GSM Timers Timer Name
Description
Value
T100 RADIO-LINK-TIMEOUT
Detects the presence of the radio link by detecting SACCH frames every 480 ms.
4 SACCH multiframes. That is 1.92 seconds if the SACCH is completely absent.
T200 Data linktimer
Used for re-transmission on the data link. The value varies depending on the message type.
155 ms for FACCH
T301 Alerting (ringing) timer
Timer used to limit the amount of time a user has to answer a call.
20 seconds
T303 Mobility Management connection timer
Time the network waits after sending a CM SERVICE REQUEST until receiving a response. This occurs before 10 seconds initiating call clearing procedures towards the MS.
T305 Release timer
Time the network waits after transmitting a DISCONNECT 10 seconds message until receiving a RELEASE message.
T306 In-band tones release timer
Time the network waits after transmitting a DISCONNECT message while in-band tones/announcements are 10 seconds provided, until receiving a RELEASE message.
T308 Release timer
Time the network waits after sending a RELEASE message until receiving a RELEASE COMPLETE message. This occurs before re-transmitting the RELEASE or releasing the Mobility Management connection.
10 seconds
T310 Call proceeding timer
Time the network waits after receiving a CALL CONFIRMED message until receiving a ALERTING, CONNECT, or DISCONNECT message before initiating clearing procedures towards the MS.
10 seconds
T313 Connectacknowledge timer
Time the network waits after transmitting a CONNECT message until receiving theCONNECT ACKNOWLEDGE message before performing clearing procedures with the MS.
10 seconds
T323 Modify complete timer
Time the network waits after sending a MODIFY message during call mode changes, until receiving a MODIFY 10 seconds COMPLETE or MODIFY REJECT message before initiating call clearing procedures.
Timer Name
Description
Time the network waits after sending the IMMEDIATE ASSIGNMENT or IMMEDIATE ASSIGNMENT T3101 Immediate assignment EXTENDED message until the main signalling link is timer established before releasing the newly allocated channels.
Value
1 second
T3103 Handover timer
Time the network waits after transmitting a HANDOVER COMMAND message until receiving HANDOVER COMPLETE or HANDOVER FAILURE or the MS reestablishes the call before the old channels are released. 2 seconds If the timer expires and the network has not received a correctly decoded L2 (format A or B) or TCH frame, then the newly allocated channels are released.
T3105 Physical information repetition timer
Time the network waits after sending the PHYSICAL INFORMATION message until receiving a correctly decoded L2 (format A or B) or TCH frame. This 50 ms occur before re-transmitting the PHYSICAL INFORMATION message or releasing the newly allocated channels.
T3107 Channel assignment timer
Time the network waits after transmitting an ASSIGNMENT COMMAND message until receiving the ASSESSMENT FAILURE message or the MS re3 seconds establishes the call before releasing the old and the new channels.
T3109 Signaling disconnection timer
Time the network waits after sending the CHANNEL RELEASE message before disconnecting the signalling link.
5 seconds
T3111 Channel deactivation Time the network waits after disconnecting the signalling 500 ms after disconnection timer link before deactivating the channel.
T3113 Paging timer
Time the network waits after transmitting the PAGING REQUEST message until receiving the PAGING RESPONSE message. This occurs before retransmitting the PAGING REQUEST (if the maximum number of re-transmissions have not been exceeded).
T3212Locationupdate timer
The location update timer is set to zero, periodic location update by the MS are disabled. If the MS camps to the BCH and decodes a new MCC or MNC from zero = infinite time the one it last camped on, it should perform a location update.
5 seconds
Timer Name
Description
Value
T3250 TMSI reallocation timer
Time the network waits after sending the TMSI REALLOCATION COMMAND until receiving TMSI REALLOCATION COMPLETE. This occurs before 5 seconds aborting theprocedure and releasing the Radio Resource connection.
T3260 Authentication response timer
Time the network waits after an AUTHENTICATION REQUEST until receiving AUTHENTICATION RESPONSE. This occurs before aborting the procedure and releasing the Radio Resource connection.
5 seconds
Timer T200 - FACCH and SDCCH supervision timer There
are
two
timers
called T200s and T200f associated
with sdcch and facch respectively for the supervision of messages which transfer from BTS
to
mobile.
Range for both of this timer are from 220 to 1260 with step of 20 and Unit is 20ms. Overview:This timer is used on different control channel types and determines the waiting time for
a
layer
2
frame
acknowledgement.
During any dedicated connection the BTS and the MS exchange specific LAPDm signalling messages in the so-called in 'acknowledged mode'. This mode is started with an SABM and normally ends with the LAPDm DISCONNECT.All messages within this 'acknowledged
mode'
are
checked
by
the LAPDm flow control mechanisms based on sequence numbers that are assigned to each transmitted LAPD message. Only for those messages that are transmitted in acknowledged mode the timer T200 is used as waiting time for the layer2 acknowledgement
to
a
transmitted
message.
MS also uses the layer 2 acknowledgement mechanisms based on T200 in the same way as the BTS. In the MS, however, the T200 timer values are not variable but hardcoded.
Functional
description:-
When the BTS transmits a DL layer-2 frame on the air (e.g. an I-frame with an embedded layer 3 message) the BTS starts the timer T200 and waits for the acknowledgement frame from the MS. The acknowledgement frame can be another Iframe sent by the MS in the UL (if the MS has to transmit a layer-3 DTAP message anyway) as well as RECEIVE READY (RR) if there is nothing else to be transmitted on layer 3. If the acknowledgement from the MS is not received within T200 the transmission of the layer 2 frame is repeated and T200 restarted. The total number of repetitions is restricted to N200, a fixed value for the BTS side specified by GSM which depends
on
the
following
control
channel
types:
N200(SDCCH)=23, N200(SACCH)=5, N200(FACCH/FR)=34, N200(FACCH/HR)=29 If T200 expires after the last layer 2 frame repetition the BTS sends an ERROR INDICATION
with
cause
'T200
expired
N200+1
times'
(followed by a RELEASE INDICATION) message to the BSC, which releases the associated Read
resources. more
about
other
GSM
GSM
timers
Optimized Based You
timers:-
on can
value project change
assignment, HOSR, TCH
trial value
and
optimized of
this
uses:-
value
for
both
timers
timer
to
improve SDCCH
are 800ms. drop, TCH Drop.
#T200 is a timer of acknowledgement trasmission from BTS to MS through LAPD. When BTS transmits a acknowledgement message to MS, T200 times is started in LAPD. If this acknowledgement message is not received by MS until T200 timer is expired then the transmission will be repeated (retransmission).The maximum retransmission is N200+1 times. T200 will be restarted in each
retransmission. So, N200 is the maximum number of retransmission of LAPD (Layer-2). If until N200+1 times of retransmission the acknwledgement message, MS still doesn’t receive this message, then the connection will be dropped.
This problem is may be caused by hardware problem, bad condition of Radio, or imbalance link (UL and DL).
#L2 - Link Release Timer T200 (ms) Parameter group ISDN Signaling
Access level Field
Possible values Integer multiples of 5, in the range 700 through 2000
Defaults 1000
Explanation Specifies the value of the T200 timer, which acts as a retry time when attempting to establish the L2 data link. On starting to establish the link, the timer is started. The timer is stopped when the switch responds. On expiry, another L2 link establish message is sent to the switch and the timer is restarted. This is done for a particular number of retries until it is assumed that the switch is not ready to activate L2. #T200 is a timer of acknowledgment transmission from BTS to MS through LAPD. When BTS transmits a acknowledgment message to MS, T200 times is started in LAPD. If this acknowledgment message is not received by MS until T200 timer is expired then the transmission will be repeated (retransmission).The maximum retransmission is N200+1 times. T200 will be restarted in each retransmission. N200 is the maximum number of retransmission of LAPD (Layer-2). If until
N200+1 times of retransmission the acknowledgment message, MS still doesn’t receive this message, then the connection will be dropped.
# Makarand 1st Query T200 is a basic timer in the LAPDm & LAPD protocol (default value 240ms). T200 is the time between retransmissions, T200 is started for every transmission of a frame, and if the timer expires the frame is retransmitted. If the error persists after N200 retransmissions a link failure is detected and the data link is re-established. If the contact between the BSC and the BTS (or BTS & the MS)is broken the protocol will detect a link failure in approximately one second when using default values, calculated as (N200+1)*T200 + transmission and processing time. 2nd Query It is just the other way round.Data link failure is the cause of HO failure 3rd Query As HO process is break before make,so the data link in case of HO is from MS to target BTS. After the HO command ,if a data link failure is observed,HO faiure happens,& then either return to old channel or call drop happens.
Br\\ Bijoy
Makarand - 3rd September 2010
(01:17 GMT)
Hi bijoy, exactly when t200 starts? Is ho failure is one of the cause for data link failure? In ho failure which data link gets broken ,i think it must be at source side , then how it gets restored as its nt necessary that call may drop after data link failure.
Bijoy - 29th July 2010
(09:12 GMT)
Hi TTALONG in the BSC controls the value of the time-alignment timer.Time Alignment is a mechanism used between the BTSs and the transcoders to minimize the time speech and data frames are stored in the BTS before being sent out on the radio interface.The timealignment timer TTA is located in the BTS and it starts when the BTS sends time-alignment change information to the transcoder and it stops after receiving a response from the transcoder. TTALONG will be used for TGs where SIGDEL is set to LONG.SIGDEL is set to LONG for Satellite A-bis.There are Ericsson specific parameters.
What is Optimum Value of T200?
#
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we like to know the optimum value for T200 on LAPDm. All vendors have different default values (Siemens 145 ms, Nokia 220 ms, Satellite Abis 400 ms etc.) for this timer - but which value is the best to reduce SDCCH drops and to keep the retransmissions at an acceptable level ? Example: SDCCH/8 During a 51er multiframe the SDCCH/8 occupies four consecutive TDMA frames (four bursts are sent). Than the MS / BTS has to wait for the next 51er multiframe (i.e. 235 ms) before the next Layer 2 frame could be sent. 145 ms / 220 ms are shorter than the 51er multiframe (235 ms) so in case of an missingacknowledgement this is always a T200 expiry. The SDCCH drop will occur if T200 expired N200+1 times. If the T200 is increased (for example to 500 ms) we have two 51er multiframe to get the acknowledgement and the SDCCH drops are reduced. The Qos Stats show a clear & strong corelation between the KPI and the parameter T200. That's amazing ! Regarding the Ack from the BTS, I'm not sure (and I'm tired to look in the 3GPP specs :) ). Take the subchannel "0" from the SDCCH ts. in DL : the BTS sends SDCCH/0 on burst 0, 1, 2, 3 and the SACCH/0 on burst 32, 33, 34, 35 in UL : th MS sends SDCCH/0 on burst 15, 16, 17, 18 and the SACCH/0 on 47, 48, 49, 50 And I ***believe*** that the Lapdm acknowledgments can be sent on either the SACCH or the SDCCH, since both of them are sent over the same LapDm link. I'm not sure at all about this though, but it sounds logical.
The value of the SDCCH Drop due to Radio failures (in ALU) is usually around 1% in a fairly good network. The SDCCH Drop due to Radio Failures is a counter that encompasses both the Radio Link Timeout and the "T200*N200+1 times" failures. I am not able to test your changes because I am not working on a live network (i am a gsm trainer, living in a world of theory...) T200 = 220ms for sDCCH SAPI0 = 450ms for SDCCH SAPI3 = 900ms for SACCH associated to SDCCH Looking at those timers, I fear that the LapDm link for SDCCH is different than the LapDm link for the SACCH of the SDCCH... I'll let you look it up though :)
#T200 SDCCH_SAPI0, T200 SACCH SDCCH, T200 SDCCH_SAPI3, and N200 of SDCCH After the SDCCH is seized, the transmit end must set the timer T200 when it sends a signaling message. When the timer expires, the transmit end regards that the receive end does not receive the message, and then the transmit end retransmits the message. The number of retransmissions depends on N200. If T200 x N200 is set to a small value, the timer expires before the transmit end receives an acknowledgement from the receive end. In this case, a forced call drop occurs. Therefore, the call drops on SDCCHs increase.
# It can also be related to Lapd but that's not the same Timer. Lapd T200 is lapd N200 are different from T200 and N200.
DangerousMinds - 27th June 2008
(10:57 GMT)
Thanks again. Someone was telling me this is related to the LapD Signalling and T200 expiry means failure on the LapD interface. is this true?
Michele - 26th June 2008
(12:45 GMT)
T200 is an air interface timer regulating the communication between MS and BTS. It defines the rate of repetition of a message (on BTS side) on the air if it is not acknowledged by MS. If the message was repeated N200 times and no answer was received by MS, an error indication with cause T200 expired is provided to BSC. T200=ny1 * N200 where ny1 is configurable on BTS database
DangerousMinds - 25th June 2008
(09:24 GMT)
Hi, Can anyone please explain what does N200 timeout mean? And what should be done to rectify this problem? Also, is this related in any way to the T200 timer expiry? Thanks!
#Dears, Am doing a DT analysis and i found that for some reason i keep having N200 timeout . as all know the N200 is a layer 2 timer and if define the number of retransmission in LAPD frams . LAPD is between the BTS and BSC , so my question what could cause the timer to finish. I think , it could be no stability in transmission (E1) , what you think ?? please advice :confused: RF engineer
2010-02-22, 06:34 PM
Dears, Am doing a DT analysis and i found that for some reason i keep having N200 timeout . as all know the N200 is a layer 2 timer and if define the number of retransmission in LAPD frams . LAPD is between the BTS and BSC , so my question what could cause the timer to finish. I think , it could be no stability in transmission (E1) , what you think ?? please advice :confused: N200 or T200 ? BR RF EngSoft N200 . T200 is other thing RF engineer
2010-02-22, 10:25 PM
2010-02-23, 12:08 AM
N200 . T200 is other thing Hi No, both of them related to each other but i never faced such a problem for N200 and face T200 expired may be other colleague may be helping BR RF hassen
2010-02-23, 04:44 AM
Hi the mobile station stops the transmitting of measurement reports the BTS never get an acknowledge on a Layer 2 message after the time T200 LAPD N200 is the maximum number of retransmissions br hassen tukangoptim
2010-02-23, 05:17 AM example time out when channel ass cmd during HO. mostly due to radio quality. or if TRanscodre timer also expired abis subslot perhaps problem. [Only registered and activated users can see links] wael
2011-01-14, 08:30 PM Usually this timer N200 come with T200 during establish the SABAM message which is in Layer 2 during the assaying the channels in the call setup(SDCCH) or during the handover(FACH/FullTCH, FACH/half TCH ) , in the TEMs will see the N200 time out come with handover failure and with data link failure and like this case can be come due to : · Link transmission · TEMS ( there is problem in the TEMS) · hardware issue in the Maine processer in the BTS itself causing delay . · Bad RxQual UL kadry N200:means the number of resend SDCCH to moble station The value specifies the maximum number of retransmitting a frame Timer T200 has expired N200 +1 times (MS does not respond any more). check if there is: bad coverage high interference hardware faulty thanks
#
2011-01-15, 10:01 PM
