Softswitch-based architecture for IP Centrex

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  1. Ordinary analog telephone sets and fax machines may be served through a Customer Gateway. On behalf of the analog devices, the Customer Gateway performs voice digitization and packetization. It also converts analog signaling into IP telephony messages.
  2. The Customer Gateway has an Ethernet interface for connecting to the LAN. It also provides jacks to connect analog devices (telephones, fax machines) and/or ISDN telephone sets. The Customer Gateway sends IP telephony messages across the LAN, over the broadband access facility, and through the managed backbone network to the Softswitch. The Softswitch provides the customer gateway with the IP address of the other party. The Customer Gateway uses this information to send packetized voice streams directly to the destination. The destination may be another Customer Gateway or IP Phone on the same LAN, a Customer Gateway or IP Phone on a different LAN across the backbone network, or the Trunk Gateway (for parties served by traditional lines on the PSTN).
  3. The IP Phone combines the customer gateway functionality and telephone set functionality into one device. The IP Phone has an Ethernet interface to the LAN. The IP Phone sends IP telephony messages across the LAN, over the broadband access facility, and through the managed backbone network to the Softswitch. The Softswitch provides the IP Phone with the IP address of the other party. The IP Phone uses this information to send packetized voice streams directly to the destination. The destination may be another IP Phone or Customer Gateway on the same LAN, an IP Phone or Customer Gateway on a different LAN across the backbone network, or the Trunk Gateway (for parties served by traditional lines on the PSTN).
  4. The Softswitch provides the call control and service logic for the IP Centrex service. The Softswitch exchanges IP Telephony messages with Customer Gateways, IP Phones, Signaling Gateways, Trunk Gateways, and other Softswitches.
  5. When a call must pass between the backbone packet network and the PSTN (e.g., an IP Centrex customer calls a traditional analog customer), the Softswitch uses the Signaling Gateway to exchange SS7 messages with PSTN Class 4 and Class 5 switches through Signal Transfer Points.
  6. When a call must pass between the backbone packet network and the PSTN (e.g., an IP Centrex customer calls a traditional analog customer), the Softswitch directs the call to a Trunk Gateway. The Trunk Gateway packetizes/depacketizes the voice stream so that it can be transmitted over a DS1 trunk to PSTN Class 4 and Class 5 switches.