diff --git a/include/openbsc/abis_nm.h b/include/openbsc/abis_nm.h
index 1ed4cce..f1b0075 100644
--- a/include/openbsc/abis_nm.h
+++ b/include/openbsc/abis_nm.h
@@ -345,7 +345,7 @@
 	NM_ATT_IPACC_RSL_BSC_IP		= 0x80,
 	NM_ATT_IPACC_RSL_BSC_PORT	= 0x81,
 	NM_ATT_IPACC_LOCATION		= 0x8e,		/* string describing location */
-	NM_ATT_IPACC_UNIT_ID		= 0x91,
+	NM_ATT_IPACC_UNIT_ID		= 0x91,		/* Site/BTS/TRX */
 	NM_ATT_IPACC_UNIT_NAME		= 0x93,		/* default: nbts-<mac-as-string> */
 	NM_ATT_IPACC_PRIM_OML_IP	= 0x95,
 	NM_ATT_IPACC_SEC_OML_IP		= 0x96,