diff --git a/src/gsm_utils.c b/src/gsm_utils.c
index 593dd5c..b392fd3 100644
--- a/src/gsm_utils.c
+++ b/src/gsm_utils.c
@@ -359,3 +359,18 @@
 	/* TS 05.02 Chapter 4.3.3 TDMA frame number */
 	return (51 * ((time->t3 - time->t2 + 26) % 26) + time->t3 + (26 * 51 * time->t1));
 }
+
+/* TS 03.03 Chapter 2.6 */
+int gprs_tlli_type(uint32_t tlli)
+{
+	if ((tlli & 0xc0000000) == 0xc0000000)
+		return TLLI_LOCAL;
+	else if ((tlli & 0xc0000000) == 0x80000000)
+		return TLLI_FOREIGN;
+	else if ((tlli & 0xf8000000) == 0x78000000)
+		return TLLI_RANDOM;
+	else if ((tlli & 0xf8000000) == 0x70000000)
+		return TLLI_AUXILIARY;
+
+	return TLLI_RESERVED;
+}