A Technique for Seamless VoIP-Codec Switching in Next Generation Networks

Vertical handovers in Next Generation Networks enable a new experience of mobility, since application layer sessions are maintained while roaming across different access networks. For real-time media services like Voice-over-IP, a change in the underlying network technology is particulary challenging. Ongoing calls are not suspended during the handover, however, the handover may go along with an audible gap during the transition time due to lost or delayed packets and an adaptation in call parameters such as those of the employed speech codec. This, in turn, may translate in an unfamiliar speech quality perception. This contribution introduces an ergonomic technique that aims at seamlessly switching the speech codec in Voice-over-IP calls during vertical handovers, based on SIP/SDP session renegotiation, the establishment of a parallel media stream and RTP packet filtering. Evaluation results are presented, showing that the proposed approach does not cause any interruption of the audio stream in about 90% of the test cases, clearly outperforming simple re-negotiation of session parameters that does not take a seamless transition into account (interruptions in all test cases). PESQ speech quality estimates reveal a quality advantage of 5.4% on average for the considered scenario.