Perceptual Quality Assessment of Packet-Based Vocal Conversations over Wireless Networks: Methodologies and Applications

2. Networking Multimedia Services

The actual trend of network evolution is characterized by the convergence of Internet and Telecom services. This convergence is driven by standardization bodies as well as industry due in part to the expected value-added (Chauveau, 2005). Basically, this is performed by integrating/adding Telecom services over IP infrastructure. Technically, this integration is merely done by dividing original digitized stream into media units which constitute the payload part of carried IP packets. Moreover, the flexibility of packet-based networks enables providing other services such as radio over IP, IPTV, and video/music streaming.

Telecom services such as conversational services (vocal/video) and instantaneous vocal/video messaging are characterized by their sensitivity to delay. However, the unmanaged packet-based networks such as the Internet are suited to deliver delay-insensitive services such as E-Mail, FTP, and WWW. This service is sometimes called elastic media since delay and delay variation do not greatly affect the quality of service. Indeed, IP data networks are designed to reliably deliver bulk media with little consideration to transit delay. Thus, packets are usually subjected to variable and unbounded delays over IP networks. These properties are unsuitable for delay-sensitive services which require the reception of each media unit before its deadline, but may tolerate some packet losses. Actually, media units of delay-sensitive services are carried using the unreliable UDP transport protocol. UDP protocol does not provide congestion and flow control mechanisms which could certainly lead, in a large scale environment, to unfairness problems and threat network stability.