Patent Publication Number: US-2007115943-A1

Title: System and method for establishing emergency communications in a telecommunication network

Description:
The present invention relates to a system and a method for establishing voice and/or data communications, in particular the invention relates to establishing emergency calls or emergency data communications, in a telecommunication network. More particularly, the invention relates to redirecting emergency voice calls or emergency data transmissions, from a faulty signaling path to an available, non-faulty, signaling path.  
     BACKGROUND OF THE INVENTION  
      Recent developments in telecommunication networks provide for the possibility of placing telephone calls through the Internet which is generally referred to as Internet Telephony. In particular, transmission of voice signals over the Internet is generally known as voice over IP, or VoIP in abbreviated form (where IP stands for Internet Protocol). In a VoIP call, the signal travels from a voice environment network to an IP environment network and vice-versa. In the following, the terms “IP network” are used for referring to any network using Internet Protocol, be it related to a global network, e.g. the so-called World Wide Web, or a network with limited reach such as a local network.  
      It is to be noted however that in the present specification, a VoIP communication is not to be construed as being limited to communicating only voice signals. Those skilled in the related art will realize that also data may be transmitted in a VoIP communication. Therefore any reference herein to VoIP is to be construed as covering both types of transmission.  
      When voice travels through an IP network, the voice signals need to be transmitted in packets. This form of transmission, known as “packet mode”, which is appropriate for communication through a packet network such as the Internet, is different from the conventional mode of transmission of voice signals, known as “circuit mode”, which is used in conventional telephony networks such as the so-called Public Switched Telephone Networks (PSTN).  
      Likewise, data transmissions that were traditionally transported using circuit-switched networks (i.e. in circuit mode), such as transmissions using a modem or an Integrated Services Digital Network (ISDN), can nowadays also be transported through an IP network.  
      When voice or data is transmitted from an IP network to a PSTN or to an ISDN, or vice-versa, it is required that the circuit mode transmission is converted into packet mode, or vice-versa, in order to maintain the communication active. The conversion is usually done by means of an interface, which may be a hardware device and/or a software program, known as a “media gateway”.  
      Media gateways are also used to connect PSTN or ISDN terminals (such as analogue phones, modems and ISDN devices) to the IP network. This kind of gateways is usually known as “access gateway”.  
      In the following, for the sake of simplification of the description, media gateway or access gateway will be referred to as “gateway”. Thus, in general terms, a gateway provides connectivity between two networks which use incompatible protocols as discussed in the examples above.  
      A gateway used for the above purposes usually communicates with a “call server”. A call server is a software application implementing call control in modern networks (e.g. Next Generation Networks), wherein packet transport is used to carry voice or multimedia flows. The term “call server” is used in the present specification as a generic term that may cover different environments and products. By way of non-limiting example a call server may be a Megaco/H.248 media gateway controller as is well-known in the art; other known types may also be used as long as their operation falls within the scope of the present invention. In summary, a call server provides centralized call intelligence.  
      In a VoIP communication, a master/slave relationship is preserved at all times between a call server and a gateway in order to ensure signaling control and connection management on the call.  
      This however causes a drawback in the sense that the availability of the service becomes dependent on the correct operation of the call server. If the call server fails or is not reachable, the service is interrupted. In order to avoid such service interruptions due to the failure of a call server one known solution is the use of one or several secondary call servers that are introduced in the telecommunication network so as to temporarily replace the primary call server in case of a failure of the latter. However, despite having secondary call servers installed in the network, situations may arise in which it would not be possible to contact any one of these call servers (neither the primary nor the secondary ones). One such situation may arise, for example, in the case of a natural disaster wherein part of a telecommunication network could become isolated from call servers. In such situations, even if the local network, from which a call is originated is not damaged, a call that in a normal situation would be controlled through the primary or secondary call centers, could not be established due the complete isolation of that part of the network from the corresponding call servers. This means that one would not be able to even establish emergency calls or emergency data transmissions, which under normal conditions are given priority as regards service availability.  
      It is therefore desired that a solution is provided in order to be able to establish at least emergency communications in case of unavailability of the primary and secondary call servers.  
     DESCRIPTION OF THE INVENTION  
      The above objective is reached by using the solution proposed by the present invention according to which, in case of loss of contact between the gateway and the call server, a peer-to-peer signaling procedure is initiated between the gateway and the emergency service, for example based on SIP (Signal Initiation Protocol) or any other suitable protocol, in order to redirect certain types of communications through an available communication path. The type of communications to be redirected may be determined by the network operator or the service providers or by any appropriate managing entity of the network. For instance, priority subscribers, such as government lines, could be enabled to send and receive voice calls or data communications.  
      For the sake of simplicity, a voice call or a data communication will be referred to in the present specification as “communication” and an emergency voice call or an emergency data communication will be referred to as “emergency communication”.  
      Such emergency communications may be established based on emergency dialing patterns for obtaining a particular response or service, such as an emergency service.  
      Accordingly one object of the present invention is that of providing a method for establishing a voice or data communication in an Internet Protocol (IP) communication network, the network comprising a gateway and at least one call server, characterized in that the method comprises the steps of; 
          detecting unavailability of a communication link between the gateway and said at least one call server;     initiating at the gateway, an alternative signaling procedure for establishing communication, through an alternative communication link with a node, said link being a peer-to-peer communication link; and     establishing communication through said alternative communication link.        

      Another object of the present invention is that of providing a voice over Internet Protocol (VoIP) communication network, the network comprising a gateway connected to the at least one call server adapted for establishing a first signaling procedure with said at least one call server, characterized in that the gateway is further connected to a node through a peer-to-peer communication link and is adapted for initiating an alternative signaling procedure for establishing a communication, through said peer-to-peer communication link with said node when said first signaling procedure is unavailable.  
      A further object of the present invention is that providing a gateway unit for use in a voice over Internet Protocol (VoIP) communication network, the gateway being connected to at least one call server adapted for establishing a signaling procedure with said at least one call server, characterized in that the gateway is further connected to a node through a peer-to-peer communication link and is adapted for initiating an alternative signaling procedure for establishing a communication, through said peer-to-peer communication link, with said node.  
      A still further object of the present invention is that of providing a node for cooperating with the gateway of the present invention by mean of a peer-to-peer communication link, and adapted for establishing a communication to a destination terminal in response to a signaling procedure initiated by said gateway and received through said peer-to-peer communication link  
      These and further features of the present invention are explained in more detail in the following description as well as in the claims with the aid of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic representation of a telecommunication network implementing an exemplary embodiment of the solution of the present invention.  
       FIG. 2  is a flow-chart representation of an example of main steps of the procedure performed by or for a gateway for establishing an emergency communication, according to the present invention.  
       FIG. 3  is a block diagram representing an exemplary embodiment of the main blocks constituting a gateway for use in the present invention. 
    
    
     EXAMPLES OF PREFERRED EMBODIMENTS  
       FIG. 1  shows an example of a telecommunication network  1  in which a VoIP communication may be implemented. It is to be noted that the network  1  shown in  FIG. 1  may comprise a plurality of networks of different type such as IP networks  12  or  31  and circuit mode networks such a PSTN networks  22 . The basic principles of operation of such a network are well known by those skilled in the related are. Nevertheless a short description is provided herein for the sake of clarity.  
      As stated further above, VoIP relates to communicating voice—and possibly data—over an IP network. In order to achieve this, voice may travel from a voice network environment to an IP network environment. In case of using voice legacy equipment, the latter can be directly connected to a gateway that provides access to the IP network.  
       FIG. 1  shows a case in which the calling party say at user terminal  11  and the called party say at destination terminal  21  are both located within respective voice network environments. However, those skilled in the art will realize that the calling party or the called party may be located in other types of combination of voice and IP network environments for the implementation of the present invention. Also both the calling party and the called party may be adapted for receiving a voice call or a data transmission.  
      According to the scheme shown in  FIG. 1 , a user terminal  11  is connected to a first IP network  12  implementing packet mode connectivity through a gateway  13  which is connected to the first IP network  12  , on the one hand, and to the end user terminal  11 , on the other. As stated further above, a gateway serves as an interface between the voice environment of the end user terminal  11  and the IP network  12 . The IP network  12  is in turn connected to intermediate equipment such as for example routers which, as is known in the art, are used for routing the packet transmission towards appropriate destinations. In the example of  FIG. 1 , the router  14  routes the transmission from IP network  12  towards router  32  which in turn routes the transmission towards the IP network  31 .  
      The IP network  31  is further connected to a circuit mode network  22 , in this example a PSTN, through a gateway  23 . The circuit mode network  22  provides connectivity to the destination terminal  21 , to which the communication is eventually addressed, through the local exchange  26  in a manner known in the art.  
      In the example of  FIG. 1 , a call server  15  is configured to control the call traffic, or data transmission, passing through gateway  13  and another call server  24  is configured to control the call traffic, or data transmission, passing through gateway  23 .  
      Call servers  15  and  24  may be located at any convenient location, for example within the IP network  31  or the IP network  12  or any other. Call servers however require connectivity with the circuit mode networks toward which the corresponding gateways act as interface. In  FIG. 1 , call server  24  is shown to be in connection with the circuit network  22  through a connection  25  and local exchange  27 .  
      The above description in relation to  FIG. 1  is a general representation of a conventional VoIP configuration, in a typical Next Generation Network (NGN). Under normal, non-faulty conditions, communications may be established between the two end points of the network, namely from user terminal  11  to destination terminal  21 .  
      However, it may so happen that communication is interrupted between the gateway  13  and the call server  15 . Due to this interruption, communications can no longer be established between the two end points. In order to remedy this interruption, the network may have provisioned the use of secondary call server(s) (not shown in the figure). The secondary call server(s) would then replace the function of the primary call server  15  in order to provide connectivity with the gateway  13  and thus ensure the possibility of placing calls or establishing communication.  
      However, in a situation where the primary call server and the secondary call server(s) become unavailable, for example because the network in which they are located is completely or partially damaged, this conventional configuration becomes unusable. Consequently, not only normal calls, but also emergency communications could not be established.  
      According to the present invention, a link is provided between gateway  13  and a node  40  based on a peer-to-peer configuration. A peer-to-peer configuration, as known in the related art, provides direct control communication from an end point to another end point without passing through intermediate call servers. The link established between the gateway  13  and node  40  is preferably a logical link, however other types of links such as physical links based on the use of cable or fiber connection may also be employed.  
      Therefore in the example provided in  FIG. 1 , due to the presence of a link—in case of failure in the conventional transmission path—gateway  13  communicates with node  40  directly and without intervention of any other intermediate call server. In case of establishing a logical link between the gateway  13  and the node  40 , the link is established by any known suitable protocol such as for example SIP. Consequently, in case of interruption of communication between gateway  13  and call server  15  (and secondary call servers, if any), the interruption does not affect node  40  and thus gateway  13  maintains connectivity with node  40 . This allows for placing calls or establishing communication in a selective manner through the link established between the gateway  13  and the node  40 .  
      Node  40 , may be configured based on any resource constituting a junction, branch or concentration of communication lines in a network such as a server, a concentrator, a front-end processor, a router or the like. Node  40  may then be configured to redirect the call, or the data communication, to the end point where the emergency communication is intended to be directed to The redirection of the communication from the node  40  may be made in various manners. One of such manners may be using a peer-to-peer link to a convenient point of the destination network. In  FIG. 1  one example of such redirection is represented by a link  41  between the node  40  and the call server  24 .  
      Alternatively, the redirection may be made indirectly, using intermediate entities between node  40  and the destination terminal of the communication. The intermediate entity may be any combination of packet mode supporting network and circuit mode supporting network, selected according to the particular requirements of each application. The intermediate entity is connected to the destination terminal to which in this alternative case, the communication is to be directed.  
      Another alternative situation may be one in which the calling party and the called party are both located in the same network while the call server is in a different network. This situation may occur frequently in cases where the communication is intended for a local emergency service, such as for example a Fire Department, located in a nearby geographical location with respect to the calling party, but the call server is in a network which is not in the same geographic area as that of the emergency service. This situation is schematically represented by the destination terminal  43 , assumed to be in the same network as the calling party user terminal  11  and gateway  13 . The call server  15  is, as previously described, connected to a different network  31 . In this case, where a faulty condition arises, gateway  13  communicates with the node  40  by means of a peer-to-peer link and node  40  then directs the communication to the destination terminal  43  that could be directly connected to node  40  (as shown in the figure) or through a gateway (not shown in the figure).  
      With the above arrangement, and referring to the procedure as shown in  FIG. 2 , the following steps are taken in order to establish an emergency communication. 
          i—In step  100 , gateway  13  receives a request for transmitting a communication.     ii—In step  101 , gateway  13  checks the status of control link (indicative of the quality of signaling in transmission) between gateway  13  and call server  14 ; in case the above control link is available, the communication is established as conventionally known. This is represented in  FIG. 2  by an arrow from step  101  to step  102 .     iii—If the above control link is not available, and assuming that the network may optionally comprise secondary call servers, the gateway  13  checks the status of the control link between gateway  13  and a secondary call server as shown by step  103 . If the control link to a secondary call server is available, gateway  13  establishes a control association with the secondary call server and the communication is established as conventionally known. This is represented by an arrow from step  103  to step  102 . If the control link is not available with a secondary call server, the procedure is repeated with other secondary call servers until an available control link is found in which case the communication is established using the available link, as conventionally known. This repetition of the procedure is represented in  FIG. 2  in a simplified manner by means of only one block stating “any link status OK?” in step  103 . This block is to be construed as an indication that the repetition of this procedure may be necessary with respect to a plurality or even to all secondary call servers in the network. As stated above, secondary call servers may be present in the network as an optional feature. Step  103  in  FIG. 2  thus represents this optional situation. However if no secondary call server is present, the procedure follows from step  101  directly to step  104  as shown by the broken line  108 .     iv—If all the above links are unavailable, gateway  13  checks, as shown in step  104 , the type of the incoming call request. If the incoming call request is not of emergency type, no communication is established and the operation is terminated as shown by the arrow from step  104  to step  105 .     v—If the communication is of an emergency type, gateway  13  initiates, as shown in step  106 , an alternative signaling procedure, through an alternative link to node  40 , the link thus established being a peer-to-peer communication link.     vi—In step  107 , node  40  redirects the emergency communication to the desired destination terminal to which the emergency communication was intended to be sent        

      It is to be noted that the above procedure is provided only in an exemplary manner and the invention may not be construed as being limited to the above procedure. Those skilled in the art will appreciate that alternative procedures may be applied as long as they remain within the scope of the present invention. In particular, the order of executing the steps taken in the procedure may vary. For example step  104  may be executed after step  100  and before step  101 .  
      The above procedure may be performed, for instance, by using one or more conventional processors included in the gateway  13  or in a separate unit being in bi-directional connectivity with the gateway  13 . The processor(s) may be programmed in a suitable manner, known by those skilled in the related art, so as to perform the required controls and generate appropriate commands.  
       FIG. 3  shows a block diagram with the main components of a gateway  13  in accordance with the present invention. As shown in the figure, user terminals of different type, generally shown by reference numeral  11 , may be used such as a POTS (plain old telephony system) unit, a computer or a facsimile machine, to communicate through a subscriber line interface  111  with gateway  13 .  
      Gateway  13  comprises two main functional blocks  131  and  134 . Signaling and control functions are performed by block  131  in order to provide signaling interface with the call server  15  in normal, non-faulty, working conditions or with the peer-to-peer node  40 , in an emergency condition. On the other hand, block  134  performs the tasks of digital signal and packet processing in order to process signals coming from the subscriber line interfaces encapsulating them in packets that are transmitted to the network. The function of the digital signal and packet processing block  134  is known in the related art, thus a detailed description thereon is considered not necessary.  
      Inside the signaling and control block  131 , there are two functional sub-blocks. Sub-block  132  is adapted to establish a control association with a given protocol  1  (for example Megaco/H.248 or any other suitable protocol) with the call server  15  in a master/slave mode, wherein the gateway  13  acquire the slave&#39;s role while the call server  15  operates as master. The second sub-block  133  is related to operation in emergency conditions, i.e. when it is not possible to reach any of the provisioned call servers as discussed above. Therefore, sub-block  133  is used for establishing a peer-to-peer association with an emergency node  40 , for example any suitable server using SIP or other suitable protocols.  
      The user terminal  11  from which the communication is initiated, may be any known device allowing for placing a voice call such as a POTS telephone or a computer or facsimile machine connected to a modem or an ISDN equipment.  
      The called party terminal  21  or  43 , to which the communication is intended for may be any known device adapted for receiving either voice calls in circuit mode such as a POTS unit, or data transmissions in voiceband data such as a digital computer, or voice and data transmissions such an ISDN device.  
      Node  40  may include programmed instructions so as to perform the following operations: 
          once the alternative signaling procedure is initiated between the gateway  13  and the node  40 , the latter establishes the communication directly with the destination terminal if the latter is connected to  40  (the link between node  40  and the destination terminal  43  in  FIG. 1 ); or     once the alternative signaling procedure is initiated between the gateway  13  and the node  40 , the latter automatically redirects the emergency communication, through a pre-established route, towards the called party gateway or to any other intermediate entity capable of transmitting the communication to the called party destination terminal; or,     once the alternative signaling procedure is initiated between the gateway  13  and the node  40 , the latter selects, by means of appropriate software and based on pre-established criteria, the route through which the communication is to be redirected towards the called party gateway or to any other intermediate entity capable of transmitting the communication to the called party destination terminal.        

      The pre-established criteria may for example be based on minimizing the resource occupancy of the network or on the type of the emergency service requested.  
      The peer-to-peer communication may be initiated based on for example a SIP (Signal Initiation Protocol) or any other suitable protocol.  
      The communication between the gateway  13  and the node  40  may be of any known kind. For example the gateway may send a message in which the destination terminal who should receive the emergency communication is identified. In an IP environment, this is typically done by including the so-called Uniform Resource Identification (URI) of the destination that can have different formats such as a “name@host” format. Alternatively, the communication may be based on the use of a directory number. Still another alternative for performing the communication would be that of including, by the gateway  13 , an indication of the nature of the emergency communication. For example, an emergency communication intended for a Fire Department may have a certain indication which may be distinguished by the node  40  from other indications related to other destinations such as the Police Department, ambulance service, etc. Thus, the node  40  will redirect the communication based on the indication provided.  
      The node  40  may be an independent node especially adapted for maintaining a peer-to-peer link with the gateway  13 . Alternatively, as already discussed, the node  40  may form part of another network, different from the networks to which gateway  13  is connected. In this case, node  40  is preferably configured to redirect the emergency communication once received, based on pre-established priority criteria.  
      It is to be noted that while the solution proposed by the present invention is in principle conceived for placing emergency communications, it is not be construed as being limited to only such type of communications. Therefore, the solution proposed herein is equally applicable to situations where it is desired to redirect a communication, for any particular reason and whatever its nature may be, using the peer-to-peer link between the gateway ( 13 ) and the node ( 40 ).  
      As can be readily appreciated, the solution proposed by the present invention provides substantial improvement in the level of reliability of a VoIP network, in particular when an emergency communication cannot be established due damages to the network.