Timers in LTE

LTE UE Timers:

Timer	Start	Stop	At expiry
T300	Transmission of RRCConnectionRequest	Reception of RRCConnectionSetup or RRCConnectionReject message, cell re-selection and upon abortion of connection establishment by upper layers	Reset MAC and Mac configuration. Inform upper layers about the failure
T301	Transmission of RRCConnectionReestabilshmentRequest	Reception of RRCConnectionReestablishment or RRCConnectionReestablishmentReject message as well as when the selected cell becomes unsuitable	Go to RRC_IDLE
T302	Reception of RRCConnectionReject while performing RRC connection establishment	Upon entering RRC_CONNECTED and upon cell re-selection	Inform upper layers
T303	Access barred while performing RRC connection establishment for mobile originating calls	Upon entering RRC_CONNECTED and upon cell re-selection	Inform upper layers
T304	Reception of RRCConnectionReconfiguration message including the MobilityControl Info or	Criterion for successful completion of handover to EUTRA or cell change order is met (the criterion is specified in the target RAT in case of inter-RAT)	In case of cell change order from E-UTRA or intra E-UTRA handover, initiate the RRC connection re-establishment procedure; In case of handover to E-UTRA, perform the actions defined in the specifications applicable for the source RAT.
	reception of MobilityFromEUTRACommand message including CellChangeOrder
T305	Access barred while performing RRC connection establishment for mobile originating signalling	Upon entering RRC_CONNECTED and upon cell re-selection	Inform upper layers
T310	Upon detecting physical layer problems i.e. upon receiving N310 consecutive out-of-sync indications from lower layers	Upon receiving N311 consecutive in-sync indications from lower layers, upon triggering the handover procedure and upon initiating the connection re-establishment procedure	If security is not activated: go to RRC_IDLE else: initiate the connection re-establishment procedure
T311	Upon initiating the RRC connection re-establishment procedure	Selection of a suitable E-UTRA cell or a cell using another RAT.	Enter RRC_IDLE
T320	Upon receiving t320 or upon cell (re)selection to E-UTRA from another RAT with validity time configured for dedicated priorities (in which case the remaining validity time is applied).	Upon entering RRC_CONNECTED, when PLMN selection is performed on request by NAS, or upon cell (re)selection to another RAT (in which case the timer is carried on to the other RAT).	Discard the cell reselection priority information provided by dedicated signalling.
T321	Upon receiving measConfig including a reportConfig with the purpose set to reportCGI	Upon acquiring the information needed to set all fields of cellGlobalId for the requested cell, upon receiving measConfig that includes removal of the reportConfig with the purpose set to reportCGI	Initiate the measurement reporting procedure, stop performing the related measurements and remove the corresponding measId

LTE UE Constants:

Constant	Usage
N310	Maximum number of consecutive "out-of-sync" indications received from lower layers. Value in whole number
N311	Maximum number of consecutive "in-sync" indications received from lower layers. Value in whole number

Taken from 3GPP TS 36.331