Figure 14.41 suggest that it is more beneficial to configure CPICH Ec/NO as SRVCC criteria to evaluate target radio conditions instead of CPICH RSCP. The used AMR codec in LTE was wideband 12.65 kbps and narrowband 5.9 kbps in WCDMA. Optimization All handovers pose an additional risk to an ongoing call; the more components and procedures are required in the process, the higher the risk of dropping an ongoing call gets. SRVCC involves inter-frequency and inter-system handovers as well as a PS to CS domain switch, making it a complex procedure and risk of dropping a call is high hence it is beneficial to keep the SRVCC probability low. First target for SRVCC optimization is to reduce the number of SRVCCs by providing adequate LTE coverage, by implementing features extending the coverage (e.g. TTI bundling) and by not setting the triggering threshold for SRVCC too early. However, when LTE coverage is getting thin, at certain point the risk of dropping the call due to the poor coverage starts to increase and there will be a point where the risk of dropping call during SRVCC is lower than the risk of dropping the call by maintaining it on LTE. Therefore, the second target for SRVCC should be to find the point where the probability of dropping the call during SRVCC gets lower than the probability of dropping the call by maintaining it on poor radio environment as illustrated in Figure 14.42. For successful SRVCC the quality of coverage in the target network plays an important role. The problem is that often the LTE networks utilize and reuse the existing 2G/3G sites and quite possibly the coverage of the SRVCC target system is also poor when the LTE coverage is getting poor. Third target for optimization is to find the best target network, for example, prefer UMTS on 900 MHz over UMTS on 2100 MHz as SRVCC target or combination of both depending on coverage. Before 3GPP release 11, in case the SRVCC handover has gone that far that the SRVCC target system MSS has already sent PS-to-CS response and received 200 OK to sess