| 摘要 |
An overflow service is provided in a virtual private network (VPN). Calls between private branch exchanges (1, 2) will be switched at a Service Switching Point (3) under the control of a Service Control Point (4). If the capacity of the VPN is already fully in use, then a further call attempt will trigger a congestion message. The Service Switching Point responds to a congestion message by routing the further call attempt onto overflow capacity, not normally allocated to the VPN. A maximum overflow capacity can be set, in accordance with a service level agreement between the network operator and the VPN customers, for instance by counting the number of re-route attempts. An advantageous embodiment provides a private branch exchange with a "hunt" group of lines for giving access to the network for a user. This provides a simple way of determining when capacity in the VPN is not available to provide a requested connection to a user.
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