diff --git a/openbsc/src/libcommon/gsm_data_shared.c b/openbsc/src/libcommon/gsm_data_shared.c
index 2488c3a..c8c9e04 100644
--- a/openbsc/src/libcommon/gsm_data_shared.c
+++ b/openbsc/src/libcommon/gsm_data_shared.c
@@ -708,3 +708,28 @@
 
 	return &ts->lchan[lch_idx];
 }
+
+static const uint8_t subslots_per_pchan[] = {
+	[GSM_PCHAN_NONE] = 0,
+	[GSM_PCHAN_CCCH] = 0,
+	[GSM_PCHAN_CCCH_SDCCH4] = 4,
+	[GSM_PCHAN_TCH_F] = 1,
+	[GSM_PCHAN_TCH_H] = 2,
+	[GSM_PCHAN_SDCCH8_SACCH8C] = 8,
+	[GSM_PCHAN_TCH_F_PDCH] = 1,
+	[GSM_PCHAN_CCCH_SDCCH4_CBCH] = 4,
+	[GSM_PCHAN_SDCCH8_SACCH8C_CBCH] = 8,
+	/*
+	 * GSM_PCHAN_TCH_F_TCH_H_PDCH should not be part of this, those TS are
+	 * handled according to their ts->dyn state.
+	 */
+};
+
+/*! According to ts->pchan and possibly ts->dyn_pchan, return the number of
+ * logical channels available in the timeslot. */
+uint8_t ts_subslots(struct gsm_bts_trx_ts *ts)
+{
+	if (ts->pchan == GSM_PCHAN_TCH_F_TCH_H_PDCH)
+		return subslots_per_pchan[ts->dyn.pchan_is];
+	return subslots_per_pchan[ts->pchan];
+}