![](https://csdnimg.cn/release/download_crawler_static/6337101/bg14.jpg)
BLUETOOTH SPECIFICATION Page 20 of 126
Hands-Free Profile 1.6
10 May 2011
available codecs> command to the AG to notify the AG of the available codecs in the
HF.
After having retrieved the supported features in the AG, the HF shall determine which
indicators are supported by the AG, as well as the ordering of the supported indicators.
This is because, according to the 3GPP 27.007 specification [2], the AG may support
additional indicators not provided for by the Hands-Free Profile, and because the
ordering of the indicators is implementation specific. The HF uses the AT+CIND=? Test
command to retrieve information about the supported indicators and their ordering.
Once the HF has the necessary supported indicator and ordering information, it shall
retrieve the current status of the indicators in the AG using the AT+CIND? Read
command.
After having retrieved the status of the indicators in the AG, the HF shall then enable the
"Indicators status update" function in the AG by issuing the AT+CMER command, to
which the AG shall respond with OK. As a result, the AG shall send the +CIEV
unsolicited result code with the corresponding indicator value whenever a change in
service, call, or call setup status occurs. When an update is required for both the call
and call setup indicators, the AG shall send the +CIEV unsolicited result code for the
call indicator before sending the +CIEV unsolicited result code for the call setup
indicator. The HF shall use the information provided by the +CIEV code to update its
own internal and/or external indications.
Once the "Indicators status update" function has been enabled, the AG shall keep the
function enabled until either the AT+CMER command is issued to disable it, or the
current Service Level Connection between the AG and the HF is dropped for any
reason.
After the HF has enabled the “Indicators status update” function in the AG, and if the
“Call waiting and 3-way calling” bit was set in the supported features bitmap by both the
HF and the AG, the HF shall issue the AT+CHLD=? test command to retrieve the
information about how the call hold and multiparty services are supported in the AG.
The HF shall not issue the AT+CHLD=? test command in case either the HF or the AG
does not support the "Three way calling" feature.
The HF shall consider the Service Level Connection fully initialized, and thereby
established, in either of the following cases:
After the HF has successfully retrieved information about how call hold and
multiparty services are supported in the AG using the AT+CHLD command, if and
only if the “Call waiting and 3-way calling” bit was set in the SupportedFeatures
attribute of the SDP records for both HF and AG.
After the HF has successfully enabled the “Indicator status update” using the
AT+CMER command, if and only if the “Call waiting and 3-way calling” bit was not
Legacy devices shall not indicate support for the Codec Negotiation Feature.