diff --git a/pcu/GPRS_Components.ttcn b/pcu/GPRS_Components.ttcn
index d3ace4d..5cf9104 100644
--- a/pcu/GPRS_Components.ttcn
+++ b/pcu/GPRS_Components.ttcn
@@ -241,6 +241,17 @@
 	return 51 * ((st.t3 - st.t2) mod 26) + st.t3 + 51 * 26 * st.t1;
 }
 
+function fn2bn(GsmFrameNumber fn) return uint32_t {
+	return (fn mod 52) / 4;
+}
+function f_next_pdch_block(GsmFrameNumber fn) return GsmFrameNumber
+{
+	var uint32_t bn := fn2bn(fn) + 1;
+	fn := fn - (fn mod 52);
+	fn := fn + bn * 4 + bn / 3;
+	return fn mod GsmMaxFrameNumber;
+}
+
 function f_ultbf_new_from_rr_imm_ass(in GsmRrMessage rr_imm_ass)
 runs on MS_BTS_IFACE_CT return UlTbf {
 	var UlTbf ul_tbf := valueof(t_UlTbf_def);