ov model for conversational speech. 12.3 Traffic models Inactive State Active State State 0 State 1 (Silence Periods) (Talk Spurts) FIGURE 12-2 The two-state Markov model for speech [6] The steady-state condition of the model requires that Po = al(a + c) and P1 = cl(a + c) where P0 and P1 are the probability of being in state 0 and state 1, respectively. As shown in Figure 12-2, the probability of a transition from state 1 (the active speech state) to state 0 (the inactive state) while in state 1 is equal to a, whereas the probability of a transition from state 0 to state 1 while in state 0 is C. The model is updated at the speech encoder frame rate R = 1/T, where T is the encoder frame duration, typically 20 ms for most speech encoders. Packets are generated at time intervals iT + T, where T is the packet arrival delay jitter, and i denotes the encoder frame index. During the active state, packets of fixed size are generated at these time intervals, while the model is updated at regular frame intervals. The size of packet and the rate at which the packets are sent depends on the corresponding voice codecs and compression schemes. The voice activity factor 2 is given as 2 = P1 = cl(a + c). A talk- spurt is defined as the time period TS between entering the active state and leaving the active state. The probability that a talk spurt has duration m speech frames is given by P(TTS = n) = a(1 - a)n-1, ,N = 1,2,... whereas the probability that a silence period has a duration of n speech frames is given as P(TSP m) c(1-c)"-",m=1,2,.... - The average talk spurt duration MTS (in number of speech frames) is defined as E[TTS 1/a; the mean silence period duration MSP (in number of speech frames) is given by MSP = E[tsp = 1/c. The distribution of the time period TAE (in number of speech frames) between successive active state entries is defined as the convolution of the distributions of TSP and TTS: PAaaa1c 1,2, (12-12) It must be noted that TAE can be further considered as the time between MAC-layer resource reser- vations,