Radio Link Timeout in AMR

Radio Link Timeout in AMR

Soc Classification level 1 © Nokia Siemens Networks

Presentation / Author / Date

RLT Background 3GPP 05.08 states that Radio Link Failure (RLF) in the MS is determined by the success rate of decoding messages on the downlink SACCH The aim of determining RLF in the MS is to ensure that calls with unacceptable voice/data quality, which cannot be improved either by RF power control or handover, are either re-established or released in a defined manner The Radio Link Timeout (RLT) parameter controls that a forced release (drop) will not normally occur until the call has degraded to a quality below that at which the majority of subscribers would have manually released it The RLF procedure is implemented in the RRM at the BSC and is as follows: • • • •

After the assignment of a dedicated channel a counter is initialized to RLT When a SACCH message is unsuccessfully decoded the counter is decreased by 1 When a SACCH message is successfully decoded the counter is increased by 2 If the counter reaches 0 a RLF is declared  Call is released

Soc Classification level 2 © Nokia Siemens Networks

RLT Background RLT is based on SACCH deletion. SACCH is though not using a dynamic codec like voice in AMR, which means: • Using the EFR RLT value an AMR customer can have the call dropped because RLT = 0 when still the FER is good • RLT is not anymore reliable with the same value in AMR than in EFR Due to the fact that the FER performance is different when comparing AMR calls to EFR calls, the Radio Link Timeout need to be defined separately for AMR The Radio Link Timeout parameter for AMR is ARLT, available from S11.5. The principle of ARLT is the same than in the RLT but it is used only for the AMR capable mobile stations. With ARLT the maximum value of the radio link counter expressed in SACCH blocks for AMR calls is defined. The values range from 4 to 64 blocks, and can be changed by 4-block steps at a time. The default value for ARLT is 20 (SACCH).

Soc Classification level 3 © Nokia Siemens Networks

Soc Classification level 4 © Nokia Siemens Networks

Soc Classification level 5 © Nokia Siemens Networks

Soc Classification level 6 © Nokia Siemens Networks