IuCS: don't remove Iu conn until release

Don't remove the gsm_subscriber_connection without an Iu Release.

From the 2G paradigm to close a subscriber connection as soon as nothing else
is pending, osmo-cscn frequently calls msc_release_connection() to see whether
a conn has anything pending, or discards it.

In 3G however, we so far don't actively release IuCS connections from the MSC
side, but wait until the IuCS is released from the UE side. So the conn is
often discarded even though the IuCS stays open and valid, which confuses the
situation: before the UE releases a bit later, we would try to page the
subscriber unsuccessfully, because the UE expects to already be connected.

To first fix the discrepancy of Iu vs. subscr release, never discard
gsm_subscriber_connections when msc_release_connection() is called.

This creates a "lazy" CN that keeps connections open as long as the UE will
tolerate. It is really fast in sending many SMS in close succession, but is
certainly a bad CN design choice: we should rather stay lean on connections.

A subsequent commit will change this, but I decided to keep this commit as a
reference, for when we'd like to test situations that should re-use an
established connection.

Change-Id: I012378cfa432d791146db387554ec1909de05297

1 files changed, 4 insertions, 0 deletions

diff --git a/openbsc/src/libmsc/osmo_msc.c b/openbsc/src/libmsc/osmo_msc.c
index 6e982d050..2d5f94b56 100644
--- a/openbsc/src/libmsc/osmo_msc.c
+++ b/openbsc/src/libmsc/osmo_msc.c
@@ -149,6 +149,10 @@ struct bsc_api *msc_bsc_api() {
 /* conn release handling */
 void msc_release_connection(struct gsm_subscriber_connection *conn)
 {
+	/* For IuCS, always wait until the UE releases. */
+	if (conn->via_iface == IFACE_IU)
+		return;
+
 	/* skip when we are in release, e.g. due an error */
 	if (conn->in_release)
 		return;