UMTS Inter Vendor Hard Handover Issue Analysis

Hard handover could be an issue if two or more vendors are involved. Following steps can be taken to identify and kill the problem:

1. Neighbor configuration verification (LAC/RAC)
1. Definitions in both source and target RNC
2. Core network (MSC) definitions
2. Parameters check related to Hard Handver
1. Switch (Some vendors have Hard Handover Switch)
2. Threshold settings (could be too tight to initiate Handover)

A solved case scenario:

Ericsson to ZTE hard handovers were not taking place (there were no attempts at all). 

• Neighbors were correctly defined at both RNCs
• Core definitions were verified as well
• RNC trace analysis showed relocation failure message from MSC to RNC with eRANAP cause as "misc_unspecified_failure"

Source RNC Trace log

Core/MSC trace showed that relocation_request was being forwarded by the MSC to target RNC when relocation_required message is sent by source RNC. However, when target RNC did not respond with relocation_request_ack, the MSC sent the relocation_preparation_failure with "unspecified failure". This showed that target RNC (Ericsson) had some functional issue. On further investigation, it was found that Ericsson RNC had a switch parameter for hard handover which was disabled. Enabling it rectified the problem and hard handovers began to take place.

GSM - Low Paging Sucess Rate Issue

Paging discards can be a source low PSR or users complaining about getting "user not responding" messages as they call party B in GSM. The steps that can be taken to reduce or eliminate discards are as follows:

1- LAC Splitting
2- Cell paging capacity
      - can be increased of worst offenders
      - Shifting of SD/PD timeslots to non-BCCH TRXs
3- Audit of Periodic Location Update BSC Timer Value (t3212)
      - Can be set to 6 hours
      - This timer value at the MSC should be greater than the BSC value
4- Activation of Precise Paging Feature
      - Paging is done only on cells where there is high probability of finding subscribers according to the location record saved in the BSC