Which G.723.1 Bit Rate? (Q55)

The information in this article applies to:

If an endpoint indicates receive capability for G.723.1 during the capabilities exchange, it is required to accept both the 5.3kbps and 6.3kbps rates--it has no control over which rate the other endpoint transmits. The transmitting endpoint indicates which rate is being used in-band, within the audio stream. The rate is not indicated out-of-band, e.g., over the H.245 control channel. Specifically, the bit rate is indicated by the least-significant bit of the first octet of each G.723.1 frame. The G.723.1 Recommendation calls this field, RATEFLAG_B0. A value of 0 means high rate; 1 means low rate. See section 4, "Bit stream packing," in G.723.1.