Digital signal processing (DSP) is the study of signals in a digital representation and the processing methods of these signals. It does analog to digital conversion and digital to analog as well. In technical terms it has three major subfields
- Audio Signal Processing
- Digital Image Processing
- Speech Processing
It is a huge subject to discuss and plethora of books have been written on Digital Signal Processing. This document will help you to understand how we use Digital Signal Processing in Cisco VoIP Technology.
Cisco provides DSP resources in ISR routers to provide voice termination, transcoding, conferencing and connectivity capabilities for IP telephony Solutions. Cisco has created DSP module called PVDM, It stands Packet Voice DSP module. Each PVDM is equipped with a number of DSPs chip on the core, the higher the number of DSP, the greater the processing power of that PVDM.
2-PVDM types are available to support first Generation (2800 series and 3800 series) and second Generation of routers (2900 series and 3900 series). The Cisco 2800 and 3800 series platform only supports PVDM-2 but Cisco 2900 and 3900 platform supports PVDM-2 and PVDM-3 as well. The PVDM3 modules provide higher density (up to 4 times higher) than the PVDM2s. They also provide improved performance in terms of the number of conference and transcoding sessions supported.
Table 1 lists the PVDM-2 models.
Table 2 lists the PVDM-3 models.
By referring above table it is understood what do the numbers 8, 16, 32, 64 etc in the PVDM-2 and PVDM-3.Number of channel supported on PVDM-2 and PVDM-3 are entirely depending on the codec-complexity. There are 3 flavors of codec-complexity refer below table.
Table -3 lists of Codec Supported in PVDM2 and PVDM3
Table -4 lists the number of voice channels supported by the PVDM2
Table -5 lists the number of voice channels supported by the PVDM3.