Feedback-Free Early VoIP Quality Adaptation Scheme in Next Generation Networks

Abstract

The Next Generation Networks (NGNs) were proposed to provide ubiquitous access to multimedia services over the Internet. With the best effort nature of the Internet, the quality of real time multimedia services such as voice and video can rapidly degrade due to network impairments.In this paper, we propose a novel feedback-free Early VoIP Quality Adaptation Scheme (EVQAS) which can adapt voice send bit rate (e.g. Adaptive Multi-Rate (AMR) codec mode) automatically according to the buildup of queuing delay in the network. This differs from existing adaptation methods which adapt send bit rate according to either packet loss information or Perceived Quality of Service (PQoS) metrics (e.g. Mean Opinion Score (MOS) ) derived from packet loss and delay. The proposed scheme can avoid congested packet loss which has an obvious impact on perceived voice quality. We implemented this adaptation mechanism in open Android mobile and tested in Open IMS Core testbed. Preliminary results show that the early adaptation mechanism can effectively release congestion before packet loss occurs. This has increased overall perceived voice quality when compared with existing adaptation method. This lightweight feedback-free early adaptation mechanism can be easily applied to other mobile devices to improve VoIP quality in current NGN VoIP applications.

Survey on application-layer mechanisms for speech quality adaptation in VoIP

“…Since they are physically implemented in the same softphone, only an internal message is needed to convey the change plan. This strategy, which is adopted by McGovern et al [2006a] and Mkwawa et al [2010], seems to be more efficient in terms of reaction time, as mentioned in Section 3.5.…”

“…While codec switching eventually requires a re-INVITE SIP request transaction, encoding rate control can use some field of the RTP payload header to carry a change plan of a particular bitrate. For example, the RTP payload header of AMR includes the codec mode request (CMR) field, which was used by Mkwawa et al [2010] and Zhou et al [2010] to change the current encoding rate. Table IV lists the main features of some known VBR codecs.…”