sd est study and possible causes

8/17/2019 SD EST Study and Possible Causes

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SD EST STUDY AND POSSIBLE

CAUSES

DRC RNPO DEPARTMENT


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INDEX

1. CCALLS Channel allocation attempt counter (on SDCCH).

2. CMSESTAB Successful MS channel establishments on SDCCH.3. CESTCHACTIV Number of SDDCH establishment failure that occurs under channel allocation

and channel activation. Please, note that this counter is stepped also in case of SDCCH

congestion.

4. CESTIMMASS Number of SDCCH establishment failure due to time-out after sending

Immediate Assignment, timer T3101 expired.

5. NLALOCTOT Total number of LU attempts in the LA

6. CSIMMASS Number of CS IMMEDIATE ASSIGNMENT messages sent on the CCCH

7. CNROCNT Number of Accepted Random Accesses.


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Main SD establishment

Reasons of Low SD estabishment

1. Low Availability

2. Too frequent Periodic Registration

3. Wrong SDCCH Dimensioning

4. Location Area Border Cell

5. Border Cell6. High SMS Usage

7. Cell Broadcast Used

8. IMSI Attach/Detach in Use

9. High Ratio of Random Accesses

10.Low Signal Strength on Down or Uplink

11.Poor Quality on Down or Uplink

12.Over-heard random access burst from another co -channel / co –BSIC cell

13.The A interference SCCP connection problem

14.The abnormal behavior of “MS”(No response of immediate assignment and keep sending random access

)


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Overview

According to statistical data records, low (89 %) S DCCH establishment success rates have been observed in

AFC radio network. An interesting point here is that, the problem is observed on all of the BSCs and many of

the cells; even tough the other key performance indicators (KPIs) related to SDCCH and TCH performance,

such as drop rates, drop reasons and handover reasons seem quite good.

In Ericsson GSM systems, CMSESTAB counter is incremented once, when a successful SCCP connection is

established between BSC and MSC; SCCP connection confirmed message arrives to BSC from MSC.

CCALLS, the call attempt counter is incremented at every attempt to allocate a SDCCH in a resource type in

the cell, regardless of whether the allocation succeeded or failed. Allocation attempts are made at signaling

connection setup, at handover and at assignment.


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Executive Summary (I)

Based on our investigation we can ensure that main issue for LOW SDCCH ESTAB is the T3101 which

could the case of Phantom RACH.

There are some random access bursts (cause value Location updating) accepted by the BTS, and BSC

allocates SDCCH resource in the BTS for signaling connection setup, and BTS sends out Immediate

assignment to the “MS”, after that there is no response from the “MS”, which causes the Timer

3101(no receiving of Establish Indication) in the BSC expired, consequently the IMMEDIATE

ASSIGNMENT procedure failed. The more no-response from the “MS”, the bigger difference between

counters CCALLS and CMSESTAB. The reason to this can be Phantom random access bursts or a MSthat is not behaving correctly)

By checking SD drop and TCH drop reason, most of drops are due to other in SD and Sudden loss of

connection. Where Sudden loss of connection an be related to Subs behavior , RF reason and HW.

While 16% of drops are related to RXLEV less than -100 Dbm.


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It was noticed also that BasCongo regions having better performance in terms of SD estab, than KIN,

this proof will neglect the coverage reason who is affecting the T3101 release

An audit and comparisons between Parameters of satellite interface cells and normal will be carried on

hour NW.

99% of Rach attempts are related to LAU, we do suggest to reduce the T3212 parameter controls the

Periodic Registration interval. A shorter interval, together with implicit detach supervision initiated in the

MSC, will reduce the amount of unnecessary paging, but it leads to more signalling on the SDCCH,thereby affecting the SDCCH dimensioning. The recommended initial setting of T3212 is 40, that is,

registration every 4th hours, while we have 6 hours on our NW.

Executive Summary (II)


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SD ESTAB VS CCALLS VS CMSESTAB

Low Value of SD ESTAB is due to the difference between CCALLS and SD ESTAB, in other hand it

was noticed that we do have 11% of failure is due to CESTIMMASS, where CESTIMMASS is

Number of SDCCH establishment failure due to time-out after sending Immediate Assignment,

timer T3101 expired


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SD ESTAB VS SD CONG

No clear relation between SD CONG and SD ESTAB, even though we have low value of

SD CONG SD estab is always 89 %


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SD ESTAB VS SD DROP

No clear relation between SD DROP and SD ESTAB, even though we have low value of SD DROP

SD estab is always 89 %


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SD ESTAB VS Immediate assign Success rate

From Above we can ensure that there is no load who is affecting our Immediate assignment


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Successful Immediate Assignment

it was noticed by dividing CESTIMASS by CSIMASS by that we do have 11% of failure is due to

CESTIMMASS, where CESTIMMASS is Number of SDCCH establishment failure due to time-outafter sending Immediate Assignment, timer T3101 expired. Reason To be investigate.


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CCALLS VS CSIMMASS VS CNROCNT

CCALLS(SDCCH channel activation) increases together with CNROCNT CSIMMASS(CS IMMEDIATE

ASSIGNMENT) increases together with CCALLS, which means SDCCH allocation succeeds. RAOTHER AND

NLALOCTOT almost the same, that is mean some attempt of CCALLS are considered as phantom RACH.


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RA Attempt percentage

99% RA Attempt percentage is mainly due to counter (RAOTHER). The counter will be stepped

for cause value Location updating (SDCCH needed). Reason to be investigate!!!


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END

sd est study and possible causes

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