DSP Provisioning
A DSP is used to translate voice and fax signals into VoIP data streams.The
number of conversions a DSP can perform is based on which CODEC complexity
is being used. Cisco supports medium and high CODEC complexity.The
following CODECs are medium complexity: G.711 (a-law and ì-law), G.726,
G.729a, G.729ab, and Fax-relay. High-complexity CODECs are G.728, G.723,
G.729, G.729b, and Fax-relay (medium-complexity CODECs can be run in
high-complexity mode, but with fewer available channels).These coder-decoder
compression algorithms convert the voice signals to packets ranging in size from
64K to 5.3K.The level of complexity, which is affected by the algorithm used by
the compression CODEC, determines the number of calls a DSP can process. By
using medium complexity, each DSP can process four calls, whereas with high
complexity, only two calls can be processed per DSP. As you can see, the compression
method used will affect the bit rate and quality of the call. Meanwhile,
the quality of the voice conversation is benchmarked against the MOS (Mean
Opinion Score) chart, shown in Table 6.1.This MOS rating is based on listeners
judging the quality of a voice call.