A method for optimising session set-up between session control nodes (21A, 21B, 21C, 21D), which nodes interface to different operator networks in a globally scalable VoIP network, said method comprising at a centralised server system: receiving a load status message indicating a load status from each session control node and storing the load status for each session control node, said load status messages comprising a required overload restriction for a session control node; receiving a session set-up request from one of said session control nodes where the session set-up request identifies the requesting session control node and a destination entity; the method being characterized in: receiving a prioritised list of session set-up policies each identifying a destination session control node the requesting session control node should use in order to reach the destination entity; modifying the prioritised list by, starting with the highest priority session set-up policy, deleting one or more session set-up policies from the list that include a destination session control node that would exceed its overload restriction if the session set-up request is allowed, until a policy is reached that includes a destination session control node that would not exceed its overload restriction if the session set-up request is allowed; and sending the modified list of session setup policies to the requesting session control node. receiving a load status message indicating a load status from each session control node and storing the load status for each session control node, said load status messages comprising a required overload restriction for a session control node; receiving a session set-up request from one of said session control nodes where the session set-up request identifies the requesting session control node and a destination entity; the method being characterized in: receiving a prioritised list of session set-up policies each identifying a destination session control node the requesting session control node should use in order to reach the destination entity; modifying the prioritised list by, starting with the highest priority session set-up policy, deleting one or more session set-up policies from the list that include a destination session control node that would exceed its overload restriction if the session set-up request is allowed, until a policy is reached that includes a destination session control node that would not exceed its overload restriction if the session set-up request is allowed; and sending the modified list of session setup policies to the requesting session control node. receiving a prioritised list of session set-up policies each identifying a destination session control node the requesting session control node should use in order to reach the destination entity; modifying the prioritised list by, starting with the highest priority session set-up policy, deleting one or more session set-up policies from the list that include a destination session control node that would exceed its overload restriction if the session set-up request is allowed, until a policy is reached that includes a destination session control node that would not exceed its overload restriction if the session set-up request is allowed; and sending the modified list of session setup policies to the requesting session control node.