Abstract:
A communication network including a first terminal is disclosed that is arranged for communication with a second terminal via a packet switched network. The first terminal is connected via a first gateway to the packet switched network, and the second terminal is connected via a second gateway to the packet switched network. The first gateway is arranged to receiving information from the second terminal that is to be connected without answering the call of the first terminal. This prevents calling costs from being incurred when transferring the information of the terminal to be called. The gateways may wait in answering the call of the first terminal until the second terminal has answered the call.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system comprising a terminal coupled via a dial-up network to a gateway, the terminal comprises means for dialing the gateway and providing an identification of a second terminal connectable to said gateway. 
     To enable communication between existing telephony systems and emerging IP-based telephony ‘devices” (E.g. an Internet Telephony software package running on a PC) as well as the communication between existing telephony systems inter-connected via IP-based networks, so-called Telephony Gateways (hereafter called gateway(s)) are used. These gateways connect to an IP-based network (such as the public Internet and private Intranets) on one side and a telephone network (E.g. PSTN/ISDN/GSM) on the other side and provide the necessary conversion functions to transmit and receive voice-band and control data on either network. 
     Because of the differences in addressing structure on both sides of the gateway and because of the nature of some of the telephone networks, connections initiated from the telephone network side are usually set up by a two-step dialing process. First, a gateway is called and this gateway answers the call to obtain an identification of the second terminal, which can be constituted by additional addressing information for either an IP-based telephony device (E.g. an IP-address) or addressing information for the combination of a remote gateway and a remote (normal) telephone terminal. Second, the gateway uses this addressing information to attempt to set up a call to the ‘remote’ telephony device, which can either be an IP-based telephony device or a regular telephony device connected (directly or indirectly) to a remote gateway. 
     The problem with this approach is that a call is answered by the gateway, to obtain numbering information, before it is known whether the actual destination will answer the call. The caller will thus pay the bill for a call that may never exist and always pay for a duration that is longer than the actual call, when it takes place. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a communication network according to the preamble in which the above problem is solved. 
     For achieving said object the communication network according to the invention is characterized in that the gateway is arranged for receiving the identification of the second terminal without answering the call. 
     When the gateway is arranged for receiving the identification of the second terminal before answering a call, no calling costs are incurred for transferring the identification of the second terminal. This can e.g. be done by using the signaling possibilities of ISDN. On ISDN interfaces complying with the ITU-T Q.931 Recommendation, calls are initiated by the transmission of a ‘setup” message from the calling to the called party (from the calling user to the network to be precise). Such a ‘setup’ message contains mandatory information elements and may contain optional information elements. The ‘called party number’, ‘called party subaddress’ and ‘keypad facility” information elements are three of these optional information elements. They (may) contain, when present, numbering and addressing information about the called terminal. It is observed that it is also possible to use ISDN interfaces which are derived from the Q.931 Recommendation, such as EURO-ISDN. 
     An embodiment of a communication network according to the invention is characterized in that the gateway is arranged for establishing communication with the second node, and in that the gateway is arranged for answering the call of the terminal after the second terminal has been contacted. 
     In this way it is obtained that the caller does not incur calling cost until the destination really answers the call, and that the behavior of the destination telephony device, as seen from the caller in the telephone network, is identical to the behavior of a destination telephony device that is located in and reached through the telephone network. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will now be explained with reference to the drawing figures. 
     FIG. 1 shows a communication network according to the invention. 
     FIG. 2 shows an alternative arrangement of the communication network according to the invention. 
     FIG. 3 shows a block diagram of a gateway according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the communication network according to FIG. 1, a node  2  comprises a gateway  4  to which a telephone terminal  6  can be connected via a telephone switch which is here a PABX  3 . It is however possible that the telephone switch is a switch in the public telephone network. The gateway  4  is connected to a telephone network  14  via a link  8  which is routed via the PABX  3 . The gateway  4  is also connected to the packet switched network  16  which can be the public Internet. Alternatively the connection of the gateway  4  to the packet switched network  16  can be a dial up connection or a leased line  12  routed via the PABX  3  to the telephone network  14  as is indicated by the dotted line. 
     The connection  5  between the terminal  6  and the gateway  4  can be a telephone line which is connected via the PABX  3  to the gateway  4 , but it is also possible that the functions of the gateway  4  and the terminal  6  are included in a single device, such as a personal computer or a telephone terminal specially arranged for Internet telephony. 
     When the terminal  6  is connected to the gateway  4  via the PABX  3 , the terminal  6  initiates a call by going off hook and dialing a number corresponding to the gateway  4 . The gateway  4  accepts the call and the terminal  6  provides the (IP) address of the gateway  24  and the terminal  26  to be called to the gateway  4 . If only one terminal is connected to the gateway  24  to be called, which is the case when the gateway function is integrated in a PC or in a special internet phone device, only the internet address of the gateway  24  is given. 
     According to the present invention, the gateway  4  does not answer the call initiated by terminal  6 , but that it only reads the numbering/addressing information in the ‘called party number’, “called party subaddress” and/or ‘keypad facility’ information elements which could be included in an ISDN set up message. 
     Alternatively, it is also possible that the address information of the terminal to be called is stored in the PABX, and that a normal telephone number is assigned to said terminal. If said number is called, the PABX retrieves the complete address information and tries to contact the terminal via the packet switched network before answering the call of the calling terminal. 
     After having received the address of the terminal  26  to be called from the terminal  6 , the gateway  4  attempts to contact the gateway  24  in the node  22  via the Internet  16 . If this attempt is successful, the addressing information of the terminal  26  is passed via the Internet  16  to the gateway  24 , which tries to set up a connection with the terminal  26  via the link  28 . When the terminal  26  accepts the connection, this is signalled by the gateway  24  to the gateway  4 , after which a connection between the terminal  6  and the terminal  26  is established. 
     If the attempt of the gateway  4  to contact the gateway  24  via the Internet  16  fails, it is assumed that the gateway  24  is not connected to the Internet  16 . In that case, the gateway  4  calls the gateway  24  directly via the PSTN using a telephone number stored locally, in order to request that the gateway  24  connects to the Internet  16 . After the request has been transmitted, the gateway  4  directly terminates the connection with the gateway  24 , in order to minimize the connection costs. Alternatively the request to connect to the internet can be included in an ISDN set up message which will be passed by the PSTN to the gateway  24  before a call is established. The latter possibility has the advantage that no connection costs are incurred at all. In response to this request, the gateway  24  connects to the Internet  16 . In general this will be done via a dial up connection over the PSTN  14  via the link  18 . 
     It is observed that it is also possible to pass the address of the calling terminal/gateway combination to the gateway during the request to connect to the packet switched network. This has the advantage that the gateway  24  directly can call the gateway  4  after it has connected to the packet switched network  16 . It is thereby prevented that the calling gateway has to wait a before contacting the called gateway over the packet switched network until it is ensured that the called gateway has connected to the packet switched network. Because this waiting time is not known, the calling gateway has to wait longer than is necessary. 
     If the gateway  4  is connected to the Internet  16  via a dial up connection over the telephone network  14  when the gateway  24  should be called directly, the call to the Internet  16  is terminated and the gateway  24  is called. After having transmitted the request to connect to the internet  16  to the gateway  24  the gateway  4  connects again to the Internet  16  and again tries to contact the gateway  24  for establishing a call between the terminals  6  and  26 . If the gateway  4  has a fixed connection  10  to the Internet or when is has more than one line  12  available to the PSTN  14 , it can stay connected to the Internet  16  when calling the gateway  24  directly. 
     In the network according to FIG. 2, the gateway  4  is present between the PSTN network  14  and the Internet  16 . If the terminal  6  wants to contact the gateway  4  in order to contact a terminal  24  via the Internet  16 , it dials the phone number of the gateway  4  to make a connection. In the present proposal the gateway does not answer calls to obtain information about the actual destination of the call, but uses the numbering/addressing information in the ‘called party number’, “called party subaddress” and/or ‘keypad facility’ information elements. The gateway uses this numbering information to set up a call to the destination terminal  26 . The destination telephony device  26  or the combination of a destination gateway and a (directly or indirectly) connected normal telephony device have a means of identifying and indicating that the telephony device is in the alerting state. The gateway sends an ‘alerting” message to the caller or network when it is informed that the IP-based telephony device or the normal telephony device behind a gateway is in the alerting state. The caller has a means of supplying the required addressing/numbering information and place that information in the ‘called party number’, ‘called Party subaddress’ information elements’ and/or ‘keypad facility’ information elements. 
     A first advantage of this way of setting up a call is that the caller does not incur calling cost until the destination really answers the call. A second advantage is that the behaviour of the destination telephony device, as seen from the caller at the terminal  6  is identical to the behaviour of a destination telephony device that is reached directly through the telephone network. 
     The gateway  4  according to FIG. 3 comprises an interface  30  for interfacing to the PABX  3  or to a local exchange of the PSTN. The interface  30  is connected to a plurality of telephone lines  31 ,  33  and  35 . It is also possible that the interface  30  is connected to the PABX or the PSTN via an E 1  (Europe) or T 1  (US, Japan) line. 
     The interface  30  is connected via a protocol converter  32  to an Internet interface  38 . The protocol converter  32  is arranged for converting the speech signal and the associated control signals received from the interface  30  into signals which can be transmitted via the Internet. Furthermore the protocol converter  32  is arranged for converting the signals received from the Internet into signals which can be transmitted via the telephone interface  30 . The conversion of the signals from the interface  30  to signals to be transmitted over the Internet interface  38  involves speech compression and packetizing the compressed speech signals into packets for transmission over the Internet. If the interface  30  is connected to an analog telephone network, the protocol converter  32  also performs analog to digital conversion. The conversion of the signals from the interface  38  to the signals for the interface  30  involves depacketizing the packets received from the interface  38  into a signal stream, and decompressing the signal stream into a digital speech signal. If the interface  30  is connected to an analog telephone network, the digital speech signal is also converted to an analog signal. 
     The internet interface  38  can be fixedly connected to the Internet, but it is also possible that the Internet interface  38  is connected to the telephone interface  30 , in order to connect to the Internet via a dial up connection. 
     The interface  30  is also connected to a control signal receiver  34  which is arranged for receiving the control signals associated with a connection to the telephone network. If the interface  30  is connected to an analog telephone network, the control signal receiver  34  comprises a tone detector for detecting various signalling tones received from the telephone network and converting them into a corresponding control message. If the telephone interface  30  is connected to an ISDN telephone network, the control signal receiver  34  is arranged for extracting several control messages from the control signals received from the telephone network. Examples of such control messages can e.g. be addressing information carried in an ISDN set up message as explained above. 
     The control signals at the output of the control signal receiver  34  are passed to a controller  40  which interprets the control signals and takes appropriate actions by sending control signals to a dialler/control signal transmitter  36 , to the protocol converter  32  and to the internet interface  38 . 
     If the gateway  4  receives via the interface  30  a set up message including the address information of a terminal to be called via the internet, the control signal receiver  34  extracts the address information from the set up message and passes it to the controller  40 . The controller  40  requests the internet interface  38  to set up a (virtual) connection between said internet interface  38  and the gateway identified with the internet address carried by the set up message. After the connection has been set up, optionally a terminal identification signal is transmitted over the connection in order to address one out of more terminals connected to the remote gateway. The remote gateway signals the status of the remote terminal (alerting, in use, off hook) via the Internet interface to the controller  40 . If the remote terminal goes off hook, the controller  40  instructs the dial/control interface  36  to accept the telephone call corresponding to the previously received set up message. Furthermore the protocol converter  32  is instructed to pass the converted signals from the telephone interface  30  to the Internet interface  38  for transmission to the remote gateway. 
     If the called terminal does not answer the call, the gateway  4  does not answer the call of the calling terminal. This way of dealing with the incoming call has the advantage that no calling costs are incurred before the remote terminal actually answers the call. 
     If the attempt to contact the remote gateway fails, the controller  40  instructs the dial/control interface  36  to dial the telephone number of the remote gateway in order to request that the remote gateway connects to the Internet. Subsequently the gateway  4  tries again to connect to the remote gateway via the Internet. 
     If the gateway  4  does not have a fixed connection to the internet, it should connect to the internet via a dial up connection. In that case, the control signal receiver  34  is arranged for receiving a message from a remote gateway requesting the gateway  4  to connect to the internet. In response to said request the controller instructs the dial/control interface  36  to establish a dial up connection to the Internet.