Linksys BUSINESS SPA922 - Manual (Page 110)

Linksys SPA9x2 Phone Administration Guide 103
Audio Configuration Parameters
Customizing SPA9x2 Extensions
codec is enabled and included in the codec list, that resource is tied up until the end of the call
whether or not the call actually uses G.729a. If the G729a resource is already allocated (and
since only one G.729a resource is allowed per SPA), no other low-bit-rate codec can be
allocated for subsequent calls. The only choices are G711a and G711u.
Since two G.723.1/G.726 resources are available per SPA9x2, you should disable the use of
G.729a to guarantee support for two simultaneous G.723/G.726 codecs.