Abstract:
The invention relates to a method for routing messages between virtual networks in a telecommunication network and to a suitable switching center for said method. According to the invention, signaling connections are set up between virtual networks using an internal signaling loop in a switching center in which virtual networks coexist. Internal signaling loop means that a logical connection has been established between the virtual networks in the switching center in the second and third levels of he message transfer part of the switching center but no physical connection in the first level of the message transfer part of the switching center. Hence, no additional hardware per virtual network is required for the connection.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is the U.S. National Stage of International Application No. PCT/DE02/04422, filed Dec. 3, 2002 and claims the benefit thereof. The International Application claims the benefits of German application No. 10159435.6 filed Dec. 4, 2001, both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention relates to a method for routing messages between virtual networks in a telecommunications network, and to a suitable exchange for said method.  
       BACKGROUND OF INVENTION  
       [0003]     Current telecommunications systems are largely based on Signaling System No 7 (SS7) which agrees modalities and information content of signaling between network nodes (exchanges) and is increasingly used in telecommunications networks.  
         [0004]     The basis of Signaling System 7 architecture is the Message Transfer Part (MTP) which establishes a connection between two adjacent signaling points and ensures fail-safe transmission of control information between them. Overlaid on the Message Transfer Part are various user parts which set up “end-to-end” connections between the originating exchange and the destination exchange.  
         [0005]     As a result of telecommunications market deregulation, different operators can offer their services in competition with one another on the telecommunications market, said operators being able to use the existing network infrastructure in order to save the costs of setting up a separate infrastructure. The networks of the individual operators are mapped onto the existing telecommunications network in the corresponding regions, with overlaps necessarily occurring. This means that in individual cases operators are obliged to e.g. share exchanges.  
         [0006]     Telecommunications networks consist of a plurality of exchanges (nodes). To control the telecommunication networks, information or signaling can be transmitted between the exchanges in parallel with the actual user data (associated) or separately therefrom (quasi associated), a basic distinction being drawn between equipment from which signaling originates or terminates (signaling end point, SEP) and equipment used to connect signaling end points (signaling transfer points, STP and signaling links).  
         [0007]     Each signaling point such as an exchange (node) is uniquely identified in the network by its own signaling point code (SPC). The exchanges forward incoming messages on the basis of routing tables in which all the possible destination signaling points and the signaling routes to be used are entered.  
         [0008]     In order to protect providers sharing an area of the telecommunication network from misuse or manipulation of their networks through the shared and undifferentiable use of the signaling point code SPC, DE 19930116 A1 discloses how separate so-called virtual networks can be set up for the individual operators.  
         [0009]     These virtual networks are completely separated from one another and provide the full functionality of a conventional network. The addresses within these fictitious networks are independent of one another and are autonomously administered by each network operator.  
         [0010]     If communication between virtual networks is required, this is possible e.g. via a gateway in the area of User Level  4  (ISDN User Part ISUP, Signaling Connection Control Part SCCP) of the so-called transit switching equipment or using an external signaling loop (PCM system) between the relevant Message Transfer Part MTP in the signaling transfer point STP.  
         [0011]     For security reasons the gateways (e.g. for STP traffic) between two virtual networks must be handled as if the networks in question were physically separate. This can be achieved by routing the signaling and possibly also the connection via a transit exchange, or by the relevant signaling transfer point STP routing the signaling back to itself via an external signaling loop (hardware loop).  
         [0012]     Additional hardware (e.g. PCM system) is required for setting up an external signaling loop. However, this additional hardware increases the operator&#39;s costs and the space requirement of the overall switching unit.  
       SUMMARY OF INVENTION  
       [0013]     The object of the invention is to specify an exchange or a routing method with which a communication connection can be created between virtual networks without using an external signaling loop.  
         [0014]     This object is achieved by the features set forth in the independent Claims, whereby signaling links are set up between virtual networks by means of an internal signaling loop in an exchange in which virtual networks co-exist. Internal signaling loop means that in the exchange a logical connection between the networks is set up at the second and third level of the Message Transfer Part of the exchange, but no physical connection between the networks at the first level of the Message Transfer Part of the exchange. Additional hardware per virtual network is no longer required for the connection.  
         [0015]     If signaling links are set up from the virtual networks of the exchange to another exchange, the signaling traffic to the other exchange can be shared between the signaling links by means of the internal signaling loop and the bandwidth increased if necessary.  
         [0016]     The invention is further developed by the features of the independent Claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The present invention will now be explained in greater detail with reference to the accompanying drawings in which:  
         [0018]      FIG. 1  schematically illustrates the sequences of the method according to the invention in the Message Transfer Part MTP of the exchange,  
         [0019]      FIG. 2  shows an example of a connection of two subscribers of an exchange who belong to different virtual networks, according to the invention,  
         [0020]      FIG. 3  shows an example of increasing the bandwidth between exchanges by means of the exchange according to the invention, and  
         [0021]      FIG. 4  shows virtual networks in a network section. 
     
    
     DETAILED DESCRIPTION OF INVENTION  
       [0022]     In Signaling System No. 7, each signaling point is uniquely identified by e.g. a 14-bit signaling point code. Each message contains both the signaling point code of the originating signaling point (originating point code, OPC) and of the destination signaling point (destination point code, DPC). Operating two SS7 nodes (exchanges) with the same signaling point code in one and the same MTP network is not possible according to the ITU-T (International Telecommunication Union) or ANSI (American National Standards Institute) standard.  
         [0023]      FIG. 4  shows a network section in which virtual networks as described in DE 19930116 A1 are set up in some exchanges  1 - 6 . Virtual networks N 1 , N 2  are set up only in the exchanges  1  and  3  with the same signaling point code (SPC) in the external network having the network indicator NAT 0 , whereas in the exchanges  2 ,  4 ,  5 ,  6  only one network (NAT 0 ) is set up. The subscribers of the networks and the link-associated trunks between the exchanges  1 - 6  are not shown.  
         [0024]     The exchanges  1 - 6  are connected using network-specific link sets LS. Viewed from the outside, all the link sets LS are assigned to the network NAT 0 . However, as seen by the exchanges  1  and  3 , the individual link sets LS are assigned to virtual networks, i.e. the link sets LS 1   a  . . . LS 1   c  are assigned to the network N 1  and the link sets LS 2   a  . . . LS 2   e  to the network N 2 . Between the exchanges  1  and  3 , the link sets LS 1   c  for the network N 1  and LS 2   c  for the network N 2  exist within the external network NAT 0 .  
         [0025]     To separate the two networks N 1  and N 2  in the exchanges  1  and  3 , each virtual network N 1 , N 2  is assigned an internal network number (network ID). Each incoming message from outside to one of the virtual networks N 1  and N 2  in the exchanges  1 ,  3  is associated with the relevant internal network number. Thus, for example, a signaling message sent from outside via the link set LS 1   a  to the exchange  1  to set up a voice connection to a subscriber on the exchange  3  is associated in the exchange  1  with the internal network number of the network N 1 .  
         [0026]     This can be performed e.g. by an input interface of the exchange  1  inserting the network identifier in a header of a signaling data block. The exchange  1  selects, on the basis of the identifier, the signaling point code SPC used for forwarding the message and detects, for example, that the message must be forwarded to the exchange  3 . For said forwarding the exchange  1  selects the link set LS 1   c  likewise assigned to the network identifier of the network N 1 .  
         [0027]     Each exchange  1 - 6  has a signaling point code which only needs to be unique within its network. The individual exchanges  1 - 6  of a virtual network N 1 , N 2  can only connect with one another by means of those exchanges  1 - 6  that are assigned to their network identifier.  
         [0028]      FIG. 2  shows a network NAT 0  in which the operators A, B, C, D and E share the exchange  1 . Each of the virtual networks N 1  . . . N 5  is autonomously administered by the telecommunications providers A . . . D separately and without affecting the other virtual networks.  
         [0029]     Operator B and operator E agree that the subscribers X and Y of their respective networks N 5  and N 2  may communicate with one another. For this purpose a gateway for the signaling is set up by an internal signaling loop S between the two separate SS7 networks N 2  and N 5  in the exchange  1  and a communication connection T (trunk) is set up for voice transmission between the local exchanges LE x  and LE y  of the subscribers X, Y.  
         [0030]     For correct handling of the SS7 messages in the Message Transfer Part MTP, the corresponding SS7 routing data (route, route set, link, link set, etc.) is set up in the exchange  1 . According to the invention, no physical SS7 data link is set up for the internal signaling loop S at MTP Level  1 , i.e. at MTP Level  3  and MTP Level  2  a logical connection is set up between the virtual SS7 networks N 2  and N 5  in the exchange  1 , but no physical connection at MTP Level  1 .  
         [0031]      FIG. 1  shows the structure and the corresponding sequences in the Message Transfer Part MTP of the exchange  1 . It may be seen that the SS7 link L 1  which is to function as an internal signaling loop S is treated in the same way as a normal link that has been set up physically. Data is exchanged by means of the link L 1  at Message Transfer Part Levels  3  and  2 .  
         [0032]     The SS7-relevant routing data (route, route set, link, link set, etc.) is set up in the known manner, the internal signaling loop S being set up by a special SS7 link L 1  which is identified as “Link L 1  without SS7 Data Link L 2 ”. When setting up said SS7 link L 1 , the logical name of the SS7 link is additionally made known in the other virtual network N 2  or N 5  in each case, i.e. no physical connection L 2  for data transmission of the signaling is switched by the exchange  1  for the communication of the subscribers X and Y. As no physical connection L 2  relating to the logical connection L 1  exists here, the link L 1  is specifically identified.  
         [0033]     The following example illustrates the setting up of the SS7 link for an internal signaling loop S between the networks N 2  and N 5  in the virtual network  1 .  
         [0034]     Setting up the SS7 link L 1  in the virtual network N 2 : 
        CreateLink:     Name=iSigLoop 1   13  N 2 ;     SigLoop=TRUE;     LinkTermination=iSigLoop 1  N 5 ; LinkSet=LinkSetA;     Setting up the SS7 link L 1  in the virtual network N 5      CreateLink:     Name=iSigLoop 1   13  N 5 ;     SigLoop=TRUE;     LinkTermination=iSigLoop 1   13  N 2 ;     LinkSet=LinkSetB;        
 
         [0045]      FIG. 3  shows an example of increasing the bandwidth of the connections between the exchange  3  (central database; e.g. SCP, HLR) and the exchanges  1  and  2  or the signaling transfer points STP preceding the local exchanges LE 1  . . . LE N .  
         [0046]     It shall be assumed that the signaling traffic caused by an increase in the data inquiries to the database  3  from the local exchanges LE 1  . . . LE N  can no longer be handled using one link set between the exchange  1  and the database  3  and the exchange  2  and the database  3  in each case. The networks N 1  and N 2  are set up in the exchange  1 , and the networks N 3  and N 4  in the exchange  2 , said networks being connected by means of internal signaling loops S 1  and S 2  respectively. The accumulated signaling traffic of the local exchanges LE 1  . . . LE N  can now be distributed over the link sets LS 1  . . . LS 4 , provided that the local exchanges LE 1  . . . LE N  remain unaffected by this expansion.  
         [0047]     To ensure that the signaling traffic (database inquiries to the database  3  and returning of results to the local exchanges LE 1  . . . LE N ) can be evenly distributed to the four link sets LS 1  . . . LS 4  now available, corresponding routes must be set up in the node exchanges  1  and  2 . For example, in the virtual network N 2  in the exchange  1  a second route is set up via the internal signaling loop S 1  and the link set LS 1  to the database  3  in addition to the originally available route LS 2  to the database  3 . Similarly, in the virtual network N 4  in the exchange  2  a second route is set up via the internal signaling loop S 2  and the link set LS 3  to the database  3  in addition to the originally available route LS 4  to the database  3 . The signaling traffic is evenly distributed over the link sets LS 1  . . . LS 4  on the basis of data from the signaling traffic and settings in the exchanges  1  and  2 .  
         [0048]     The example shows that data transmission and signaling traffic between the exchanges  1  and  3  and  2  and  3  can be increased using the exchange according to the invention, with no corresponding virtual networks having to be set up in the partner exchange (database)  3 .