Abstract:
A first multi protocol label switching (MPLS) enabled Internet Protocol (IP) data network is able to transmit data to a second MPLS enabled IP network via a legacy optical network, which would not otherwise be able to handle the user network interface (UNI) protocols required to be used within an MPLS network environment, by means of configuring the legacy optical network and its traditional network management system (TNMS) so that they simulate or emulate an MPLS enabled optical network. The simulation/emulation of an MPLS network is performed as follows: when a first legacy network element (NE) receives a connection request (a UNI request) from the MPLS network under a UNI protocol, the UNI request is passed to the TNMS, which then sets the required connection across the legacy network via a second edge NE to an NE of the second IP network. Once the connection has been set, the TNMS instructs the edge NE to send a return signal to the requesting network indicating that the connection has been successfully set. Data packets may then be transmitted across the network.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of communicating across a telecommunications network and associated apparatus. In particular, the invention relates to a method of communicating across a telecommunications network, to a telecommunications network, to a network management system for setting connections in a network and to a network element of such networks. 
     Telecommunications networks, particularly optical networks, have in the past routed data across the network by setting routes by means of a manually operated network management system. When changes are required to be made to the route or routes set in the network, response times can be very long in comparison to the rate of transmission of data. 
     Significant improvements in routing of data have been made in recent years in the context of electrical networks. One such improvement is the ability of network elements of the network to route data packets without reverting to a separate network management system. Recently, the use of Multi Protocol Label Switching (MPLS), which is currently used in both IP and ATM networks, has been recognised as being particularly advantageous. One of the benefits of MPLS is that network elements of the network are able to route a given data packet quickly, by reference to a label in the data packet. Furthermore, since the routing of data packets does not require the exchange of data with a network management system the use of MPIS has a major advantage in that it facilitates dynamic network control without the delays often associated with networks controlled by a network management system. 
     It has been proposed, so as to facilitate dynamic network control, to introduce MPLS, in the form of a Generalised Multi-protocol Label Switching (GMPLS) method, into optical networks. However, incorporating GMPLS into an optical network is not straightforward. Two proposals have been made for implementing GMPLS in an optical network as will now be described. 
     The first proposal may be referred to as the “Peer-to-Peer Model” and is illustrated by  FIG. 1  of the accompanying drawings. With reference to  FIG. 1 , a first IP network  1  is connected via an optical network  2  to a second IP network  3 . The optical network  2  is required to make available to the IP networks  1 ,  3  topological information (in the form of IP information) so that data packets can be routed from the first IP network  1  to the second IP network  3  via the optical network  2  by means of IP data in the data packet. If the optical network  2  is privately owned, making such topological information publicly available may however be undesirable. For example, such information may be considered to be commercially sensitive and it may be desired to keep such information confidential. 
     The second proposal, which may be referred to as the “Client-Server Model”, does not require the optical network to make public such topological information. In this second proposal, which is described with reference to  FIG. 2  of the accompanying drawings, a first IP network  1  is connected via an optical network  2  to a second IP network  3  in a manner similar to that of the first proposal. However, in this proposal the interfaces between the first and second IP networks  1 ,  3  (the clients) and the optical network  2  (the server) each include a user network interface  4  (UNI). Thus the first IP network  1 , via a first UNI  4   a , effectively request a connection across the optical network  2  by means of IP data in a data packet. Topology information relating to the optical network  2  is however not made available outside the optical network  2 . 
     Both of the proposals described above suffer from a significant disadvantage. In order for the optical network to operate in a GMPLS environment it is necessary, in the proposals made, for the network elements of the optical network to process and handle network topology information and to set up and tear down network connections. In order for the individual network elements to be able to perform such tasks the network elements each require significant processing capability and access to significant amounts of memory. Whilst such requirements can be met when installing new optical networks, many existing optical network elements are not able to perform at the required level. Replacing such existing optical networks (often referred to as legacy networks) would be costly and is therefore undesirable. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a method of communicating across a telecommunications network which allows a given protocol, for example a protocol used in an MPLS environment, to be used in combination with other networks, for example optical networks, and which mitigates one or more of the problems associated with the above-mentioned proposals. The present invention also seeks to provide suitable means or apparatus for performing such a method or aspects of such a method. 
     According to a first aspect of the invention there is provided a method of operating a connection-oriented communications network, the communications network comprising a plurality of network elements in which connections across the network elements are established by a network management system; the communications network being connectable to a second communications network by an edge network element, the second communications network comprising a plurality of network elements each of which is capable of making connections or routing data across the second network in accordance with a connection request received by the element; the connection request being in accordance with a predetermined protocol, the method being for establishing a connection across the connection-oriented network in response to a connection request from the second network and characterized by: the edge network element upon receiving a connection request from the second network, sending to the network management system information relating to the connection request; the network management system sending signals to set a connection across the network in response to said information received from the edge network element; and the network management system causing the edge network element to send a return signal according to the predetermined protocol to the second network indicating the status of the setting of a connection. 
     The method of the present invention enables a connection-oriented network to establish connections in response to connection requests, which it would otherwise be unable to handle, by the steps of passing the connection request from a suitably configured edge network element to a suitably configured network management system, which is able to process the request, make the connection in accordance with the request and respond via the edge network element in accordance with the given protocol. As far as the second network is concerned the connection-oriented communications network is able to communicate with it under the given protocol. In the context of the method of the invention, the manner in which connection requests are made can be considered as being a client-server arrangement, in which the connection-oriented network is the server network and the second network is the client network. 
     The return signal indicating the status of the setting of the connection may for example indicate either that the connection has been successfully made or that the connection could not be made. After the second network receives a return signal indicating that the connection has been successfully made, data can then be transmitted from the second network across the communications network. 
     Advantageously the connection-oriented communications network is further connectable to a third communications network by a further edge network element, the third network comprising a plurality of network elements each of which is capable of making connections or touting data across the third network in accordance with a connection request received by the element, and the method further comprises: the network management system causing the further edge network element to send a connection request according to the predetermined protocol to the third network thereby enabling connection of the second and third networks via the connection-oriented network. 
     Preferably the connection-oriented network is operated such that, in use, topology information relating to the network is not made available outside the network to for example the second and/or third networks. Of course, information concerning the possible connections to and from network elements within, but at the edge of the network, may be made available to network elements outside the communications network and accordingly such information may be considered as not relating to topology information relating to the communications network. 
     Advantageously the predetermined protocol is a user network interface (UNI protocol The UNI protocol may be such that topology information is not revealed over the interface between the communications networks. The user network interface protocol used may, for example, be in accordance with the standards laid down by the Optical Interface Forum (OIF). An appropriate standard is described in document number OIF 2000.125 available from the Optical Interface Forum. In the case where the communications network is connected to MPLS enabled networks, the arrangement may be such that the MPLS network elements require a connection request in order to make a connection and transmit data. Such MPLS network elements may also be arranged automatically to send appropriate connection requests. Thus, when setting a connection from the communications network to the third network that is MPLS enabled, the network management system advantageously causes the further edge network element to send an appropriate connection request, for example, a UNI request. 
     The method may be such that other protocols are used when further connection requests are made between network elements of the network. For example, a network network interface (or NNI) protocol may be used. An NNI protocol may be especially convenient when connection requests are made between MPLS enabled network elements. The NNI protocol may be such that topology information is revealed over the interface between the relevant network elements. 
     According to a second aspect of the invention there is provided a connection-oriented communications network comprising a plurality of network elements in which connections across the network elements are established by a network management system; the communications network being adapted to be interoperable with a second communications network by an edge network element, the second network comprising a plurality of network elements each of which is capable of making connections or routing data across the second network in accordance with a connection request received by the element; the connection request being in accordance with a predetermined protocol, the connection-oriented network being characterized by the edge network element upon receiving connection request from the second network, sending to the network management system information relating to the connection request; the network management system sending signals to the network elements to set a connection across the network in response to said information received from the edge network element; and the network management system causing the edge network element to send a return signal according to the predetermined protocol to the second network indicating the status of the setting of a connection. 
     The present invention finds particular application to legacy connection-oriented networks that comprise network elements unable to make connections or route data in accordance with connection requests. The step in which the edge network element sends to the network management system information relating to the connection request can comprise relaying, or repeating, the connection request. The edge network element may therefore be required to perform little or preferably no processing of the connection request. Conveniently the edge network element can comprise a legacy edge network element that has been appropriately adapted. Conversion of the legacy network element may include a step of programming the network element with appropriate updated software. The requirements of such computer software will be apparent to the relevant persons skilled in the art and, as such, further details of such software are not provided here. Alternatively, the conversion could be made by means of extra hardware in addition to, or instead of, providing such software. 
     The network management system advantageously comprises the legacy network management system that has been appropriately adapted. The conversion of such a legacy network management system may include a step of programming the network management system with appropriate updated software. Again the requirements of such computer software would be apparent to those skilled in the art, when presented with the details of the present invention. Alternatively, the conversion could be made by means of extra hardware in addition to, or instead of, providing such software. 
     Advantageously the communications network further comprises a further edge network element for connecting the communications network to a third communications network, the third network comprising a plurality of network elements each of which is capable of making connections or routing data across the third network in accordance with a connection request received by the element, the network management system being configured to cause the further edge network element to send a connection request according to the predetermined protocol to the third network thereby enabling connection of the second and third networks via the communications network. Such a network is advantageous where the third network requires a connection request according to the predetermined protocol to be received before a connection can be made. Since the network management system causes the further edge network to send the connection request this eliminates the need for the further edge network element to be able to itself generate the connection request. 
     Preferably the communications network is operated such that, in use, topology information relating to the network is not made available outside the network. 
     Advantageously the predetermined protocol is a user network interface (UNI) protocol. The network management system may also be able to handle that some UNI protocol insofar as is necessary to enable it to cause the edge network element to send the return signal under the same UNI protocol. The relevant edge network elements of the network may simply be programmed with appropriate software to enable them to handle the same UNI protocol. 
     Preferably the second and/or third networks are packet based networks, such as Internet Protocol (IP) networks in which data packets are routed by the network elements in dependence upon the connection request within the packets. Alternatively the second and/or third networks can comprise Asynchronous Transfer Mode (ATM networks, and alike, in which connections are established by the network elements in dependence upon connection requests. The invention finds particular application for connection to networks able to handle Multi-Protocol Label Switching (MPLS). It will be understood that multi-protocol label switching may take many forms, any of which could be used in the context of the present invention. For example, a generalised form of MPLS (GMPLS) may be used The form of multi-protocol label switching used may however be conveniently chosen to be in accordance with an accepted standard, for example a standard set by the Internet Engineering Task Force. 
     According to a farther aspect of the invention there is provided an edge network element for use in a communications network in accordance with the second aspect of the invention. 
     According to a yet further aspect of the invention there is provided a network management system for use in a communications network in accordance with the second aspect of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings, of which: 
         FIGS. 1 and 2  show prior art proposals for a telecommunications network; 
         FIG. 3  illustrates a telecommunications network in accordance with a first embodiment of the invention; and 
         FIG. 4  illustrates a telecommunications network in accordance, with a second embodiment of the invention. 
     
    
    
       FIGS. 1 and 2  relate to prior art proposal and are described above. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A telecommunications network according to the first embodiment of the invention is shown in  FIG. 3 . With reference to  FIG. 3  the network includes a first MPLS enabled IP network  11  connectable to a second MPLS enabled IP network  13  via a legacy optical network  12 . The legacy optical network  12  includes a plurality of internal network elements  15  (only one of which is shown in  FIG. 3  for the sake of clarity) and a plurality of edge network elements  14   a ,  14   b  (only two of which are shown). The legacy optical network  12  is also connected to a traditional network management system  16 . 
     At the interface between the first IP network  11  and the optical network  12 , signals may be received and sent by an edge network element  14   a  of the optical network  12 . Similarly, at the interface between the second IP network  13  and the optical network  12 , signals may be received and sent by an edge network element  14   b  of the optical network  12 . Network access and connection requests may be made through the edge network elements of the optical network. The network may thus be considered as forming a client/server system with interfaces, between the server (the optical network  12 ) and the client (the first or second IP networks  11 ,  13 ). 
     The protocol used at such interfaces, in relation to the provision of network access and connection requests, is a UNI (user network interface) protocol. 
     A UNI protocol is also used throughout the first and second IP networks  11 ,  13  and connection requests in the form of UNI requests are, in the IP networks, processed by the local network elements, connections being established by use of the topology protocols running across the network. The topology protocols used may for example be an OSPF (Open Shortest Path First) protocol. However, the network elements within the legacy optical network  12  are not able to process such requests locally. The making of a connection across the optical network  12 , including the handling of UNI requests made to edge network elements of the optical network  12 , will now be described. 
     A UNI request is sent to a first edge network element  14   a  of the optical network  12  from a network element (not shown separately) of the first IP network  11 , the request effectively requesting a connection to a network element of the second WP network  13 . The request is sent (arrow A) directly to the network management system  16 . The network management system  16  then processes the request and determines an appropriate connection across the optical network  12 . The network management system  16  then sends signals (arrows B) instructing the edge network element  14   a , the relevant internal network elements  15  and a second network element  14   b  of the optical network to establish the required connection. The network management system  16  then formulates a suitable response for sending to the network element of the first network  11  that sent the UNI request. The network management system  16  then sends (arrow C) a signal to the edge network element  14   a  originally receiving the UNI request, causing that edge network element  14   a  to send such a suitable response to that network element of the first network  11 . 
     The response sent from the edge network element  14   a  originally receiving the UNI request to the network element of the first network  11  indicates either that a connection has been successfully made or that the connection failed, as appropriate. If the connection is successfully made the network element of the first network  11  is then able to send data via the optical network  12  to the appropriate network element of the second IP network  13 . 
     The IP networks  11 ,  13  are not able to discover the topology of the optical network  12 , as such information is not made available outside of the optical network  12 . 
     Thus it will be appreciated that such an arrangement enables a client/server UNI network to be established without the need for network elements of the server network (the legacy optical network  12 ) to run locally any topology protocols. This is especially advantageous in legacy networks, such as the optical network  12  illustrated in  FIG. 3 , where the network elements do not have the required memory and/or processing power to handle such protocols. 
     A telecommunications network according to a second embodiment of the invention is illustrated with reference to  FIG. 4 . In this second embodiment, MPLS enabled network elements are combined with legacy network elements in a common transport network. The MPLS enabled parts of the network can operate with full topology protocols, whereas the legacy part of the network effectively emulates a UNI interface to enable connections across the legacy part of the network to be provided automatically on request. 
     With reference to  FIG. 4 , the network includes a first MPLS enabled IP network  21   a  connectable to a second MPLS enabled IP network  23   a  via an optical network  20 . The optical part of the network comprises a legacy optical network  22  connectable between first and second MPLS enabled optical networks  21   b ,  23   b . The legacy optical network  22  includes a plurality of internal network elements (not shown) and a plurality of edge network elements  24   a ,  24   b  and is connected to a traditional network management system  26 , in a manner similar to that of the legacy optical network  12  shown in  FIG. 3 . 
     In  FIG. 4 , the first IP network  21   a  has a UNI interface to the optical network  20 . Topology information relating to the first MPLS optical network  21   b , the second MPLS optical network  23   b  and the legacy optical network  22  is not made available outside each network, respectively. As far as the first IP network  21   a  is concerned the optical network  20  may, or may not, be separated into MPLS enabled and legacy optical networks. The making of a connection from the first IP network  21   a  to the second IP network  23   a  will now be described. 
     The first IP network  21   a  sends a UNI request to the first MPLS enabled optical network  211   b  of the optical network  20 , the UNI request effectively, requesting a connection to a network element (not shown separately) of the second IP network  23   a  via the optical network  20 . The UNI request is processed locally within the first MPLS optical network  21   b , and the requested connection made to the edge of that network, where it meets another UNI interface (the interface between the first MPLS optical network  21   b  and the legacy optical network  22 ). A new UNI request is therefore sent from an edge network element of the first MPLS optical network  21   b  to a first edge network element  24   a  of the legacy optical network  22 . This UNI request effectively requests a connection from the interface between the MPLS optical network  21   b  and the legacy optical network  22  to the destination network element of the second IP network  23   a . Since the network receiving the UNI request is a legacy optical network  22 , the request cannot be processed locally by the network elements of the network  22 . 
     In a manner similar to that described above with reference to the first embodiment, the request is sent (arrow A) directly to the traditional network management system  26 . The network management system  26  then processes the request and determines an appropriate connection across the optical network  22 . The network management system  26  then sends signals (arrow B) instructing the edge network element  24   a , the relevant internal network elements and a second network element  24   b  of the optical network to establish the required connection. In this embodiment, however, the legacy optical network  22  interfaces to another optical network, which is MPLS enabled (i.e. the second MPLS optical network  23   b ). 
     The second MPLS optical network  23   b  requires a UNI request to cause it to make the connection to the second IP network  23   a . Thus the network management system  26  sends (arrow X) to the second edge network element  24   b  of the legacy network  22  a signal causing the second edge network element  24   b  to send a UNI request to an edge network element of the second MPLS optical network  23   b . This UNI request again effectively requests a connection to be made to the destination network element of the second IP network  23   a . The UNI request is processed locally within the second MPLS optical network  23   b , and the requested connection made across that network to the destination network element of the second IP network  23   a.    
     The edge network element of the second MPLS optical network  23   b  receiving the UNI request from the second edge network element  24   b  of the legacy network  22 , sends a return signal under the UNI protocol to the second edge network element  24   b , the return signal indicating that the requested connection has been successfully made. The return signal is sent (arrow Y) directly to the network management system  26 . On receipt of that return signal the network management system  26  formulates a suitable response for sending to the network element of the first MPLS optical network  21   b  that sent the UNI request to the legacy network  22 . The network management system  26  then sends (arrow C) a signal to the edge network element  24   a  originally receiving the UNI request from the first MPLS optical network  21   b , causing that edge network element  24   a  to send such a suitable response under the UNI protocol to the relevant edge network element of the first MPLS optical network  21   b.    
     The indication of the successful connection is then finally relayed to the first IP network  21   a  by the first MPLS optical network  21   b  to complete the connection process. The network element of the first IP network  21   a  is then able to send data via the optical, network  20  to the appropriate network element of the second IP network  23   a . Should the process fail at any stage, then a failure response is sent back to the requesting network. The network is arranged such that on such a failure any intermediate connections that have been made in relation to the given connection request are cleared down. 
     As will be appreciated, various modifications may be made to the above described embodiments. For example, two IP networks could be connected via an optical network, such that a first IP network is connected to a single MPLS optical network, which is connected to a single legacy network, which is connected to a second IP network. In such a case, the receipt from the first network of a UNI request requesting connection to the second IP network would be handled in a similar manner to that described with reference to the first embodiment. The UNI request passed on by the MPLS optical network would be passed from an ingress legacy network element to the network management system of the legacy network, which would set a connection across the legacy network to the second IP network, and then cause the ingress legacy network element to send an appropriate response to the requesting IP network, data thereafter being transmitted from the first IP network across the optical network and to the second IP network. 
     Also, two IP networks could be connected via an optical network, such that a first IP network is connected to a single legacy network, which is connected to a single MPLS optical network, which is connected to a second IP network. In such a case, the receipt from the first network of a UNI request requesting connection to the second IP network would be handled in a similar manner to that described with reference to the second embodiment. The UNI request would be passed from an ingress legacy network element to the network management system of the legacy network, which would set a connection, send a UNI request via an egress legacy network element to the MPLS optical network, receive an appropriate response via the egress legacy network element from the MPLS optical network, and then cause the ingress legacy network element to send an appropriate response to the requesting IP network, data thereafter being transmitted from the first IP network across the optical network and to the second IP network. 
     Other permutations of legacy optical, optical MPLS, and IP networks will of course be apparent to those skilled in the art. 
     Whilst MPLS optical networks have been referred to above, the embodiments described would of course also be of use if the MPLS optical networks were in the form of GMPLS (generalised MPLS) optical networks. 
     The IP based networks described above need not be IP data networks and could alternatively be ATM data networks, since such networks may also be used with MPLS and user network interfaces (UNI) 
     The topology protocols used across the MPLS networks need not be OSPF. For example, the topology protocol used may alternatively be an IS/IS (Intermediate System to Intermediate System Routing Exchange) protocol from the OSI (Open Systems Interconnection).