libmsc/gsm_04_11.c: clarify implicit CP-ACK handling
Change-Id: I3c5327a5019590c65d0ccb33a52f07b3988ea952
diff --git a/src/libmsc/gsm_04_11.c b/src/libmsc/gsm_04_11.c
index 434f878..da0744a 100644
--- a/src/libmsc/gsm_04_11.c
+++ b/src/libmsc/gsm_04_11.c
@@ -1238,11 +1238,13 @@
LOG_TRANS(trans, LOGL_DEBUG, "receiving SMS message %s\n",
gsm48_pdisc_msgtype_name(gsm48_hdr_pdisc(gh), gsm48_hdr_msg_type(gh)));
- /* 5.4: For MO, if a CP-DATA is received for a new
- * transaction, equals reception of an implicit
- * last CP-ACK for previous transaction */
+ /* According to section 5.3.4, due to structure of message flow on
+ * SAPI 0 and 3 it is possible that the CP-ACK of a short message
+ * transfer might not be received. In this case the reception of
+ * CP-DATA may be interpreted as the reception of the awaited
+ * CP-ACK (implicit) and CP-DATA message. */
if (trans->sms.smc_inst.cp_state == GSM411_CPS_IDLE
- && msg_type == GSM411_MT_CP_DATA) {
+ && msg_type == GSM411_MT_CP_DATA) {
int i;
struct gsm_trans *ptrans;