Adaptive VoIP Transmission over Heterogeneous Wired/Wireless Networks

Abstract

Abstract. In this paper, we present an adaptive architecture for the transport of VoIP traffic over heterogeneous wired/wireless Internet environments. This architecture uses a VoIP gateway associated with an 802.11e QoS enhanced access point (QAP) to transcode voice flows before their transmissions over the wireless channel. The instantaneous bit rate is determined by a control mechanism based on the estimation of channel congestion state. Our mechanism dynamically adapts audio codec bit rate using a congestion avoidance technique so as to preserve acceptable levels of quality. A case study presenting the results relative to an adaptive system transmitting at bit rates typical of G.711 PCM (64 kbit/s) and G.726 ADPCM (40, 32, 24 and 16 kbit/s) speech coding standards illustrates the performance of the proposed framework. We perform extensive simulations to compare the performance between our adaptive audio rate control and TFRC mechanism. The results show that the proposed mechanism achieves better voice transmission performance, especially when the number of stations is fairly large.

Simulation and Analysis of Quality of Service (QoS) Parameters of Voice over IP (VoIP) Traffic through Heterogeneous Networks

“…This was achieved by selecting the appropriate adaptive audio codec with the suitable bitrate and then implementing a call stopping method where needed to fix congestions. www.ijacsa.thesai.org An earlier similar scheme [17] was also explained with the use of edge VoIP gateway between the WLAN and the Internet Cloud. The task of the edge VoIP gateway was to determine the pertinent variable speech coding rate (64, 40, 32, 24 and 16 Kbit/s) to lessen the network congestion with a subsequent increase in the overall QoS of speech traffic.…”

“…A technique that reduces VoIP traffic's packetization delay (also known as transmission delay or store-and-forward delay) utilized a Transmission Control Protocol (TCP), Friendly Rate Control (TFRC) algorithm based 802.11e network which applied the EDCF (Enhanced Distributed Coordination Function)/HCF (Hybrid Coordination Function) scheme [17].…”

Improving UDP performance using intermediate QoD‐aware hop system for wired/wireless multimedia communication systems

“…The frequent handoffs that result in temporal disconnections between communicating end hosts due to the limitations of radio coverage and user mobility is another drawback of wireless networks [2]. One more consequence of adapting wireless network is the link (or rate) asymmetry, which refers to the situation where the forward and reverse paths of a transmission have different channel capacities [1][2][3]. Actually, the wireless hops are likely to be congested due to asymmetric rate of arrival versus outgoing packets.…”

“…If the discrepancy of rates between the incoming and outgoing network is high, most of the packets are dropped due to buffer overflows [5,35]. Trad et al try to adjust the rate of VoIP to overcome this problem [3]. The frames are unnecessarily dropped until the sender reacts to the congestion.…”

VoIP Codec Adaptation Algorithm in Multirate 802.11 WLANs: Distributed vs. Centralized Performance Comparison

“…Some similar solutions proposing codec adaptation are the ones mentioned here. The authors in [18] focus on the Access Point (AP) acting as a bottleneck problem and propose a centralized element which performs transcoding of incoming calls to the wireless network. The work presented in [17] measures cell congestion and changes the codecs of all active calls accordingly, while performing admission control for new calls.…”