Themyscira Wireless RTP jitter buffer implementation (twjit) was originally designed for continuous streaming, as opposed to RTP streams with intentional gaps. However, intentional gaps in the case of DTX pauses or radio errors are called for by 3GPP AoIP specs and are the default mode for UL RTP Tx in OsmoBTS - therefore, this philosophical incompatibility between twjit and RTP intentional gaps is likely to be an obstacle to the desired replacement of Belledonne ortp with twrtp+twjit in OsmoBTS. The greatest practical effect of this philosophical mismatch occurs with RTP streams that apply intentional gaps for DTX: with standard twjit algorithm, isolated-island comfort noise update packets throughout each DTX pause will be dropped.
Underrun extension is an optionally-enabled modification to twjit algorithm that solves the problem of isolated-island CN update packets during DTX pauses - i.e., delivers these packets to the application on the output side of twjit. As detailed in the included document update, this solution is not perfect in that these isolated CN update packets will be delivered only in steady flow state but not in new flow acquisition states - but it is the best solution this author can currently provide for the problem of RTP intentional gaps.
