Speech Quality Requirements over DSL Networks

Quality of service (QoS) has been a feature of voice communication networks almost since their inception. The extension of traditional voice QoS methods to data communication networks and the Internet has been a longstanding research topic, although for many years it was not considered a critical issue due to the inherent differences between data and voice traffic and the relatively low cost of over provisioning bandwidth. In particular, over-provisioning of network bandwidth has been common practice since the earliest fiber-optic local-area networks (LANs) were deployed, and bandwidth on an optical network was found to be very economical. As VoIP moves from being an interesting and cheap application for enthusiasts to a public service for everybody, the speech quality requirements will be of increasing importance. There are a number of factors that contribute to the user perceived speech quality. Voice over a packet network may introduce new degradations such as packet loss, and increase other degradations such as delay. In this paper, we address Voice-over-IP (VoIP) as a trend of transferring voice over DSL access network and explaining the reasons of packet loss in speech signals and the solutions for preventing and recovering from packet loss. We concluded that retransmission of voice packets is not feasible for real-time applications like voice since they have very tight delay-bounds. Keywords-com VoIP, QoS, DSL Networks, CODEC, FEC, Concealment, Jitter, DSLAM and ATM, Virtual Private Network (VPN), PPTP (VPN Protocol), IPSec (VPN Protocol), SIP (Signalling Protocol), H323 (Signalling Protocol), RTP (Real Time Transmission Protocol).