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.
Digital Signaling Processor (DSP) provisioning is something that people have the
tendency to neglect and is consequently added at the end of a project. By the
time you finish reading this chapter, we hope you will have a better understanding
of what a DSP is, on which platforms DSP resources are provided, and
some of the more common scenarios in which DSPs are used.
Armed with this information, it is then possible to find out the requirements
of your AVVID network and make the correct decision when provisioning your
DSPs. In this chapter, we will discuss the available DSP resource solutions.These
solutions include modules for the Catalyst 4000 and 6000, and NM-HDV modules,
which are available in the 2600/3600/VG200 Series routers/gateways.This
will be a good place to start when you are looking to understand how DSP
resources will be involved in the planning and layout of your Voice over IP
(VoIP) solution.We will discuss what DSPs are, what is provisioning, why they
are necessary, and why planning and designing their usage in the overall AVVID
design is important.