The single server distributed systems over IP network and WAN-connected media gateways and port networks have introduced the need for dial plan transparency. When a single server is fragmented into a multiple server configuration, the dial plan transparency becomes a problem. For example, when the media gateway loses contact with the primary controller, the media gateway attempts to re-register with an alternate controller or Local Survivable Processor (LSP).

An LSP might become active for different reasons.

• The network connection between the media gateway and the primary controller fails.

• The primary controller itself fails.

In all the following examples, both the callers are nonIP phones.

In Figure 1, S8300 is the primary controller for six media gateways: MG1, MG2, and MG3 in Network Region 1, and MG4, MG5, and MG6 in Network Region 2. Each media gateway is administered with a primary controller and an alternate controller or a survivable remote server (LSP). LSP1 is an alternate controller for Network Region 1, and LSP2 is an alternate controller for Network Region 2. When a media gateway loses contact with the primary controller, each media gateway attempts to re-register with the LSP. After successful registration, if caller A on MG1 attempts to call caller B on MG6, LSP1 determines whether caller B exists on the originating LSP, the location where caller B resides, and the LDN number for Network Region 2. The LSP places an outgoing trunk call to the LDN for Network Region 2. When one of the media gateways in NR 2 receives the call, DPT is triggered and the call is routed to caller B through an IP inter-gateway connection. In this example, the call is routed from MG1 to MG6.

In Figure 2, S8300 is the primary controller for six media gateways: MG1, MG2, and MG3 in Network Region 1, and MG4, MG5, and MG6 in Network Region 2. Each media gateway is administered with a primary controller and an alternate controller or LSP. LSP1 is an alternate controller for Network Region 1, and LSP2 is an alternate controller for Network Region 2. When a network failure occurs, each of the media gateways MG4, MG5, and MG6 loses contact with the primary controller and attempts to re-register with the LSP. In this scenario, if there is a call from PSTN to MG1 for caller B on MG6, S8300 determines whether it can reach caller B through the IP network, determines the Network Region where caller B resides, and places an outgoing trunk call. When a media gateway in Network Region 2 receives a call, DPT is triggered and the call is routed to caller B.

In Figure 3, S8300 is the primary controller for six media gateways: MG1, MG2, and MG3 in Network Region 1, and MG4, MG5, and MG6 in Network Region 2. Each media gateway is administered with a primary controller and an alternate controller or LSP. LSP1 is an alternate controller for Network Region 1, and LSP2 is an alternate controller for Network Region 2. When a network failure occurs, the media gateway (MG1) loses contact with the primary controller and attempts to re-register with LSP1. In this scenario, if caller A on MG1 attempts to call caller B on MG6, LSP1 determines whether it can reach caller B, determines the Network Region to which caller B belongs, and places an outgoing trunk call. When a media gateway in Network Region 2 receives the call, DPT is triggered, and the call is routed to caller B.