Abis Fail Call

(1)

1 © NOKIA FILENAMs.PPT/ DATE / NN

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 Drop %, S3 (sdr_1a)

Use:

To follow up the performance of SDCCH from technical point of view.

Experiences on use:

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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Random Access

Nbr of RACH slots

ave_rach_slot/res_acc_denom1

Peak RACH load

peak_rach_load

Average RACH busy

ave_rach_busy/res_acc_denom3

RACH slot is counted as busy when level is above -100dBm estimated at the RACH slot

Capacity

Load

BTS

TRX

RACH

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

BSC

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

Average value over the whole measurement period Higest value of

ave_rach_busy during the meas. period

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 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

GHOSTS

or

MS

Before B9 around 10 ghosts per hour to BSC

CCCH

LOAD

IND (every 30s)

After B9 around 1 ghosts per hour to BSC

Max Number Retransmission (RET) (1,2,4,7) defines nbr of repetition by MS

Rach_3 Rach_4

*) T3126

*) 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.

Immediate Assignment

Number of Slots Spread Trans (SLO)

(3..12, 14, 16, 20, 25, 32, 50 TDMA frames between retransmissions) MML default 10.

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

Known phenomenom:

Handover Access bursts causing SDCCH failures, blocking and Ghosts

Channel Required

NOTE: triggered related to level based RACH detection

(not what is accepted as RACH and passed as Channel Req)

If RACH passed all tests

NOTE: triggered related to what is accepted as RACH

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Ghosts

Author: J.Neva 12/96

Version: 1.0 5.12.96

Level

White noise

1.467282

1.497941

1.225209

1.485909

1.401945

1.467282

1.497941

1.225209

1.485909

1.401945

1.391514

1.467282

1.385073

1.012121

1.252343

0

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1

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9

1

6 ₁₁

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₆₁

In-band

Disturbances

Real Mobiles

White Noise

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Access Grant capacity (S8-9)

AG BLOCKING (blck_13) sum(del_ind_msg_rec) 100 * ---% sum(imm_assgn_rej+imm_assgn_sent) table = p_nbsc_res_acc

BSC

c3005 del_ind_msg_rec

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.

Author: J.Neva 10/96 Version: 1.2 1/2000 PMWG approval.:1.1 11.2.98 c3001 imm_assgn_sent c3002 imm_ass_rej

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

MS

BTS

Overflow of AG buffer 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 AG<>0, Paging has priority on PCH

If AG<>0, only Access Grant is sent on AG blocks

Buffer capacity = 8 Abis messages

Immediate Assignment

Immediate Assignment Rejected

Delete indication OR

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

Returned for each deleted AGCH message MS is not allowed to

attempt new RR-establishment i.e channel request until T3122 expires

Channel Request

(RACH) _{Channel Required} Channel Activation

Channel Activation Ack

RACH on CCCH /c3004

ch_req_msg_rec

/c1007

sdcch_assign

Ghosts having valid establishment cause get trhough even if cell was barred.

Abort if

T3126

expires

T9103

OR

Channel Activation Nack

e.g. SCCH blocking

SDCCH released with clear code 500341. /c1000 sdcch_seiz_att CCCH overload c1155 sdcch_unsucc_i mm_assign_att

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SDCCH requests (S9)

SDCCH REQUESTS /c1000 sdcch_seiz_att ASSIGNMENTS FOR CALLS,LU,SS /c1007 sdcch_assign BLOCKED /blck_15 sdcch_busy_att - tch_seiz_due_sdcch_ con RACH on CCCH /c3004 ch_req_msg_rec REJECTED DUE TO ILLEGAL EST.CAUSE (3/8 of ghosts in ph.1´) /c3030 ghost_ccch_res 5/8 OF GHOSTS (ph.1) AND OTHER FAILURES BEFORE ESTABL. IND.

(incl.IMSI detach):

/SD_1a

c1007- TRF_25a

MOC (incl.SMS and SS) /c3013 succ_seiz_orig MTC (incl.SMS) /c3012 succ_seiz_term CALL RE-EST. /c3020 sdcch_call_re_est LOCATION UPDATE /c3019 sdcch_loc_upd EMERGENCY CALL /c3021 sdcch_emerg_call

SDCCH ACCESSES REJECTED IN BSC

TRUE SDCCH SEIZURES

/TRF_25a (not updated in SDCCH HO)

SEIZURES FOR HO

/c1006

sdcch_ho_seiz

SDCCH FAILURES

/c1075

sdcch_abis_fail_call

(blocked chan.,corrupted

msgs, failed chan.act.)

Author: J.Neva 5/96 Version: 1.5 25.1.2001

PMWG approval.: v 1.5 25.1.2001

TRUE SDCCH SEIZURES FOR CALL,SMS, SS /TRF-27 IMSI DETACH /c3033 (S7) imsi_detach_sdcch TRUE SDCCH SEIZURES FOR CALL /TRF-26 TRF-27 - succ_sdcch_sms_est - unsucc _sdcch_sms_est TRUE SDCCH SEIZURES FOR SMS succ_sdcch_sms_est + unsucc _sdcch_sms_est SDCCH BLOCKING (blck_5a)

SDCCH-SDCCH HO

other than

**sdcch_abis_* failures**

small part of failures

Normal LU Periodic LU IMSI attach MS accessing, noise (ghosts) NOTE:

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

SDCCH-SDCCH HO

TCH

FACCH call setups

/c1099 tch_seiz_due_sdcch_ con Distance checking BSS5280 (S5) REJECTED DUE TO DISTANCE /c3031 (S5) rej_seiz_att_due_dist SDCCH FAILURES /c57020 (S7) t3101_expired

(Ghosts)

CALL RE-EST. ASSGN.

/c57022 (S7)

sdcch_re_est_assign

SUPPLEMENTARY SERVICE REQUEST

/c3044 (S9)

succ_seiz_supplem_serv

T3101 adjustable by MML

ZEGT:T3101..

BCSU Lower Limit = 34 unhandled reqs

/c3039 (S7)

bcsu_overload_lower_li mit

BCSU Upper Limit = 53 unhandled reqs /c3040 (S7) bcsu_overload_upper_li mit Limit per CCCH = 20 req.per BTS (CCCH) /c3041 (S7) bcsu_overload_deleted_ra ch Call_assign_after_sms /c??? S10.5 ND report 134