Basic Counters of GSM Network Performance

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Basic Counters of Network Performance
Accessibility
Accessibility counter is one of the most important statistics and it is the performance expression of the network at the first glance. Accessibility is calculated by multiplying SDDCH serviceability by TCH accessibility.

Accessibility = SDCCH Serviceability * TCH Accessibility

For accessibility performance of the network, repeated short call set–ups must be performed by drive tests.
Retainability
Retainability is the clue to network continuity and targets TCH Call Success rate of the network. It takes all type of drops into consideration.

Retainability = TCH Call Access Rate = 1 – TCH Call Drop Rate

TCH Call Drop rate is calculated by dividing total number of drop calls to number of total TCH seizures and attempts. Total number of drop calls
contains all types of TCH drops including any radio related, user activated, network activated, ABIS fail, A interface, LAPD, BTS failure or BSCU
reset drops. Please note that any TCH re–establishment should be subtracted from TCH call drop rate as call is somehow able to continue.

Total number of TCH attempts and seizures will include any TCH seizures for new calls and TCH to TCH attempts during Handover and number of
intracell handovers as well.

Retainability is wanted to be as near as to 100 percent. For measuring retainability and integrity of a network, long continuous calls must be performed by drive tests.
Access Fails
Access failures are the total number of unsuccessful TCH attempts which is calculated by subtracting number of assigned TCH seizures from number of TCH attempts – including the ones during handovers.