Gsm Immediate Assignment Failure To Thrive Syndrome

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by , 12-07-2011 at 06:20 PM (11502 Views)
Overview of the Immediate Assignment Success Rate :
Immediate assignment success rate indicates the success rate of the MS accessing the signaling channel. It concerns the procedure from the MS sending a channel required message to the BTS to the MS sending an establish indication message to the network.

Immediate assignment success rate is a key access counter. It directly reflects the success rate of the MS accessing the signaling channel and affects the user experience.

The immediate assignment success rate is calculated from traffic statistics. The recommended formula is as follows:
Immediate Assignment Success Rate = (Successful Immediate Assignments/Immediate Assignment Requests) x 100%

Signaling Procedure and Measurement Points
Immediate Assignment Success Rate-1.JPG

Symptom Description :

If the immediate assignment success rate decreases, the following symptoms may occur:
  1. Call setup success rate decreases.
  2. Congestion occurs frequently on the SDCCH
  3. Traffic volume on the TCH decreases
  4. Short messages cannot be successfully sent


Factors Concerning Immediate Assignment Success Rate:
1. Signaling Factors:
According to the signaling flow, the factors concerning the immediate assignment success rate during each phase are as follows:
(1) Random access request phase: whether the small interference signal on the Um interface is regarded as the random access request by the BSC. Affecting factor: Um interface problems;
(2) SDCCH assignment phase: whether the SDCCH is available after the random access request is accepted. Affecting factor: SDCCH congestion;
(3) Channel activation phase: whether the channel activation is successful after the channel assignment succeeds. Affecting factor: CHAN ACTIV NACK message is received because of equipment faults during SDCCH activation;
(4) Immediate assignment command phase: whether the timer for the acknowledgment of the immediate assignment expires. Affecting factor: Um interface problems;
(5) Link establishment phase: whether the link can be established on the SDCCH after the immediate assignment command is sent. Affecting factor: MS features.
The following analysis is based on these factors.

2 Factor Analyzing According to the Definition of the KPI :
As shown in the previous section, the following four factors are related to immediate assignment success rate: Um interface problems, SDCCH congestion, reception of CHAN ACTIV NACK because of equipment faults during SDCCH activation, MS problems.
These factors are related to the definition of the KPI. There are three formula that can define the immediate assignment success rate, the mapping between formula and factors are as follows:

Immediate Assignment Success Rate-2.JPG

Reasons for Immediate Assignment Failures :

• Answer to paging
• Emergency call
• Call reestablishment
• Other services (Orig. call, SMS, SS)
• Mobile Originating call
• Location update
• Other procedures (IMSI detach, SMS, SS, etc.)

There are three main reasons for immediate assignment failures

1. Unsuccessful Immediate Assignment Procedure, No SDCCH Available “SD Blocking”
2. Unsuccessful Immediate Assignment Procedure, No AGCH Available (AGCH Overload)
“Check for configuration being used in cell. Is it combined BCCH or non combined BCCH.”
3. Unsuccessful Immediate Assignment Procedure, assigned SDCCH is not seized by the MS (Phantom RACH Scenario)
“Check if cell is serving a very large area then we might need to increase ‘RxLevAccessMin’ as the cell is taking traffic from a large distance.

There are two cases when phantom RACHs are rejected

a. Call attempted from a high TA i.e. TA > 63
b. MS received level at the BTS in UL is less than a minimum threshold

Updated 12-31-2011 at 12:55 PM bytelecominfo

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GSM

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