Terminology » GSM » GSM Timers: Network Side (BTS)

GSM Timers: Network Side (BTS)

gsm timers bts network mobile communication

This document details the various timers used in GSM on the network side (BTS), including T3101, T3103, T3105, T3107, T3109, T3111, T3113, T3115, T3121, T3123, T3141, T3151, T3153, T3155 and T3157.

TimerFunction/Value
T3101The timer starts upon allocation of a channel using an immediate assignment message. It stops when the mobile subscriber seizes the channel. The timer value is set by the network, ensuring it’s higher than the maximum time for L2 establishment attempts.
T3103This timer starts when a handover message is sent by the mobile. It stops when the mobile correctly captures the newly assigned channel. The timer value should be greater than the maximum transmission time of the handover command + the T3124 timer value + the maximum duration to establish a data link in multi-frame mode.
T3105This timer controls the repetition of the PHYSICAL INFORMATION message during the handover procedure. Its value is network-dependent. This timer can be set to a very low value, effectively causing the message to be transmitted continuously.
T3107This timer is initiated when an ASSIGNMENT COMMAND or a DTM ASSIGNMENT COMMAND message is sent. It typically stops when the MS correctly seizes the new RR channels. Its purpose is to release the new channels (and, in the case of Enhanced DTM CS establishment, the old PS resources) if the MS is lost. Except when used for Enhanced DTM CS Establishment, it keeps the old channel available long enough for the MS to return to the previous old channels. Its value is network dependent. It could be higher than the maximum transmission time of the ASSIGNMENT COMMAND message plus twice the maximum duration of an attempt to establish a data link in multiframe mode.
T3109This timer starts upon lower layer failure detection by the network. It’s used for the channel release procedure, specifically to release channels when communication is lost. Its value is network-dependent and should be large enough to ensure that the MS detects a radio link failure.
T3111This timer introduces a delay in channel deactivation after the disconnection of a signaling link. This provides time for repetition of the disconnection. The time value is equal to the value of timer T3110.
T3113This timer starts when the network sends a PAGING REQUEST message and stops when the network receives the PAGING RESPONSE message. Its value is network-dependent. The value could allow for repetitions of the Channel Request message and the requirements associated with T3101.
T3115This timer is used for the repetition of the VGCS UPLINK GRANT message during the uplink access procedure or priority uplink request procedure. Its value is network dependent. This timer may be set to such a low value that the message is in fact continuously transmitted.
T3121This timer starts when an INTER SYSTEM TO UTRAN HANDOVER message is sent. The timer stops after the mobile seizes the UTRAN channels. Its value is network-dependent.
T3123This timer is started by the sending of an INTER SYSTEM TO CDMA2000 HANDOVER message. It is normally stopped when the MS has correctly seized the CDMA2000 channel(s). Its value is network dependent.
T3141This timer is initiated when a temporary block flow is allocated with an IMMEDIATE ASSIGNMENT message during a Packet Access Procedure. It stops when the MS seizes the TBF. The timer value is set by the network.
T3151This timer is used by the network to supervise the periodic transmission of the UPLINK BUSY message on the FACCH of the voice group call channel. Its value is network-dependent.
T3153This timer is used by the network to supervise the periodic transmission of the VGCS ADDITIONAL INFORMATION message on the SACCH of the voice group call channel. Its value is network dependent.
T3155In a network supporting validation of Priority Uplink Requests, the timer T3155 supervises the broadcast of a new token after a valid Priority Uplink Request has been received. If a Priority Uplink Request is received, and the token matches the token in the BSS then the request is accepted, the token is invalidated and T3155 is started. On T3155 expiry a new token, and the priority of the accepted request, shall be sent in the UPLINK BUSY message on the FACCH of the voice group call channels. The T3155 timer should be set to a value that allows other service subscribers who sent a Priority Uplink Request at the same time as the one accepted by the network, to be back on the voice group call channel, in order to receive the new token. The default value for T3155 is 500ms.
T3157In a network supporting validation of Priority Uplink Requests, the timer T3157 supervises an additional validity period for an unused (old) token. When T3151 (supervising the periodic UPLINK BUSY) expires a new token is sent in the UPLINK BUSY message on the FACCH of the voice group call channels and timer T3157 is started. If a Priority Uplink Request is received before T3157 expires and the token matches either token in the BSS (old or new), the request is considered to be valid, both tokens in the BSS are invalidated and T3157 is stopped. If T3157 expires (i.e. no valid Priority Uplink Request has been received within T3157 seconds) the old token is invalidated. The value of timer T3157 is operator specific. The value chosen should allow for the reception of requests from service subscribers, who have left the group call channel before receipt of the UPLINK BUSY message with the new token. Its default value is 1s.