3.4.6 Channel mode modify procedure

3GPP44.018GSM/EDGE Radio Resource Control (RRC) protocolMobile radio interface Layer 3 specificationRelease 16TS

In dedicated mode, dual transfer mode or group transmit mode, higher layers can request the setting of the channel mode.

The channel mode modify procedure allows the network to request the mobile station to set the channel mode for one channel or one channel set. The procedure shall not be used if the multislot configuration contains more than one channel set. The channel mode covers the coding, decoding and transcoding mode used on the indicated channel.

This message shall not be used to modify the mode of a non-multislot configured traffic channel when the MS has requested a multislot configuration, ie it cannot be used to modify the mode of a traffic channel when the channel was assigned during the immediate assignment procedure and the user has requested a multislot configuration.

This procedure is always initiated by the network.

NOTE: Direct transitions between full rate speech coder version 1 and full rate speech coder version 2 (and vice versa) may cause unpleasant audio bursts.

3.4.6.1 Normal channel mode modify procedure

3.4.6.1.1 Initiation of the channel mode modify procedure

The network initiates the procedure by sending a CHANNEL MODE MODIFY message to the mobile station. This message contains:

– a channel description of the channel(s) on which the mode in the CHANNEL MODE MODIFY message shall be applied; and

– the mode to be used on that channel, or on all the channels of a channel set in a multislot configuration.

– Optionally, when the channel mode indicates that a multi-rate speech codec must be applied, the MultiRateconfiguration to be used. The MultiRateConfiguration IE defines the set of codec modes and related information to use after the mode modify procedure.

If the channel mode is changed from a non multi-rate speech codec to a multi-rate speech codec or if the channel mode is changed from a multi-rate speech codec to another mutli-rate speech version but the old multi-rate speech version and the new multi-rate speech version are not the same, the CHANNEL MODE MODIFY message shall contain the MultiRate Configuration IE, which defines the set of codec modes and related information to use as a new mode.

If the old channel mode and the new channel mode are both multi-rate speech codec and if the old multi-rate speech version and the new multi-rate speech version are the same, the MultiRate Configuration IE may not be present. If not present, the MS shall go on with the current multi-rate speech configuration.

3.4.6.1.2 Completion of channel mode modify procedure

When it has received the CHANNEL MODE MODIFY message, the mobile station sets the mode for the indicated channel, and if that is in a multislot configuration, the whole channel set and then replies by a CHANNEL MODE MODIFY ACKNOWLEDGE message indicating the ordered channel mode.

This applies whether the mode commanded by the CHANNEL MODE MODIFY is different from the one used by the mobile station or whether it is already in use.

3.4.6.1.3 Abnormal cases

If the new mode is multi-rate speech codec and if the MultiRate Configuration IE is inconsistent, the MS shall ignore the CHANNEL MODE MODIFY message and shall not send CHANNEL MODE MODIFY ACKNOWLEDGE message to the network.

No other specific action for a lower layer failure is specified in this sub-clause. If the mobile station does not support the indicated mode, it shall retain the old mode and return the associated channel mode information in the CHANNEL MODE MODIFY ACKNOWLEDGE message.

3.4.6.2 Channel mode modify procedure for a voice group call talker

3.4.6.2.1 Initiation of the channel mode modify procedure

The network initiates the procedure by sending a CHANNEL MODE MODIFY message to the mobile station. This message contains:

– a channel description of the channel on which the CHANNEL MODE MODIFY message is sent; and

– the new channel mode to be used on the channel; and

– optionally, the VGCS target mode information element defining which RR mode (i.e. dedicated mode or group transmit mode) is to be used with the new channel mode. If this information element is not present, the RR mode shall be assumed to be the same as with the previous channel mode. The VGCS target mode information element shall also indicate the group cipher key number for the group cipher key to be used after the channel mode change. If the information element is not present, the ciphering mode and ciphering key shall be the same as with the previous channel mode. Mobile stations not supporting VGCS talking shall ignore the CHANNEL MODE MODIFY message if the VGCS target mode information element is included in the message and shall send an RR STATUS message to the network with cause #96.

When the RR mode to be used after the channel mode change is group transmit mode and the group cipher key number indicates that the resource is ciphered (ie group key number is non zero), then the VGCS Ciphering Parameters Information Element shall be included to provide the VSTK_RAND and Cell_Global_Count. The MS shall adjust and maintain the Cell Global Count using the procedure described in sub-clause 3.3.3.1. The MS shall then calculate the ciphering keys as described in 3GPP TS 43.020. Also, the MS shall fetch from the USIM the identity of its ciphering algorithm to use on the resource, as described in 3GPP TS 43.020.

When the RR mode used before the channel mode change and the RR mode to be used after the channel mode change are both dedicated mode and the channel was ciphered before the channel mode change, then new channel shall continue to be ciphered after the channel mode change with the same ciphering algorithm and ciphering keys as previously used.

If a VGCS target mode information element indicating a RR mode of dedicated mode and a non zero group cipher key number is included, the mobile station shall behave as if it would not support the indicated channel mode.

3.4.6.2.2 Completion of mode change procedure

When it has received the CHANNEL MODE MODIFY message, the mobile station changes the mode for the indicated channel and then replies by a CHANNEL MODE MODIFY ACKNOWLEDGE message indicating the new channel mode.

3.4.6.2.3 Abnormal cases

No specific action for a lower layer failure is specified in this sub-clause. If the mobile station does not support the indicated mode, it shall retain the old mode and return the associated channel mode information in the CHANNEL MODE MODIFY ACKNOWLEDGE message.