**3.3.1 Case 1 – Optimizing for coder selection**

The goal of this case is to find the optimal voice coder given link bandwidth, packet loss level, and background link utilization level. Table 4 and Table 5 are containing the coding parameters used in Case1 1 of the simulation. OPNET is configured by these parameters which are according to the ITU-T G.107 (ITU-T Rec. G.107 2005).

Table 7 shows the main differences between the different codecs G.711,G.729 and G.723.1 with respect to the coding type, coder bit rate, frame length , number of voice frames per packet and finally the Ie for each coder in case of no packet loss.

Table 8 also shows other differences between voice codes G.711, G.729 and G.723.1 with respect to the bandwidth calculations like voice payload size, number of packets per second and the bandwidth required after adding the headers of other protocols. For Case 1 with a link speed of 1.544 Mbps, The simulation was run for 2 hours and 4 hours and in all cases G.723.1 gave the max. Number of calls with R value more than 70, so G.723.1 was selected as the optimum Coder. G.711 gave the max. Quality of service (Highest R value) but the lowest number of calls, G.729 gave middle number of calls between G.711 and G.723 and also 84 Mobile Networks

2. Find the optimal voice coder and the optimal packet loss level given link bandwidth

3. Find the optimal voice coder and the optimal background link utilization level given

The results are divided into three general cases. For all cases, the aim is to maximize the number of calls that can be carried on a link while maintaining a minimum voice quality level (R > 70).If two combinations produce the same number of calls, the highest R value

The goal of this case is to find the optimal voice coder given link bandwidth, packet loss level, and background link utilization level. Table 4 and Table 5 are containing the coding parameters used in Case1 1 of the simulation. OPNET is configured by these parameters

Table 7 shows the main differences between the different codecs G.711,G.729 and G.723.1 with respect to the coding type, coder bit rate, frame length , number of voice frames per

Table 8 also shows other differences between voice codes G.711, G.729 and G.723.1 with respect to the bandwidth calculations like voice payload size, number of packets per second and the bandwidth required after adding the headers of other protocols. For Case 1 with a link speed of 1.544 Mbps, The simulation was run for 2 hours and 4 hours and in all cases G.723.1 gave the max. Number of calls with R value more than 70, so G.723.1 was selected as the optimum Coder. G.711 gave the max. Quality of service (Highest R value) but the lowest number of calls, G.729 gave middle number of calls between G.711 and G.723 and also

Table 6 shows standard parameters for each codec used in the analysis

and background link utilization.

Table 6. Codec Parameters

will be considered the best selection.

**3.3.1 Case 1 – Optimizing for coder selection** 

which are according to the ITU-T G.107 (ITU-T Rec. G.107 2005).

packet and finally the Ie for each coder in case of no packet loss.

**3.3 Results** 

link bandwidth and packet loss level.


Table 7. Codec Parameters for case1-1 (ITU-T Rec. G.107 2005) & (ITU-T Rec. G.113 2007)


Table 8. Codec Parameters for case1-2 (ITU-T Rec. G.107 2005) & (ITU-T Rec. G.113 2007)

middle R value. As shown in figure 5. Figure 4 shows the average packet end to end delay for different codecs and figure 6 shows the number of connected calls for different coders.

Table 9 contains data collected from OPNET in this case of 4 hours observation and shows that G.723.1 provides the maximum number of calls with accepted voice quality (R=78.2 >70)


Table 9. OPNET Results for case (1)

The results of this case are shown in Figure 6 not surprising, as G.723.1 is a more efficient but lower quality of voice.

Design and Analysis of IP-Multimedia Subsystem (IMS) 87

**R-Value and Number of Calls Vs. Coder**

R-Value Number of Calls Thershold R-Value

Fig. 6. R Value, Number of Calls vs. Coder – case (1)

**R-Value** 

 **Number of Calls**

**3.3.2 Case 2 – Optimizing for Coder and Packet Loss Level Selection** 

G.711 G.729 G.723 **Coder**

Table 10. Codec Parameters for case 2 (ITU-T Rec. G.113 2007)

% was the combination chosen.

The goal of this case is to find the optimal voice coder and the optimal packet loss level given link bandwidth and background link utilization. Table 10 contains the parameters used for case 2 of the simulation which is according to the ITU-T recommendation G.113

The OPNET simulation is configured by the above parameters like the codec bit rate and the packet size and the number of voice frames per packet but other values like Ie and Bpl are coming from ITU-T G.107 and G.113 for the mentioned codecs. The simulation was run for 1 hour, 2 hours and 4 hours and for the 3 coders G.711, G.729 and G.723 with different values of packet loss ratio. For the 3 coders G.711, G.729 and G.723 with different values of packet loss ratio (0.5 %, 1 %, 1.5 %, 2 % and 5 %) knowing that the maximum allowable ratio is 2% but the simulation was run for PL% equal 5% to observe the network behavior in case of big crisis as shown in Figure 7.The test was run with a link speed of 1.544 Mbps. The maximum number of calls was 29 calls. G.723.1 with packet loss of 0.5% was the combination chosen and the same combination was chosen till packet loss of 1.5 %. When packet loss ratio reached 2 %, G.723.1 became not feasible as its R value is less than 70 and G.729 with packet loss 2% was the combination chosen. For packet loss more than 2 % G.723.1 and G.729 became not feasible and the only feasible coder is G.711.G.711 with packet loss more than 2

Fig. 4. Average Packet End to End Delay

Fig. 5. Number of Connected Calls for different codecs

86 Mobile Networks

Fig. 4. Average Packet End to End Delay

Fig. 5. Number of Connected Calls for different codecs

Fig. 6. R Value, Number of Calls vs. Coder – case (1)
