Establishing connection across a connection-oriented first telecommunications network in response to a connection request from a second telecommunications network

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.