sdcch failures, 3 possibilities =
1 – radio problems (low coverage, interference, ghost rach, timer issue …)
3- BSS (hardware failure, VERY rare in this case)
find which is your current issue, then analyse the problem with drive test or advanced QoS analysis. Keep in mind that average SDCCH failure = 20% in alcatel system, and up to 50% if going through satellite Abis.