A voice gateway (VGW) is a device that connects a traditional telephony network, such as a TDM trunk, to a voice over IP (VoIP) network, such as a Cisco Unified Communications Manager (CUCM) cluster. A VGW performs signaling and media conversion between the two networks, and can also provide supplementary services, such as call routing, digit manipulation, transcoding, conferencing, and fax relay. A VGW can be a standalone device, such as a Cisco Integrated Services Router (ISR), or a software module, such as a Cisco Unified Border Element (CUBE). A CUBE is a special type of VGW that can also provide security, demarcation, and interworking functions for VoIP calls. A CUBE can be deployed between two VoIP networks, such as CUCM and a service provider SIP trunk, or between a TDM trunk and a VoIP network, in which case it acts as both a CUBE and a VGW. A CUCM is not a VGW, but a call control platform that manages VoIP endpoints, such as IP phones, and interacts with VGWs for call routing and signaling. A CUSP is a Cisco Unified SIP Proxy, which is a device that provides SIP routing and load balancing for VoIP networks. A CUSP is not a VGW, but a SIP proxy server that can work with CUCM and CUBE to optimize SIP call flows. References:
Troubleshooting Cisco Contact Center Enterprise (CCET), Module 1: Voice Gateway Overview1
Cisco Contact Center Enterprise Implementation and Troubleshooting (CCEIT), Module 2: Voice Gateway Configuration2
Cisco Unified Border Element Configuration Guide3
Cisco Unified SIP Proxy Configuration Guide4
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