**3.1.2 Calculation of the equipment impairment Ie**

The loss impairment Ie captures the distortion of the original voice signal due to low-rate codec, and packet losses in both the network and the play out buffer. Currently, the E-Model (ITU-T Rec. G.107 2005) can only cope with speech distortion introduced by several codecs i.e. G.729 (ITU-T Rec. G.729 2007) or G.723 (ITU-T Rec. G.723 2006). Specific impairment factor values for codec operation under random packet-loss have formerly been treated using tabulated, packet-loss dependent Ie values. Now, the Packet-loss Robustness Factor Bpl is defined as codec specific value. The packet-loss dependent Effective Equipment Impairment Factor Ie-eff is derived using the codec specific value for the Equipment Impairment Factor at zero packet-loss. Ie and the Packet-loss Robustness Factor Bpl are listed in Table I for several codecs. With the Packet-loss Probability Ppl, (ITU-T Rec. G.113 2007).Ie-eff is calculated using formula (44)

$$\text{Te}-\text{eff}=\text{Ie} + (\text{95}-\text{Ie}) \frac{\text{Ppl}}{\text{Ppl}+\text{Bpl}} \tag{45}$$


As can be seen from this formula (44), the Effective Equipment Impairment Factor in case of Ppl = 0 (no packet-loss) is equal to the Ie value defined in Table 4.Ie represents the effect of degradation introduced by codecs, Packet Loss. (ITU-T Rec. G.113 2007) provides parameters for use in calculating Ie from codec type and Packet Loss rate.


Table 4. Provisional planning values for the equipment impairment factor Ie and for packetloss robustness factor Bpl (ITU-T Rec. G.113 2007)

Coming to the VoIP traffic Characterization, Human speech is traditionally modeled as sequence of alternate talk and silence periods whose durations are exponentially distributed and referred as to ON-OFF model. On the other hand all of the presently available codecs with VAD (Voice Activity Detection) have the ability to improve the speech quality by reproducing Speakers back ground by generating special frame type called SID (Silence Insert Descriptor). SID frames are generated during Voice Inactivity Period.
