an background classes. The first two classes correspond to real time classes, while the 2nd two to non-real time. Table 6.4 illustrates these classes. Table 6.4 QoS Classes in UMTS Traffic class Conversational Streaming Interactive Background Characteristics Preserve time Preserve also Request re- Connectionless, and applications relation between time relation sponse pattern generally packet information between infor- preserving data communications entities - low mation entities integrity. (e.g. preserving data delay (e.g. (e.g. multi- Internet or web integrity (e.g. voice, video- media) browsing) ftp, email, etc.) telephony) MULTIMEDIA TRANSMISSION - UMTS TRAFFIC CLASSES 6.4.1 Conversational Typical speech over CS bearers, voice over IP (VoIP) and video-telephony represent the conversational class, which in turn represent real-time services. The latter corresponds to symmetric traffic with end-to-end delay thresholds below 399 ms. 6.4.1.1 Enabling Speech The adaptive multi-rate (AMR) techniques will enable the UMTS speech codec. This codec consists of single integrated speech codec with eight source rates controlled by the RAN, i.e: 12.2 (GSM-EFR), 10.2, 7.95, 7.40 (IS-641), 6.70 (PDC-EFR), 5.90, 5.15 and 4.75 kbps. The use of the average required bit rate has impacts on interference lev- els, thereby on capacity, and battery life. Logically, lower rates will favour capacity and battery life duration, but not necessary quality. The AMR coder [4] works with speech frames of 20 ms, i.e. 160 samples at a sampling rate of 8000 sample/s. It may switch its bit rate at every frame through in-band signal- ling or through a dedicated channel. It uses Multi-rate Algebraic Code Excited Linear Prediction Coder (MR-ACELP) as a coding scheme. We extract CELP parameters at each 160 speech samples for error sensitive tests. The latter consist of three error classes (A-C), where class A has the highest sensitivity and requires strong channel coding. The AMR speech codec can tolerate about 1% frame error rate (FER) of class A bit