27025315534946849-2G-KPI-Description.ppt

Ercisson 2G kpi description

1. Ericsson
2G KPI formulae and their description

2. STS
 
• Statistics
and Traffic Measurement Subsystem (STS) is implemented in
the
BSC (and MSC). It gives statistics about events in different parts of the
system
such as cells and equipment. By continuously supervising the
results
from STS the operator can obtain a very good overview of the radio
network
performance which can help to detect problems early.
• Different
events occurring in an Ericsson GSM network are counted and
collected
by a subsystem called Statistics and Traffic Measurement
Subsystem
(STS).

3. •

STS
is available in two different versions, STS on APG and STS on
SP.
STS on SP is available on IOG equipped BSCs and STS on APG is
available
on APG40 equipped BSCs
• The
central part in STS is the Measurement Database (MDB) where all
measurements
are collected from different blocks in the Central
Processor
(CP). The contents of the MDB are written to STS report files
defined
by the user. These STS files are then fetched from the BSC and
processed
by OSS or a user defined external tool.
• By
combining and comparing different counters a general
understanding
of the radio network behavior can be obtained.

4. .
• During
a call several counters are affected. The allocation of a Stand-
alone
Dedicated Control Channel (SDCCH) can be successful or can fail
due
to congestion or the SDCCH could later drop due to low signal
strength.
Each event will result in different counters to be stepped.
• In
the BSC these events can be handovers, call setups, dropped calls,
allocation
of different channels etc. There are also a number of status
counters,
reporting the status of equipment within the network such as the
current
number of occupied channels.
• Some
of the 2G KPIs are explained next.

5. The
following formula, T_TRAFF, shows the average level of all TCH
traffic
in a cell (UL+OL) in Erlang or, more accurate, the mean number
of
allocated TCH channels.
Total (FR+HR) TCH Traffic Level in a Cell:
TFTRALACC Traffic
level accumulator for full-rate TCH
.
The
corresponding
counter for half-rate is
THTRALACC
TFNSCAN Number
of accumulations of traffic level counter for
full-rate
TCH. The corresponding counter for half-rate is
THNSCAN
T_TRAFF

6. T_AVAIL
• The
channel availability is very difficult to measure despite counters such
as
TAVAACC, number of available TCHs. This is due to the fact that
TNUCHCNT,
number of defined TCHs, depends on whether the number is
system
defined or operator defined.
• System
defined means that the number of TCHs is based on the number
of
allocated frequencies instead of the number of installed TRXs.
• Operator
defined means that the number of defined TCH channels is
calculated
as the required number of Basic Physical Channels (BPCs)
defined
by command (parameter NUMREQBPC) for the cell/channel group
minus
the number of BPCs used for BCCH and SDCCH in the cell/channel
group.
This is especially useful when synthesizer hopping is used (more
frequencies
than hardware).

7. • The
equation below can be used to calculate the number of available
TCHs
of total number of defined TCHs but the result will not be correct if
the
feature Adaptive configuration of logical channels is used. If Adaptive
configuration
of logical channels is activated the number of TCHs might
change
in the cell depending on the SDCCH traffic level. If the number of
TCHs
are operator defined or if synthesizer hopping is not active the
following
formula can be used:

8. TCH
Drop.
The
total number of terminated calls in a cell is then expressed as:
N_CALLS = I_CALLS + Inc(AB+AW) - Outg(AB+AW)
(Net Sum of Calls Terminated in Cell)
N_CALLS Number
of calls terminated in a cell
.
I_CALLS Number
of initiated calls in a cell, e.g. the sum of the
four
“CASSALL” counters for TCH or CMSESTAB for SDCCH.
Inc : Sum
of all incoming handovers to a cell from all its neighbors.
Outg
: Sum of all outgoing handovers from a cell to all its neighbors.
AW
Number of successful assignments to worse cell, counter
HOSUCWCL.
AB
Number of successful assignments to better cell
, counter

HOSUCBCL.
T_DR_S

9. TFNDROP The
total number of dropped full-rate TCH in underlaid
subcell.
The counter is also available for half-rate and
for
overlaid subcells, e.g.
THNDROPSUB.
TN_DROP = TFNDROP + TFNDROPSUB + THNDROP +
THNDROPSUB
(Total Number of Drops on TCH)

10. The
formula for drop on SDCCH, drop due to TCH congestion
excluded,
is:
CNDROP : The
total number of dropped SDCCH channels in a cell
.
CNRELCONG : Number
of released connection on SDCCH due to TCH
—
and transcoder congestion in underlaid and overlaid sub cell. The
subset
for overlaid sub cells is
CNRELCONGSUB . The
two counters are
located
in CLSDCCH and CLSDCCHO respectively. CNDROP is stepped
at
the same time.

CMSESTAB : Successful
MS channel establishments on SDCCH
S_DR

11. There
are 6 different stats available in Ericsson system which give
the
individual percentage contribution of each possible factor that
can
contribute towards the net SDCCH Drop:
Drop
Reason, Low Signal Strength Uplink (%).
Drop
Reason, Low Signal Strength Downlink (%).
Drop
Reason, Bad Quality Uplink (%).
Drop
Reason, Bad Quality Downlink (%).
Drop
Reason, Excess TA (%).
Drop
Reason, Other (%).

12. Call
Setup Success Rate.
CSSR = [(CCALLS-CCONGS)/(CCALLS)] * [(CMESTAB-(CNDROP-
CNRELCONG))/(CMESTAB)]* (TCASSALL/TASSALL)* 100
CCALLS
: Call attempt counter (on SDCCH).
CCONGS
:Congestion counter for under laid sub cell. Stepped per
congested
allocation attempt.
CMESTAB
: Successful MS establishment on SDCCH. This counter is a
sum
of both overlaid and under laid.
CNDROP
: The total number of dropped SDCCH channels in a cell.
CNRELCONG
: Number of released connections on SDCCH due to TCH-
or
Transcoder (TRA) congestion in both under laid and overlaid sub cell.
CSSR

13. TASSAL
: Number of first assignment attempts on TCH for all MS power
classes.
Successful attempts are counted in the target cell and failed
attempts
are counted in the serving cell. The serving cell is the cell where
the
mobile station was tuned to an SDCCH or TCH
TCASSALL
: 'Assignment complete' counter (TCASSALL) is
incremented
for the same conditions as the 'Assignment attempt' counter
(TASSALL)
if the attempt was successful. The 'Assignment complete'
counter
is incremented for the target cell. As TCASSALL is fetched by
STS
from the same object type as TASSALL they are always
synchronized.

14. CSSR = 100 * ([TCASSALL + TFCASSALLSUB + THCASSALL +
THCASSALLSUB]/ TASSALL) * (1 - ([RAOREQ + RAAPAG +
RACALRE]/CNROCNT) * (CCALLS-CMSESTAB)/CCALLS) * (1 -
([RAOREQ + RAAPAG + RACALRE]/CNROCNT)* (CNDROP -
CNRELCONG)/CMSESTAB)
In
general,
CSSR
= TCH Assignment * (1-SD Establishment for TCH Calls) * (1-SD
Drops
for TCH Calls)
Successful
attempts are counted in the target cell and failed attempts are
counted
in the serving cell.
Ericsson formula for CSSR

15. CNROCNT
: Number of accepted random accesses
RAACCFA :
Failed random access.
RAANPAG
: Number of random accesses, answer to paging.The
counter
will be stepped for cause value 100x xxxx.
RACALRE
:Call re-establishment.The counter will be stepped for cause
value
110x xxxx, Call reestablishment, TCH/F is needed, or originating
call
and NECI bit not set to 1, or procedures that can be completed with
an
SDCCH and NECI bit not set to 1.
TFCASSALLSUB
: Number of assignment complete messages for all
MS
power classes in underlaid subcell, full-rate.
THCASSALLSUB :

Number
of assignment complete messages for all
MS
power classes in underlaid subcell, half-rate.

16. This
KPI does not only cover TCH handover but also handovers during
assignment
and SDCCH handovers.
HOT_SUC = 100 * ( SUMOHOSUCC + SUMEOHSUCC ) / ( SUMOHOATT
+ SUMEOHATT )
HOT_SUC
SUMEOHOSUCC
: Sum of Successful External Handovers (Outgoing
Handover)
SUMOHOSUCC
:Sum of Successful Internal Handovers (Outgoing
Handover)
SUMOHOATT
: Sum of Internal Handover Attempts (Outgoing Handover)
SUMEOHOATT
:Sum of External handover Attempts (Outgoing
Handover)

17. •The
handovers that are not successful or not revert to the old cell. A high
rate
of reverted Handovers could indicate that there exists two cells with the
same
BSIC -BCCH combination, and both of them are defined as neighbors
• Other
reasons are that the handover is attempted before the uplink in the
new
cell works, and the old cell is sufficiently good for allowing a reversion.
The
failure in the new cell can be due to too aggressive settings for HO, or
an
indication of a faulty RX in the target cell with lower sensitivity.
• Handover
reversions do occur in any network even at good conditions -
normally
the rate is around 1%. The reason for this is likely temporary dips,
collisions
in the air interface etc. The Handover failure is not perceived by
the
subscriber,
but could lead to a subsequent drop due to penalties in locating
and
handovers to other cells that are not good candidates