By default, Mitel devices compress 20 milliseconds of sampled speech input into output frames, that is, a default "packet rate" of 20 ms. Different endpoints (for example, SIP devices) may require different packet rates for successful audio streaming. NuPoint UM interworking with MiVoice Business Release 4.0 (3300 ICP Release 10.0) or later, allows you to configure a variable packet rate for these devices.
Variable packet rate is not supported for SIP connectivity with the MiVoice Office 250 or DMG (formerly PIMG/TIMG) deployments. These deployment options will maintain the fixed rate of 20 ms. even when the Variable Packet rate option is selected.
Variable packet rate is not supported on MiVoice Business software prior to Release 4.0 (3300 ICP Release 10)