Patent Publication Number: US-2013242858-A1

Title: Method and apparatus for wideband and super-wideband telephony

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     BACKGROUND 
     The disclosed subject matter relates generally to wideband telephony and, more particularly, to a method and apparatus for wideband and super-wideband telephony. 
     Analog telephones have evolved since their inception in the late 1800&#39;s and offer enhanced capabilities such as DTMF dialing, speed dialing, speakerphone, Caller ID, etc. However, the audio range that is supported by such telephones has remained limited to about 3.4 kHz, the bandwidth of the traditional public switched telephone network (PSTN). The PSTN was originally designed as an analog circuit-switched network and the frequency band that was available to the subscriber&#39;s voice calls was set from 300 Hz to 3.4 kHz. 
     The PSTN has evolved over the years and is now almost entirely digital in its core. However, the basic plain old telephone service (POTS) has remained analog with an audio bandwidth of about 3.4 kHz, even on short loops that are capable of carrying very high frequencies such as those used by DSL modems. The main reason and benefit for making this limitation is compatibility. New and old analog telephones alike can operate on POTS service offered by modern digital central offices as well as older systems, such as electromechanical ones, that may still be used in some rural areas. Today, there are over one billion analog telephones in use around the world for POTS service. 
     The rapid growth of broadband technology has given rise to voice over Internet Protocol (VoIP) services, which use an IP network such as the Internet for placing and transporting the calls. In the early days of VoIP, customers bought an Analog Telephone Adapter (ATA) and connected their home analog telephones to it. The ATA provides an analog telephone line with similar electrical characteristics and signaling as a PSTN line and performs the conversion between the analog signals from the connected telephone and the VoIP servers. Standalone ATAs are giving way to more integrated “gateways” that offer additional functions such as a broadband modem or a wired and/or wireless router. One example gateway is a Motorola Netopia 2247-42, which combines an ADSL2+ modem with a 4-port Ethernet switch and router, a WiFi router, and two analog telephone voice ports, also known as FXS (or Foreign eXchange Station), for VoIP calling. 
     VoIP ATAs and gateways feature FXS circuits which can offer the same signaling characteristics found on the POTS service from a PSTN. This includes limiting the audio channel to 3.4 kHz (or Narrowband). Newer FXS circuits, such as those based on the Microsemi VE8910 series, can also support wideband (WB) telephony with a 7 kHz bandwidth. Future FXS chipsets can expand the audio bandwidth to 12 kHz or more, effectively making them super-wideband (SWB) capable. Various studies have shown that expanding the bandwidth of telephone calls can enhance the voice quality and allow subscribers to distinguish confusing sounds, better understand accented speakers, decipher words that have close sounds such as ‘s’ and ‘f’, and reduce listening fatigue. These benefits improve the customer experience and can result in increased use of the telephone service. Higher audio bandwidth will also make speech recognition more accurate in interactive voice response systems. 
     Many ATAs and gateways feature FXS chipsets and circuitry that can readily support wideband telephony as a software option with no hardware modifications. VoIP standards and many service providers support 7 kHz wideband audio based on coder-decoders (CODECS) such as G.722 and will soon support super-wideband CODECS such as G.722.1 Annex C (or G.722.1C) for 14 kHz telephony. However, since VoIP ATAs and gateways are designed for compatibility with the large installed base of narrowband (NB) analog telephones and due to compatibility issues, the FXS ports on such devices are usually configured for narrowband-only operation. Connecting narrowband telephones or modems and fax machines to wideband FXS ports can cause compatibility issues. For example, narrowband telephones can “hear” wideband noise if no real wideband audio content is present. Modems and fax machines can have degraded performance when connected to wideband FXS ports. Another problem is that the ATA or gateway does not readily know if an analog telephone connected to it is wideband capable. Reserving higher bandwidth on the VoIP link at all times when only a small fraction of telephones may actually be wideband capable is not economical. 
     For these reasons, the FXS ports on VoIPs ATA and gateways are normally set to narrowband. Telephone equipment manufacturers have shied away from making wideband analog telephones since they could not be used on the PSTN and since VoIP ATA and gateways do not currently support wideband. Wideband VoIP service today is limited to IP Phones and PC-based soft clients. Users of such services have enjoyed the increased voice quality and some VoIP service providers have recently started offering super-wideband service for even greater clarity. 
     This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
     BRIEF SUMMARY 
     The following presents a simplified summary of the disclosed subject matter in order to provide a basic understanding of some aspects of the disclosed subject matter. This summary is not an exhaustive overview of the disclosed subject matter. It is not intended to identify key or critical elements of the disclosed subject matter or to delineate the scope of the disclosed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. 
     One aspect of the disclosed subject matter is seen in a gateway that includes at least one network interface, at least one analog telephony interface, and a processing unit operable to receive a bandwidth signal over the at least one analog telephony interface from a telephony device and configure an audio bandwidth of a telephony connection for the telephony device over the at least one network interface based on the bandwidth signal. 
     Another aspect of the disclosed subject matter is seen in a telephony device that includes a speaker, an interface for coupling to an analog telephone line, a signal detector operable to receive a bandwidth alert signal over the interface, a signal generator operable to send a bandwidth acknowledgement signal over the interface indicating a bandwidth capability of the telephony device, and a processor operable to receive an analog voice signal over the interface having an audio bandwidth corresponding to the bandwidth capability and transmit the analog voice signal to the speaker. 
     Yet another aspect of the present subject matter is seen in a method for configuring a telephony device. The method includes receiving a bandwidth alert signal, generating a bandwidth acknowledgement signal indicating a bandwidth capability of the telephony device, receiving an analog voice signal having an audio bandwidth corresponding to the bandwidth capability, and transmitting the analog voice signal to a speaker of the telephony device. 
     One of a plurality of filters may be selected for use by the telephony device based on the bandwidth capability. Each of the plurality of filters has a different bandwidth. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The disclosed subject matter will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a simplified block diagram of a gateway for providing telephony services and negotiating call bandwidth in accordance with an illustrative embodiment of the present subject matter; 
         FIG. 2  is a diagram of an exemplary software architecture employed by the gateway of  FIG. 1 ; 
         FIG. 3  is a diagram illustrating typical bandwidth ranges associated with narrowband, wideband, and super-wideband telephony services; 
         FIG. 4  is a simplified block diagram of an exemplary wideband telephony device; 
         FIG. 5  is a simplified block diagram of an exemplary wideband cordless telephone base station telephony device; 
         FIG. 6  is a flow diagram illustrating the operation of the gateway of  FIG. 1  for detecting the bandwidth capabilities of the interfacing telephony device for an outgoing call sequence; 
         FIG. 7  is a flow diagram illustrating the operation of the gateway of  FIG. 1  for detecting the bandwidth capabilities of the interfacing telephony device for an incoming call sequence; 
         FIG. 8  is a flow diagram illustrating the operation of a telephony device for communicating its bandwidth capabilities to the gateway of  FIG. 1  for an incoming or outgoing call sequence; 
         FIG. 9  is a diagram of an exemplary bass boost equalization profile that may be employed by the gateway of  FIG. 1 ; and 
         FIG. 10  is a diagram of exemplary high frequency equalization profiles for different bandwidths and line lengths that may be employed based on measurements of received levels of test tones by the gateway of  FIG. 1 . 
     
    
    
     While the disclosed subject matter is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the disclosed subject matter to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosed subject matter as defined by the appended claims. 
     DETAILED DESCRIPTION 
     One or more specific embodiments of the disclosed subject matter will be described below. It is specifically intended that the disclosed subject matter not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the disclosed subject matter unless explicitly indicated as being “critical” or “essential.” 
     The disclosed subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the disclosed subject matter with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the disclosed subject matter. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. 
     Referring now to the drawings wherein like reference numbers correspond to similar components throughout the several views and, specifically, referring to  FIG. 1 , the disclosed subject matter shall be described in the context of a gateway  100 . The gateway  100  includes a one or more network interfaces  102  (e.g., wide area network interfaces) for communicating with an IP network and one or more analog telephony interfaces  103  for communicating with telephony devices  104 . The gateway  100  may also include one or more local network interfaces  105  (local area network interfaces) that may provide local data access or telephony access through IP telephony devices  106 . Exemplary network interfaces  102  include an RJ-11 port  102   a  (e.g., a DSL and/or PSTN), an RJ-45 port  102   b  (e.g., Ethernet WAN port), a coaxial cable port  102   c , an optical fiber port  102   d , and a mobile station antenna  102   e  (e.g., a 3G or 4G antenna). 
     Exemplary analog telephony interfaces  103  include a femtocell antenna  103   a  (e.g., short range cellular antenna) for interfacing with a mobile telephone  104   a , a cordless base station antenna  103   b  for interfacing with a cordless telephone  104   b , an RJ-45 ISDN port  103   c  for interfacing with an ISDN telephone  104   c , or an RJ-11 port  103   d  for interfacing with an analog telephone  104   d . Exemplary local network interfaces  105  include a WiFi antenna  105   a  (e.g., 802.11x) for interfacing with a WiFi telephone  106   a , an RJ-45 port  105   b  (e.g., Ethernet LAN port) for interfacing with an IP telephone  106   b , an RJ-45 port  105   c  for interfacing with a personal computer  106   c  (i.e., equipped with headset or a microphone and speakers). 
     The particular number and type of network interfaces  102 , analog telephony interfaces  103 , telephony devices  104 , local network interfaces  105 , and/or IP telephony devices  106  may vary depending on the particular implementation. Interface types other than those illustrated in  FIG. 1  may be employed. Also, not all of the interface types may be present in an actual implementation. For example, if the provider for the gateway  100  is a cable operator, it may only have the coaxial cable port  102   c  as its network interface  102 . The gateway  100  may provide both telephony services through a telephony connection and parallel network services through a data connection. For example, the WiFi antenna  105   a  and/or the RJ-45 ports  105   b ,  105   c  may provide general network connectivity. The gateway  100  may thus serve as a router, access point, etc. The particular analog telephony interface  103  used to connect to a telephony device  104  may differ from the interface  105  used to provide general network connectivity. 
     The gateway  100  includes a processing unit  110  (e.g., a microprocessor, system-on-chip (SoC), digital signal processor, or combinations thereof), non-volatile memory  112  (e.g., flash) and/or volatile memory  114  (e.g., synchronous or dynamic random access memory). One or more power regulators  116  may be provided for generating power supplies at various voltages for the components of the gateway  100 , and one or more oscillators  118  may be provided for generating clock or synchronization signals for the components. 
     The gateway  100  includes physical layer (PHY) and/or media access control (MAC) hardware for supporting communication over the various network interfaces  102  and analog telephony interfaces  103 . In general, hardware and/or software for supporting these functions is known to those of ordinary skill in the art, and they are not described in greater detail herein for sake of clarity and to avoid obscuring the present subject matter. 
     A DSL interface  120  (e.g., analog front end and modem) and digital access arrangement (DAA)  122  interface through the RJ-11 port  102   a  to establish DSL connectivity and PSTN voice service. An Ethernet interface  124  (e.g., Ethernet physical layer (PHY) and transformer) interfaces though the RJ-45 port  102   b . A diplexer, silicon tuner, and cable modem unit  126  interfaces via the coaxial cable port  102   c . A gigabit passive optical network (GPON) optical module  128  interfaces through the optical fiber port  102   d . A baseband and radio unit  130  provides a wireless network connection via the mobile station antenna  102   e.    
     A femtocell baseband and radio unit  132  provides an interface using the femtocell antenna  103   a . A cordless baseband and radio unit  134  provides an interface using the cordless base station antenna  103   b . An ISDN transceiver  136  provides an interface via the RJ-45 port  103   c . A subscriber line audio circuit (SLAC)  138  and subscriber line interface circuit (SLIC)  140  combine to provide a foreign exchange service (FXS) port  141  to interface with the RJ-11 port  103   d.    
     A WiFi baseband and radio unit  142  provides an interface via the WiFi antenna  105   a . An Ethernet switch  144  and Ethernet interfaces  146 ,  148  (e.g., Ethernet physical layer (PHY) and transformer) provide interfaces via the RJ-45 ports  105   b ,  105   c . The gateway  100  may also have one or more other units  150  to provide functions not within the scope of this description. Also, although certain units are illustrated as being distinct, it is contemplated that one or more of them may be integrated into the processing unit  110 . For example, the cordless baseband processing functionality, the power regulation functionality, and/or the SLAC functionality may be integrated into the processing unit  110 . 
     As will be described in greater detail below, one or more of the telephony devices  104  may support extended bandwidth audio services, commonly referred to as wideband or super-wideband. The gateway  100  is adapted to identify the capabilities of the telephony device  104  and communicate those capabilities with a far-end telephony device and to enhance the actual or perceived audio quality to the telephony device  104 . The availability of extended audio bandwidth may depend on the particular telephony device  104  used to place or answer a particular call and on the far-end telephony device. The gateway  100  may support multiple simultaneous devices, so the audio bandwidth may vary between devices. The gateway  100  implements a call manager  152  to negotiate at call time the highest level of telephony audio bandwidth. 
     Turning now to  FIG. 2 , a diagram illustrating the software architecture of the gateway  100  is provided. The gateway  100  runs under the control of an operating system  200 . Higher level software includes a call manager module  202  (i.e., corresponding to the call manager  152  of  FIG. 1 ) for controlling the telephony services. Other gateway applications  204  may also be provided. For example, applications related to non-telephony network services may be provided. A session initiated protocol (SIP) module  206  and SIP user agent  208  are provided for negotiating the parameters of voice-over-IP (VoIP) calls. Typically, the SIP protocol is an application layer that is independent of the transport protocol. The transport protocol is handled by a TCP/IP module  210 , a routing module  212 , a gateway services module  214 , a quality of service (QoS) module  216 , an address translation and security module  218 , and a WAN protocol module  220 . An Ethernet bridge  222  is provided for communicating over Ethernet networks. Network communication support is provided for the physical layer interface units depicted in  FIG. 1  by broadband network device drivers  224 , LAN device drivers  226 , WiFi device drivers  228 , and other device drivers  230 . Telephony support is provided via a foreign exchanges service (FXS) module  232  that provides functionality for dual tone multi-frequency (DTMF) detection, wideband expansion of narrowband speech (WENS), equalization, etc., a VOIP audio processing module  234  that provides functionality for jitter buffering, packet loss concealment, echo canceling, voice activity detection, etc., a CODEC module  236 , a SLIC/SLAC application programming interface (API) and driver module  238 , a coefficient profile module  240  including coefficients for narrowband, wideband, and super-wideband communication, and a DSP hardware driver module  242 . The design and operation of software modules suitable for implementing the functionality of the gateway  100  are known to those of ordinary skill in the art, and they are not described in greater detail herein. 
     It is contemplated that some of the functionality described in  FIG. 2  as being associated with the processing unit  110 , may be integrated into the SLAC  138 . For example, the call manager module  202  functionality or portions of the FXS module  232  functionality may be provided by the SLAC  138 . Also, various functions associated with the SLAC  138  may be provided by the processing unit  110 . 
     Conventional analog FXS ports and telephone devices support narrowband signals, as illustrated in  FIG. 3  on a logarithmic scale. Wideband and super-wideband telephony devices use a wider audio frequency spectrum to provide an improved user experience. In the illustrated embodiment, the gateway  100  provides the highest bandwidth supported by the telephony device  104 . As will be described in greater detail below, the call manager  152  in the gateway  100  signals the telephony device to determine which bandwidth is supported. The gateway  100  sends a bandwidth alert signal to the telephony device  104 , and the telephony device  104  responds with a bandwidth signal and then negotiates with the far-end telephone&#39;s gateway based on the determined capabilities. In the event the far-end station only supports a lower bandwidth than the local telephony device  104  is capable of receiving, the gateway  100  extends the audio bandwidth of the audio from the far-end before transmitting it to the telephony device  104 . In that case, the gateway  100  also filters out the wideband or super-wideband frequencies from the telephony device  104  before transmitting them to the far-end station. 
       FIG. 4  is a simplified block diagram of an exemplary telephony device  400 . In the illustrated embodiment, the telephony device  400  is a wideband telephone, such as the telephony device  104   g . The telephony device  400  interfaces with conventional tip and ring lines using a hook switch  402  and a 2-wire to 4-wire hybrid circuit  404 . A ringing detector  406  detects a ringing signal on the tip and ring lines and controls a buzzer  408  to inform a user of an incoming call. A caller ID decoder  409  detects caller ID data on the telephone line (tip and ring wires). A DC hold circuit  410  provides the DC loop characteristics necessary to interface over the telephone line and feeds power to a regulator  412 . An optional battery  414  provides power when the telephone is on-hook and not powered from the line. 
     The hybrid  404  converts the 2-wire Tip/Ring telephony signals to separate Receive (RX) and Transmit (TX) paths. The receive path includes a tone detector  416  for identifying wideband alert tones (WBAT), also referred to as a bandwidth alert tone or bandwidth alert signal. A receiver mute circuit  418  is provided for muting the receive path to prevent signaling tones from being heard by a user. A processing unit  420  (e.g., microcontroller, DSP, or a combination thereof) is provided to implement the functionality of the telephony device  400 . The processing unit  420  interfaces with one or more of a light emitting diode (LED)  424 , a liquid crystal display (LCD)  426 , and a keypad  428  to provide a user interface for operating the telephony device  400 . An oscillator  422  provides a clock signal for the processing unit  420 . The receive signal is provided to a super-wideband filter  430 , a wideband filter  432 , or a narrowband filter  434 . Depending on the type of session established for the telephony device  400 , an earpiece audio analog switch  436  selects the output from of the filters  430 ,  432 ,  434  and provides the output to an earpiece  438  in a handset  440  of the device  400  or some other speaker of the device  400  (e.g., for a speakerphone). 
     Transmit audio signals in the telephony device  400  are generated through a microphone  442  in the handset  440 . A bias circuit  444  powers the microphone  442 . Transmit filters  446 ,  448 ,  450  are provided according to the bandwidth selected, super-wideband, wideband, or narrowband, respectively, and the output of one of the filters  446 ,  448 ,  450  is selected by a microphone audio analog switch  452 . A microphone mute circuit  454  is provided for selectively muting the microphone  442 . A tone generator  456  is provided for generating dialing DTMF tones or wideband acknowledge (ACK) tones, also referred to as a bandwidth signal or a bandwidth acknowledgement signal. Although illustrated as separate units, it is contemplated that one or more of the units, such as the caller ID decoder  409 , the tone detector  416 , and/or the tone generator  456 , may be integrated into the processing unit  420 . 
       FIG. 5  is a simplified block diagram of another embodiment of a telephony device  500 . In the illustrated embodiment, the telephony device  500  is a wideband cordless telephone base station. As shown in  FIG. 1 , the wideband cordless telephone base station may be integrated into the gateway  100  using the cordless baseband and radio unit  134 , the antenna  103   b , and the cordless handset  104   b . The telephony device  500  interfaces with conventional tip and ring lines using an electronic hook switch  502  controlled by an associated hook control circuit  503  and a 2-wire to 4-wire hybrid circuit  504 . A ringing detector  506  detects a ringing signal on the tip and ring lines. A narrowband filter  508  is used in detecting caller ID data on the tip and ring lines. A DC hold circuit  510  provides the DC loop characteristics necessary to interface over the tip and ring lines. 
     The hybrid  504  provides a transmit path and a receive path. A processing unit  520  (e.g., microcontroller, DSP, or a combination thereof) is provided to provide the functionality of the telephony device  500 . An oscillator  522  provides a clock signal for the processing unit  520 . The processing unit  520  performs functions such as muting and tone processing (e.g., detection or generation) for identifying or generating dialing tones (i.e., DTMF tones) and wideband signaling tones (WBAT and ACK). The processing unit  520  interfaces with one or more of a light emitting diode (LED)  524 , a liquid crystal display (LCD)  526 , and one or more keys  528 . The receive signal is provided to a super-wideband filter  530 , a wideband filter  532 , or a narrowband filter  534 . Depending on the type of session established for the telephony device  500 , an analog switch  536  selects the output from of the filters  530 ,  532 ,  534 . Transmit signals for the telephony device  500  are provided to transmit filters  546 ,  548 ,  550  according to the bandwidth selected, and the output of one of the filters  546 ,  548 ,  550  is selected by an analog switch  552 . 
     Processing of the analog transmit and receive signals is performed by a CODEC  554  that interfaces with the processing unit  520 . In the illustrated embodiment, the sampling rate of the CODEC  554  is controlled by the processing unit  520  and is adjusted to correspond to the desired bandwidth. For example, the CODEC  554  will typically sample audio at the rate of 8,000 samples per second for Narrowband, 16,000 samples per second for Wideband, and 32,000 samples per second for Super-Wideband. The processing unit  520  communicates voice and control signals to a cordless baseband processor  556 . The baseband processor  556  controls a cordless radio  558 , which in turn, generates cordless radio signals through an antenna  560 . Oscillator  562  provides one or more clocks to the cordless baseband processor  556 . 
     A docking station  564  may be provided for receiving a cordless handset  566 . The docking station  564  includes charging contacts  568 . A charger circuit  570  monitors the charging state of the cordless handset  566  and provides a charging current at the handset charging contacts  568  as necessary. An external AC/DC adaptor  572  powers the various blocks of the telephone device through one or more power regulators  574 . Although illustrated as separate units, it is contemplated that one or more of the units, such as the CODEC  554 , the cordless baseband processor  556 , one or more power regulators  574 , and/or the charger circuit  570 , may be integrated into the processing unit  520 . In the illustrated embodiment, the air interface and audio CODEC used for communication between the cordless radio  558  and the cordless handset  566  are configured to support Wideband or Super-Wideband to take advantage of the expanded bandwidth capability. 
       FIG. 6  is a flow diagram illustrating the operation of the gateway  100  for detecting the bandwidth capabilities of the interfacing telephony device  104  for an outgoing call sequence. In some cases, the far-end station/VoIP connection to which the telephony device  104  connects supports a lower audio bandwidth than the telephony device  104 . In one embodiment, rather than delivering the lower bandwidth audio to the telephony device  104 , the gateway  100  performs bandwidth expansion on the received signal from the far-end station prior to transmitting it to the telephony device  104  to estimate the frequency components that would have been present had the far end-station supported a higher bandwidth audio. This expansion is commonly referred to as wideband expansion of narrowband speech (WENS). Techniques for performing bandwidth expansion of acoustic signals are known to those of ordinary skill in the art, so they are not described in greater detail herein. In general, the bandwidth expansion improves the quality of the signal perceived by the local user of the telephony device  104 , but has no impact on the quality perceived by the user of the far-end station. The quality improvement is not as high as what would be achieved if both stations had supported the higher audio bandwidth connection, but better than what would be realized by restricting the telephony device  104  to a lower bandwidth audio connection. The far-end user does not perceive any improvement in the audio quality as the WENS is applied only to the audio going to the local telephony device  104 . 
     In the illustrated embodiment, the gateway  100  may employ NB/SWB expansion (e.g., expand received NB audio [300 Hz-3.4 KHz] to SWB audio [50 Hz to 12 KHz]), NB/WB expansion (e.g., expand received NB audio [300 Hz-3.4 KHz] to WB audio [50 Hz to 7 KHz]), or WB/SWB expansion (e.g., expand received WB audio [50 Hz-7 KHz] to SWB audio [50 Hz to 12 KHz]). In the illustrated embodiment, the WENS capability is provided by the FXS module  232  shown in  FIG. 2 . 
     When using audio bandwidth expansion, the gateway  100  also filters out the enhanced bandwidth audio from the telephony device  104  before encoding and transmitting it to the far-end station. When using NB/SWB expansion, the gateway  100  filters out the SWB audio [50 Hz-300 Hz and 3.4 KHz to 12 KHz] prior to transmitting audio to the far end station. When using NB/WB expansion, the gateway  100  filters out the WB audio [50 Hz-300 Hz and 3.4 KHz to 7 KHz]. When using WB/SWB expansion, the gateway  100  filters out the SWB audio [7 KHz to 12 KHz]. In the illustrated embodiment, the transmit filtering capability is provided by the FXS module  232  shown in  FIG. 2 . 
     In method block  600 , the terminal goes off-hook (e.g., the hook switch  402  in  FIG. 4  or the hook switch  502  in  FIG. 5  is opened and detected by the gateway  100 ), indicating a user is initiating a call. In method block  602 , the gateway  100  generates a dial tone (e.g., via the SLAC  138  and SLIC  140  in  FIG. 1 ). The gateway  100  loops between method blocks  604  and  602  until the first digit is detected in method block  604 . After detecting the first digit, the dial tone is terminated and the gateway  100  looks for additional digits. The gateway  100  determines if dialing is complete in method block  608  (e.g., based on an elapsed time interval or based on the detection of a predetermined number of digits) and loops back to method block  606  until dialing completion is detected. 
     After dialing is complete in method block  608 , the gateway  100  applies SWB coefficients (provided by the coefficient profile module  240  in  FIG. 2 ) for the FXS port  141  in method block  610 . In method block  612 , the gateway  100  sends a SWB alert tone, and waits for an acknowledgement (ACK) in method block  614 . In method block  616 , the gateway  100  determines if a SWB acknowledgement, a WB acknowledgement, or no acknowledgement has been detected. 
     If no acknowledgement has been detected in method block  616 , indicating that the telephony device  104  supports only NB connections, the gateway  100  applies NB coefficients (provided by the coefficient profile module  240  in  FIG. 2 ) for the FXS port  141  in method block  618 , sends a SIP Invite indicating that only NB (e.g., G.711 CODEC) is supported to the far-end station in method block  620 , and connects the NB call in method block  622  using the G.711 CODEC provided in the CODEC module  236  in  FIG. 2 . As used herein, the term far-end station is intended to cover a telephony device and/or a gateway for servicing the telephony device. 
     If a SWB acknowledgement has been detected in method block  616 , indicating that the telephony device  104  supports SWB connections, the gateway  100  applies SWB coefficients (provided by the coefficient profile module  240  in  FIG. 2 ) for the FXS port  141  in method block  624  and sends a SIP Invite indicating that SWB, WB, and NB are supported far-end station in method block  626 . Based on the SIP response of the far-end station, the local gateway  100  determines what bandwidth is supported. If the SIP response indicates SWB support in method block  628 , the gateway  100  connects the SWB call in method block  630  using the G.722.1c CODEC provided in the CODEC module  236  in  FIG. 2 . If the SIP response indicates WB support in method block  632 , the gateway connects the WB call in method block  634  using the G.722 CODEC provided in the CODEC module  236  in  FIG. 2 . In method block  636 , the gateway  100  performs a WB/SWB expansion of the far-end audio prior to transmission to the telephony device  104  and a filtering of the audio from the telephony device  104  prior to transmission to the far-end station. 
     If the SIP response indicates only NB support in method block  632 , the gateway connects the NB call in method block  638  using the G.711 CODEC provided in the CODEC module  236  in  FIG. 2 . In method block  640 , the gateway  100  performs a NB/SWB expansion of the far-end audio prior to transmission to the telephony device  104  and a filtering of the audio from the telephony device  104  prior to transmission to the far-end station. 
     If a WB acknowledgement (ACK) has been detected in method block  616 , indicating that the telephony device  104  supports WB connections, the gateway  100  applies WB coefficients (provided by the coefficient profile module  240  in  FIG. 2 ) to the FXS port  141  in method block  642  and sends a SIP Invite indicating that WB and NB are supported to the far-end station in method block  644 . Based on the SIP response of the far-end station, the gateway  100  determines what bandwidth is supported. If the SIP response indicates WB support in method block  646 , the gateway connects the WB call in method block  648  using the G.722 CODEC provided in the CODEC module  236  in  FIG. 2 . If the SIP response indicates NB support in method block  646 , the gateway connects the NB call in method block  650  using the G.722 CODEC provided in the CODEC module  236  in  FIG. 2 . In method block  652 , the gateway  100  performs a NB/WB expansion of the far-end audio prior to transmission to the telephony device  104  and a filtering of the audio from the telephony device  104  prior to transmission to the far-end station. 
       FIG. 7  is a flow diagram illustrating the operation of the gateway  100  for detecting the bandwidth capabilities of the interfacing telephony device  104  for an incoming call sequence. In method block  700 , a SIP Invite is received from a far-end station. The SIP Invite includes the CODEC supported by the far-end station. In method block  702 , the gateway  100  sends a “Trying” message to the far-end station. In method block  704 , the gateway sends a “Ringing” message to the far end station and generates a ringing signal to the connected telephony device  104  in method block  706 . In method blocks  706  and  708 , the gateway  100  monitors for an off-hook state of the telephony device  104 . Once, the off-hook state is identified in method block  708 , the gateway  100  stops ringing and applies SWB coefficients (provided by the coefficient profile module  240  in  FIG. 2 ) for the FXS port  141  in method block  710 . In method block  712 , the gateway  100  sends an SWB alert tone and waits for an acknowledgement (ACK) in method block  714 . In method block  716 , the gateway  100  determines if a SWB acknowledgement, a WB acknowledgement, or no acknowledgement has been detected. 
     If no acknowledgement has been detected in method block  716 , indicating that the telephony device  104  supports only NB audio, the gateway  100  applies NB coefficients (provided by the coefficient profile module  240  in  FIG. 2 ) for the FXS port  141  in method block  718 , sends a SIP Acknowledgement indicating that only NB (e.g., G.711 CODEC) is supported to the far-end station in method block  720 , and connects the NB call in method block  722  using the G.711 CODEC provided in the CODEC module  236  in  FIG. 2 . 
     If a SWB acknowledgement has been detected in method block  716 , indicating that the telephony device  104  supports SWB audio, the gateway  100  applies SWB coefficients (provided by the coefficient profile module  240  in  FIG. 2 ) for the FXS port  141  in method block  724 . If the SIP Invite indicates SWB support by the far-end station in method block  726 , the gateway  100  sends a SIP Acknowledgement indicating that SWB is supported to the far-end station in method block  728  and connects the SWB call in method block  730  using the G.722.1c CODEC provided in the CODEC module  236  in  FIG. 2 . If the SIP Invite indicates WB support for the far-end station in method block  740 , the gateway sends a SIP Acknowledgement indicating that WB is supported in method block  742  and connects the WB call in method block  744  using the G.722 CODEC provided in the CODEC module  236  in  FIG. 2 . In method block  746 , the gateway  100  performs a WB/SWB expansion of the far-end audio prior to transmission to the telephony device  104  and a filtering of the audio from the telephony device  104  prior to transmission to the far-end station. 
     If the SIP Invite indicates only NB support in method block  748 , the gateway connects the NB call in method block  750  using the G.711 CODEC provided in the CODEC module  236  in  FIG. 2 . In method block  752 , the gateway  100  performs a NB/SWB expansion of the far-end audio prior to transmission to the telephony device  104  and a filtering of the audio from the telephony device  104  prior to transmission to the far-end station. 
     If a WB acknowledgement has been detected in method block  716 , indicating that the telephony device  104  supports WB audio, the gateway  100  applies WB coefficients (provided by the coefficient profile module  240  in  FIG. 2 ) for the FXS port  141  in method block  754 . If the SIP Invite indicated WB support by the far-end station in method block  756 , the gateway  100  sends a SIP Acknowledgement indicating that WB is supported to the far-end station in method block  758  and connects the WB call in method block  760  using the G.722 CODEC provided in the CODEC module  236  in  FIG. 2 . If the SIP Invite indicates only NB support for the far-end station in method block  756 , the gateway sends a SIP Acknowledgement indicating that NB is supported in method block  762  and connects the NB call in method block  766  using the G.711 CODEC provided in the CODEC module  236  in  FIG. 2 . In method block  768 , the gateway  100  performs a NB/WB expansion of the far-end audio prior to transmission to the telephony device  104  and a filtering of the audio from the telephony device  104  prior to transmission to the far-end station. 
       FIG. 8  is a flow diagram illustrating the operation of the telephony device  104  for communicating its audio bandwidth capability for an incoming or outgoing call sequence. In method block  800 , the telephony device  104  goes off-hook due to an incoming call being answered or an outgoing call being placed. In method block  802 , the telephony device  104  determines if it is set to NB mode or AUTO mode. If the telephony device  104  is set to NB mode in method block  802 , the audio filters are set to NB in method block  804  (e.g., by selecting filters  434  and  450  in  FIG. 4  or filters  534  and  550  in  FIG. 5 ). Normal phone operation based on the configured filters is continued in method block  806 . The telephony device  104  does not respond to any WBAT signals that may be provided on the line by the FXS port  141 . 
     If the telephony device  104  is set to AUTO mode in method block  802 , the audio filters are set to NB in method block  808 . In method block  810 , the telephony device  104  looks for a WB alert tone (WBAT) and starts a timer in method block  812 . If no WBAT is received in method block  814  (e.g., using the tone detector  416  in  FIG. 4 ), the telephony device  104  detects if a digit is dialed in method block  816 . If a digit is dialed, the timer is reset in method block  812 . If the timer expired without the detection of a WBAT in method block  818 , the telephony device  104  designates the call as a NB call in method block  820  and normal phone operation is continued in method block  806 . 
     The dashed lines exiting method block  814  indicate that the dialing timer is being run in parallel with WBAT detection. If a WBAT is received in method block  814  and the dialing timer has elapsed, the telephony device  104  looks for a second WBAT in method block  822 . If a second WBAT is detected, it indicates that SWB Is supported, and the telephony device  104  designates the call as a SWB call in method block  824 . The earpiece  438  and microphone  442  are muted in method block  826  to prevent the user from hearing the subsequent signaling tones. The telephony device  104  waits for a predetermined time period after receiving the WBAT in method block  828  and sends a SWB acknowledgment tone in method block  830 . After waiting a predetermined time interval in method block  832 , the telephony device  104  sets the audio filters to SWB in method block  834  (e.g., by selecting filters  430  and  446  in  FIG. 4  or filters  530  and  546  in  FIG. 5 ). After waiting a predetermined time interval in method block  836 , the telephony device  104  un-mutes the earpiece  438  and microphone  442  in method block  838 . A SWB icon may be provided on the LCD  426  in method block  840  to indicate the audio quality of the call. Normal phone operation based on the configured filters is continued in method block  806 . 
     If a second WBAT is not detected in method block  822 , it indicates that WB Is supported, and the telephony device  104  designates the call as a WB call in method block  842 . The earpiece  438  and microphone  442  are muted in method block  844  to prevent the user from hearing the subsequent signaling tones. The telephony device  104  waits for a predetermined time period in method block  846  and sends a WB acknowledgment tone (ACK) in method block  848 . After waiting a predetermined time interval in method block  850 , the telephony device  104  sets the audio filters to WB in method block  852  (e.g., by selecting filters  432  and  448  in  FIG. 4  or filters  532  and  548  in  FIG. 5 ). After waiting a predetermined time interval in method block  854 , the telephony device  104  un-mutes the earpiece  438  and microphone  442  in method block  856 . A WB icon may be provided on the LCD  426  in method block  858  to indicate the audio quality of the call. Normal phone operation based on the configured filters is continued in method block  806 . 
     Although  FIGS. 6-8  include paths for both wideband and super-wideband, it is contemplated that only one enhanced bandwidth technique may be supported. For example, if the system only supports WB telephony, the SWB branches in the exemplary process flows may be eliminated. 
     In some embodiments, the gateway  100  may also provide support for low frequency bass boost.  FIG. 9  illustrates a bass boost equalization profile that may be applied to the far-end audio before it is sent by the gateway  100  to the telephony device  104 . Bass boost enables small-sized speakers (e.g., the earpiece  438  or a speaker (not shown) in a speakerphone) to provide enhanced low frequency response, since their natural response is weak at these frequencies. 
     Higher frequency signals experience increased attenuation as the length of the subscriber line increases (i.e., defined by the distance between the gateway  100  and the telephony device  104 . This attenuation is due to the fact that the telephone line behaves as an RC low-pass filter. To address this attenuation, a gateway  100  may use line equalization to increase the gain applied to higher frequencies. The line equalization may apply to both directions between the gateway  100  and the telephony device  104 .  FIG. 10  illustrates gain profiles that may be employed with wideband connections for different subscriber line lengths. Typical curves are shown for 26 AWG 2 Kft, 8 Kft, and 14 Kft telephone copper cable for wideband and super-wideband. As will be described below, the line equalization gains may be configured dynamically during the bandwidth negotiation exchanges. The equalization profiles of  FIGS. 9 and 10  may be combined to provide bass boost and to recover attenuated higher frequency components. The high frequency line equalization profile may be applied to both transmit and receive signals, while the low frequency bass boost profile may be applied only to the audio transmitted by the gateway  100  to the telephony device  104 . 
     The gateway  100  generates WB alert tones using one or more bursts of signaling tones that do not harmonically relate to telephony call signaling and are not common in human speech at this combination and exact duration. For example, the alert tone may be generated using the dual tones 5480 Hz+7080 Hz for a predetermined time period, such as 100 ms. Of course, other signaling techniques or frequencies may be employed, such as in-band or out-of-band tones, DC level variations or polarity reversals, AC signals, FSK signals, or a combination thereof. In the illustrated embodiment, the gateway  100  queries the telephony device  104  for WB capability using a single dual tone pulse of a predetermined duration and queries for SWB capability using two dual tone pulses of predetermined duration separated by a silent interval of a predetermined duration. Techniques for detecting the signaling pulses and silent intervals and measuring their durations are known to those of ordinary skill in the art, so they are not described in greater detail herein. For example, switched capacitor tone detectors and DSP-based implementations may be employed. An exemplary signaling technique for communicating the capabilities of the telephony device  104  to the gateway  100  is described below in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Alert Tones 
               
            
           
           
               
               
               
            
               
                   
                 Response to 
                 Response to 
               
               
                   
                 WB Alert 
                 SWB Alert 
               
               
                   
                 Tone 
                 Tone 
               
               
                   
                 (ACK Tones) 
                 (ACK Tones) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Narrowband Telephone 
                 None 
                 None 
               
               
                 Set or WB- or SWB- 
               
               
                 Capable Telephone Set 
               
               
                 Configured for NB 
               
               
                 Operation 
               
               
                 WB-Capable Telephone 
                 DTMF A 
                 DTMF A 
               
               
                 Set without Line 
               
               
                 Equalization Support 
               
               
                 SWB-Capable Telephone 
                 DTMF A 
                 DTMF C 
               
               
                 Set without Line 
               
               
                 Equalization Support 
               
               
                 WB Capable Telephone 
                 DTMF B + 4000 Hz + 
                 DTMF B + 4000 Hz + 
               
               
                 Set with Line 
                 7400 Hz 
                 7400 Hz 
               
               
                 Equalization Support 
               
               
                 SWB-Capable Telephone 
                 DTMF B + 4000 Hz + 
                 DTMF D + 9000 Hz + 
               
               
                 Set with Line 
                 7400 Hz 
                 13500 Hz 
               
               
                 Equalization Support 
                   
                 followed by 
               
               
                   
                   
                 DTMF B + 4000 Hz + 
               
               
                   
                   
                 7400 Hz 
               
               
                   
               
            
           
         
       
     
     In general, DTMF tones are used in telephony for generating dialing tones. A DTMF pair includes a lower band component and an upper band component that are combined to generate a DTM pair. DTMF pairs are defined for each of the digit keys 0-9, the “*” key, and the “#” key. The DTMF industry standards also defines tones for “A”, “B”, “C”, and “D” digits that are not normally generated by keypads, but may be used for signaling. In the illustrated embodiment the telephony device  104  uses DTMF tones for communicating its audio bandwidth capability to the gateway  100 . Other signaling methods may be employed, such as in-band or out-of-band tones, FSK, modem, white noise, DC signaling, or a combination thereof. 
     As shown in Table 1, a legacy telephony device  104  or a WB or SWB-capable telephony device  104  configured for “NB only” operation will not communicate any acknowledgement bandwidth tones (ACK) in response to the SWB or WB alert tones. Referring to  FIG. 8 , if only one WB alert tone is received in method block  822 , signifying a WB call, the telephony device  104  (WB or SWB) responds with a DTMF A tone. If both alert tones are received in method block  822 , signifying support for a SWB call, a WB telephony device  104  responds with a DTMF A tone to indicate that it can only support WB. A SWB telephony device  104  responds with a DTMF C tone, indicating that it can support WB or SWB. 
     For telephony devices  104  that also support line equalization, the signaling scheme uses different DTMF tones. In addition to the WB acknowledgement tones, test tones in higher frequency bands are also provided by the telephony device  104 . Each of the four tones (i.e., the low and high components of the DTMF signal plus two test tones) are transmitted by the telephony device  104  at the same level. The gateway  100  may measure the attenuation in the test tones to measure the attenuation at each of the frequencies and estimate the attenuation curve at frequencies between 1 KHz and 7 KHz for WB and 1 KHz and 14 KHz for SWB. The FXS module  232  of the gateway  100  can then apply a corrective equalization to negate the estimated losses over that frequency range. The equalization results in a flatter transmission of the high frequency components and a more natural audio experience. 
     Table 1 also provides an exemplary signaling scheme for telephony devices  104  that support the optional line equalization. A WB-capable telephony device  104  responds to a single WBAT, signifying a WB call, with a DTMF B tone with the test tones at 4 KHz and 7.4 KHz superimposed thereon (i.e., with all tones transmitted at the same level). If both alert tones are received in method block  822 , signifying support for a SWB call, a WB telephony device  104  responds with a DTMF B tone and the WB test tones at 4 KHz and 7.4 KHz superimposed thereon (i.e., with all tones transmitted at the same level) to indicate that it can only support WB. A SWB telephony device  104  responds with a DTMF D with test tones at 9 KHz and 13.5 KHz superimposed thereon, followed by a predetermined delay and then a burst of DTMF B with the test tones at 4 KHz and 7.4 KHz superimposed thereon. All the tones in both ACK bursts (e.g., 8 tones) are transmitted at the same level. 
     In one embodiment, after the telephony device  104  goes off-hook on an incoming or outgoing call, the gateway  100  analyzes the audio that is received from the telephony device  104 , analog tone detectors or using digital signal processing techniques, to determine if there is a significant level of 50 Hz or 60 Hz hum that may be induced from AC sources to the telephone line. If such hum levels exceed a predetermined threshold, the gateway  100  applies coefficients for a notch filter to filter out the 50-60 Hz hum. If, after applying this notch filter, there is a significant level present from the first harmonic (i.e., 100-1120 Hz), then the gateway  100  may apply a second notch filter to filter out the harmonic. The hum filter or filters attempts to prevent AC hum from entering into the wideband or super-wideband audio stream. In another embodiment, the telephony device  104  may detect and filter AC hum on the signal received from the gateway  100  using one or more notch filters. 
     The use of the techniques described herein provides an enhanced user experience for adopters of wideband telephony. During early adoption phases for wideband telephony, most calls to far-end stations are not likely to be WB or SWB. The use of audio bandwidth expansion on the audio received from the far-end station provides for an improved user experience, even if the other user has not employed a wideband device. The use of bass boost improves the response of the earpiece speakers. The use of line equalization addresses high-frequency roll off on long loops. The detection and filtering of AC hum also improves the audio characteristics of the call. The use of signaling between the gateway  100  and the telephony device  104 , as described herein allows the audio bandwidth capabilities of the telephony device  104  to be determined on a per call basis and allows negotiation with the far-end station regarding the CODEC used for the call. A user may employ different types of telephony devices  104  each with different bandwidth support, and the gateway  100  may dynamically adapt to the particular device selected on a per call basis. In an embodiment that uses tonal signaling, the negotiation technique described provides backwards compatibility with the vast number of legacy analog telephones and PSTN lines. 
     The particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.