Cisco Fourth-Generation Packet Voice Digital Signal Processor Module for Cisco Unified Communications Solutions The Cisco® Fourth-Generation Packet Voice Digital Signal Processor Module (PVDM4) enables Cisco 4451-X Integrated Services Routers (ISRs) to provide rich-media capabilities such as high-density voice connectivity, conferencing, transcoding, media optimization, transrating, and secure voice in Cisco Unified Communications Solutions. The fourth-generation packet voice digital-signal-processor (DSP) modules are available in four densities: PVDM4-32, PVDM4-64, PVDM4-128, and PVDM4-256, with 32, 64, 128, and 256 channels, respectively.