5G NR RRC Timers, Counters and Constants
March 22, 2020admin5G, 5G Network Architectures, 5G Network Planning, Future Network Optimization, New
Radio, NR, Radio Resource Management, RRC, RRC Signalling, Signaling
5G NR radio resource control (RRC) has introduced following listed timers,
counters and constant for reliable functioning of procedures like
RRCsetuprequest, RRCreestablishment, RRCresume, RRCsuspend etc.
RRC timer indicates the timer duration and event when to start, event when to stop and
actions to be taken if the timer is expired. These timers are denoted by letter
“T” followed by 3 digit number e.g. T300. Each timer start we zero value and when the
UE applies zero value for a timer, the timer shall be started and immediately expire
unless explicitly stated otherwise.
RRC constant and counter defines the count or no. of attempts for particular event.
Counter are denoted by letter “N” and followed by 3 digit number e.g. N310.
Following is the complete list and details about timers, constant and counter.
Timer: T300
o Start Point:
Upon transmission of RRCSetupRequest
o Stop Point:
Upon reception of RRCSetup or RRCReject message
Upon Cell re-selection
Upon abortion of connection establishment by upper layers
o Action upon Timer Expiry:
Timer: T301
o Start Point:
Upon transmission of RRCReestabilshmentRequest
o Stop Point:
Upon reception of RRCReestablishment or RRCSetupmessage
when the selected cell becomes unsuitable
o Action upon Timer Expiry:
Go to RRC-IDLE
Timer: T302
o Start Point:
Upon reception of RRCReject while performing RRC connection
establishment or resume,
Upon reception of RRCRelease with waitTime
o Stop Point:
Upon entering RRC-CONNECTED or RRC-IDLE
Upon cell re-selection
Upon reception of RRCReject message
o Action upon Timer Expiry:
Inform upper layers about barring alleviation
Timer: T304
o Start Point:
Upon detecting physical layer problems for the SpCell i.e. upon
receiving N310 consecutive out-of sync indications from lower
layers
o Stop Point:
Upon receiving N311 consecutive in-sync indications from lower
layers for the SpCell,
Upon receiving RRCReconfiguration with reconfiguration With
Sync for that cell group, and upon initiating the connection re-
establishment procedure.
Upon SCG release, if the T310 is kept in SCG
o Action upon Timer Expiry:
If the T310 is kept in MCG: If security is not activated: go
to RRC_IDLE else: initiate the connection re-
establishment procedure
If the T310 is kept in SCG, Inform E-UTRAN/NR about the
SCG radio link failure by initiating the SCG failure information
procedure as specified in 5.7.3 of specification 38.331
Timer: T311
o Start Point:
Upon initiating the RRC connection reestablishment procedure
o Stop Point:
Upon selection of a suitable NR cell or a cell using another RAT
o Action upon Timer Expiry:
Enter RRC_IDLE
Timer: T319
o Start Point:
Upon transmission of RRCResumeRequest
o Stop Point:
Upon reception of RRCResume, RRCSetup, RRCRelease,
RRCRelease with suspendConfig or RRCReject message, cell
re-selection
Upon abortion of connection establishment by upper layers
o Action upon Timer Expiry:
Perform the actions as specified in 5.3.13.5 of 3GPP specification
38.331
Timer: T320
o Start Point:
Upon reception of t320
upon cell (re)selection to NR from another RAT with validity time
configured for dedicated priorities (in which case the remaining
validity time is applied)
o Stop Point:
Upon entering RRC-CONNECTED,
Upon reception of RRC Release, when PLMN selection is
performed on request by NAS
Upon cell (re)selection to another RAT (in which case the timer is
carried on to the other RAT)
o Action upon Timer Expiry:
Discard the cell re-selection priority information provided
by dedicated signalling
Timer: T321
o Start Point:
Upon receiving measConfig including a reportConfig with the
purpose set to report CGI
o Stop Point:
Upon acquiring the information needed to set all fields of cgiinfo
Upon receiving measConfig that includes removal of
the reportConfig with the purpose set to reportCGI
upon detecting that a cell is not broadcasting SIB1
o Action upon Timer Expiry:
Initiate the measurement reporting procedure, stop performing the
related measurements and remove the corresponding measId
Timer: T325
o Start Point:
Upon reception of RRCRelease message
with deprioritisationTimer
o Action upon Timer Expiry:
Stop deprioritisation of all frequencies or NR signalled
by RRCRelease
Timer: T380
o Start Point:
Upon reception of RRCRelease including suspendConfig
o Stop Point:
Upon reception of RRCResume, RRCSetup or RRCRelease
o Action upon Timer Expiry:
Perform the actions as specified in 5.3.13 of 3GPP 38.331
Timer: T390
o Start Point:
When access attempt is barred at access barring check for an
Access Category
The UE shall maintain one instance of this timer per Access
Category
o Stop Point:
As specified in 5.3.14.3 of 3GPP 38.331
o Action upon Timer Expiry:
Perform the actions as specified in 5.3.14.4 of 3GPP 38.331
Timer: T3xx
o Start Point:
Upon transmitting UEAssistanceInformation message
with DelayBudgetReport
o Stop Point:
Upon initiating the connection re-establishment procedures
o Action upon Timer Expiry:
No action.
Counter and Constant
N310: Maximum number of consecutive “out-of-sync” indications for
the PCell received from lower layers
o Reset
Upon reception of “insync” indication from lower layers
Upon
receiving RRCReconfiguration with reconfigurationWithSync for
that cell group
Upon initiating the connection reestablishment procedure
o Incremented
Upon reception of “out-of-sync” from lower layer while the
timer T310 is stopped
o When reaching max value
Start timer T310
N311: Maximum number of consecutive “in-sync” indications for the PCell
received from lower layers
o Reset
Upon reception of “outof-sync” indication from lower layers
Upon
receiving RRCReconfiguration with reconfigurationWithSync for
that cell group
Upon initiating the connection reestablishment procedure
o Incremented
Upon reception of the “in-sync” from lower layer while the
timer T310 is running
o When reaching max value
Stop the timer T310
Refereneces:
3GPP TS 38.331 5G; NR; Radio Resource Control (RRC); Protocol
specification
