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CUCM Codec Selection

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Prior to CUCM 9.0
In CUCM codec selection is based on regions. CUCM will check the regions for originating and destination endpoints and, accordingly, allocate the configure inter-region/intra-region codec.
CUCM will apply the codec based on Max Audio Bit Rate. It won't select specific codec (e.g. G.711 or G.729). For example, if the max audio bit rate configured is 64 kbps (G.722, G.711) & advertise G.722 Codec enterprise parameter is enabled, CUCM will advertise G.722 for this call. If the enterprise service parameter is disabled, CUCM will advertise G.711. CUCM will never advertise G729 for this call, although it has bit rate of 8kbps which is lower than configured max audio bit rate, even if it requested by the other party (in this case xcoder will be deployed or call will fail).
In Summary CUCM codec selection is based on Best Quality which fits within the configure Max Audio Bit Rate.
Note: Within G711 you can choose between alaw or ulaw by changing the service paramete…