**3.3.3 Case 3 – Optimizing for coder and background link utilization**

The goal of this case is to find the optimal voice coder and the optimal background link utilization level given link bandwidth and packet loss level. The simulation was run for link speed T1 1.544 Mbps with variable background link utilization (90%, 92%, 94% and 95%) and different coders; the packet loss ratio was considered 0 % in all cases. G.711 with Back ground link utilization 90 % was the combination chosen as the all coders gave the same number of calls and G.711 gave the highest R-value which means the highest quality. With Back ground link utilization 92%, 94% and 95%, G.723.1 became the chosen coder. With back ground link utilization 95% G.711 became not feasible as its R value was below 70 and the feasible coders were G.729 and G.723.1 as shown in figure 9. Looking at Figure 8 we can see that all three coders were in a feasible range until background link utilization reached approximately 94%. In Figure 9 R remains constant for all coders until a point where R declines rapidly. This is important because it suggest that there is optimal link utilization where the system can be operated prior to the R value decline. The sudden 88 Mobile Networks

The optimization Results for case (2) is listed in Table 11 from the results in table 7we can

2. With Packet Loss more than 3.5% G.723 and G.729 are not feasible as their R-value < 70 and you have no choices because G.711 is the only feasible coder with R >70.

The goal of this case is to find the optimal voice coder and the optimal background link utilization level given link bandwidth and packet loss level. The simulation was run for link speed T1 1.544 Mbps with variable background link utilization (90%, 92%, 94% and 95%) and different coders; the packet loss ratio was considered 0 % in all cases. G.711 with Back ground link utilization 90 % was the combination chosen as the all coders gave the same number of calls and G.711 gave the highest R-value which means the highest quality. With Back ground link utilization 92%, 94% and 95%, G.723.1 became the chosen coder. With back ground link utilization 95% G.711 became not feasible as its R value was below 70 and the feasible coders were G.729 and G.723.1 as shown in figure 9. Looking at Figure 8 we can see that all three coders were in a feasible range until background link utilization reached approximately 94%. In Figure 9 R remains constant for all coders until a point where R declines rapidly. This is important because it suggest that there is optimal link utilization where the system can be operated prior to the R value decline. The sudden

**Case # Packet Loss % Optimum Coder**  1 0.5% G.723.1 2 1% G.723.1 3 1.5% G.723.1 4 2% G.729 5 >3.5% G.711

Fig. 7. R Value and PL % vs. Coder – case (2)

Table 11. Results of E-Model Optimization Case (2)

**3.3.3 Case 3 – Optimizing for coder and background link utilization** 

1. With Packet Loss 2% G.723 is not feasible as its R-value < 70.

notice that:

decrease in R is due to the fact that as utilization values approach 100%, the delay becomes unbounded, which negatively affects the R value. It is noticed that at 90% background Link utilization that all coders give the same number of calls, so the selection in this case is based on the R-Value which is the highest for G.711. It is also noticed that the most affected parameter in this case is the Id which is expected as the Background Link Utilization is affecting the Delay (Id) parameters as shown in Figure 10.The optimization Result for case (3) is listed in Table 12

Fig. 8. R Value, Background link Utilization % vs. Coder – case (3)

Fig. 9. Background Link Utilization % and Id vs. Coder – case (3)


Table 12. Results of E-Model Optimization Case (3)

Design and Analysis of IP-Multimedia Subsystem (IMS) 91

Case 2 required additional analysis because not all of the packet loss percentages have been tested and recorded. A polynomial fit was completed for each of the three coders. For G.711, the following polynomial was generated, where x represents the level of packet loss and y represents the level of impairment (Ie).Figure 11, shows a graph of the observed results

The following equation was driven and could be added to enhance E-Model for some codecs. For G.711, the following polynomial was generated, where x represents the level of packet

For G.729, the following polynomial was generated, where x represents the level of packet loss and y represents the level of impairment (Ie). Figure 12, shows a graph of the observed

For G.729A, the following polynomial was generated where x represents the level of packet

y = 0.0046 x3 - 0.156x2 + 3.8x - 0.00035 (46)

y = 0.0081x3 - 0.22x2 + 4.4x + 11 (47)

Fig. 10. PL % and Ie vs. Coder – case (2)

versus the curve fit.

Fig. 11. G.711 Polynomial Fit

results versus the curve fit.

loss and y represents the level of impairment (Ie).

loss and y represents the level of impairment (Ie):

Table 12 shows that G.711 with Back ground link utilization 90 % was the combination chosen as the all coders gave the same number of calls and G.711 gave the highest R-value which means the highest quality. With Back ground link utilization 92%, 94% and 95%, G.723.1 became the chosen coder. With back ground link utilization 95% G.711 became not feasible as its R value was below 70 and the feasible coders were G.729 and G.723.1.
