analog circuit 1 12, converted at switch 130 into a four wire circuit and passed on through echo canceller 310 to gateway 150. It should be undet'stood that echo czncellers, 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 1 ~0 may packetize the voice call into an appropriate protocol for nec'ork 170 and forv.'ard the voice call over network 170. Gateway 160 receives the voice call and for'vards the voice call through echo canceller 320 to switch 140. It should be understood that switches l30 and 140 may be included in the same or different circuit switched neovorks. In either case, the voice call is converted back to a two-wire analoe circuit at switch 140 for transmission to telephone 120. ~t the same time the voice call is being forwarded through switch 140 to telephone 120. a portion of the voice call ma~~
reflect or echo back toward switch 130. Echo canceller 320 receives this echo and ..c'lnccls" the echo (i.e., prments the echo from beltlg tr;iI15111111C~1 baC6: uvcr the ~.~uii:e path to telephone 1 i O). In a similar manner, echo r~tnceilur 310 prevents the echo associated ~~~lth ;1 wOlCe Call made iron telephone I ~0 tiwm ecltoin« back to telephone i ~0.
[00-12J In this manner, stand-alone echo caocell~rs 310 and 3''0 are strategically lo~amd to prevent ei:ho ti~om reducing voice quality. In addition. in situations where one ur both of the gateways 150 and 160 include integrated echo cancellers, these integrated echo cancellers may be disabled.
J0043J In an exemplaw implementation consistent with the present invention.
echo cancellers 310 and 320 may be conventional devices, such as Quad-Tl echo canceliers manufactured by Ditech Communications Corporation. :Aternatively, other conventional echo cancellers may be used in implementations consistent with the present invention.
Details of the particular echo cancellers used are not described herein in order not to unduly obscure the thrust of the present invention. However, one of ordinary skill in the art would be able to select the particular echo canceller given the guidance disclosed herein.
(004=tJ In each case, however, echo cancellers 310 and 320 are located externally from the switches and gateways of system 300. For example, echo canceller 310 is coupled between switch 130 and gateway 150. Echo canceller 310, however, is located externally from these devices. Similarly, echo canceller 320 is located externally from switch 1:~0 and ~~atewav 160.
[OOa~J In addition, the stand-alone echo cancellers 310 and 320 are not controlled by either the switches or gateways of system 300. For example, echo canceller 310 is not controlled by anv particular control logic. ~urh a~ conventional Q.l I ~ c~ho control lo~~~i~.
bein« executed at switch 130, switch 1-J0: ~~:iieway 1 ~0 or r~atewav 160.
Echo canccilcr 310 is also not tied to w orkin~ in copunction with ativ particular protocol.
:mh .,~
conventioltai Q.~~ echo control protocol. ti;at may he included in switci~ i 3(i. sv iuh I-1(i.
gateway i s0 or gateway 160. In other words; echo canccller 310 operates imich~ndentlv From the switches and gateways in system 300 and may be used I11 any mixed PST\~1P
network ttl whlCh 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 working in conjunction with any particular control protocol.
[0046] Echo cancellers 310 and 320 may also introduce "comfort noise" onto the voice path between telephones 110 and 120. That is, echo cancellers 310 and 320 may introduce noise onto the voice path to prevent a listener from perceiving loss of connectivity with the other party. In addition, echo cancellers 3 I 0 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.
(0047] 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 -includes telephones -I1 OA, -I1 OB and 410C. switches 420, 430 and =1=J0, gateways ~s0 and 460, network =1?0, switches 180 and 485 and echo cancellers =190 atld 495. The exemplary configuration illustrated in Fly. =1 is for simplicity. It should be understood that other device: may be included in sysmm -fUU I11 1171p1~117~11t;t11011~
lonsistent w ith the present invention.
[004b[ The teiephon;a ~IIO.A-C may include come ntional ti:lephones, such as those that intert'acc with the PST\ (not showm to make and receive telephone ~:jlls. In an exemplary implementation of the present invention. the connection bmvren t~l~phone 410A and switch 420 may be a m~o-wire analog circuit. Similary. the respective connections bet'veen telephones 410B and 410C and switches 430 and 440 may be two-wire analog circuits.
[00-19J Each of switches =120, 430 and 4-10 may represent a conventional switch. For example, switches 420-4-~0 may be PB~s that are located at various customers' premises or at a telephone service provider's premises. In an exemplary implementation of the present invention, switches 420-440 each include hybrid circuits that convert nvo-wire circuits from telephones 410A-C into four wire circuits and vice versa. As discussed previously, these hybrid circuits may cause echo problems.
[0050] Gateway 450 may include a conventional gateway used to convert input channels from a circuit switched network into the format needed for a packet switched nom ork, such as network 470. In an exemplay implementation, Gateway 450 may include an enterprise gateway that interfaces with a particular customer's equipment, such, as switch 420, and may be located at the customer's premises. For example, when switch 420 is a customer PBX, enterprise 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.
~00~1J Gateway 460 rnay include a direct access line ID:~Lt '~amvay. :\ D:\L
;_amv,y may be a specialized gateway used to allow customers to copmunirate w ith ea:h other over a virtual private network (\-'P\ j.
~OU~2) Switches-DSO and 4Cj may include conventional class 3 (C3) switches n~mi to perform various switching functions for voice calls in a nemork. The connectir.n between switches 4S0 and 4S5 may represent an inter-machine trunk (I1~1'i~).
[0053] 'vetwork 470 may be a conventional packet switched network, such as an IP
network. \etwork 470 may include the Internet, an intranet, a 1\'A\. a L:~\ or a similar network that transmits data packets. such as IP data packms.
[0054] Echo cancellers 490 and 495 may each be conventional echo canceller~
loc;3ted gn the IMT between class 3 switches 480 and 485. Echo_ cancellers -490 and 495 may he used to cancel echo in the IMT between class 3 switches 480 and 455.
[0055] In an exemplary implementation consistent with the present invention. 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.
[0056] Fig. ~ 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-wire hybrid circuits included at switches 420, 430 and 4-10 are potential sources ~t~echo caused by impedance mismatch. l'heref~ore. in wmn -I~al.~. tlm tcl~phonc ~crvi~e provider may identify switches 420--l-I0 as potential erim sources.
(00;7J \cxt. the telephone service provider determine; wlmah~r the round trip W!a~.
introduced by any voice; echo bath in system -ICAO is vl'oaml' than a predm:rmlr~ed .
threshold. For example. similar to the discussion above w ith reahect to Fi~?.
~. in an memplary implementation of the present invention. if tllc round trip d~lav introdmed by a particular voice/echo path is 35 ms or more. then echo problems may ultimately reduce voice quality.
(0058) Referring to Fiy~. 4, in an exemplary implementation. the telephone service provider determines whether the round trip delay for a si«nal on voice.-echo path D..~e, for example, is greater than or equal to 35 1115 (act 520). That is, if the time it takes for a sienal 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 41 OB
will by degraded due to the echo.
[009] If the round trip delay is Jess than 35 ms, no external echo cancellers are needed on voice path D..~B (act 530). If, however, the round trip delay on path D.~B
is greater than or equal to 35 ms, external echo cancellers are needed (act 540j. In this case. the telephone service provider determines the appropriate locations) for the exteral echo cancellers and inserts the external echo cancellers at the desired locations (act ~50).
[0060) Fig. 6 is.a block diagram of an exemplary system 600, consistent with the present 111~~~I1L1011, which illustrates the insertion of exreral echo cancellers in system 400 to combat echo problems. Refen-ing to Fig. 6, echo canceller 610 may be located in system 600 beuveen switch 420 and gateway 450. Echo canceller 610 may then cancel echo associated with a caller at telephone ~ I OB. That is. echo vameller ~ ; CI
cancels the echo caused by a reflection.in the signal tli;lt occurs at the hybrid circuit at :witch X30 and propagates back toward switch=1~0. il. an memplary ilaplemcntatiol;. c~ho canccllcr 61U
is preferably located near the source ofthe ec(;o. which il this case _ switch -4'0.
[0061 ( Echo canceller 620 may be !ov:lted I11 S~ ~ICIII 61]0 between r';:~s 3 switch ~1y0 and ~atewav 460. Echo canccller 620 may then cancel echo asso,:iatrd ~.v ith a caller at telephone 410P,. That is, echo canceller 620 cancels the echo caused by a reflection in the signal that occurs at the hybrid circuit at switrh =13t) and propa~~aus back toward switch -120. In the exemplary configuration illustrated in Fig. 6. echo cancellcr 620 is located between aatewav -160 and class 3 switch :DSO. A!ternativel~.. mho cancrller 620 could be located between class 3 switch 4S0 and switch =130.
(0062] Referring back to Fig. 4, the telephone service provider may then identify whether system 400 includes any other voice/echo paths that do not include external echo cancellers (act 5601. In system 400, however, each of the paths D,;;~ and DBE
include external echo cancellers along the potential echo paths. For example. echo cancellers 190 and =19~ may cancel echo on the path between telephones =110I3 and -I 1 OC.
These echo cancellers 490 and 495 may similarly cancel echo associated with calls between telephones 410A and 410C. Alternatively, echo cancellers 610 and 6?0 (Fig. 6) may be used to cancel echo on voice calls between telepl2ones 410A and =110C. In either case. no additional external echo cancellers are needed.
(0063) If. however. additional paths existed in system 400 in which no ewernal echo cancellers are provided. processing returns to act 520 to determine whether the round trip delay on any identified voice/echo paths is 3~ ms or more. If any _ uch path existed. the telephone s~rvicc provider would dricrminc the appropri;ttc locationtsl for ihc eternal who cancellers to reduce the echo on this particular voice path.
(0060 In this manner, stand-alone echo cancell~rs 610 and 621_1 re str;3te'~icallv located to prevent echo prom reuocin~ voice qttalitv. In addition, in situ;aion~ where one or both of the gateways ~1~0 and -X60 ltlclude integrated echo canrellers. these imegrat~d ccl2o cancellers ma~.~ l~: disabled.
(0065) In an exemplary implementation consistent with the present invention, echo cancellers 610 and 620 may be conventional devices, such as (quad-T 1 echo cancellers described previoustv or other conventional echo cancellers. Similar to the discussion with regard to Fig. 3, the external echo canceliers 610 and 620 are located externally from the switches and gateways of system 600.
/0066) In addition, similar to the previous discussion with regard to Fig. 3, the stand-alone echo cancellers 6i0 and 620 are not controlled by any particular control logic executed by the switches or gateways of system 600, such as conventional Q. l 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 cam entional Q.s~ echo control protocol. that may be included in the switches or gateways of system 600. In other words, echo cancellers 610 and 620 operate independently from the switches and ~ateways in system 600 and may be used in any mixed PS'Ti'I,~IP network in which echo may be a problem.
(0067] Echo cancellers 610 and 620 may also introduce comfon noise onto the voice path benvzen telephones 410A and =I l OB to prevent a listener from perceiving toss of connectivity with the other party. In addition. echo cancellers 610 and 620 may also be ~unii~urc~i to support the tone disabler function. This allows swtm~ 600 to suppor~
vuiccband data traffic.
(OOGB( Fi;;. - is a block diagram of anotimr memplary wstern %Or_~ r, which rnethuds and wstems m~nsisteut with the present invention mau be imhlementeii. The _~.;tero -OCR
includes telephones 710A. 710B and 71 OC, switch 720. networks -: 0. 7-lU and 7 70.
~,atcwavs ?~0 and ; 60. switches 780 and ~ S~ and echo cancellers -90 and 79~.
The ~xemplaiy configuration illustrated in Fie. 7 is for simplicity. It should be understood that other devices may be included in system 700 in irnplwentatie~s consistent with the present invention.
(0069 The telephones 710A-C may include conventional telephones, such as those that interface with the PST:~r (not shown) to make and receive telephur,~ calls. In an exemplary implementation of the present invention, the connection between telephone 710A and switch 720 may be a hvo-wire analog circuit. Similarly, the respective connections between telephones 710B and 710C and networks 730 and 7-l0 may be two-wire analog circuits.
(0070] Switch 720 ma~~ represent a conventional switch. For evat:~ple, switches 7 ?0 may be a PBX located at a customer's premises or at a telephone service provid:r's premises.
In an exemplary implementation of the present invention, switch -'_'0 includes a hybrid circuit that converts a r\vo-wire circuit from telephone 710A into a four-wire circuit and vice versa. As discussed previously, these hybrid circuits may ca~~~e echo problems.
(0071( Gateway 7~0 may include a com~entional gateway used to ~onver-t input channels from a circuit switched nenvork into the format needed for a pacl:~t s~~~itched network.
such as network 770. In an exemplary implementation, gateway -~0 may include an cnterpri5c ~:atev,~ay that interfaces with a particular customer's equipment.
amh a; ;v, itch ?20, and may be located at the customer's premises. For ~.~ample, mlt~n 5u~itcf~ 7 ~0 is a customer PB\. enterprise ~,~ateway %>0 may be located at the customer':
hr~mises to interface "ith PB\ 720. a Iternativelw. gamvay 7s0 may be located rat a telephone servicz provider's central office.
J0072J Gateway 760 may include a network.gatevway. \ctvwork gateway %60 may be a conventional gateway used to interface with a class 3 (C3) switch, such as switch 780.
\~etwork gateway 760 may be located at the telephone service provider's central oftice.
[0073) Switches 780 and 78S may include com~entional class 3 switches used to perform various switching funeti~~ns for voice calls in a network. The connection b~m~een switches 780 and 785 may represent an inter-machine trunk (IMT).
[0074] \eOwork 770 may be a conventional packet switched network, such as an IP
network. Network 770 may include the Internet, an intranet, a V'AN, a LAN or a similar network that transmits data packets, such as IP data packets.
[0075) \'etworks 730 and 740 may include a circuit switched network, such as the PST\'.
\etworks 730 and 740 niay be associated with a local exchange carrier (LEC) and may include hybrid circuits that convert the 2-wire local loop circuits to 4-wire circuits and vice versa for interfacing with class 3 switches 780 and 785, respectively.
(0076] Echo cancellers 790 and 795 may each be conventional echo cancellers located on the 1\~tT between class 3 switches 780 and 785. Echo cancellers 790 and 795 may be used to cancel echo in the IMT bem~een class 3 switches 780 and 785.
)0077) In an exemplary lntple117tillallOn COnSlSlent Witll the (!I-~scl:l I!1\u IllIUll. a telephone service provider determines whether s~~stem %110 needs a>:ternal echo caricell~rs, in a similar manner as that described with respect to Fi~~. ~.
(0078) That is, the telephone service provider identities potential ~Lho source: system X00. .~s describe above. in system 700. the 2-wire to -1-~~ ire hyL~r;a cirmits included at switch 7?0 and LEC new~orks 730 alld 7:I0 are potential sources of echo caused by impedance mismatch. \Text, the telephone set~~ice provider determines whether the round trip delay introduced by any voice/echo path in system ; 00 is Ureater than a predetet~tnined threshold. For example. similar to the discussion above with respect to Fig. ~, in an exemplary implementation of the present invention. i' the round trip delay introduced by a particular voice; echo path is greater than or equal to 3~ ms.
then external echo cancellers may be needed.
[0079] Referring t~ Fig. 7, in an exemplary implementation, the telephone service provider checks whether the round trip delay time for a signal on voice,'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 travel from switch 720 to LEC 730 and echo back to :witch ~?~~ is 3~ ms or more.
external echo cancellers are needed on that path. If the round trip delay is loss than 3~
ms, no external echo cancellers are needed on voice/echo path D..,a.
[0080] Assume that the round trip delay on voice/echo path D.~B is greater than 35 ms. In this case, the telephone service provider determines the appropriate locations) for the external echo cancellers.
[0081 ] Fig. 8 is a block diagram of an exemplary system 500, con_istent with the present invention, which illustrates the inseation of external echo canceller: in system 700 to '' 0 COlllbat echo problems. Referring to Fig. ~, rcho cancell~r SIU may be located in ;yslm 800 bew~een switch 720 and gateway 7 ~0. Erho canceller 810 may then ranc~l crho associaud with a caller at telephone -l OB or -IUC. That i. echo canc~ll~r s lU nt;y cancel the echo caused by a retlection in the signal that o~cur~ at the hybrid eirmit as switch 720 and propagates back toward LEC 730 or LEC 7.~0. In an ewmplary implementation. echo canccller S 10 is preferably located near the sourm of the echo.
which in this case is switch 720.
[0082] Echo cancealer S20 may be located in system S00 bem~een class 3 switch 7S0 cnd 'ateway 760. Alternatively, echo canceller 820 may be located 111 Sy5te111 SOU
bewuen class 3 switch 780 and LEC 730. In either case, eC170 CallCellel' 820 may cancel echo associated with 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.
(0083] Referring back to Fig. 7, the telephone service provider may then determine whether system 700 includes any other voice; echo paths that do not include eternal echo cancellers. lrl system 700, however, each of the paths D,~,o and DBO 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 sen-ice 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 3~ ms. If any such paths existed, the telephone service provider would identify the appropriate locations) for the extzrnal echo cancellers on that voice path.
~008~J In this mannrr. stand-along cc110 canmllrrs SIO al.i ~~U .:Iw ~tr,m~_iu,tllv Imatcd to prevent echo i~rom reducing voice quality. In addition. 111 SIlU:1t10I1~ ~~
here om ur loth of th a >iatewavs 7~t) and 760 include integrated echo canrellers. tl~~se ime'~rated ec!so rancellers Itiav be disabled.
[008~J In an esemplatw implementation consistent with the pre~~:lt Invention.
echo cancellers 810 and 820 may be conventional devices. such as Qu::~i-Tl echo canceli~rs described previously or other conventional echo cancellers. Similar to the discussion with regard to Fig. 3, the external echo cancellers 810 and S20 .~r~ ~lorate~i ~.w~rnaiiy from the switches and gateways of system S00.
[00$6) In addition, similar to the previous discussion with regard to Fi«. ~, the stand-alone echo cancellers 810 and 820 are not controlled by any pal-ticular control logic executed by the switches or gateways of system 800, such as conventional Q.1 1 ~ echo control logic. Echo cancellers 810 and 820 are also not tied to working in conjunction with any particular echo control protocol, such as conventional Q.S~ echo control protocol, that may be included in the switches or gateways of system 500. In other words, echo cancellers 810 and S?0 operate independently from the switches and gateways in system 800. and may be used in any mixed PST''~tilP new~ork in which echo may be a problem.
[0087) Echo cancellers 810 and 820 may also introduce comfort noise onto the voice path between telephones 710A and 7108 to prevent a listener from perceiv°ina loss of connectivity with the other party. In addition, echo cancellers 810 and 820 may also be configured to support the tone disables function to allow system 800 to support vciceband data traffic.
[U08tiJ S~'pClll~ and mctltuds consistent witiv the present invention prw i~lc c~lo~ control for voice calls transmitted over both circuit switched ami pa~kct ;v.it~l~c~i nrw.~rk;. :1n adwanta«e of the invention is that the echo i:rlt;ccllers are indy,,_ndent of~lhc various devices in the networks and may be used in networks that operate in a~rordance with an..
protocol. .-W other advaata~~e of the inventio;t is that the echo cancell~rs may cancel objectionable echo a°hile introducing comfort noise into a voice path.
This results in more reliable and accurate conversations between parties and prevents parties from perceiving a loss of connectivity. A furthea advantage of the present invention is the aystem is tlexible and can be easily modified. That is. the echo cancellers may be easily inserted or removed from a voice path in which echo control is neeued or in which echo control is nu longer needed.
[0089) In this disclosure, there is shown and described only the preferred embodiments of the invention, but, as aforementioned, it is to be understood that the.invention is capable of use in variotas other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.
(0090) For example, the present invention has been described mainlw in relation to mixed network that includes the PSTN and an IP network. The present invention may also be used in other mined circuit switched/packet switched networks. For example, the present invention may be used in conjunction with a circuit switched network that includes an integrated sewices digital network (ISD~). The present invention may also be used in a non-mined network. such as a separate circuit switched network or a separate packet switched network.
~UU91] The present invr-ration has also been described as detenninin~~
whetl;er the round trip delay introduced h;,~ a voice; echo path is greater than a predeteumined ;:mount of time. such as 33 ms. In implementations consistent with this present invention.
conventional reflecto~;~~trv may he usi:d to measure the actual time associated with the round trip delay. In aitcmative in;pleinentations. the round trip delay may be estimated based on a distance. Fog example. if the dista:lce betlveen an echo source and a telephone or a switch located directly upstream of the telephone is a predetermined distance. such as 300 miles. the round trip delay introduced by such a voice-echo path may be estimated to be;3 ms or more. .~~ltemativelv. the measured distance rnav be the distance between ram telephones. i.e., a caliing pam~ and a called party. In systems with complex components. 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. In such systems. the predetermined distance may be less, such as 300 miles.
[0092] The present invention has also been described with examples of hybrid circuits that introduce echo in a voice call. It should be understood that other circuics!components n~av also introduce echo in a voice path or acoustic coupling betz~~een circuits/components may introduce Pcho. The present invention may advantageously be used in any network in which echo may occur.
[0093] The present invention has further been described with the example of echo cancellers being placed in systems based on a determination associated with the delay introduced by a voice!echo path. In implementations consistent with the present invention, 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. ~\-hen the dyamically measured delay in the voice~echo path is greater than a predetermined period.
such as ~~
ms. the external echo canceller may be activated. Similarly, when the dynamically measured delay in the yoice'echo path is less than ~~ ms. the external echo ca~~celler may !~e deactivated. The activation.%deactiyation may be accomplished usin~~
control circuitry in either or both the timing device and the external echo canceller to automatically acti~~ate'deactivate tl-:e echo canceller based on the measured delay. One of ordinan~ skill in the art v=.~ould be able to provide such comrol circuitw liven the guidance provided herein.
j009~J In addition. aspects of the present invention have been described as a series of acts in relation to Figs. 2 and 5. Jt should be understood that the order of these acts may vary in other implementations of the present invention.
(0095] Lastly; the round trip delay associated with a voice/echo path has been described as corresponding to the time associated v~ith 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. For example. in Fig. 1. the round trip delay may be the time associated with transmitting a signal from telephone 110 to s~~tch 140 and back to telephone 110. In other v-ords. the yoice!echo path rnav include the portion of the path labeled 112 in Fig. 1. In typical systems. the time associated with transmitting the signal from the caller.
(i.e.. telephone I l 0 in Fig. 1 ) to the switch located directly upstream of the caller (i.e..
switch 130 in Fig.l) is small compared to the time associated with transmitting the signal and receiving the echo over the remainder of the yoice!echo path (i.e.. voice/echo path D in Fig. 1 ).
~009GJ \o element. act or instt action used in the description of the present application :houid he construed as critical or essential to the invention unless explicitly described as such. .~)so. as used herein. the article "a" is intended to include one or more items.
v'h~re only one item is intended. the te:-m "one'' or similar lan~ua~e is used.
(00971 The scope of the invention is defined b~~ the claims and their equivalents.
(OOOS] Voice and voice-band traffic has traditionally L~e~n transport~.i by circuit switched nenworks, such a~ the public switched telephone nmwork (PST\). Tudav, an increasine amount of voice u~affic is carried over a combination of~ir~uit wwitched neavorks alld packet switched nenworks, such as Internet Protocol (IPj nm~~orks.
(U006] The PST\ typically uses both 2-wire circuits and rt-wire circuits for carrying full duplex voice traffic. The 2-wire circuits are typically used in the local loop portion of the PST's, such as the connection from the end user to a local switch or a local central office.
For example, a voice call from a typical telephone may be routed to ., switch over the PST\ as an analo'z signal on a standard two-wire circuit. .-\t the switch. a hybrid circuit may convert the ?-wire circuit connection to a 4-wire circuit connection. The switch may also forward the voice call to one or more conventional gateways that provide various services associated with transmitting information over an IP nehwork. For example, the ~atevway may convert analog voice signals in pulse code modulation (PC\t) format into packets for transmission over the IP nenwork. .At a second gateway. the packetized signal may be converted back to an analog signal. Another switch located in relative proximitw to the called pane m:lv include ~l hybrid circuit that converts :1 -l-wire ~
irmit to a. _'-w ire circuit for connection to tllr called party's l~:lephone.
~0007~ One problem with t! ansmittin~ ~,~oicc data in this manner is th;lt mho stay ucrur as a I'eslllt Of IIllped311Ce 1111~i11:11C17 ~tl lily 11', brt0 CIrCIIIIS, l.e..
llle pOllll ~~ ll~e llle ~-w 11'e circuits are converlwd to -t-wire circuits and vice versa. This echo is oaten perceivable by the hllillall ear and ultimately degrades the quality of the voice call.
Conventional gatewa}-s may include integrated echo cancellers to combat echo. That is, the gateways themselves perfoml echo cancellation.
(0008] One problem with gatwvays that include integrated echo cancellers is that they oaten do not support the tone disables function. The tone disables function reicrs to a 1 UO 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 with voiceband data traffic. Since the gateways do not support the tone disables function, voiceband data traffic cannot be supported over the network.
(0009] Another problem with gateways with integrated echo cancellers is they often fail to introduce "COIllt01't~~ noise alter echo cancellation has been perfonlled.
This results in the listener perceiving a loss of connectivity. In addition. the conventional gateways often do not adhere to the echo cancellation convergence criteria specified by the International Telecommunication Union (ITU) 6.168. As a result. the echo may be objectionable in voice calls made over an IP network.
[0010] SUW\iARI' OF THE I\'VE\T10\
(0011 ] There exists a need for systems and methods that improve problems associated with echo control in an IP network.
;0011) These and other needs arc ntet by the pre~.mt invention, where sUtnd-alone c~ho ~:,tncellcr; are strafe«icallv located to perform echo eancullation. By lomltin~ the echo ~,tnrcll~rs at particular !ovations, the echo problem ntay be eliminawd or substantially ~~c~iuced, tlterety, improvip~ the quality of \'OICe CaIlS 1r31151711t1~d over an IP nom ork.
;t1013J According to one aspect of the invention. a sysmm that includes a first echo ~anceller, a first gateway, a second v~atewav and a second echo cancell~r is provided. The first echo canceller is coupled to a first switch in a circuit switched network and is coati<aured to cancel echo associated with voice calls transmitted over a circuit switched nmvork and a packet switched network. The first gateway is coupled to the first echo canceller and is configured to forward a first voice call owr the packet switched 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 switch and is configured to cancel echo associated evith 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.
(0014( 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 fowarding 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 converts a wo-wire circuit to ~ four-wire circuit. T~I1C Illethod ,tl,o m~!tiiius tran~m:ttint~
the voii:c call over the lour-wire circuit to a first gateway. convertintT.
:~t the lirst '~~~teway.
tltc voice call to a format compatible ~.vith the packet switched nmvork, and transmutin~~
tl;e voice call over the packet switcl-~ed network to a second gateway. Tlte IllelhOd further incU.ides converting, at the second «atwvay, the voice call to a format compatible w ith a second circuit switched neavork and transmitting the voice call to a second switch included in the second circuit switched network. The second switch includes a hybrid .ciucuit that convents the four-wire circuit to a two-wire circuit. The method also includes forwarding 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 o1 the voice call using an echo canceller. The echo canccllen is located cxmrnally ti-om each of the first switch, the second switch. the first gateway and the second gateway alld is not controlled by any of the first switch, the second switch, the first gateway and the second gateway.
[OOI~J ~ccordina to a further aspect of the invention, a method for providing echo control in a system that routes voice calls over a circuit switched new~ork and a packet switched network is provided. The method 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 neW ~orks and receiving a retlected portion of the first signal at the first echo source is greater than or equal to 3~
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 voice path and receivine a reflected portion of the second signal at the mound cvho ;our~c is greater than or equal to 35 milliseconds. The method also includes inserting lirst anii aecond stand-alone echo eancellers on the voice path when the lint and second tinms are both Ur~atcr than or equal to 3~ milliseconds.
(0016] Other features and advantages of the present invention will become readily apparent to those skilled in this art from the following dmailed description.
The embodiments shown and described provide illustration of the best mode contemplated for aarryin~ out the invention. The invention is capable of modifications in various obvious raspects, all without departing from the invention. .Accordingly, the drawings are to be reUarded as illustrative in nature, and not as restrictive.
(U017] BRIEF DESCRIPT10?~ OF THE DRAB\'I\GS
[0018] Reference is made to the attached drawings, wherein elements having the same reference number designation may represent like elements throughout.
(0019] Fig. 1 is a block diagram of an exemplary system in which methods and systems consistent with the present invention may be implemented.
[0020] 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.
[0021] Fig. 3 is a block diagram of an exemplary system, consistent with the present invention, which illustrates the insertion of external echo cancellers in the system of Fib.
1.
J0022 J Fi'~. -1 i' a block dia~~ram ot~ another e~:rmplan w>tcm ~n w ill~Il nmllod> aml systems consistent with the present invention may be implemented.
[0023] Fig. ~ is an exemplary flow diagram. consistent with the present invention.
illustrating processing for determininU whether external echo c:~mellers are needed in the system~of Fig. ~.
(002] Fig. 6 is a block diagram of an exemplary system. consister;t with the present invention, which illustrates the insertion of external echo cancellers in the s~~snm of Fig.
[002] Fig. % is a block diagram of another exemplary system in which methods and systems consistent with the present invention may be Implemented.
[0026] Fig. 8 is a block diagram of an exemplan- system. consistent with the present invention, which illustrates the inset~tion of external echo cancellers in the system of Fig..
7.
[0027] DETAILED DESCRIPTIO\
[0028] Systems and methods consistent with the present invention avoid the problems associated the occurrence of echoes for a voice call transmitted over a mixed PST\; IP
network by providing echo.cancellers located externally from the various switches and gateways in the network. By strategically locating the echo cancellers, problems associated with echo may be avoided.
[0029] Fig. 1 is a block diagram of an exemplary system 100 in mhich methods and systems consistent with the present invention may be implemented. The system l00 includes telephones l 10 and 120, switches 130 and 1~0, gateways 1 ~0 and 160 and ncw~ork 1?0. The eacmplarv configuration illustrated in Fi~~. I is t~or sinnpli~iy. It should be understood that other devices may be included in system l0u in implementations consistent with the present invention.
[0030) The telephones 1 10 and 1 ?0 may include conventional tel~J,honcs. such a; tl~osc that interface with the PST\ (not showm) to place and r~ccive tel~phooc galls.
in an exetnplarv implementation of the present invention. the connection betvee;t telephone 1 10 and switch 130, labeled I 12 in Fig. 1, rnay be a two-wire analog circuit. Similarly, the connection between telephone 120 and switch 1=10, labeled 122 in Fi~~. 1.
Illa~~ be a two-wire analoe circuit.
[0031] Each of switches 130 and 140 may represent a conventional switch, 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 provider's premises. In an exemplary implementation of the present invention, the connection between switch 130 and gateway 150, labeled 1 14 in Fig. 1. may be a four-wire circuit.
In this implementation, the switch 130 includes a hybrid circuit that converts the two-wire circuit 1 12 from the telephone 1 10 into the four-wire circuit 1 1-1. as illusu~ated in Fig. I. The hybrid circuit in switch 130 similarly converts four-wire circuits from gateway 150 into two-wire circuits for routing the analog voice signals to telephone 1 10.
[0032) Switch 140 may similarly include a hybrid circuit that converts two-wire circuit.
labeled 122, to four-wire circuit 124, and vice versa, as illustrated in Fig.
1. As discussed previously, these two-wire to four=wire hybrid circuits at switches 130 and 1-10 may cause echo problems as a result of impedance mismatch.
[0033] Gatewa~.~; (G~~') I ~0 and I(s0 may inclu:lc ~_onvcntional ~~.ocwws umd to mnvrrt input channels tuom a circuit switched new~ork into the t~ormat n~Wed for a packet switched new~ork. such as new~ork 170. In an eaentplarv imple;mntatiort.
;_atewws I ~~.
and 150 may be enterprise ~~atewaw that imerface v,~ith .~ partiru::;r cuaomer' equipment. such as the respective switches 130 and 1-10. Gateways 1 ~0 alld I6U Illa~' be located at the customers premises. For eaampl~. ~.~ hen switches 1 30 and i W%
arc customer PBXs, enterprise g,atewavs 150 and 160 may be located at a customer's premises to interface with PBXs 130 and 140, respectively.
[0034] \'etwork 170 maybe a conventional packet switched newor',;, such as an nemork. \em~ork 170 may include the Internet, an intranet, a ~V.~\, a L ~,\ or a similar network that transmits data packets, such as IP data packets.
[003] In an exemplary implementation consistent with the present invention, a telephone service provider determines whether system I00 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.
[0036] 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 sen~ice provider identifying potential echo sources in the sen~ice provider's system (act 2101. For example, in system 100. the ?-wire to =I-wire hybrid circuits included at switches 130 and 110 are potential sources of echo caused by impedance mismatch. Therefore. in sv~tem 100, the telephonz sen~ice provider may identify switches 130 and 140 as potential echo sources.
a (0037] \ext, the telephone ser\.ice pro\ iWr iirtermines \\ Nether tl?~ round trip dcla~.
introduced by any \~oice;echo bath in sysmn 100 is greater than a prcdetcrmimd amount of time (art 2?0). For example. if the round trip delay introduced by the voice echo path between switches 130 and i-Iti. Inbeled D in Fi~~. I. ~s ~~r~ater than approvimatc:y ?~
milliseconds (ms), then ecl;o may be pcr~eivable by the 1?uman ear and tlla\' ultllll~itel_, reduce voice quality. In oti,er w ords, if the time it takes .~ signal to travel from sw itch 130 to switch 140 and reflect back (i.e., echo) to switch 130 takes more than 25 ms, then the quality of voice signals ~c:ceived via telephones 1 10 and 1?0 may be reduced due to the echo.
(0038) In an exemplary implementation of the present invention, : ~ ms has been set as the design criteria in \vhich echo tray be considered to be objectionable.
That is, if the round trip delay introduced by a voice/echo path is less than 35 ms, the echo may not be significant enough to be objectionable and external echo cancellers may not be needed (act 230). If, on the other hand, the round trip delay is 3~ ms or more, external echo cancellers may be needed (act ?=10). In this case, the telephone sewice provider determines the appropriate locations) for the external echo cancellers and inserts the echo cancellers at these locations (act 250).
[0039] Fig. 3 is a block diagram of an exemplary system 300, consistent with the present invention, which illustrates the insertion of external echo cancellers in system 100 to combat echo problems. Referring to Fig. 3, echo canceller 310 may be located in system 300 between switch 130 and gateway 1~0. Echo canceller 310 may then cancel echo associated with caller 120. That is, echo canceller 310 cancels the echo caused by a reflection in the signal that occurs at the hybrid circuit at switch 1.0 and propagates back toward s,vitch 1-I0. In an rvemplary imple111Cill;ltl011. CCIIO ~amcll~r 311.1 is pref~c;~ablv located as close to the source of thi: echo as possible, which in this example is the hybrid aircait at switch 1 30. Therefore, echo canceller 310 may be locamd near switch 1 ~0.
X00-IO[ Echo canceller 3'!O may be located in system 300 hmueen switch 140 anil ~~atewav 16;J. Echo canccller 3'0 may then cancel echo associated with caller 1 1U. That is, echo cat:celler 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. which in this case. is the hybrid circuit in switch 140. Therefore. echo canceller 320 may be iocatcd near switch 140.
[0041) In system 300., when a voice call is placed from telephone 1 10. it is transmitted to switch 130 over a hvo-wire analog circuit 1 12, converted at switch 130 into a four wire circuit and passed on through echo canceller 310 to gateway 150. It should be undet'stood that echo czncellers, 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 1 ~0 may packetize the voice call into an appropriate protocol for nec'ork 170 and forv.'ard the voice call over network 170. Gateway 160 receives the voice call and for'vards the voice call through echo canceller 320 to switch 140. It should be understood that switches l30 and 140 may be included in the same or different circuit switched neovorks. In either case, the voice call is converted back to a two-wire analoe circuit at switch 140 for transmission to telephone 120. ~t the same time the voice call is being forwarded through switch 140 to telephone 120. a portion of the voice call ma~~
reflect or echo back toward switch 130. Echo canceller 320 receives this echo and ..c'lnccls" the echo (i.e., prments the echo from beltlg tr;iI15111111C~1 baC6: uvcr the ~.~uii:e path to telephone 1 i O). In a similar manner, echo r~tnceilur 310 prevents the echo associated ~~~lth ;1 wOlCe Call made iron telephone I ~0 tiwm ecltoin« back to telephone i ~0.
[00-12J In this manner, stand-alone echo caocell~rs 310 and 3''0 are strategically lo~amd to prevent ei:ho ti~om reducing voice quality. In addition. in situations where one ur both of the gateways 150 and 160 include integrated echo cancellers, these integrated echo cancellers may be disabled.
J0043J In an exemplaw implementation consistent with the present invention.
echo cancellers 310 and 320 may be conventional devices, such as Quad-Tl echo canceliers manufactured by Ditech Communications Corporation. :Aternatively, other conventional echo cancellers may be used in implementations consistent with the present invention.
Details of the particular echo cancellers used are not described herein in order not to unduly obscure the thrust of the present invention. However, one of ordinary skill in the art would be able to select the particular echo canceller given the guidance disclosed herein.
(004=tJ In each case, however, echo cancellers 310 and 320 are located externally from the switches and gateways of system 300. For example, echo canceller 310 is coupled between switch 130 and gateway 150. Echo canceller 310, however, is located externally from these devices. Similarly, echo canceller 320 is located externally from switch 1:~0 and ~~atewav 160.
[OOa~J In addition, the stand-alone echo cancellers 310 and 320 are not controlled by either the switches or gateways of system 300. For example, echo canceller 310 is not controlled by anv particular control logic. ~urh a~ conventional Q.l I ~ c~ho control lo~~~i~.
bein« executed at switch 130, switch 1-J0: ~~:iieway 1 ~0 or r~atewav 160.
Echo canccilcr 310 is also not tied to w orkin~ in copunction with ativ particular protocol.
:mh .,~
conventioltai Q.~~ echo control protocol. ti;at may he included in switci~ i 3(i. sv iuh I-1(i.
gateway i s0 or gateway 160. In other words; echo canccller 310 operates imich~ndentlv From the switches and gateways in system 300 and may be used I11 any mixed PST\~1P
network ttl whlCh 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 working in conjunction with any particular control protocol.
[0046] Echo cancellers 310 and 320 may also introduce "comfort noise" onto the voice path between telephones 110 and 120. That is, echo cancellers 310 and 320 may introduce noise onto the voice path to prevent a listener from perceiving loss of connectivity with the other party. In addition, echo cancellers 3 I 0 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.
(0047] 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 -includes telephones -I1 OA, -I1 OB and 410C. switches 420, 430 and =1=J0, gateways ~s0 and 460, network =1?0, switches 180 and 485 and echo cancellers =190 atld 495. The exemplary configuration illustrated in Fly. =1 is for simplicity. It should be understood that other device: may be included in sysmm -fUU I11 1171p1~117~11t;t11011~
lonsistent w ith the present invention.
[004b[ The teiephon;a ~IIO.A-C may include come ntional ti:lephones, such as those that intert'acc with the PST\ (not showm to make and receive telephone ~:jlls. In an exemplary implementation of the present invention. the connection bmvren t~l~phone 410A and switch 420 may be a m~o-wire analog circuit. Similary. the respective connections bet'veen telephones 410B and 410C and switches 430 and 440 may be two-wire analog circuits.
[00-19J Each of switches =120, 430 and 4-10 may represent a conventional switch. For example, switches 420-4-~0 may be PB~s that are located at various customers' premises or at a telephone service provider's premises. In an exemplary implementation of the present invention, switches 420-440 each include hybrid circuits that convert nvo-wire circuits from telephones 410A-C into four wire circuits and vice versa. As discussed previously, these hybrid circuits may cause echo problems.
[0050] Gateway 450 may include a conventional gateway used to convert input channels from a circuit switched network into the format needed for a packet switched nom ork, such as network 470. In an exemplay implementation, Gateway 450 may include an enterprise gateway that interfaces with a particular customer's equipment, such, as switch 420, and may be located at the customer's premises. For example, when switch 420 is a customer PBX, enterprise 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.
~00~1J Gateway 460 rnay include a direct access line ID:~Lt '~amvay. :\ D:\L
;_amv,y may be a specialized gateway used to allow customers to copmunirate w ith ea:h other over a virtual private network (\-'P\ j.
~OU~2) Switches-DSO and 4Cj may include conventional class 3 (C3) switches n~mi to perform various switching functions for voice calls in a nemork. The connectir.n between switches 4S0 and 4S5 may represent an inter-machine trunk (I1~1'i~).
[0053] 'vetwork 470 may be a conventional packet switched network, such as an IP
network. \etwork 470 may include the Internet, an intranet, a 1\'A\. a L:~\ or a similar network that transmits data packets. such as IP data packms.
[0054] Echo cancellers 490 and 495 may each be conventional echo canceller~
loc;3ted gn the IMT between class 3 switches 480 and 485. Echo_ cancellers -490 and 495 may he used to cancel echo in the IMT between class 3 switches 480 and 455.
[0055] In an exemplary implementation consistent with the present invention. 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.
[0056] Fig. ~ 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-wire hybrid circuits included at switches 420, 430 and 4-10 are potential sources ~t~echo caused by impedance mismatch. l'heref~ore. in wmn -I~al.~. tlm tcl~phonc ~crvi~e provider may identify switches 420--l-I0 as potential erim sources.
(00;7J \cxt. the telephone service provider determine; wlmah~r the round trip W!a~.
introduced by any voice; echo bath in system -ICAO is vl'oaml' than a predm:rmlr~ed .
threshold. For example. similar to the discussion above w ith reahect to Fi~?.
~. in an memplary implementation of the present invention. if tllc round trip d~lav introdmed by a particular voice/echo path is 35 ms or more. then echo problems may ultimately reduce voice quality.
(0058) Referring to Fiy~. 4, in an exemplary implementation. the telephone service provider determines whether the round trip delay for a si«nal on voice.-echo path D..~e, for example, is greater than or equal to 35 1115 (act 520). That is, if the time it takes for a sienal 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 41 OB
will by degraded due to the echo.
[009] If the round trip delay is Jess than 35 ms, no external echo cancellers are needed on voice path D..~B (act 530). If, however, the round trip delay on path D.~B
is greater than or equal to 35 ms, external echo cancellers are needed (act 540j. In this case. the telephone service provider determines the appropriate locations) for the exteral echo cancellers and inserts the external echo cancellers at the desired locations (act ~50).
[0060) Fig. 6 is.a block diagram of an exemplary system 600, consistent with the present 111~~~I1L1011, which illustrates the insertion of exreral echo cancellers in system 400 to combat echo problems. Refen-ing to Fig. 6, echo canceller 610 may be located in system 600 beuveen switch 420 and gateway 450. Echo canceller 610 may then cancel echo associated with a caller at telephone ~ I OB. That is. echo vameller ~ ; CI
cancels the echo caused by a reflection.in the signal tli;lt occurs at the hybrid circuit at :witch X30 and propagates back toward switch=1~0. il. an memplary ilaplemcntatiol;. c~ho canccllcr 61U
is preferably located near the source ofthe ec(;o. which il this case _ switch -4'0.
[0061 ( Echo canceller 620 may be !ov:lted I11 S~ ~ICIII 61]0 between r';:~s 3 switch ~1y0 and ~atewav 460. Echo canccller 620 may then cancel echo asso,:iatrd ~.v ith a caller at telephone 410P,. That is, echo canceller 620 cancels the echo caused by a reflection in the signal that occurs at the hybrid circuit at switrh =13t) and propa~~aus back toward switch -120. In the exemplary configuration illustrated in Fig. 6. echo cancellcr 620 is located between aatewav -160 and class 3 switch :DSO. A!ternativel~.. mho cancrller 620 could be located between class 3 switch 4S0 and switch =130.
(0062] Referring back to Fig. 4, the telephone service provider may then identify whether system 400 includes any other voice/echo paths that do not include external echo cancellers (act 5601. In system 400, however, each of the paths D,;;~ and DBE
include external echo cancellers along the potential echo paths. For example. echo cancellers 190 and =19~ may cancel echo on the path between telephones =110I3 and -I 1 OC.
These echo cancellers 490 and 495 may similarly cancel echo associated with calls between telephones 410A and 410C. Alternatively, echo cancellers 610 and 6?0 (Fig. 6) may be used to cancel echo on voice calls between telepl2ones 410A and =110C. In either case. no additional external echo cancellers are needed.
(0063) If. however. additional paths existed in system 400 in which no ewernal echo cancellers are provided. processing returns to act 520 to determine whether the round trip delay on any identified voice/echo paths is 3~ ms or more. If any _ uch path existed. the telephone s~rvicc provider would dricrminc the appropri;ttc locationtsl for ihc eternal who cancellers to reduce the echo on this particular voice path.
(0060 In this manner, stand-alone echo cancell~rs 610 and 621_1 re str;3te'~icallv located to prevent echo prom reuocin~ voice qttalitv. In addition, in situ;aion~ where one or both of the gateways ~1~0 and -X60 ltlclude integrated echo canrellers. these imegrat~d ccl2o cancellers ma~.~ l~: disabled.
(0065) In an exemplary implementation consistent with the present invention, echo cancellers 610 and 620 may be conventional devices, such as (quad-T 1 echo cancellers described previoustv or other conventional echo cancellers. Similar to the discussion with regard to Fig. 3, the external echo canceliers 610 and 620 are located externally from the switches and gateways of system 600.
/0066) In addition, similar to the previous discussion with regard to Fig. 3, the stand-alone echo cancellers 6i0 and 620 are not controlled by any particular control logic executed by the switches or gateways of system 600, such as conventional Q. l 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 cam entional Q.s~ echo control protocol. that may be included in the switches or gateways of system 600. In other words, echo cancellers 610 and 620 operate independently from the switches and ~ateways in system 600 and may be used in any mixed PS'Ti'I,~IP network in which echo may be a problem.
(0067] Echo cancellers 610 and 620 may also introduce comfon noise onto the voice path benvzen telephones 410A and =I l OB to prevent a listener from perceiving toss of connectivity with the other party. In addition. echo cancellers 610 and 620 may also be ~unii~urc~i to support the tone disabler function. This allows swtm~ 600 to suppor~
vuiccband data traffic.
(OOGB( Fi;;. - is a block diagram of anotimr memplary wstern %Or_~ r, which rnethuds and wstems m~nsisteut with the present invention mau be imhlementeii. The _~.;tero -OCR
includes telephones 710A. 710B and 71 OC, switch 720. networks -: 0. 7-lU and 7 70.
~,atcwavs ?~0 and ; 60. switches 780 and ~ S~ and echo cancellers -90 and 79~.
The ~xemplaiy configuration illustrated in Fie. 7 is for simplicity. It should be understood that other devices may be included in system 700 in irnplwentatie~s consistent with the present invention.
(0069 The telephones 710A-C may include conventional telephones, such as those that interface with the PST:~r (not shown) to make and receive telephur,~ calls. In an exemplary implementation of the present invention, the connection between telephone 710A and switch 720 may be a hvo-wire analog circuit. Similarly, the respective connections between telephones 710B and 710C and networks 730 and 7-l0 may be two-wire analog circuits.
(0070] Switch 720 ma~~ represent a conventional switch. For evat:~ple, switches 7 ?0 may be a PBX located at a customer's premises or at a telephone service provid:r's premises.
In an exemplary implementation of the present invention, switch -'_'0 includes a hybrid circuit that converts a r\vo-wire circuit from telephone 710A into a four-wire circuit and vice versa. As discussed previously, these hybrid circuits may ca~~~e echo problems.
(0071( Gateway 7~0 may include a com~entional gateway used to ~onver-t input channels from a circuit switched nenvork into the format needed for a pacl:~t s~~~itched network.
such as network 770. In an exemplary implementation, gateway -~0 may include an cnterpri5c ~:atev,~ay that interfaces with a particular customer's equipment.
amh a; ;v, itch ?20, and may be located at the customer's premises. For ~.~ample, mlt~n 5u~itcf~ 7 ~0 is a customer PB\. enterprise ~,~ateway %>0 may be located at the customer':
hr~mises to interface "ith PB\ 720. a Iternativelw. gamvay 7s0 may be located rat a telephone servicz provider's central office.
J0072J Gateway 760 may include a network.gatevway. \ctvwork gateway %60 may be a conventional gateway used to interface with a class 3 (C3) switch, such as switch 780.
\~etwork gateway 760 may be located at the telephone service provider's central oftice.
[0073) Switches 780 and 78S may include com~entional class 3 switches used to perform various switching funeti~~ns for voice calls in a network. The connection b~m~een switches 780 and 785 may represent an inter-machine trunk (IMT).
[0074] \eOwork 770 may be a conventional packet switched network, such as an IP
network. Network 770 may include the Internet, an intranet, a V'AN, a LAN or a similar network that transmits data packets, such as IP data packets.
[0075) \'etworks 730 and 740 may include a circuit switched network, such as the PST\'.
\etworks 730 and 740 niay be associated with a local exchange carrier (LEC) and may include hybrid circuits that convert the 2-wire local loop circuits to 4-wire circuits and vice versa for interfacing with class 3 switches 780 and 785, respectively.
(0076] Echo cancellers 790 and 795 may each be conventional echo cancellers located on the 1\~tT between class 3 switches 780 and 785. Echo cancellers 790 and 795 may be used to cancel echo in the IMT bem~een class 3 switches 780 and 785.
)0077) In an exemplary lntple117tillallOn COnSlSlent Witll the (!I-~scl:l I!1\u IllIUll. a telephone service provider determines whether s~~stem %110 needs a>:ternal echo caricell~rs, in a similar manner as that described with respect to Fi~~. ~.
(0078) That is, the telephone service provider identities potential ~Lho source: system X00. .~s describe above. in system 700. the 2-wire to -1-~~ ire hyL~r;a cirmits included at switch 7?0 and LEC new~orks 730 alld 7:I0 are potential sources of echo caused by impedance mismatch. \Text, the telephone set~~ice provider determines whether the round trip delay introduced by any voice/echo path in system ; 00 is Ureater than a predetet~tnined threshold. For example. similar to the discussion above with respect to Fig. ~, in an exemplary implementation of the present invention. i' the round trip delay introduced by a particular voice; echo path is greater than or equal to 3~ ms.
then external echo cancellers may be needed.
[0079] Referring t~ Fig. 7, in an exemplary implementation, the telephone service provider checks whether the round trip delay time for a signal on voice,'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 travel from switch 720 to LEC 730 and echo back to :witch ~?~~ is 3~ ms or more.
external echo cancellers are needed on that path. If the round trip delay is loss than 3~
ms, no external echo cancellers are needed on voice/echo path D..,a.
[0080] Assume that the round trip delay on voice/echo path D.~B is greater than 35 ms. In this case, the telephone service provider determines the appropriate locations) for the external echo cancellers.
[0081 ] Fig. 8 is a block diagram of an exemplary system 500, con_istent with the present invention, which illustrates the inseation of external echo canceller: in system 700 to '' 0 COlllbat echo problems. Referring to Fig. ~, rcho cancell~r SIU may be located in ;yslm 800 bew~een switch 720 and gateway 7 ~0. Erho canceller 810 may then ranc~l crho associaud with a caller at telephone -l OB or -IUC. That i. echo canc~ll~r s lU nt;y cancel the echo caused by a retlection in the signal that o~cur~ at the hybrid eirmit as switch 720 and propagates back toward LEC 730 or LEC 7.~0. In an ewmplary implementation. echo canccller S 10 is preferably located near the sourm of the echo.
which in this case is switch 720.
[0082] Echo cancealer S20 may be located in system S00 bem~een class 3 switch 7S0 cnd 'ateway 760. Alternatively, echo canceller 820 may be located 111 Sy5te111 SOU
bewuen class 3 switch 780 and LEC 730. In either case, eC170 CallCellel' 820 may cancel echo associated with 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.
(0083] Referring back to Fig. 7, the telephone service provider may then determine whether system 700 includes any other voice; echo paths that do not include eternal echo cancellers. lrl system 700, however, each of the paths D,~,o and DBO 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 sen-ice 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 3~ ms. If any such paths existed, the telephone service provider would identify the appropriate locations) for the extzrnal echo cancellers on that voice path.
~008~J In this mannrr. stand-along cc110 canmllrrs SIO al.i ~~U .:Iw ~tr,m~_iu,tllv Imatcd to prevent echo i~rom reducing voice quality. In addition. 111 SIlU:1t10I1~ ~~
here om ur loth of th a >iatewavs 7~t) and 760 include integrated echo canrellers. tl~~se ime'~rated ec!so rancellers Itiav be disabled.
[008~J In an esemplatw implementation consistent with the pre~~:lt Invention.
echo cancellers 810 and 820 may be conventional devices. such as Qu::~i-Tl echo canceli~rs described previously or other conventional echo cancellers. Similar to the discussion with regard to Fig. 3, the external echo cancellers 810 and S20 .~r~ ~lorate~i ~.w~rnaiiy from the switches and gateways of system S00.
[00$6) In addition, similar to the previous discussion with regard to Fi«. ~, the stand-alone echo cancellers 810 and 820 are not controlled by any pal-ticular control logic executed by the switches or gateways of system 800, such as conventional Q.1 1 ~ echo control logic. Echo cancellers 810 and 820 are also not tied to working in conjunction with any particular echo control protocol, such as conventional Q.S~ echo control protocol, that may be included in the switches or gateways of system 500. In other words, echo cancellers 810 and S?0 operate independently from the switches and gateways in system 800. and may be used in any mixed PST''~tilP new~ork in which echo may be a problem.
[0087) Echo cancellers 810 and 820 may also introduce comfort noise onto the voice path between telephones 710A and 7108 to prevent a listener from perceiv°ina loss of connectivity with the other party. In addition, echo cancellers 810 and 820 may also be configured to support the tone disables function to allow system 800 to support vciceband data traffic.
[U08tiJ S~'pClll~ and mctltuds consistent witiv the present invention prw i~lc c~lo~ control for voice calls transmitted over both circuit switched ami pa~kct ;v.it~l~c~i nrw.~rk;. :1n adwanta«e of the invention is that the echo i:rlt;ccllers are indy,,_ndent of~lhc various devices in the networks and may be used in networks that operate in a~rordance with an..
protocol. .-W other advaata~~e of the inventio;t is that the echo cancell~rs may cancel objectionable echo a°hile introducing comfort noise into a voice path.
This results in more reliable and accurate conversations between parties and prevents parties from perceiving a loss of connectivity. A furthea advantage of the present invention is the aystem is tlexible and can be easily modified. That is. the echo cancellers may be easily inserted or removed from a voice path in which echo control is neeued or in which echo control is nu longer needed.
[0089) In this disclosure, there is shown and described only the preferred embodiments of the invention, but, as aforementioned, it is to be understood that the.invention is capable of use in variotas other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.
(0090) For example, the present invention has been described mainlw in relation to mixed network that includes the PSTN and an IP network. The present invention may also be used in other mined circuit switched/packet switched networks. For example, the present invention may be used in conjunction with a circuit switched network that includes an integrated sewices digital network (ISD~). The present invention may also be used in a non-mined network. such as a separate circuit switched network or a separate packet switched network.
~UU91] The present invr-ration has also been described as detenninin~~
whetl;er the round trip delay introduced h;,~ a voice; echo path is greater than a predeteumined ;:mount of time. such as 33 ms. In implementations consistent with this present invention.
conventional reflecto~;~~trv may he usi:d to measure the actual time associated with the round trip delay. In aitcmative in;pleinentations. the round trip delay may be estimated based on a distance. Fog example. if the dista:lce betlveen an echo source and a telephone or a switch located directly upstream of the telephone is a predetermined distance. such as 300 miles. the round trip delay introduced by such a voice-echo path may be estimated to be;3 ms or more. .~~ltemativelv. the measured distance rnav be the distance between ram telephones. i.e., a caliing pam~ and a called party. In systems with complex components. 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. In such systems. the predetermined distance may be less, such as 300 miles.
[0092] The present invention has also been described with examples of hybrid circuits that introduce echo in a voice call. It should be understood that other circuics!components n~av also introduce echo in a voice path or acoustic coupling betz~~een circuits/components may introduce Pcho. The present invention may advantageously be used in any network in which echo may occur.
[0093] The present invention has further been described with the example of echo cancellers being placed in systems based on a determination associated with the delay introduced by a voice!echo path. In implementations consistent with the present invention, 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. ~\-hen the dyamically measured delay in the voice~echo path is greater than a predetermined period.
such as ~~
ms. the external echo canceller may be activated. Similarly, when the dynamically measured delay in the yoice'echo path is less than ~~ ms. the external echo ca~~celler may !~e deactivated. The activation.%deactiyation may be accomplished usin~~
control circuitry in either or both the timing device and the external echo canceller to automatically acti~~ate'deactivate tl-:e echo canceller based on the measured delay. One of ordinan~ skill in the art v=.~ould be able to provide such comrol circuitw liven the guidance provided herein.
j009~J In addition. aspects of the present invention have been described as a series of acts in relation to Figs. 2 and 5. Jt should be understood that the order of these acts may vary in other implementations of the present invention.
(0095] Lastly; the round trip delay associated with a voice/echo path has been described as corresponding to the time associated v~ith 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. For example. in Fig. 1. the round trip delay may be the time associated with transmitting a signal from telephone 110 to s~~tch 140 and back to telephone 110. In other v-ords. the yoice!echo path rnav include the portion of the path labeled 112 in Fig. 1. In typical systems. the time associated with transmitting the signal from the caller.
(i.e.. telephone I l 0 in Fig. 1 ) to the switch located directly upstream of the caller (i.e..
switch 130 in Fig.l) is small compared to the time associated with transmitting the signal and receiving the echo over the remainder of the yoice!echo path (i.e.. voice/echo path D in Fig. 1 ).
~009GJ \o element. act or instt action used in the description of the present application :houid he construed as critical or essential to the invention unless explicitly described as such. .~)so. as used herein. the article "a" is intended to include one or more items.
v'h~re only one item is intended. the te:-m "one'' or similar lan~ua~e is used.
(00971 The scope of the invention is defined b~~ the claims and their equivalents.
Claims (31)
1. A system. comprising:
a first echo canceller configured to cancel echo associated with voice calls transmitted over a circuit switched network and a packet switched network, the first echo canceller being coupled to a first switch in the circuit switched network:
a first gateway coupled to the first echo canceller, the first gateway configured to forward a first voice call over the packet switched network:
a second gateway coupled to the first gateway via the packet switched network, the second gateway being 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; and a second echo canceller coupled to the second gateway and the second switch, the second echo canceller being configured to cancel echo associated with voice calls transmitted over the circuit switched network and the packet switched network, wherein 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.
a first echo canceller configured to cancel echo associated with voice calls transmitted over a circuit switched network and a packet switched network, the first echo canceller being coupled to a first switch in the circuit switched network:
a first gateway coupled to the first echo canceller, the first gateway configured to forward a first voice call over the packet switched network:
a second gateway coupled to the first gateway via the packet switched network, the second gateway being 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; and a second echo canceller coupled to the second gateway and the second switch, the second echo canceller being configured to cancel echo associated with voice calls transmitted over the circuit switched network and the packet switched network, wherein 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.
2. The system of claim 1, wherein the time associated with transmitting the first voice signal comprises the time associated with transmitting the first voice signal from the first switch to the second switch and receiving a reflection of the first voice signal at the first switch.
3. The system of claim 2, wherein the predetermined threshold is 35 milliseconds.
4. The system of claim 1, wherein the first echo canceller is configured to cancel echo associated with a voice call that propagates from the second switch to the first switch and reflects back to the second switch when a time associated with transmitting a second voice signal from the second switch to the first switch and receiving a reflection of the second voice signal at the second switch is greater than or equal to 35 milliseconds.
5. The system of claim 1, wherein both of the first and second echo cancellers are configured to operate independently from each of the first switch, the second switch, the first gateway and the second gateway.
6. The system of claim 5, wherein both of the first and second echo cancellers are located externally from the respective first and second gateways and the first and second switches.
7. The system of claim 1, wherein the first and second gateways include integrated echo cancellers, the integrated echo cancellers being configured in a non-active or disabled mode.
8. The system of claim 1, wherein the first switch comprises a first private branch exchange and the first gateway is located at a customer's premises, the first gateway being configured to interface with the first private branch exchange and convert voice calls from the first private branch exchange into a format compatible with the packet switched network.
9. The system of claim 8, wherein the second switch comprise a second private branch exchange and the second gateway is located at a customer's premises the second gateway being configured to interface with the second private branch exchange and convert voice calls from the second private branch exchange into a format compatible with the packet switched network.
10. The system of claim 8, wherein the second gateway is located at a telephone service provider's central office and comprises a direct access line gateway that is coupled to a class 3 switch.
11. The system of claim 8, wherein the second gateway is located at a telephone service provider's central office and comprises a network gateway that is coupled to a class 3 switch.
12. A method for cancelling echo in a voice call from a first party to a second party, the voice call being routed from the first party to the second party over circuit switched and packet switched networks. the method comprising:
forwarding the voice call from the first party to a first switch included in a first circuit switched network, the first switch including a hybrid circuit that converts a two-wire circuit from the first switch to a four-wire circuit:
transmitting the voice call over the four-wire circuit to a first gateway:
converting, at the first gateway, the voice call to a format compatible with the packet switched network:
transmitting the voice call over the packet switched network to a second gateway:
converting, at the second gateway, the voice call to a format compatible with a second circuit switched network;
transmitting the voice call to a second switch included in the second circuit switched network, the second switch including a hybrid circuit that converts the four-wire circuit to a two-wire circuit;
forwarding the voice call to the second party, wherein a portion of the voice call reflects from the second switch toward the first party; and cancelling the reflected portion of the voice call using an echo canceller that is located externally from each of the first switch, the second switch, the first gateway and the second gateway and wherein the echo canceller is not controlled by any of the first switch, the second switch, the first gateway and the second gateway.
forwarding the voice call from the first party to a first switch included in a first circuit switched network, the first switch including a hybrid circuit that converts a two-wire circuit from the first switch to a four-wire circuit:
transmitting the voice call over the four-wire circuit to a first gateway:
converting, at the first gateway, the voice call to a format compatible with the packet switched network:
transmitting the voice call over the packet switched network to a second gateway:
converting, at the second gateway, the voice call to a format compatible with a second circuit switched network;
transmitting the voice call to a second switch included in the second circuit switched network, the second switch including a hybrid circuit that converts the four-wire circuit to a two-wire circuit;
forwarding the voice call to the second party, wherein a portion of the voice call reflects from the second switch toward the first party; and cancelling the reflected portion of the voice call using an echo canceller that is located externally from each of the first switch, the second switch, the first gateway and the second gateway and wherein the echo canceller is not controlled by any of the first switch, the second switch, the first gateway and the second gateway.
13. The method of claim 12, further comprising:
determining whether a time associated with transmitting a voice signal from the first switch to the second switch and receiving a reflected portion of the voice signal at the first switch is greater than or equal to a predetermined threshold.
determining whether a time associated with transmitting a voice signal from the first switch to the second switch and receiving a reflected portion of the voice signal at the first switch is greater than or equal to a predetermined threshold.
14. The method of claim 13, wherein the predetermined thereshold is 35 milliseconds.
15. The method of claim 13, wherein the determining comprises estimating the time based on at least one of a distance between the first and second switches and a distance between the first and second parties.
16. The method of claim 12, further comprising:
introducing noise, by the echo canceller, to a voice path between the first party and the second party.
introducing noise, by the echo canceller, to a voice path between the first party and the second party.
17. The method of claim 12, wherein the first and second gateways include integrated echo cancellers, the method further comprising:
disabling the integrated echo cancellers in the first and second gateways.
disabling the integrated echo cancellers in the first and second gateways.
18. The method of claim 12, wherein the first switch comprises a first private branch exchange and the first gateway is located at a customer's premises and interfaces with the first private branch exchange.
19. The method of claim 18, wherein the second switch comprises a second private branch exchange and the second gateway is located at a customer's premises and interfaces with the second private branch exchange.
20. The method of claim 18. wherein the second gateway is located at a telephone service provider's central office and comprises a direct access line gateway that is coupled to a class 3 switch.
21. The method of claim 18, wherein the second gateway is located at a telephone service provider's central office and comprises a network gateway that is coupled to a class 3 switch.
22. The method of claim 12. further comprising:
dynamically determining a time associated with transmitting the voice call from the first switch to the second switch and receiving the reflected portion of the voice call at the first switch;
automatically activating the echo canceller when the time is greater than or equal to a predetermined threshold; and automatically deactivating the echo canceller when the time is less than the predetermined threshold.
dynamically determining a time associated with transmitting the voice call from the first switch to the second switch and receiving the reflected portion of the voice call at the first switch;
automatically activating the echo canceller when the time is greater than or equal to a predetermined threshold; and automatically deactivating the echo canceller when the time is less than the predetermined threshold.
23. In a system that routes voice calls over a circuit switched network and a packet switched network, a method for providing echo control, comprising:
identifying a plurality of echo sources in the system:
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;
determining whether a second time associated with transmitting a second signal from a second one of the echo sources over the voice path and receiving a reflected portion of the second signal at the second echo source is greater than or equal to 35 millisecond; and inserting first and second stand-alone echo cancellers on the voice path when the first and second times are both greater than or equal to 35 milliseconds.
identifying a plurality of echo sources in the system:
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;
determining whether a second time associated with transmitting a second signal from a second one of the echo sources over the voice path and receiving a reflected portion of the second signal at the second echo source is greater than or equal to 35 millisecond; and inserting first and second stand-alone echo cancellers on the voice path when the first and second times are both greater than or equal to 35 milliseconds.
24. The method of claim 23. wherein the circuit switched network comprises a first switch and the packet switched network comprises a first gateway and the inserting includes:
coupling the first echo canceller behveen the first switch and the first gateway, and configuring the first echo canceller to operate without external control from either the first switch or the first gateway.
coupling the first echo canceller behveen the first switch and the first gateway, and configuring the first echo canceller to operate without external control from either the first switch or the first gateway.
25. The method of claim 24, wherein the circuit switched network comprises a second switch and the packet switched network comprises a second gateway. and the inserting includes:
coupling the second echo canceller between the second gateway and the second switch and configuring the second echo canceller to operate without external control from either the second switch or the second gateway.
coupling the second echo canceller between the second gateway and the second switch and configuring the second echo canceller to operate without external control from either the second switch or the second gateway.
26. The method of claim 25, the second echo canceller is configured to cancel echo from a first party to a second party and the first echo canceller is configured to cancel echo from the second party to the first party.
27. The method of claim 23, wherein the packet switched network comprises a plurality of gateways, the method further comprising:
disabling integrated echo cancellers associated with the respective plurality of gateways.
disabling integrated echo cancellers associated with the respective plurality of gateways.
28. A system, comprising:
circuit switching means for transmitting a voice call over a circuit switched network:
packet switching means coupled to the circuit switching means for transmitting the voice call over a packet switched network; and echo cancellation means for cancelling echo on a voice path between a first party and a second party, the voice path including a portion of the circuit switched network and the packet switched network, wherein the echo cancellation means is located externally from the circuit switching means and the packet switching means and is not controlled by either the circuit or packet switching means.
circuit switching means for transmitting a voice call over a circuit switched network:
packet switching means coupled to the circuit switching means for transmitting the voice call over a packet switched network; and echo cancellation means for cancelling echo on a voice path between a first party and a second party, the voice path including a portion of the circuit switched network and the packet switched network, wherein the echo cancellation means is located externally from the circuit switching means and the packet switching means and is not controlled by either the circuit or packet switching means.
29. The system of claim 28, further comprising:
determining means for dynamically determining a time associated with transmitting a voice signal on the voice path and receiving a reflection of the voice signal: and means for activating and deactivating the echo cancellation means based on the dynamically determined time.
determining means for dynamically determining a time associated with transmitting a voice signal on the voice path and receiving a reflection of the voice signal: and means for activating and deactivating the echo cancellation means based on the dynamically determined time.
30. The system of claim 28, wherein the echo cancellation means comprises means for disabling the echo cancellation means when a tone having a predetermined frequency is received.
31. The system of claim 30, wherein the tone corresponds to a tone from a data modem.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1687401A | 2001-12-14 | 2001-12-14 | |
| US10/016,874 | 2001-12-14 | ||
| PCT/US2002/037825 WO2003052959A1 (en) | 2001-12-14 | 2002-11-25 | Systems and methods for providing echo control |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2470097A1 true CA2470097A1 (en) | 2003-06-26 |
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ID=21779467
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002470097A Abandoned CA2470097A1 (en) | 2001-12-14 | 2002-11-25 | Systems and methods for providing echo control |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1464123A1 (en) |
| AU (1) | AU2002359480A1 (en) |
| CA (1) | CA2470097A1 (en) |
| WO (1) | WO2003052959A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US7525918B2 (en) * | 2003-01-21 | 2009-04-28 | Broadcom Corporation | Using RTCP statistics for media system control |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6768796B2 (en) * | 2001-02-05 | 2004-07-27 | 3Com Corporation | System and method for echo cancellation |
-
2002
- 2002-11-25 CA CA002470097A patent/CA2470097A1/en not_active Abandoned
- 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 EP EP02794022A patent/EP1464123A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP1464123A1 (en) | 2004-10-06 |
| AU2002359480A1 (en) | 2003-06-30 |
| WO2003052959A1 (en) | 2003-06-26 |
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| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |