diff --git a/sysinfo/GSM_Types.ttcn b/sysinfo/GSM_Types.ttcn
index 98f6dd5..4529371 100644
--- a/sysinfo/GSM_Types.ttcn
+++ b/sysinfo/GSM_Types.ttcn
@@ -303,9 +303,25 @@
 		bitstring	ra length(8),
 		uint5_t 	t1p,
 		uint6_t 	t3,
-		uint5_t		t1
+		uint5_t		t2
 	} with { variant "" };
 
+	template RequestReference t_RequestReference(template bitstring ra, template uint5_t t1p, template uint6_t t3, template uint5_t t2) := {
+		ra := ra,
+		t1p := t1p,
+		t3 := t3,
+		t2 := t2
+	}
+
+	/* compute the expected request reference for given RA + FN */
+	function f_compute_ReqRef(uint8_t ra, GsmFrameNumber fn) return RequestReference {
+		var RequestReference req_ref := { ra := int2bit(ra, 8) };
+		req_ref.t1p := (fn / 1326) mod 32;
+		req_ref.t2 := fn mod 26;
+		req_ref.t3 := fn mod 51;
+		return req_ref
+	}
+
 	/* 10.5.2.40 */
 	type integer TimingAdvance (0..219);