Implement checks for duplicate uplink UL L3 message
According to TS 24.007 Section 11.2.3.2.3, it is possible that uplink L3
messages are duplicated in some scenarios, particularly during
assignment/handover procedure.
To avoid L3 entities from seeing duplicated messages, there's a modulo-2
or modulo-4 message sequence counter, based on which the MSC can detect
and suppress such duplicate messages.
It appears that even our unit tests were wrong in that regard so far.
Rather than manually adjusting each and every message, let's make sure
that the sequence number generation always increments as expected, and
that during matching of incoming messages, sequence numbers are masked
out.
Note: the tests will only pass from libosmocore Change-Id
Iec875a77f5458322dfbef174f5abfc0e8c09d464 onwards, due to
gsm48_hdr_msg_type() being broken in earlier versions.
Change-Id: Id15e399ab7e1b05dcd426b292886fa19d36082b1
Closes: #2908
diff --git a/include/osmocom/msc/gsm_data.h b/include/osmocom/msc/gsm_data.h
index 27324d7..16e83f3 100644
--- a/include/osmocom/msc/gsm_data.h
+++ b/include/osmocom/msc/gsm_data.h
@@ -184,6 +184,9 @@
uint16_t lac;
struct gsm_encr encr;
+ /* N(SD) expected in the received frame, per flow (TS 24.007 11.2.3.2.3.2.2) */
+ uint8_t n_sd_next[4];
+
struct {
unsigned int mgcp_rtp_endpoint;
uint16_t port_subscr;