Abstract:
A signal relay device, method thereof, and system using the same. The system utilizes SCTP with multiple transmission addresses to share communication layers above the transmission layer in signal gateway cluster, automatically switching to an available signal gateway for maintaining online status and increasing availability of signal. transmission.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a signal relay device and method thereof, and in particular to a system using the signal relay device, relaying an SS7 (Signaling System 7) signal from a PSTN (public switched telephone network) to an IP (Internet protocol) network.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventional PSTNs, used in analog stations and fax transmission, and IP networks, used in digital data transmission, function under different networking protocols. For development of digital signal processing (DSP) and computer telephone integration (CTI) technologies, modern products and services extend new applications in computers and telephones like computer telephone application generators, unified message systems (UMS), and automatic call distribution, integrating them with Internet function to provide Internet telephone gateways.  
           [0005]    Voice over Internet protocol (VoIP), based on international telecommunication union-telecommunication standardization sector (ITU-T) H.323, provides basic call services. The H.323 architecture, however, cannot equip current VoIP systems for future integration with PSTN. Signals for a PSTN call are passed via a trunk gateway and SS7 signals network. SS7-ISUP (Integrated Service Digital Network User Part) signaling takes charge of the call, passing between an originating switch and a terminal switch through signal transfer points of an SS7 network for general communication. In an Internet telecommunication architecture, an IP network works with a conventional telecommunication network through an SS7 network and signal gateway (SG), receiving signals from the SS7 network, which is then converted and transferred to a media gateway controller (MGC), capable of call control and routing, signaling processing, media gateway control, and call detail recording (CDR).  
           [0006]    In a conventional PSTN, signaling is transferred through signal transfer points to a local exchange to be marked and then transmitted to a telephone receiver. In addition, signaling is transferred among signal transfer points according to routing tables internally established, wherein the signal transfer points pick an available route to determine a new transfer point when a subsequent transfer point is unavailable. A signal gateway is a bridge between an SS7 network and an IP network, transferring call control messages as ISUP signaling. The single channel between a signal gateway and a media gateway controller, however, cannot bridge an SS 7  network and an IP network.  
           [0007]    In U.S. patent application Pub. No. 2002/0027983, Suzuki et al disclose a gateway system having a redundant structure of media gateway controllers, relating to a gateway system utilizing a common channel signaling system to connect an existing telephone network to an IP network, enhancing reliability without system downtime even during failure. The gateway system comprises a media gateway and a controller group therefor, comprising a plurality of media gateway controllers assigned with a common point code. Any of the media gateway controllers can terminate an SS7 signal representative of a control signal of the common channel SS7 in the telephone network and carry out call and connection control to the IP network by controlling the media gateway through the IP network. Thus, a communication path is established between the telephone network and the media gateway. Drawbacks of the application include the combination of signal gateways and media gateway controllers being unusual and lacking flexibility for receiving signals and synchronization data traffic between media gateway controllers is heavier due to synchronization signals from other media gateway controllers  
         SUMMARY OF THE INVENTION  
         [0008]    Accordingly, an object of the present invention is to provide a signal relay device and method thereof for bridging a PSTN and an IP network and enabling data synchronization.  
           [0009]    Another object of the invention is to provide a signal relay system relaying SS7 signals from a PSTN to a media gateway controller, allowing online backup to reestablish connection when a primary connection is broken.  
           [0010]    The present invention provides a signal relay system using the signal relay device and method thereof. The system comprises a signal relay device, comprising a master signal relay process module and at least one slave signal relay process module, and a media gateway controller for sending an online request.  
           [0011]    The master signal relay process module comprises a first M3UA-LM (Message Transfer Protocol 3—User Adaptation Layer—Layer Management) module corresponding to the communication layer of M3UA and a first SCTP-LM (Stream Control Transmission Protocol—Layer Management) module corresponding to the transmission layer of SCTP. The slave signal relay process module comprises a second M3UA-LM module corresponding to the communication layer of M3UA and a second SCTP-LM module corresponding to the transmission layer of SCTP.  
           [0012]    The master signal relay process module sends first synchronization data using the first SCTP-LM module when receiving an online request from the media gateway controller, returning an IP message to the media gateway controller, and the slave signal relay process module receives the first synchronization data using the second SCTP-LM module. The media gateway controller connects with the master signal relay process module when receiving the IP message and sends a service-received request.  
           [0013]    The master signal relay process module sends second synchronization data using the first SCTP-LM module when communication data is transferred between the media gate controller and the signal relay device, synchronizing information between the first SCTP-LM module and the second SCTP-LM module. Next, the slave signal relay process module receives the second synchronization data using the second SCTP-LM module, thereby updating an SCTP database. Next, the first M3UA-LM module sends third synchronization data when the communication data, such as ASPUP, ASPDN, ASPAC and ASPIA messages, changes the service status of the media gateway controller and the slave signal relay process module receives the third synchronization data using the second M3UA-LM module, thereby updating a M3UA database. Finally, the slave signal relay process module reestablishes the connection when connection between the master signal relay process module and the media gateway controller is broken.  
           [0014]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
         [0016]    [0016]FIG. 1 is a schematic diagram showing the architecture of a signal relay system according to the present invention;  
         [0017]    [0017]FIG. 2 is a flowchart showing detailed steps of establishing an SCTP connection between a media gateway controller and a signal relay device according to the present invention; and  
         [0018]    [0018]FIG. 3 is a flowchart showing detailed steps of data synchronization between a master signal relay process module and a slave signal relay process module when service status of the media gateway controller is changed according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    The present invention provides a signal relay device and method thereof and a signal relay system using the same.  
         [0020]    The method of the present invention provides transmission for telecommunication signaling with complete backup architecture to cope with unexpected errors in software and hardware. Signal gateways utilize SCTP, with multiple transmission addresses, in a transmission layer, enabling communication protocol layers thereabove to be shared between signal gateways for increased reliability.  
         [0021]    One reason to replace Transmission Control Protocol (TCP) with SCTP is that SS7 signals transmission is urgent and the retransmission mechanism of TCP creates unacceptable delays. The other is that TCP is easily susceptible to resource limitation, resulting in system crash.  
         [0022]    SCTP, defined by Internet Engineering Task Force Signaling Transport (IETF SIGTRAN), is a connection-oriented transmission protocol, transmitting signal messages from a PSTN to an IP network and satisfying application requirements, and, similar to TCP, a reliable transmission protocol in packet switching networks. Compared to TCP, SCTP provides more functions of non-sequential transmission, Internet protocol version 6 (IPv6) and IPv4 addressing, multiple transmission addresses, and others.  
         [0023]    MTP3 takes charge in establishing routes for signaling packets and traffic control  
         [0024]    M3UA, based on SCTP, transmits SS7 signals between signal gateways and media gateway controllers. In addition, layer management defined in M3UA (M3UA-LM herein) sets M3UA parameters, establishes an SCTP connection, and maintains online status of media gateway controllers. The invention provides a layer management for SCTP (SCTP-LM herein), similar to M3UA-LM, to establish an internal network in which signal relay devices connect with each other for data synchronization.  
         [0025]    [0025]FIG. 1 is a schematic diagram showing the architecture of a signal relay system according to the present invention. The architecture comprises a signaling point  100 , a signal relay device  200  comprising a master signal relay process module  210  and a slave signal relay process module  230 , and a media gateway controller (MGC)  300 . In addition, master signal relay process module  210  comprises a first M3UA-LM module  211  corresponding to the communication layer of M3UA and a first SCTP-LM module  213  corresponding to the transmission layer of SCTP. Slave signal relay process module  230  comprises a second M3UA-LM module  231  corresponding to the communication layer of M3UA and a second SCTP-LM module  233  corresponding to the transmission layer of SCTP.  
         [0026]    First, MGC  300  sends an online request and master signal relay process module  210  sends first synchronization data using first SCTP-LM module  213  when receiving the online request and returns an IP message to MGC  300 , in which the IP message includes IP addresses for master signal relay process module  210  and slave signal relay process module  230 . Slave signal relay process module  230  then receives the first synchronization data using second SCTP-LM module  233 .  
         [0027]    Next, master signal relay process module  210  sends second synchronization data using first SCTP-LM module  213  when communication data is transferred between MGC  300  and signaling point  100 , synchronizing information between first SCTP-LM module  213  and second SCTP-LM module  233 .  
         [0028]    Next, slave signal relay process module  230  receives the second synchronization data using second SCTP-LM module  233 , thereby updating an SCTP database thereof. Master signal relay process module  210  then sends third synchronization data using first M3UA-LM module  211  when the communication data changes service status of MGC  300  and slave signal relay process module  230  receives the third synchronization data using second M3UA-LM module  231 , thereby updating the service status of MGC  300  for M3UA thereof.  
         [0029]    Synchronization data between the master signal relay process module and the slave signal relay process module uses SCTP connections, synchronized when connection is established or broken, or transmission control blocks (TCB), identification tags for SCTP, and others, synchronized when communication data is transferred through SCTP. Another is available service status of application server processes maintained by M3UA-LM and routing databases, synchronized when service status of media gateway controllers or routing data is changed.  
         [0030]    [0030]FIG. 2 is a flowchart showing detailed steps of establishing an SCTP connection between a media gateway controller and a signal relay device according to the present invention.  
         [0031]    In Step S 11 , a media gateway controller sends an online request, comprising an IP address of the media gateway controller, through M3UA when connecting with a signal relay device, establishing an SCTP connection.  
         [0032]    In Step S 12 , a master signal relay process module of the signal relay device receives the online request through SCTP, sends a connection prompt to upper M3UA, updates an SCTP status of a first SCTP-LM module thereof, and returns an IP message to the media gateway controller. Thus, a connection between the master signal relay process module and the media gateway controller is established.  
         [0033]    In Step S 13 , the master signal relay process module sends first synchronization data using the first SCTP-LM module to a second SCTP-LM module of a slave signal relay process module of the signal relay device, since, because online data is changed, the SCTP connection is established, synchronizing online information.  
         [0034]    In Step S 14 , the slave signal relay process module receives the first synchronization data using the second SCTP-LM module and updates an SCTP database thereof, completing the online backup with the media gateway controller.  
         [0035]    The above describes the process for establishing an SCTP connection between a media gateway controller and a signal relay device. The service status of M3UA must be updated if the online status of SCTP is changed, described as follows.  
         [0036]    [0036]FIG. 3 is a flowchart showing detailed steps of data synchronization between a master signal relay process module and a slave signal relay process module when service status of the media gateway controller is changed.  
         [0037]    In Step S 21 , it is determined whether communication data is transferred between the media gateway controller and the signal relay device. If so, the process goes to step S 22 , and, if not, to step S 24 .  
         [0038]    In Step S 22 , when communication data is transferred between the media gateway controller and the signal relay device, changing TCB information of SCTP, the master signal relay process module sends the second synchronization data using the first SCTP-LM module thereof to the second SCTP-LM module of the slave signal relay process module for synchronization of the TCB information of SCTP.  
         [0039]    In Step S 23 , the slave signal relay process module receives the second synchronization data using the second SCTP-LM module thereof and thereby updates the SCTP database thereof, completing synchronization of the TCB information of SCTP with the master signal relay process module.  
         [0040]    In Step S 24 , it is determined whether the communication data has changed the service status of the media gateway controller. If so, the process goes to step S 25 , and, if not, to step S 21 .  
         [0041]    In Step S 25 , when the communication data changes the service status, the master signal relay process module sends third synchronization data using the first M3UA-LM module thereof to the second M3UA-LM module of the slave signal relay process module for synchronization of the service status of the media gateway controller.  
         [0042]    In Step S 26 , the slave signal relay process module receives the third synchronization data using the second M3UA-LM module thereof and thereby updates a M3UA database thereof, completing synchronization of the service status of the media gateway controller with the master signal relay process module.  
         [0043]    The media gateway controller switches the IP address and transfers the communication data from the master signal relay process module to the slave signal relay process module when connection between the master signal relay process module and the media gateway controller is broken, synchronizing SCTP online status, TCB information, and service status of Application Server Processes (ASP) of the slave signal relay process module with the master signal relay process module for continuing the data transmission.  
         [0044]    The present invention&#39;s transport layer provides increased availability with quick diagnostic reaction, without processing or retention of additional information, such that media gateway controllers&#39; corresponding standards are thoroughly supported.  
         [0045]    When the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.