Cisco 521SG Administration Guide - Page 307

Cisco SPA IP Phone Field Reference Ext Tab A Audio Configuration A codec resource is considered as allocated if it has been included in the SDP codec list of an active call, even though it eventually might not be the one chosen for the connection. So, if the G.729a 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 G.729a resource is already allocated and since only one G.729a resource is allowed per device, no other low-bit-rate codec might be allocated for subsequent calls; the only choices are G711a and G711u. On the other hand, two G.723.1/G.726 resources are available per device. Therefore it is important to disable the use of G.729a in order to guarantee the support of two simultaneous uses of the G.723/G.726 codecs. Parameter Preferred Codec Use Pref Codec Only Second Preferred Codec Description Preferred codec for all calls. (The actual codec used in a call still depends on the outcome of the codec negotiation protocol.) Select one of the following: G711u, G711a, G722, G726-16, G726-24, G726-32, G726-40, G729a, or G723. Cisco SPA525G or Cisco SPA525G2: G711u, G711a, G726-32, G729a, and G722. G.723 (not available on Cisco SPA300 Series or Cisco SPA500 Series). G722 not available on Cisco WIP310. Defaults to G711u. To use only the preferred codec for all calls, select yes. (The call fails if the far end does not support this codec.) Otherwise, select no. Defaults to no. The second preferred codec when the preferred codec cannot be used. If Use Pref Codec Only is enabled (set to yes), this parameter is not used. Defaults to Unspecified. Cisco Small Business SPA300 Series, SPA500 Series, and WIP310 IP Phone Administration Guide 306