Excerpts from TDE100/200 manual

Getting Started for Virtual IP Cards
Installation
Installing the DSP16/DSP64 Card
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Depending on the number and the type of IP trunks and IP telephones you wish to use, required activation
keys are determined, and either the DSP16 or DSP64 card is selected to be installed.
Note
If the preinstalled activation keys on the DSP16 or DSP64 cards are not enough for the desired
configuration, refer to "4.1.3 Installing Additional Activation Keys".
DSP16: 16-channel DSP (Digital Signal Processor) card with a 4-Channel IP Trunk activation key and
an 8-Channel IP Proprietary Telephone activation key preinstalled. Compliant with ITU-T
G.729a and G.711 CODEC methods. To be mounted on the IPCMPR card.

About G.711 (www.voip-info.org/wiki/view/ITU+G.711)
Using G.711 for VoIP will give the best voice quality; since it uses no compression and it is the same codec used by the PSTN network and ISDN lines, it sounds just like using a regular or ISDN phone. It also has the lowest latency (lag) because there is no need for compression, which costs processing power. The downside is that it takes more bandwidth then other codecs, up to 84 Kbps including all TCP/IP overhead. However, with increasing broadband bandwith, this should not be a problem.

About G.729a (www.voip-info.org/wiki/view/ITU+G.729)
It offers toll quality speech at a reasonably low bit rate of 8Kbps. However, it is a rather "costly" codec in terms of CPU processing time, therefore some VoIP phones and adapters (notably the Linksys/Sipura/Cisco brands) can only handle one G.729 call (channel) at a time. This can cause calls to fail if the user attempts to use three-way calling, or place simultaneous calls on both lines of a two-line device, and G.729 is the only allowed codec.
Use of this codec in a product requires licensing.