Abis Fail Call

Statistic: Signaling links in BSS • about 10% of SDCCH request will be unsuccessful due to A-bis failure (001075, A-bis fail call) and transaction attempt will be drop • 001075 has 19 different reasons (DX causes) • • •

Call set up picture (MOC.doc) T3101 expiry (SDCCH reservation) Retransmission in BTS level

• example: BSC Manila1,2,3,Vito Cruz 1 and 2 under MSCVC4 (1075.xls)

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SDCCH_ABIS_FAIL_CALL(1)

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SDCCH_ABIS_FAIL_CALL(2)

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SDCCH Drop %, S3 (sdr_1a) Use: Experiences on use:

To follow up the performance of SDCCH from technical point of view. 1) High SDCCH drop rates usually result from ghost accesses. A BTS decodes them from environmental or background noise and filters out most of them. However, all of them cannot be filtered out and the RACH request is passed on to the BSC for processing and for the allocation of a SDCCH channel. The counter GHOST CCCH RES (3030) is updated each time a CHANNEL REQUIRED is rejected because of an invalid establishment cause. In GSM ph.1 there exist altogether eight establishment causes, three of which are undefined as invalid, for example,resulting in that this counter shows only 3/8 of all the ghost accesses the BTS has decoded. For the rest, a SDCCH is allocated and this will result in SDCCH_ABIS_FAIL_CALL failure. Because of ghost attempts the SDCCH drop ratio is high with low traffic. As the amount of call attempts increases, the influence of ghosts becomes smaller and the drop ratio approaches its real value. 2) The rate of ghosts coming to SDCCH dropped when BTS B9 with improved ghost filtering was taken into use.

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Trigger Point(s)

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Trigger Point1

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T9103 TIMER

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Trigger Point2

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T9108 TIMER

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Trigger Point3

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AUGMENTATION OF COUNTER 1075

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T3101 TIMER

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T10 TIMER

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T10 TIMER

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T3107 TIMER

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T3107 TIMER

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T3122 TIMER

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T3122 TIMER

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GHOSTS = SDCCH seizures that do not lead to a useful benefit - thermodynamical type of noise - in band noise from network or environment - MS at the limit of sensitivity

Random Access

Known phenomenom: Handover Access bursts causing SDCCH failures, blocking and Ghosts Number of Slots Spread Trans (SLO) (3..12, 14, 16, 20, 25, 32, 50 TDMA frames between retransmissions) MML default 10. Max Number Retransmission (RET) (1,2,4,7) defines nbr of repetition by MS

Author: J.Neva 10/96 Version: 1.5 17.3.2000 PMWG approval.: 1.5 29.3.2000

BSC Capacity Nbr of RACH slots ave_rach_slot/res_acc_denom1

GHOSTS RACH or MS *) T3126 Immediate Assignment RACH slot is counted as busy when level is above -100dBm estimated at the RACH slot

BTS TRX

CCCH LOAD IND (every 30s)

Rach_3

Channel Required

If RACH passed all tests

Load Peak RACH load peak_rach_load

RACH has to pass - S/N test (pattern) - parity test

Before B9 around 10 ghosts per hour to BSC After B9 around 1 ghosts per hour to BSC

Rach_4

BTS sw B9.0 and DF2.0 has enhanced filtering of ghosts - energy level check with previous burst info - All 41 bits of training sequence used

Higest value of ave_rach_busy during the meas. period

Average RACH busy

NOTE: triggered related to level based RACH detection (not what is accepted as RACH and passed as Channel Req) Average value over the whole measurement period

ave_rach_busy/res_acc_denom3 RACH accesses ave_rach_access

NOTE: triggered related to what is accepted as RACH

In BTS sw B12 and DF5 the filtering of accesses with illegal establishment causes will be moved to BTS

*) T3126: In GSM Ph.1 waiting period is not defined (e.g. a Nokia MS has 800ms) but in GSM ph.2 it is defined by a complex algoritm and can be as long as 5 sec. GSM 04.08 says: This timer is started either after sending the maximum allowed number of CHANNEL REQUEST messages during an immediate assignment procedure or on receipt of an IMMEDIATE ASSIGNMENT REJECT message,whichever occurs first. It is stopped at receipt of an IMMEDIATE ASSIGNMENT message, or an IMMEDIATE ASSIGNMENT EXTENDED message. At its expiry, the immediate assignment procedure is aborted.

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Ghosts Real Mobiles

9 8

Level

Author: J.Neva 12/96 Version: 1.0 5.12.96

1.467282 7 1.467282 1.391514 6 0

1.497941 1.497941 1.467282 1

1.225209 1.225209 1.385073 2

1.485909 1.485909 1.012121 3

1.401945 1.401945 1.252343 4

In-band Disturbances

5 4 3 2

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41

36

31

26

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16

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6

1

0

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White noise White Noise

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Access Grant capacity (S8-9)

Parameters: AG = = Number of Blocks Reserved for Access Grant (0..7 if noncombined, 0..2 if combined, 1..7 if SBCH used in SDCCH/8) NOTE: If AG=0, Access Grant has priority over Paging If AG0, Paging has priority on PCH If AG0, only Access Grant is sent on AG blocks Channel Request (RACH)

MS

BTS

Abort if T3126 expires

BSC

Ghosts having valid establishment cause get trhough even if cell was barred. RACH on CCCH /c3004 ch_req_msg_rec

Channel Required Channel Activation

T9103

Channel Activation Ack OR Channel Activation Nack

Immediate Assignment OR

MS is not allowed to attempt new RRestablishment i.e channel request until T3122 expires

Author: J.Neva 10/96 Version: 1.2 1/2000 PMWG approval.:1.1 11.2.98

Immediate Assignment Buffer capacity = 8 Abis messages

OR Immediate Assignment Rejected

Immediate Assignment Rejected

e.g. SCCH blocking

Overflow of AG buffer CCCH overload

/c1000 sdcch_seiz_att

c3001 imm_assgn_sent c3002 imm_ass_rej

Returned for each deleted AGCH message

SDCCH released with clear code 500341.

Sent on AGCH or alternatively on PCH if there is free capacity

One message can include 1 - 4 Immediate Assignment Reject -Messages (from S6) !

AG BLOCKING (blck_13)

table = p_nbsc_res_acc

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c1155 sdcch_unsucc_i mm_assign_att

c3005 del_ind_msg_rec

Delete indication

sum(del_ind_msg_rec) 100 * ----------------------------------------------------% sum(imm_assgn_rej+imm_assgn_sent)

/c1007 sdcch_assign

How many times Immediate Assignment or Immediate Assignment Reject have been lost due to AG buffer overflow. MS needs to send a new Channel Request.

ND report 134

SDCCH ACCESSES REJECTED IN BSC BCSU Lower Limit = 34 unhandled reqs /c3039 (S7) bcsu_overload_lower_li mit

RACH on CCCH /c3004 ch_req_msg_rec

BCSU Upper Limit = 53 unhandled reqs /c3040 (S7) bcsu_overload_upper_li mit

Distance checking BSS5280 (S5) REJECTED DUE TO DISTANCE /c3031 (S5) rej_seiz_att_due_dist

SDCCHSDCCH HO

REJECTED DUE TO ILLEGAL EST.CAUSE (3/8 of ghosts in ph.1´) /c3030 ghost_ccch_res

ASSIGNMENTS FOR CALLS,LU,SS /c1007 SDCCH REQUESTS /c1000

sdcch_assign SEIZURES FOR HO /c1006

sdcch_seiz_att

sdcch_ho_seiz BLOCKED /blck_15

SDCCH BLOCKING (blck_5a)

sdcch_busy_att tch_seiz_due_sdcch_ con

Limit per CCCH = 20 req.per BTS (CCCH) /c3041 (S7) bcsu_overload_deleted_ra ch 5/8 OF GHOSTS (ph.1) AND OTHER FAILURES BEFORE ESTABL. IND. (incl.IMSI detach): /SD_1a c1007- TRF_25a

NOTE: Triggered also in case of HO attempt if there are no free SDCCH

FACCH call setups /c1099 tch_seiz_due_sdcch_ con

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SDCCH FAILURES /c1075 sdcch_abis_fail_call

(Ghosts) T3101 adjustable by MML ZEGT:T3101..

(blocked chan.,corrupted msgs, failed chan.act.)

small part of failures

TRUE SDCCH SEIZURES /TRF_25a (not updated in SDCCH HO) TRUE SDCCH SEIZURES FOR CALL,SMS, SS /TRF-27 MOC (incl.SMS and SS) /c3013 succ_seiz_orig

CALL RE-EST. /c3020

MTC (incl.SMS) /c3012 succ_seiz_term

EMERGENCY CALL /c3021 sdcch_emerg_call

TRF-27 - succ_sdcch_sms_est - unsucc _sdcch_sms_est

LOCATION UPDATE /c3019 sdcch_loc_upd

IMSI DETACH /c3033 (S7) imsi_detach_sdcch

TRUE SDCCH SEIZURES FOR SMS

sdcch_call_re_est

Periodic LU IMSI attach

TRUE SDCCH SEIZURES FOR CALL /TRF-26

succ_sdcch_sms_est + unsucc _sdcch_sms_est Call_assign_after_sms /c??? S10.5

SUPPLEMENTARY SERVICE REQUEST /c3044 (S9) succ_seiz_supplem_serv

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SDCCH FAILURES /c57020 (S7) t3101_expired

other than sdcch_abis_* failures

Normal LU

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Author: J.Neva 5/96 Version: 1.5 25.1.2001 PMWG approval.: v 1.5 25.1.2001

SDCCH requests (S9)

MS accessing, noise (ghosts)

CALL RE-EST. ASSGN. /c57022 (S7) sdcch_re_est_assign

SDCCHSDCCH HO

TCH