COMMUNICATION SYSTEM COMPRISING SEVERAL NETWORK ELEMENTS, COMMUNICATION METHOD, AND NETWORK ELEMENT

Abstract: AThe invention provides a communication system and method wherein information can be properly routed also across network borders between networks of different types. The communication system comprises several network elements, wherein a first network element is adapted to convert a destination indication, e.g. a Destination Point Code (DPC) contained in a message, into an interrogation form suitable for interrogation of a server entity. The server entity is adapted to return an address when interrogated using the interrogation form. The message may then be sent by the first network element or another network element to the address returned by the server entity. The message may be a MAP (Mobile Application Part) message. The first network element may be part of a protocol converting entity which preferably contains a SIGTRAN protocol stack having a SCCP layer on top of a M3UA layer, the SCCP layer supplying the destination indication to the M3UA layer for conversion into the interrogation form. The server entity preferably is a Domain Name Server (DNS), and the address returned by the server entity may be an IP address. For achieving load-sharing, the server entity can store two or more alternatively selectable addresses for at least one of the destination indications.

Description: COMMUNICATION SYSTEM COMPRISING SEVERAL NETWORK ELEMENTS, COMMUNICATION METHOD, AND NETWORK ELEMENT FIELD OF THE INVENTION The invention generally relates to a communication system and method allowing a proper routing of messages to an intended destination. Furthermore, the invention relates to a network element usable in such a communication system and method. BACKGROUND OF THE INVENTION When connections are to be established in a communication system e.g. for establishing a call or sending a message, a proper routing of the information to be transmitted is necessary. In particular in a case where two or more networks of different types are involved in providing a connection, the correct connection establishment may become difficult. As an example, in an All-IP network, a protocol stack such as SIGTRAN (Signalling Transport) protocol stack as defined by IETF (Internet Engineering Task Force) may be used to carry a Mobile Application Part (MAP) protocol over Internet Protocol (IP) . The routing of MAP messages to the correct IP host requires a mechanism for proper address definition. SUMMARY OF THE INVENTION The invention provides a communication system wherein information can be properly routed also across network borders between networks of different types. According to one aspect of the present invention, a communication system is provided which comprises several network elements, wherein a first network element is adapted to convert a destination indication contained in a message into an interrogation form suitable for interrogation of a server entity. The server entity is adapted to issue an address when interrogated using the interrogation form. The message may then be sent by the first network element or another network element to the address issued by the server entity. The server entity may return the issued address to the same network element which sent the interrogation form, e.g. to the first network element, or may send the issued address to another network element, e.g. to the another network element which, as an alternative, sends the message to the address issued by the server entity. The message may be a MAP (Mobile Application Part) message. Preferably, the first network element is a layer of a third network element such as a M3UA (Message Transfer Part layer 3 User Application) layer. In a preferred embodiment, the server entity is a Domain Name Server (DNS) , and the address issued by the server entity may be an IP address. For achieving load-sharing, the server entity can store two or more alternatively selectable addresses for at least one of the destination indications. The server entity is preferably adapted to alternatingly select one of the stored two or more alternatively selectable addresses for a destination indication so as to provide a load sharing. The destination indication contained in the message* preferably is a Destination Point Code (DPC) . The first network element may be part of a protocol converting entity which preferably contains a SIGTRAN protocol stack having a SCCP layer on top of a M3UA layer, the SCCP layer supplying the destination indication to the M3UA layer for conversion into the interrogation form. The protocol converting entity may be an interworking entity arranged between an All-IP network and a packet- or circuit- switched network. In accordance with another aspect of the invention, a method is provided as defined in any one of the method claims. Furthermore, the invention provides a network element adapted to perform a specific form of destination indication conversion, as indicated in the network element claims. In accordance with a preferred embodiment, the invention provides a mechanism for resolving the Signalling Point Code (SPC) - IP address relation so as to enable a proper routing of e. g. MAP messages to the correct IP host. A SPC is the code- of a signalling point (SP), i.e. the code of a node in a signalling network which originates and/or receives signalling messages from one signalling link to another. A SP may comprise the Message Transfer Part (MTP) functional block and possibly user part functional blocks. A Destination Point Code (DPC) is one type of SPC, namely the one identifying the destination. The DPC in an address normally requires no translation. According to a specific implementation, a protocol stack such as SIGTRAN defines a specific network element which may be a M3UA (Message Transfer Part Layer 3 User Application) layer to be responsible for the address mapping. Generally, a preferred embodiment of the invention provides a DNS (Domain Name Server) based mechanism to resolve the Signalling Point Code - IP address relation. In accordance with a further aspect of the invention, a simple method and procedure to provide load sharing is introduced. This solution according to the invention is based on resolving of the IP address of the destination on the basis of a destination point code in the SIGTRAN model. The method and system according to the invention are easy and inexpensive to maintain and do not require significant hardware changes of the network structure. According to a preferred aspect of the invention, it is based on existing DNS. In more detail, according to a preferred embodiment of the invention, the network element where the SIGTRAN protocol stack is used, operates in such a manner that the SCCP (Signalling Connection Control Part) layer gives the DPC to the underlying M3UA layer. The M3UA layer in turn forms a DNS formatted host name based on the DPC, e. g. "xdpc.nokia.fi". There, "xdpc" is denoting the destination point code prefixed with letter x. The destination point code is presented preferably in hexadecimals . The DNS server is requested to resolve the IP address corresponding to the domain name, and returns this IP address. In accordance with the returned IP address, the message is routed to the destination host. Thus, a numerical point code information such as "3F81" is prefixed with letter x (or any arbitrary other letter) and combined with the network address (e. g. "operator.fi") to get an information which may be used in a DNS query. The prefixing of a letter, e.g. "x", ensures that the generated domain name always starts with a letter even in case the "dpc" is a numerical value. The invention provides an easy and simple way to carry out the necessary mapping (e. g. Signalling Point Code - IP address mapping) . BRIEF DESCRIPTION OF THE FIGURES Fig. 1 shows a schematic layout of a first embodiment of the present invention; Fig. 2 illustrates the basic architecture of an All-IP network in which the invention can be implemented; Fig. 3 illustrates an embodiment showing the signalling interworking between All-IP and legacy networks (SIGTRAN model) ; and Fig. 4 shows an embodiment of a method in accordance with the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT'S OF THE INVENTION Fig. 1 shows the basic layout of an embodiment of a communication system in accordance with the present invention which provides a DNS-based solution. An IP-based network 1 providing connections by using Internet protocol, is accessible by, or incorporates Network Elements (NE) 2, 4, 6, 11. One or more of the network elements may be connectable to a legacy network 3 for legacy purposes, i.e. for allowing customers to use their existing network along with more advanced services. The legacy network 3 comprises several network elements 13 (only one network element is shown) such as subscriber end terminals or nodes. The IP network 1 comprises, or co-operates with, a DNS server 8 which represents a primary DNS server and is accessed for mapping logical names, aliases, etc. of users, hosts, etc. to IP addresses. The IP network 1 furthermore comprises, or cooperates with, one or more additional DNS servers 5, 7 which are secondary DNS servers and contain copies of the database of primary DNS server 8. Therefore, the secondary DNS servers 5, 7 can provide an identical address mapping between logical names, aliases, etc. and IP addresses, similar to the primary DNS server 8. The IP network 1 may comprise, or co-operate with, more than one primary DNS server 8 and may contain, or co-operate with, more than two secondary DNS servers. Fig. 2 shows a basic layout of the architecture of an All-IP network such as IP network 1 of Fig. 1. As the illustration of the network architecture shown in Fig. 2 is self- explanatory and the topic of standardisation, no further explanations are necessary. For further details, it is referred to the appropriate standards. Fig._3 shows a basic configuration of a network element 12 which provides an interworking function between a circuit- switched network such as 2G/R99 network (Network of Second Generation, Release 1999) having a network element such as network element 13, and a packet-based network which is an All-IP network comprising network element 11. The network element 13 has a known configuration where the Message Transfer Part layers 1, 2, 3 (MTP1, MTP2, MTP3) are underlying the SCCP (Signalling Connection Control Part) . On top of SCCP is TCAP and MAP. The network element 13 may be part of the legacy network 3 as shown in Fig. 1. Interworking network element 12 can e.g. be network element 2 shown in Fig. 1. The All-IP network of Fig. 3 may be the IP network 1 shown in Fig. 1. The network element 11 shown in Fig. 3 may also correspond to one of the network elements 4, 6. The interworking network element 12 (e.g. network element 2 in Fig. 1) has a structure as shown in Fig. 3 and comprises, on its part assigned to the circuit-switched network such as legacy network 3 (right half of element 12 as shown in Fig. 3), a structure similar to network element 13, apart from lack of TCAP and MAP. On its part assigned to the All-IP network (left half of element 12 as shown in Fig. 3) , it has a protocol stack configuration which includes, above layers 1 and 2 (LI, L2), Internet Protocol IP, SCTP (Stream Control Transmission Protocol) , and M3UA (Message Transfer Part Layer 3 User Application) layers 12a. M3UA 12a represents a function or network element which is part of interworking network element 12 below SCCP. The network element 11 of All-IP network has essentially the same layer arrangement as network element 12 (left half) and additionally includes, on top of SCCP, TCAP and MAP. MAP and TCAP may be directly connect to MAP and TCAP layers of network element 13 as shown by direct solid lines interconnecting MAP and TCAP across the network borderline (represented by a dot/dash-line) . For converting a destination indication such as DPC into an interrogation form suitable for interrogation of a server entity such as DNS server 5, 7, or 8, the communication system and method may be basically arranged as follows. The domain part, e.g. nokia.fi, is configured by the operator of the network and network element (NE) 12, and is stored in a non-volatile way inside the NE 12. The information is accessible by M3UA. When M3UA receives the DPC from upper layer it first prefixes it with x and after that it combines the prefixed DPC with defined domain part. Then the formatted domain name is passed to resolver of the host, where the M3UA resides. This is done by operating system specific means. The resolver is the actual entity, which communicates with the DNS server by means of DNS protocol. The response to M3UA is returned via the same route (DNS server -> resolver -> M3UA) . Fig. 4 shows operational steps performed in the communication system in accordance with a preferred embodiment of a method according to the invention. In the example shown in Fig. 4, a SPC to be translated is a DPC. At the network element 12 where the SIGTRAN protocol stack is used as shown in Fig. 3, the SCCP layer gives the Destination Point Code (DPC) contained in the message received from network element 13 to the underlying M3UA layer 12a (step SI) . The M3UA layer 12a generates a DNS formatted host name based on the received DPC. This DNS formatted host name may for example have a structure "xdpc.nokia.fi" where "xdpc" denotes the destination point code DPC in hexadecimals prefixed with letter x. Instead of letter x, any other letter may -also be used. This corresponds to step -S2 shown in Fig. 4. Thereafter, in step S3, the formatted host name e. g. "xdpc.nokia.fi" is send to the DNS server 8 or to one of the secondary DNS servers 5, 7, preferably to one of the closest DNS servers. The requested DNS server resolves the IP address corresponding to the domain name in a customary manner by using its database for finding the IP address mapped to the received host name. The necessary information for the database has been entered beforehand preferably when attributing an IP address to the destination in the IP network indicated by the DPC. Alternatively, the IP address may be dynamically assigned. The DNS server returns, in step S4, the resolved IP address corresponding to DPC to the interworking network element 12 which had sent the formatted DPC to the DNS server. In accordance with the returned IP address, the message is routed to the indicated IP address, that is to the destination host, as represented by step S5. The domain name servers 5, 7, 8 can, in accordance with an embodiment of the invention, be implemented so as to contain several IP addresses allocated to the same domain name in order to be able to perform a load sharing within a single network element. As an example, the domain name "AABBCCDD.nokia.fi" may be allocated to the two following internet protocol addresses: IN A 172.172.172.172 IN A 172.172.172.173. The DNS servers 5, 7, 8 may also contain more than two alternative IP addresses for the same domain names. Two or more IP addresses may be assigned to each of the domain names which can be generated by M3UA layer 12a, ox may be associated to only some of these domain names, for instance to those destination points which are more frequently addressed than others. The DNS servers 5, 7, 8 are preferably implemented in such a manner that they select, when again addressed using the same domain name as already used earlier, to select not the IP address returned last time but another one of the list assigned to the domain name, for instance the next IP address of the list. This function may be achieved by setting a marker to the last returned IP address and then using, when again queried using the same domain name, an IP address from the list different from the marked one, e.g. the next IP address. The marker is then shifted to the actually returned IP address. In accordance with a preferred embodiment of the invention, the M3UA layer is hence capable of forming a domain name from a destination point code and of making a DNS query using the generated domain name. To enhance the performance of DNS queries, the secondary copies of the master DNS server 8, that is . the secondary domain name servers 5, 7, are preferably located near the requesting entities, that is e.g. near the interworking network element 12. The secondary DNS servers 5, 7 may also be implemented in the same host as the requesting entity, that is may be implemented as part of the interworking network element 12. Although the invention has been described above with reference to preferred implementations, the invention is not limited thereto and also covers modifications, amendments, omissions or additions of or to the disclosed features.

Claims: CLAIMS 1. Communication system comprising several network elements, wherein a first network element is adapted to convert a destination indication contained in a message into an interrogation form suitable for interrogation of a server entity, the server entity being adapted to issue an address when interrogated using the interrogation form , the first network element or a second network element being adapted to send the message to the address issued by the server entity. 2. Communication system according to claim 1, wherein the first network element is a layer in a procotol stack of a third network element. 3. Communication system according to claim 1 or 2, wherein the first network element is a M3UA (Message Transfer Part layer 3 User Application) layer. 4. Communication system according to any one of the preceding claims, wherein the server entity is a Domain Name Server (DNS) . 5. Communication system according to any one of the preceding claims, wherein the address issued by the server entity is an IP address. 6. Communication system according to any one of the preceding claims, wherein the server entity stores two or more alternatively selectable addresses for at least one of the destination indications. 7. Communication system according to any one of the preceding claims, wherein the server entity is adapted to select one of the stored two or more alternatively selectable addresses for a destination indication in such a manner that a load sharing is achieved. 8. Communication system according to any one of the preceding claims, wherein the destination indication contained in the message is a Destination Point Code (DPC) . 9. Communication system according to claim 8, wherein the first network element is adapted to convert the destination indication contained in the message by prefixing a letter to the Destination Point Code (DPC) . 10. Communication system according to any one of the preceding claims, wherein the message is a MAP (Mobile Application Part) message. - 11. Communication system according to -any one of the preceding claims, wherein the first network element is part of a protocol converting entity. 12. Communication system according to claim 11, wherein the protocol converting entity contains a SIGTRAN protocol stack having a SCCP layer on top of a M3UA layer, the SCCP layer supplying the destination indication to the M3UA layer for conversion into the interrogation form. 13. Communication system according to claim 11 or 12, wherein the protocol converting entity is an interworking entity arranged between an All-IP network and a packet- or circuit-switched network. 14. Method to be performed in a communication system comprising several network elements, preferably in a communication system as defined in any one of the preceding claims, wherein a first network element converts a destination indication contained in a message into an interrogation form suitable for interrogation of a server entity, the interrogation form being sent to a server entity which issues an address mapped to the destination indication, the first network element or another network element sending the message to the address issued by the server entity. 15. Method according to claim 14, wherein the first network element is a layer of a protocol stack of another network element. 16. Method according to claim 14 or 15, wherein the first network element is a M3UA (Message Transfer Part layer 3 User Application) layer. 17. Method according to any one of claims 14 to 16, wherein the server entity is a Domain Name Server (DNS) . 18. Method according to any one of claims 14 to 17, wherein the address issued by the server entity is an IP address . 19. Method according to any one of claims 14 to 18, wherein the server entity stores two or more alternatively selectable addresses for at least one of the destination indications . 20. Method according to any one of claims 14 to 19, wherein the server entity selects one of the stored two or more alternatively selectable addresses for a destination indication in such a manner that a load sharing is achieved. 21. Method according to any one of claims 14 to 20, wherein the destination indication contained in the message is a Destination Point Code (DPC) . 22. Method according to claim 21, wherein the first network element converts the destination indication contained in the message by prefixing a letter to the Destination Point Code (DPC) . 23. Method according to any one of claims 14 to 22, wherein the message is a MAP (Mobile Application Part) message . 24. Method according to any one of claims 14 to 23, wherein the first network element is part of a protocol converting entity. 25. Method according to claim 24, wherein the protocol converting entity contains a SIGTRAN protocol stack having a SCCP layer on top of a M3UA layer, the SCCP layer supplying the destination indication to the M3UA layer for conversion into the interrogation form. 26. Method according to claim 24 or 25, wherein the protocol converting entity is an interworking entity arranged between an All-IP network and a packet- or circuit-switched network. 27. Network element, preferably for a communication system in accordance with any one of claims 1 to 13, or for use in a method in accordance with any one of claims 14 to 26, wherein the network element is adapted to convert a destination indication contained in a message into an interrogation form suitable for interrogation of a server entity for translating the destination indication into an address to which the message is to be sent. 28. Network element according to claim 27, wherein the network element is a layer of a protocol stack of another network element. 29. Network element according to claim 27 or 28, wherein the network element is a M3UA (Message Transfer Part layer 3 User Application) layer. 30. Network element according to claim 27, 28, or 29, wherein the address is an IP address. 31. Network element according to any one of claims 27 to 30, -wherein the destination indication contained in the message is a Destination Point Code (DPC) , and the message is a MAP (Mobile Application Part) message. 32. Network element according to any one of claims 27 to 31, wherein the network element is part of a protocol converting entity which contains a protocol stack having a SCCP layer on top of a M3UA layer forming the network element, the SCCP layer supplying the destination indication to the M3UA layer for conversion into the interrogation form.

Inventors: TAMMI KALLE, VIRTANEN KARI, TAMMI, KALLE, VIRTANEN, KARI
Applicants: NOKIA CORP, TAMMI KALLE, VIRTANEN KARI, NOKIA CORPORATION, TAMMI, KALLE, VIRTANEN, KARI
Application year: 2000
Main classification: H04L29
IPC codes: H04L29, H04Q3, H04Q7