Fast Dormancy

Some intelligent UEs on a live network send a Signaling Connection Release Indication (SCRI) message to the RNC after PS data transmission is complete. By sending the SCRI message, intelligent UEs request for a transition to idle mode or the CELL_PCH or URA_PCH state to reduce battery consumption. Upon receiving the SCRI, the RNC can release the signaling connection and put the UE into idle mode, or the RNC can maintain the signaling connection and put the UE to CELL_FACH or CELL_PCH/URA_PCH state. Controls the UE through CELL_FACH to CELL_PCH/URA_PCH or directly to CELL_PCH/URA_PCH can reduce battery consumption, depending on the UE capability and feature activation on the RNC. By default, the RNC puts the UE into idle mode. A UE setting up PS services in idle mode consumes more signaling resources than that in the CELL_PCH or URA_PCH state. If there are a large number of UEs transited between idle mode and CELL_DCH state, signaling storms may occur. The EFD feature puts UEs into the CELL_FACH or CELL_PCH state to reduce signaling resource consumption and eliminate signaling storms.

The UEs on a live network can be divided into three types:

• UEs that do not send SCRI messages because there is no PS data to be transmitted. Pre fast dormancy UEs. This type of UE does not read the T323 information element (IE) carried in the system information block type 1 (SIB1) message. After PS data transmission is complete, this type of UE sends an SCRI message to the RNC, but the SCRI message does not carry the IE Signaling Connection Release Indication Cause. Both T323 and Signaling Connection Release Indication Cause are introduced in 3GPP Release 8.
• R8 fast dormancy UEs. This type of UE reads the T323 IE carried in the SIB1 message and sends an SCRI message to the RNC after PS data transmission is complete. The SCRI message carries the IE Signaling Connection Release Indication Cause that is set to "UE Requested PS Data session end."

The T323 IE carried in the SIB1 message controls the frequency at which the R8 fast dormancy UEs send SCRI messages with the IE Signaling Connection Release Indication Cause set to "UE Requested PS Data session end". The T323 timer starts after an SCRI message is sent by the R8 fast dormancy UEs, and the second SCRI message with the IE Signaling Connection Release Indication Cause set to "UE Requested PS Data session end" can be sent only after the T323 timer expires.

The EFD feature applies only to the pre fast dormancy UEs and R8 fast dormancy UEs. Users can configure EFD to be enabled for only the pre fast dormancy UEs or R8 fast dormancy UEs.

When this feature is disabled, the RNC releases the signaling connection and puts the UE into idle mode after receiving the SCRI message regardless the UE types.

When this feature is enabled, the RNC performs different processing based on the UE type:

• For the pre fast dormancy UEs, the RNC checks for compatibility issues after receiving an SCRI message. If there are no compatibility issues, the RNC puts the UE into the CELL_FACH or PCH state. If there is a compatibility issue, the RNC puts the UE into idle mode.
• For the R8 fast dormancy UEs, the RNC puts the UE into the CELL_FACH or PCH state after receiving an SCRI message.

Some pre fast dormancy UEs may have compatibility issues after moving to the CELL_FACH, CELL_PCH, or URA_PCH state. As a result, new services cannot be initiated. This feature has been tested by using iPhones and no compatibility issue occurred.

When there is no PS data to be transmitted, the intelligent UE sends the RNC an SCRI message to request the UTRAN to release the signaling connection. This procedure saves power. In addition, the UE periodically sends heartbeat messages to the core network, for example, to check for new mails on the mail server. If the EFD feature is disabled, the RNC releases the signaling connection and puts the UE into the idle state. In this case, sending heartbeat messages leads to the procedures for RRC connection setups, authentication, encryption, and RAB setups. These procedures increase the RNC signaling processing load.

EFD addresses this problem. With EFD, the RNC transits a UE to the CELL_FACH or PCH state instead of idle mode upon receiving an SCRI message from the UE. In this case, when the UE periodically sends heartbeat messages, the signaling procedure between the UE and RNC is simplified because the RRC connection is maintained. As the number of signaling exchange messages decreases, significant CPU resources can be saved for the RNC, and the UE consumes about the same low amount of battery power as a UE in idle mode.

The RNC identifies the pre fast dormancy UEs and R8 fast dormancy UEs using the following mechanisms:

• R8 fast dormancy: The T323 parameter that can be set in the SET UCONNMODETIMER command is sent to the UE by the SIB1 message. The R8 fast dormancy UEs send an SCRI message with the IE Signaling Connection Release Indication Cause set to "UE Requested PS Data session end" after PS data transmission is complete. The RNC identifies the R8 fast dormancy UEs by reading the value of IE Signaling Connection Release Indication Cause. This mechanism is standardized by 3GPP Release 8.
• Pre fast dormancy: The RNC identifies the pre fast dormancy UEs using the Type Allocation Codes (TACs). This mechanism, which is not standardized, is used for the early proprietary implementations of fast dormancy.

The international mobile equipment identity (IMEI), which consists of 14 decimal digits and one check digit, contains TAC and SNR. TAC indicates a particular type of device that has been approved by a national GSM/WCDMA approval body. SNR is the serial number identifying the UE. The structure of the IMEI, which is shown as follows, is specified in 3GPP TS 23.003.

State Transitions for Fast Dormancy UEs

When EFD is disabled, upon receiving an SCRI message from a UE, the RNC releases the UE’s RRC connection. The EFD switches are specified by the RNC-level subparameter FAST_DORMANCY_SWITCH of the parameter PROCESSSWITCH.

When EFD is enabled, state transition procedures vary according to the UE type as follows:

• For R8 fast dormancy UEs and pre fast dormancy UEs in EFD list:
• If the RNC received the SCRI, The RNC transfers the UE to CELL_FACH or CELL_PCH/URA_PCH. The RSVDBIT1_BIT29 subparameter of the RsvdPara1 parameter in the SET URRCTRLSWITCH command controls whether the UE moves to CELL_FACH or CELL_PCH/URA_PCH.
• After PS data transmission is complete, If UE is in CELL_DCH, the PS inactivity timer (PsInactTmrForFstDrmDch) for EFD in CELL_DCH is started. If the PS inactivity timer for EFD in CELL_DCH expires, the RNC transfers the UE to CELL_FACH or CELL_PCH/URA_PCH.
• After PS data transmission is complete, If UE is in CELL_FACH, the PS inactivity timer (PsInactTmrForFstDrmFach) for EFD in CELL_FACH is started. If the PS inactivity timer for EFD in CELL_FACH expires, the RNC transfers the UE to CELL_PCH/URA_PCH.
• If UE is transferred to CELL_PCH/URA_PCH, the PS inactivity timer (PsInactTmrForPreFstDrm) is started. If the PS inactivity timer for EFD in CELL_PCH expires, the RNC transfers the UE to IDLE.
• If UE is in CELL_PCH/URA_PCH and has something to send and the condition for P2D is not satisfied, the RNC instructs the UE to enter the CELL_FACH state.
• If UE is in CELL_FACH and send messages whose traffic volume is higher than FastDormancyF2DHTvmThd, The RNC will transfer the UE from CELL_FACH to CELL_DCH.
• When the switch RSVDBIT1_BIT20 of RsvdPara1 in the SET URRCTRLSWITCH command is turned on and the UE tries to originate or terminate a CS service and the FACH is congested, the RNC instructs the UE to perform a P2D (instead of P2F) state transition.
• When the switch FACH_DTCH_CONGEST_P2D of PROCESSSWITCH2 in the SET URRCTRLSWITCH command is turned on and the UE tries to originate or terminate a PS service and the FACH is congested, the RNC instructs the UE to perform a P2D (instead of P2F) state
• For pre fast dormancy UEs not in EFD list:
• If the RNC received the SCRI, the RNC transfers the UE to IDLE state.
• The D2F/F2P/P2F/F2D/P2D state transition for pre fast dormancy UEs not in EFD list is the same to ordinary UEs.

Data configuration for state transitions for a fast dormancy UE.

Type	Description
D2P D2F F2P	D2P indicates a transition from CELL_DCH to CELL_PCH, F2P from CELL_FACH to CELL_PCH, and D2F from CELL_DCH to CELL_FACH.
D2I	D2I indicates a transition from CELL_DCH to idle. When the FACH is congested, D2F is not triggered for inactive CELL_DCH users. Instead, the RNC triggers a D2I transition to release the UE's RRC connection. The switch for D2I is turned off by default. Run the following command to switch it on:
P2I	P2I indicates a transition from CELL_PCH to idle.
P2D	P2D indicates a transition from CELL_PCH to CELL_DCH.

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