in every radio or TRX you have 8 Time slot but always is basicaly to have 1 TS for SDCCH 1 TS for BCCH and the rest of the channel to have traffic channels TCHs the meaning about SDCCH Seizure Attempts Rate is percentage of conexions between the mobil and the radio or TRX all attempts must be successfuly because your BTS has to link your mobil, you have to have a percentage above 99% (the depends of the target from your company)