Number of Loopback Start Failures (Speech Version Adjustment Failure)

Measurement Counter

R3821:CELL_LOCALSWITCH_LOOP_FAIL_SVR_ADJUST_FAIL

Description

When the BSC local loopback is started, the calling MS must have the same voice coding rate as the called MS. In AMR mode, the calling and called MSs must have the same voice coding rate. The rate cannot be changed. If the calling and called MSs have different voice coding rates, the BSC must adjust them through forced handover. If the adjustment fails, the BSC local switch is suspended.

During the speech version selection for BSC local switch, the speech version intersection supported by both parties must be calculated. If there is speech version intersection and the speech versions used by the two parties are within the intersection, the selection should be performed according to the policy listed in Table 1

If only one speech version in use is within the intersection, it is selected as the target speech version.
If neither speech versions are within the intersection, the higher speech version in the intersection should be selected. If both the full-rate and half-rate speech versions are supported, the full-rate one should be selected.

**Table 1** Policy for selecting local switch speech version
AMR	Whether ACSs Are Consistent and Voice Coding Rates Are the Same	Full Rate /Half Rate	Speech Version	Adjustment Policy
Used by both parties	Yes	NA	NA	Local loopback conditions are met and adjustment is not required.
	No	NA	NA	Adjustment should be made at both ends.
Used by either party	NA	NA	NA	The MS should be swtiched from AMR to non-AMR. The rate and speech version should be consistent with the peer end.
Used by neither party	NA	Inconsistent	NA	The MS should be switched from half-rate mode to full-rate mode. The rate and speech version should be consistent with the peer end.
		Consistent	Identical	Local loopback conditions are met and adjustment is not required.
		Consistent	Different	The high-rate MS should have the same speech version as the low-rate MS.

This measurement provides the number of loopback start failures due to speech version adjustment failures.

Unit

Integer number or integer.

Measurement Point

After the BSC receives the CONNECT ACK message from the MSC in the MS terminated call procedure, as shown in Figure 1(A1), or after the BSC receives the HANDOVER CMP message from the MS in the incoming BSC handover procedure, as shown in Figure 2(B1), the BSC selects the BSS local switch policy, determines whether the conditions for initiating the local switch are met, and performs local switch call detection. If all the local switch conditions are met, the call processing module initiating loopback start at one end sends a loopback request message to the call processing module at the peer end. The speech versions of the calling and called MSs are inconsistent, so the BSC makes an adjustment to the speech versions according to Table 1-1 to achieve consistency. If the speech versions, however, do not have an intersection, the adjustment fails. A loopback acknowledgement message is returned, informing that the loopback start fails with the cause value of speech version adjustment failure. In this case, this counter is measured in the cell where the loopback start is initiated.

Figure 1 Local switch in MS terminated call procedure

Figure 2 Local switch in the incoming-BSC handover procedure for the speech service

Formula

This is an original counter without involving any formula.