GSM Timers

This page covers timers used in GSM which include T100, T200, T301, T3126, T3146, T3182, T3190, T3192, T3124, T3230 and T3330.

Timer	Function/value
T100	It helps detect presence of the GSM radio Link by checking SACCH frames every 480 milli-sec. (Radio link timeout)
T200	It is used as retransmission on data link layer. Value varies depending on different messages (for FACCH it is set to 155ms)
T301	(Alerting or ringing timer); this timer limits the time user need to answer to an incoming call. (Value: 20 sec)
T3126	When this timer T3126 expires immediate assignment procedure is aborted. Starting procedure is same as timer T3146 mentioned below.
T3146	Started after sending maximum allowed CHANNEL REQUEST messages OR on receipt of Immediate Assignment Reject message whichever occurs first during a PS call. When T3146 expires   Packet Access Procedure is aborted. Maximum Value is set to 5 second.
T3182	Started when MS transmits final Uplink data block. If Uplink packet ACK is received everything is fine, if not and timer expires and with N3102>0; MS releases resources and attempts to re-establish communication on the cell again.
T3190	Packet DL Assignment on CCCH; started on reception of IMMEDIATE ASSIGNMENT or PDCH ASSIGNMENT COMMAND message when in dedicated mode. When T3190 timer expires; mobile returns to packet idle mode. Value of this timer is set to about 5 second.
T3192	Called TBF release timer, when T3192 expires UE (mobile) releases TBF related resources and begins scanning paging channel.
T3124	It is stated to wait for physical handover information from the network. It is stopped when Physical Information message is received at UE. It expires after waiting typical value of 320ms when physical information is not received.
T3230	It is started when mobile subscriber sends CM service request OR CM Re-Establishment Request, It stops when mobile subscriber receives CM service accept, CM service reject or it receives setting need for ciphering mode. If the timer T3230 times out then the call is terminated by mobile subscriber itself. It has value of 15 seconds.
T3330	RAU(Routing Area Update) request timer,expires when default value set (typically-15sec) is passed.Usually either RAU accept or RAU reject is sent by network to the UE upon receipt of RAU request.