GSM Timers.pptx

7/15/2019 GSM Timers.pptx

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GSM Timers

Sahrish Afsar

RF Optimization - South



Introduction

•GSM resource allocation and terminationdepends primarily on timers. The functionality

and protocols may vary, but the presence of timer

based signaling and resource allocation is

ubiquitous. Timer implementation is present in

each domain of the GSM system from MS to NSS

end.

• This presentation covers all the major BSS timersinvolved in the GSM architecture along with their

implementation in the PTML network.



Table of contents

• Timers categorization – Entity based categorization

– Process flow based categorization



Timers Categorization

•Entity based categorization

• Process flow based categorization



Entity Based Categorization

• One categorization can be done on the basisof entity which includes the following

categories:



Process flow based categorization

• GSM timers can also be classified on the basisof process flows involved in the system. These

include the following basic categories:

–

Call Processing• Call Setup

• Call Release

– Handovers

– Miscellaneous



Call Setup



T3120 (MS Timer)

•

This timer is included in the Call Requestprocedure which starts with the RACH request.

• This timer starts when the RACH request is sentto the network.

• The timer stops once the RACH acknowledgmentis received.

• Once the timer expires, the RACH request is

re‐Transmitted on the air interface.• This is a MS based Timer and hence vendor

implementation data is not applicable.



T3126 (MS Timer)

•

This timer is included in the Call Request procedurewhich starts with the RACH request.

• This timer starts when the maximum amount of Channel requests have been sent by the MS.

• The timer stops when immediate assignment message

is received from the BSS.• Once the timer expires, the procedure for immediate

assignment is aborted.

• The value of this timer depends on the setting of RACH

re‐transmission. • This is a MS based Timer and hence vendor

implementation data is unavailable.



T3122 (Cell Timer)

• This timer is included in the Call Request procedure whichstarts when MS receives the IMMEDIATE ASSIGNMENTREJECT message

• The MS starts this timer on the receipt of the “ImmediateAssignment Reject” message with the indicated value takenfrom the “wait indication information element” containedwithin the “Immediate Assignment Reject” message andreturns to idle mode

• The MS is not permitted to make a new attempt toestablish a radio resource connection in the same cell untilT3122 expires

• The vendor recommended values for this timer are givenbelow for reference

Timer Motorola Alcatel Huawei Nortel Ericsson NSN Ufone

T3122 - - 10 s 10 s



T3101 (Cell Timer)

•

This timer is included in the Call Setup procedurewhich starts with the immediate assignmentprocedure.

• This timer starts when the immediate assignmentmessage is sent to the MS by the BSS entity.

• The timer stops when the Establish indicationmessage is sent by the MS to the BSS entity.

• Once the timer expires, the procedure for call

setup is aborted.• The vendor recommended values for this timer

are given below for referenceTimer Motorola Alcatel Huawei Nortel Ericsson NSN Ufone

T3101 5 s 3 s 3 s 3 s



T3230 (MS Timer)

•


• This timer starts when the CM service request is sentby the MS to the BSS entity

• The timer stops when the MS receives the message of CM Service request acknowledged. It is also stopped incase a CM service reject is received.

• Once the timer expires, the release indication is

provided to the BSS entity.• This is a MS based Timer and hence vendor




T303 (MS Timer)

•


• This timer starts when the UA frame for theSDCCH connection is received by the MS.

• The timer is stopped when the CM servicerequest is sent by the MS.

• In case of an expiry event of this timer, the Call

setup procedure is aborted.• This is a MS based Timer and hence vendor




T310 (MS Timer)

•


• This Timer starts when the MS receives Call proceedingmessage.

• The timer stops once the Altering procedure beginsand the call is established.

• In case the timer expires and the altering procedurehas not begun, the call setup procedure is aborted and

No user Responding message is sent.• This is a MS based Timer and hence vendor




T11 (BSS/Cell Timer)

•

This parameter indicates the queue timer forassignment.

• This timer starts when an assignment resourcerequest is queued by the BSS entity when nochannel is available for assignment.

• The timer is stopped when the resource requestis allocated a resource by the BSS entity.

• Once the timer expires, the resource request is

rejected and the call setup procedure is aborted.• The vendor recommended values for this timer

are given below for reference

Timer

Motorol

a Alcatel Huawei Nortel Ericsson NSN Ufone

T11 28 s 6 s 8 s 8 s



T10 (BSC Timer)

•

This timer starts when assignment request is sentto the MS by the BSS entity.

• The timer is stopped when the assignmentcomplete message is sent by the MS to the BSS

entity.• Once the timer expires, the assignment request is

released and the call setup procedure is aborted.

•

The vendor recommended values for this timerare given below for reference

Timer

Motorol


T10



T313 (MSC Timer)

•This timer starts when the call connectmessage is sent to the call originating mobile.

• The timer stops when connect acknowledge

message is received by the network entityfrom the MS.

• In case of an expiry even of this timer, the call

setup procedure is aborted and the call isreleased.



T3107 (Cell Timer)

•

This timer starts when the assignment commandis sent by the BSS entity to the MS.

• The timer is stopped when the Assignmentcomplete message is received by BSS entity.

• In case of an expiry event of this timer, anassignment failure command is sent and thechannels are released.

•


Timer

Motorol


T3107 28 s 14 s 10 s 10 s



T1 (BSC Timer)?

• This timer starts when a blocking message is sent bythe BSS entity to the MSC entity in case of non‐usableA interface timeslot.

• The timer is stopped when a Blocking acknowledgmentmessage is received by the BSS entity.

• On first expiry of the timer, the BSS entity retransmitsthe Blocking message. In case of a second expiry, thechannel is set to non‐usable without MSCacknowledgment.

• The vendor recommended values for this timer aregiven below for reference

Timer

Motorol


T1 30 s 16 s 30 s



Call Release



T13 (BSC Timer)

•

This timer is used in the Reset Procedure initiatedby the MSC.

• The timer starts when a Reset message is sent bythe MSC to the BSS entity.

•

The timer stops on when the MSC receives ResetAcknowledgement by the BSS entity.

• In case of expiry event, the Resetacknowledgment is sent by the BSS to the MSC.

•


Timer

Motorol


T13 60 s



T3111 (Cell Timer)

• This timer is included in the Call release procedurewhich includes releasing of TCH channels

• This timer starts with the reception of Releaseindication message from the BSS entity.

• The timer stops when the BSS entity sends the

message for RF channel release to the respective BTS.• The expiry of this timer causes the forced channel

release procedure to start and the channel is releasedfrom all ends of the network.

•

The vendor recommended values for this timer aregiven below for reference

Timer

Motorol


T3111 1 s 1 s



T3109 (Cell Timer)

•

This timer is included in the Call release procedurewhich includes releasing of TCH channels

• This timer starts when the channel release message issent by the BSS entity to the subsequent BTS.

•

The timer is stopped when the release indicationmessage is received by the BSS entity.

• In case of an expiry event of this timer, the channelsare released and call procedure is aborted.

•



T3109 27s 27 s



T3110 (MS Timer)

•

This timer is included in the Call release procedurewhich includes releasing of TCH channels

• This timer starts when the MS receives the Channelrelease message from the BSS entity.

•

The timer stops once the MS receives a layer‐2‐message from the BSS entity for channel release.

• In case the timer expires, the normal channel releasecontinues till the call is released.

•

This is a MS based Timer and hence vendorimplementation data is unavailable.



Normal Channel Release



Normal Channel Release

• The system initiates the release of a channel by sending a channel release message

to the MS and will start an internal timer T3109, coincidentally SACCH messagesare deactivated.

• On receipt of the channel release, the MS will start an internal timer (T3110) anddisconnect the main signaling link by sending a Layer 2 disconnect frame. WhenT3110 times out or when the signaling is disconnect confirmed on receipt of alayer 2 numbered acknowledgement, the MS deactivates all RF links and returns toBCCH idle mode.

• On the system side, when the Layer 2 disc is received the BSS will stop T3109 andstart T3111. When T3111 has expired all RF links are terminated and are then freeto be allocated to other MS. The purpose of T3111 is to allow time for thedisconnect frame to be acknowledged with a Unnumbered Acknowledgement(UA) frame and to protect the channel in case the acknowledge frame is lost.Additionally, as T3111 runs for a shorter time than T3109, the channel is able to bere –assigned far quicker.

• If T3109 times out all RF channels will be deactivated and are then free to beallocated to other MSs. The value of T3109 should always be greater than T3110so that there is a high probability of normal termination.

• N.B. The value of T3111 must be set to a value equal to the value of T3110.



Handover



T3103 (Cell Timer)

•

The timer starts when the initiate Handovercommand is sent to the BTS by the BSC.

• The Timer is stopped when handover completemessage is received by the BSS entity.

• In case the timer expires, the handoverprocedure is aborted and the Handover attemptis termed as unsuccessful.

• The vendor recommended values for this timerare given below for reference

Timer

Motorol


T3103 30 s 16.5 s 10 s 10 s



T8 (Cell Timer)

•

The timer starts when the Handover command issent to the MS via the BSS entity.

• The Timer is stopped when handover completemessage is received by the BSS entity.



Timer

Motorol


T8 28 s 14 s 10 s 10 s



T7 (Cell Timer)

•

The timer starts when a Handover Requestmessage is sent to the MSC for an external BSChandover.

• The Timer is stopped when handover responsemessage is received by the BSS entity.



Timer

Motorol


T7 10 s 5 s 10 s 10 s



TQHO (Cell/BSC Timer)?

• This timer defines the maximum Queuing time for aHandover request.

• The timer starts when the BSS places a Handoverrequest in the resource queue for allocation.

• The timer is stopped when the Handover request is

allocated the required resource by the BSS entity.• In case of an expiry event of this timer, the handover

request is removed from the queue and the handoverprocedure is aborted.

•


Timer

Motorol


TQHO 30 s 5 s 8 s 8 s



T3121 (Cell Timer)

• This timer IS related with inter BSC and 2G/3Ghandovers.

• The timer is started when a request is sent for aninter‐BSC or 2G/3G handover.

•

The timer is stopped when a Handover completemessage is received by the BSS entity.

• In case of an expiry event of this timer, Clear request issent and the handover procedure is aborted.

•


Timer

Motorol


T3121 - 14 s 10 s 10 s



Miscellaneous



T3212 (Cell Timer)

• T3212 specifies the length of the timer for periodic location update.

• In the GSM system, it is possible that a powered-on MS is identifiedas implicit off-line if the MS sends no location update requestwithin a long period.

• When the MS reselects another cell (in the same LAC), the MS isrestarted through T3212 timeout if the T3212 of the new cell differs

from that of the original cell.• When this parameter differs in the cells of the same LAC, it is

possible that the MS is identified as implicit off-line if the MS sendsno location update request for a long period. In this case, systemplays "The subscriber you dial is power off." even though the calledMS is on.

• The vendor recommended values for this timer are given below forreference


T3212 120 min 360 min



T200 (BTS Timer)

• T200 is a timer in the LAPD protocol.

• The value of the timer indicates the time when the LAPDlink waits for the response or acknowledgement frameafter sending the command frame.

• T200 is set such that it is possible to receive an

acknowledgement from the peer entity of the transmittingData Link Layer, taking into account all processing andpropagation delays.

• If T200 Expires then the frame transmitted which startedT200 is retransmitted and the counter N200 is

incremented.• The value of this parameter must be smaller than "T203".


T200

Depends on

Transmission

quality



T203 (BTS Timer)

•

T203 is a timer in the LAPD protocol.• The value of the timer indicates the maximum

duration for no frame exchange in the LAPD

link.Timer Motorola Alcatel Huawei Nortel Ericsson NSN Ufone

T203

Depends on

Transmission

quality



Layer 2 Alignment



Huawei Timers

•

T200 SDCCH (60 ms)• T200 FACCH/F (50 ms)

• T200 FACCH/H (50 ms)

• T200 SACCH TCH SAPI0 (150 ms)

• T200 SACCH TCH SAPI3 (200 ms)

• T200 SACCH SDCCH (60 ms)

• T200 SDCCH SAPI3 (60 ms)



Thank You

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