Abstract:
A monitoring device monitors headers of packets on a communications session with a primary communications device, and when it detects packets of a medium that is incompatible with the primary device, it causes those packets to be diverted to a secondary device that is associated with the primary device and that is compatible with that medium. During set-up of the communications session, the monitoring device replaces or supplements the handshake of the primary device, thereby providing to the network a single handshake that identifies the media supported by the combination of the primary and secondary devices.

Description:
TECHNICAL FIELD 
     This invention is directed generally to communications, and illustratively to communications in different multiple media. 
     BACKGROUND OF THE INVENTION 
     People who are hearing-impaired or unable to speak communicate via the telephone network by using specialized text terminals, commonly referred to as a telecommunication device for the deaf (TDD) or a teletypewriter (TTY). A TTY converts symbols (letters, numbers, punctuation, etc.) typed on its keyboard into audio signals that it transmits through the telephone network to another TTY. The receiving TTY converts the audio signals back into symbols and displays them on its display screen. A call between TTYs is established and terminated in the same manner as between telephones: either the TTY emulates the call signaling of a telephone, or the TTY user uses a standard telephone to initiate, dial, answer, and terminate the call, and uses the TTY only for the traffic-exchange portion of the call. The TTY usually connects to the same analog RJ-11 line as the telephone via an RJ-11 splitter. 
     In a Voice over Internet Protocol (VoIP) network, a SIP (Session Initiation Protocol) network, or an H.323 network, IP endpoints negotiate communication call-path parameters between themselves as part of the call set-up process prior to establishing the communication path. This is necessary in packet systems because, unlike analog telephones on the public network, IP endpoints can generate many different types of specialized packets that vary depending on the media type. Examples include voice packets, text packets, and video packets. As a part of the call set-up process, endpoints specify the types of packets that will be supported during the call. For calls between an analog endpoint on the public network and an IP endpoint, a similar call set-up negotiation occurs between the IP endpoint and the associated IP/analog gateway. 
     Looking now at the issue of text transmissions, analog text terminals such as TTYs do not emit a self-identifying handshake tone or rely on a carrier tone. (In this sense, they are different from computer modems and fax machines.) The devices are silent when not transmitting text. A complicating factor when attempting to use these devices in conjunction with IP networks is that, when the user is typing a message, the audio tones emitted by these devices are often not transmitted reliably by the voice-optimized audio channels of IP systems. Packet loss and audio comprehension levels commonly seen in IP networks can distort the TTY signals so badly that they cannot be decoded. For this reason, it is often necessary to transmit text via specialized non-audio mechanisms, such as the RFC-2833 protocol (“RTP Payload for DTMF Digits, Telephone Tones and Telephony Signals”) or the RFC-4103 protocol “RTP Payload for Text Conversation”). 
     The RFC-2833 approach transports text via IP by sending what are, in essence, verbal descriptions of the corresponding analog Baudot TTY tones. The RFC-4103 approach transports T.140-encoded text as a real-time media stream in parallel with the voice stream. Although both RFC-2833 and RFC-4103 have been demonstrated to provide reliable transport of text on IP networks, a problem remains: 
     Because analog TTY devices are not self-identifying, if a call is placed by a TTY user on the analog public network to the user of an IP telephone, the call set-up negotiation between the IP endpoint and the associated IP/analog gateway is likely to assume erroneously that a non-text voice-only media stream and a non-text voice-only IP endpoint will be satisfactory. The result will be, that the user of the IP endpoint will not know that he or she has received a call from a TTY user (because distorted TTY tones will be audible on the handset), but will be unable to respond because the IP endpoint is unable to receive or transmit text packets. 
     At least three techniques exist for providing TTY-type functionality on IP endpoints. One manufacturer has demonstrated a telephone that allows a keyboard to be connected thereto via a USB port; the keyboard is used to transmit text, and the phone&#39;s display is used to display incoming text. Others have demonstrated a soft TTY—essentially a soft phone that emulates a TTY. A third manufacturer&#39;s phone, while having no inherent text capability, allows users in telecommuter mode to set-up and control calls for which the endpoint is a traditional analog TTY device. The first and last configurations are regarded by customers as expensive and clumsy because they require additional hardware. And the chief limitation of the second configurations is that it is not supported on physical telephones. 
     The preceding discussion illustrates a general problem in networks: during call set-up, they negotiate (e.g., via SIP) the capabilities that the call endpoints must have in order to engage in the call. These capabilities include the medium or media that the endpoints must be able to communicate in, such as audio, text, or video. If one of the endpoints should deviate from the negotiated capabilities—by introducing a new medium into the call, for example—the other endpoint may not have the corresponding capability and thus may not be able to communicate via the call. 
     SUMMARY OF THE INVENTION 
     This invention is directed to solving these and other problems and disadvantages of the prior art. According to one aspect of the invention, a communications session, established with a first communication device of at least two communication devices that are associated with each other, for communications having a first characteristics—for example, communications in a first medium that is compatible with the first device—is monitored, and when a communication having a second characteristic different from the first characteristic—for example, a communication in a second medium that is incompatible with the first device, but is compatible with the second device of the two or more devices—is detected, the communication having the second characteristic is diverted to the second device. Consequently, communications having the first characteristic are rendered—presented to a user in a user-perceivable form—on the first device, and communications having the second characteristic are rendered to the user on the second device. The invention thus advantageously allows communications characteristics to be changed dynamically in an existing communications session with a communications device, even though the communications session may not be set up for communications having the changed characteristics and even though the changed characteristics are incompatible with the communications device. 
     The invention may illustratively take the form of a method, an apparatus that performs the method, or a computer-readable medium containing instructions that cause the computer to perform the method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       These and other features and advantages of the invention will become more apparent from considering the following description of an illustrative embodiment of the invention together with the drawing, in which: 
         FIG. 1  is a block diagram of a communications system that includes an illustrative embodiment of the invention; and 
         FIG. 2  is a functional-flow diagram of operation of the system of  FIG. 1  implementing the illustrative embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an illustrative communications system comprising one or more communications devices  102  interconnected by a network  104  through a routing entity such as a gateway  106  with one or more communications devices such as VoIP telephones  110 , in a conventional manner. Communications devices  102  may be any desired devices, such as conventional analog or digital telephones, VoIP telephones, softphone-equipped personal computers, personal digital assistants, etc. At least one device  102  is able to communicate in multiple media or comprises a plurality of devices that are together capable of communicating in multiple media, such as voice, text, and/or video. For example, a device  102  may comprise a telephone and an associated TTY device. Network  104  is any desired network, such as a time-division multiplexed network like the conventional telephone network, a packet network such as the Internet or a local area network, a wireless network, etc. Gateway  106  is a conventional gateway that connects network  104  to conventional VoIP telephones  110  in a conventional manner either directly or via an intermediary switch or server. As described so far, the system of  FIG. 1  is conventional. 
     According to the invention, at least one VoIP telephone  110  has associated ( 120 ) therewith an auxiliary device  112  that is capable of rendering media that are not compatible with VoIP telephone  110 . The compatible medium of VoIP is audio, and auxiliary device  112  is capable of rendering an incompatible medium or media, such as text and/or video. Auxiliary device  112  may be any desired device, such as a TTY, a personal computer, a personal digital assistant, etc. Auxiliary device  112  is capable of receiving and displaying a window  114  of information in the incompatible medium or media, such as text or images. Auxiliary device  112  is connected to gateway  106  either via the same communication link  116  as VoIP phone  110 , or via a separate communication link  118 . Associating auxiliary device  112  with VoIP telephone  110  is accomplished in a conventional manner, such as by administratively registering auxiliary device  112  as an adjunct to VoIP telephone on gateway  106 . For example, a single user may be associated with a plurality of client devices  110  and  112  through a SIP address of record (AOR) that provides a unifying identifier which is mapped across the multiple client devices. Accordingly, the sending client device may dial the user&#39;s AOR and gateway  106  or a server may be employed to determine to which client device the call should be routed. 
     Also according to the invention, an enhanced detector/classifier  108  is interposed between gateway  106  and devices  110  and  112 . In one embodiment, detector/classifier  108  is a separate device from gateway  106  that is located on link  116  between gateway  106  and VoIP telephone  110 . In another embodiment, detector/classifier  108  may be incorporated into gateway  106 . Detector/classifier  108  acts as a “packet sniffer”, monitoring the headers of packets being carried by communications link  116  to, and optionally also from, VoIP telephone  110  and detecting therefrom the packets&#39; types. The enhancement of detector/classifier  108  resides in the fact that detector/classifier  108  preferably participates in the communication session set-up process between telephone  110  and gateway  106  or device  102 . 
     The operation of gateway  106  and detector/classifier  108  that is relevant to this invention is shown in  FIG. 2 . As a part of setting up a call, communications device  102  or gateway  106  and VoIP telephone  110  would normally negotiate a communications session between them in a medium that is compatible with VoIP telephone  110 , namely audio. For example, if telephone  110  uses the Session Initiation Protocol (SIP), the SIP call-initiating entity  102 ,  106 , or  110  sends an “INVITE” message specifying the medium in which it wants to conduct the communications, and the SIP call-terminating entity  102 ,  106 , or  110  responds with a “200 OK” message specifying the medium in which it can conduct the communications. Detector/classifier  108  monitors link  116 , and when it detects call set-up being performed, at step  200 , it assumes responsibility for the set-up handshake of telephone  110 : it substitutes for the “INVITE” or “200 OK” message sent by telephone  110  a corresponding message that specifies not only the compatible medium of telephone  110  but also the medium or media that can be handled by auxiliary device  112 , at step  202 . For example, telephone  110  would say only “I can do G.711 and G.729 audio.” That message is blocked, and the actual call set-up handshake from detector/classifier  108  is something like, “I can do G.711 audio, G.729 audio, and RFC-2833 text.” This is important because, in many systems, the transmitting device will refuse to send packets that the receiving station does not indicate that it can accommodate. In systems where the transmitting device does not refuse to send packets that the receiving station cannot accommodate, the enhancement of detector/classifier  108  is not needed. 
     When the communications session is established, detector/classifier  108  begins to monitor the headers of packets moving across link  116  to VoIP telephone  110  for the packet type, at step  204 . As long as device  102  and VoIP telephone  110  are engaging only in audio communications, detector/classifier  108  does not detect, at step  206 , an incompatible medium type of packets on link  116 , so it continues to monitor the packet type at step  204 . 
     Now let us assume that device  102  begins to communicate on the established communication session in a medium other than audio—in TTY tones, text, or video, for example. Gateway  106  detects this new medium in the communication and sends the medium across link  116  in packets of non-audio type. For example, gateway  106  converts TTY tones into text, in a conventional manner, and communicates the text in text packets on link  116 . Gateway  106  also communicates text from device  102  in text packets on link  116 , and communicates video in video packets on link  116 . But, as was mentioned before, VoIP telephone  110  is not capable of rendering text or video. Detector/classifier  108  therefore detects the non-audio type of the text or video packets, at step  206 , and signals this detection to gateway  106 . In an alternative embodiment, detector/classifier  108  also sends the text or video packets back to gateway  106  with a request to send them to auxiliary device  112 . 
     In response to this signal, gateway  106  checks its records to determine whether VoIP telephone  110  has associated therewith an auxiliary device that is capable of rendering the detected type of non-native medium, at step  208 . If not, gateway  106  ceases to transmit packets of the incompatible type on link  116  and merely drops the information of the incompatible type, at step  210 . But if it finds that VoIP telephone  110  does have associated therewith an auxiliary device  112  that is capable of rendering the detected type of incompatible medium, gateway  106  determines how the auxiliary device  112  is connected to gateway  106  and then begins to transmit all packets of the incompatible medium type to auxiliary device  112  via that connection, at step  212 , while continuing to transmit packets of the compatible medium type to VoIP telephone  110 . For example, if auxiliary device  112  is connected to gateway  106  via the same physical link  116  as VoIP telephone  110 , gateway  106  transmits the packets of the incompatible medium type on link  116  to a different address—the address of auxiliary device  112 —as opposed to the address of VoIP telephone  110 . If auxiliary device  112  is connected to gateway  106  via a separate physical link  118 , gateway  106  transmits the packets of the incompatible medium on link  118  to auxiliary device  112 , thereby bypassing detector/classifier  108 . 
     In an alternative embodiment, the functionality described in the preceding paragraph may be performed by detector/classifier  108  instead of gateway  106 . In this embodiment, detector/classifier  108  may be connected to auxiliary device  112  either via link  116  or via a separate physical link  118 . 
     Auxiliary device  112  responds to receipt of the packets of the incompatible medium by rendering the medium on window  114 . For example, it displays the received text or video in window  114 . Consequently, the medium of communication between devices  102  and a user of VoIP telephone  110  and auxiliary device  112  may be changed dynamically, on the fly, during an established communication session, even though the new medium is not compatible with VoIP telephone  110 . 
     Of course, various changes and modifications to the illustrative embodiment described above will be apparent to those skilled in the art. For example, the invention is not limited to assisting a VoIP telephone in rendering non-audio media, but may be used to assist any communication device in rendering incompatible media or providing any other incompatible communication capability. Instead of a different medium, the characteristic that is incompatible with the primary device may be a different encoding of the same medium. Or, communication entities that are in communication with each other do not have to negotiate any media characteristics during the initial communication setup. The type of media transmitted by a device or group of devices associated with a communication entity can be detected by the communication system and delivered to proper devices associated with the other entity with which the communication was initially set up. Furthermore, detector/classifier  108  may not be interposed into a communication session automatically, but only in response to a signal from telephone  110  or auxiliary device  112  that is generated by a user of telephone  110  or device  112  upon detecting an incompatible medium, e.g., a TTY tone. These changes and modifications can be made without departing from the spirit and the scope of the invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the following claims except insofar as limited by the prior art.