GSM TimersTimer Name Description Value

T100 RADIO-LINK-TIMEOUTDetects 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 linktimerUsed for re-transmission on the data link. The value varies depending on the message type.

155 ms for FACCH

T301 Alerting (ringing) timerTimer 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 initiating call clearing procedures towards the MS.

10 seconds

T305 Release timerTime the network waits after transmitting a DISCONNECT message until receiving a RELEASE message.

10 seconds

T306 In-band tones release timer

Time the network waits after transmitting a DISCONNECT message while in-band tones/announcements are provided, until receiving a RELEASE message.

10 seconds

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 COMPLETE or MODIFY REJECT message before

10 seconds

Timer Name Description Value

initiating call clearing procedures.

T3101 Immediate assignment timer

Time the network waits after sending the IMMEDIATE ASSIGNMENT or IMMEDIATE ASSIGNMENT EXTENDED message until the main signalling link is established before releasing the newly allocated channels.

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 re-establishes the call before the old channels are released. 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.

2 seconds

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 occur before re-transmitting the PHYSICAL INFORMATION message or releasing the newly allocated channels.

50 ms

T3107 Channel assignment timer

Time the network waits after transmitting an ASSIGNMENT COMMAND message until receiving the ASSESSMENT FAILURE message or the MS re-establishes the call before releasing the old and the new channels.

3 seconds

T3109 Signaling disconnection timer

Time the network waits after sending the CHANNEL RELEASE message before disconnecting the signalling link.

5 seconds

T3111 Channel deactivation after disconnection timer

Time the network waits after disconnecting the signalling link before deactivating the channel.

500 ms

T3113 Paging timer

Time the network waits after transmitting the PAGING REQUEST message until receiving the PAGING RESPONSE message . This occurs before re-transmitting the PAGING REQUEST (if the maximum number of re-transmissions have not been exceeded).

5 seconds

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 the one it last camped on, it should perform

zero = infinite time

Timer Name Description Value

a location update.

T3250 TMSI reallocation timer

Time the network waits after sending the TMSI REALLOCATION COMMAND until receiving TMSI REALLOCATION COMPLETE. This occurs before aborting theprocedure and releasing the Radio Resource connection.

5 seconds

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 t imer

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 I-

frame 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 resources.

Read more about other GSM timers:-

GSM timers

Optimized value and uses:-

Based on project trial optimized value for both timers are 800ms.

You can change value of this timer to improve SDCCH drop, TCH

assignment, HOSR, 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 time-alignment 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?Email This BlogThis! Share to Twitter Share to Facebook

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, 18and 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 itsends a signaling message. When the timer expires, the transmit end regards thatthe receive end does not receive the message, and then the transmit end

retransmits the message. The number of retransmissions depends on N200. IfT200 x N200 is set to a small value, the timer expires before the transmit endreceives an acknowledgement from the receive end. In this case, a forced calldrop 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 engineer2010-02-22, 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 ?BRRF

EngSoft2010-02-22, 10:25 PM

N200 . T200 is other thing

RF engineer2010-02-23, 12:08 AM

N200 . T200 is other thingHiNo, 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 BRRF

hassen2010-02-23, 04:44 AM

Hithe mobile station stops the transmitting of measurement reportsthe BTS never get an acknowledge on a Layer 2 message after the time T200LAPD N200 is the maximum number of retransmissions

br hassen

tukangoptim2010-02-23, 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]

wael2011-01-14, 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

kadry2011-01-15, 10:01 PM

N200:means the number of resend SDCCH to moble stationThe value specifies the maximum number of retransmitting a frameTimer T200 has expired N200 +1 times (MS does not respond any more).check if there is:bad coveragehigh interferencehardware faulty

thanks

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