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 (Figure 1). Tables 1 and 2 show the number of voice channels and codecs that each PVDM4 module supports.
Figure 1. PVDM4 Top View
Features and Benefits
The PVDM4 modules are supported on the Cisco 4451-X platform. You can plug them directly into the single slot on the router motherboard or onto the network interface module (NIM) that supports T1/E1 ports. Enhanced DSP architecture accommodates a new packet-processing engine optimized for rich-media voice applications, while concurrently supporting the time-division multiplexing IP (TDM-IP) voice framework.
A PVDM4 module plugged onto the motherboard delivers IP-based voice services such as conferencing, media optimization, and transcoding. A PVDM4 module plugged onto the NIM daughter card would be used for voice T1/E1 connectivity.
All the PVDM4 modules have the same form factor and are field-upgradable to allow you to easily scale your voice deployments.
Codec Support and Capacity
The PVDM4 modules support a wide range of codecs of different complexities. They support all codecs that are supported by the PVDM3 modules. Table 1 lists the codecs supported on the PVDM4 modules, and Table 2 gives the channel densities of the PVDM4 modules. Table 3 lists the media-enhancement features.
Table 1. Voice, Fax, and Modem Codec Support on PVDM4 Modules
Fax and Modem Pass-through
Internet Low Bitrate Codec (iLBC), and
Table 2. Channel Densities of PVDM4 Modules
Number of Channels
32-channel voice DSP module
64-channel voice DSP module
128-channel voice DSP module
256-channel voice DSP module
Table 3. Media Enhancement Features
Acoustic shock prevention
Conferencing, Transcoding, and Transrating Services
The PVDM4 modules support digital voice connections, conferencing, and universal transcoding services. The PVDM4-256 can support up to 8conferences with 64 participants in each conference and up to 88 conferences with 8 participants in each conference. Please refer to the PVDM4 Q&A for more information about the number of supported sessions.
In conjunction with Cisco IOS® Software, the PVDM4 modules support universal transcoding and the same codec repacketization as the PVDM3 modules. Universal transcoding allows transcoding from any supported codec to any other supported codec. Refer to the PVDM4 Q&A for more details about the number of supported sessions for each codec.
The PVDM4 modules support transrating, where repacketization of the same codec is used to connect dissimilar networks that have different codec packetization periods.
The PVDM4 modules perform compression, voice-activity-detection, jitter-management, and echo-cancellation functions. The echo cancellation offered in the PVDM4 modules has a tail length of 128 milliseconds (ms) and complies with ITU-T G.168.
The PVDM4 DSPs offer multiple power-saving modes, including a power-saver mode when the module is not in use. In power-saver mode each PVDM4 can save up to 5 watts of power.
Cisco Platform Availability
The PVDM4 modules are supported on Cisco 4451-X platforms. The platform has one slot for the PVDM4 module. You can plug any additional PVDM4 modules onto the T1/E1 NIMs.
Note that PVDM3 modules are not supported on the Cisco 4451-X, and PVDM4 modules are not supported on the Cisco 2900 and 3900 Series platforms.
Table 4 gives module specifications.
Table 4. Module Specifications
Multicore DSP technology
DSP external memory
512-megabit double-data-rate (DDR) synchronous dynamic random access memory (SDRAM) for each DSP
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