sgsn: Make P-TMSI a local TLLI to avoid clash
Some broken equipment does not convert the P-TMSI to a Local TLLI.
This leads to the SGSN ignoring the GPRS Attach Complete message
from the phone. Proprietary SGSNs and some documentation we found
state that one should always set the two highest bits of a P-TMSI
to one. This will help broken equipment and will avoid a potential
P-TMSI/TLLI clash. The P-TMSI/Local TLLI mapping is now bijective.
diff --git a/openbsc/src/gprs/gprs_sgsn.c b/openbsc/src/gprs/gprs_sgsn.c
index 84bf512..f92b2de 100644
--- a/openbsc/src/gprs/gprs_sgsn.c
+++ b/openbsc/src/gprs/gprs_sgsn.c
@@ -361,7 +361,7 @@
uint32_t ptmsi;
restart:
- ptmsi = rand();
+ ptmsi = rand() | 0xC0000000;
llist_for_each_entry(mm, &sgsn_mm_ctxts, list) {
if (mm->p_tmsi == ptmsi)
goto restart;