Support Neighbor Address Resolution over PCUIF IPA multiplex

While NACC was initially developed, it became clear there was need for
a way to interact PCU<->BSC in order resolve ARFCN+BSIC into CGI-PS
for later RIM usage.
Hence, this resolution was first (until today) implemented using an out
of bands RPC system using the CTRL interface, which required specific
config to be written and matches in osmo-pcu and osmo-bsc VTY (ip+port
of the CTRL interface to use).
However, this has several shortcomings:
* As explained above, specific configuration is required
* Since recently, we do support BSC redundancy in osmo-bts. Hence the BTS
  may switch to a BSC other than first one. If that happened, that'd mean
  the CTRL interface would still point to the initially configured one,
  which may not be the same currently serving the PCU.

During recent development of ANR related features, a similar need for
PCU<->BSC was required, but this time it was decided to extend the IPA
multiplex of the Abis OML connection to pass PCUIF messages,
transparently forwarded to each side by the BTS.
This has the advantage that connection PCU<->BTS is handled by BTS and
both sides send messages transparently.

Let's switch by default to using this new interface, while still
maintaing the old way for a while (announcing them as deprecated) to
avoid breaking existing deployments until they are upgraded to new
versions of osmo-pcu and osmo-bsc.

Change-Id: I9073a121564503f483c84263ac72476041e47c03
Related: SYS#4971

2 files changed, 32 insertions, 0 deletions

diff --git a/include/osmocom/bsc/neighbor_ident.h b/include/osmocom/bsc/neighbor_ident.h
index 0565d528c..58300ba48 100644
--- a/include/osmocom/bsc/neighbor_ident.h
+++ b/include/osmocom/bsc/neighbor_ident.h
@@ -86,6 +86,10 @@ int neighbors_check_cfg();
 	"for all BSICs / use any BSIC in this ARFCN\n"
 void neighbor_ident_vty_parse_arfcn_bsic(struct cell_ab *ab, const char **argv);
 
+int neighbor_address_resolution(const struct gsm_network *net, const struct cell_ab *ab,
+				uint16_t lac, uint16_t cell_id,
+				struct osmo_cell_global_id_ps *res_cgi_ps);
+
 struct ctrl_handle *neighbor_controlif_setup(struct gsm_network *net);
 int neighbor_ctrl_cmds_install(struct gsm_network *net);
 
diff --git a/include/osmocom/bsc/pcuif_proto.h b/include/osmocom/bsc/pcuif_proto.h
index 3e6f6510e..4921fc38d 100644
--- a/include/osmocom/bsc/pcuif_proto.h
+++ b/include/osmocom/bsc/pcuif_proto.h
@@ -26,6 +26,10 @@
 #define PCU_IF_MSG_TXT_IND	0x70	/* Text indication for BTS */
 #define PCU_IF_MSG_CONTAINER	0x80	/* Transparent container message */
 
+/* msg_type coming from BSC (inside PCU_IF_MSG_CONTAINER) */
+#define PCU_IF_MSG_NEIGH_ADDR_REQ	0x81	/* Neighbor Address Resolution Request */
+#define PCU_IF_MSG_NEIGH_ADDR_CNF	0x82	/* Neighbor Address Resolution Confirmation */
+
 /* sapi */
 #define PCU_IF_SAPI_RACH	0x01	/* channel request on CCCH */
 #define PCU_IF_SAPI_AGCH	0x02	/* assignment on AGCH */
@@ -226,6 +230,30 @@ struct gsm_pcu_if_container {
 	uint8_t		data[0];
 } __attribute__ ((packed));
 
+/*** Used inside container: NOTE: values must be network byte order here! ***/
+/* Neighbor Address Resolution Request */
+struct gsm_pcu_if_neigh_addr_req {
+	uint16_t	local_lac;
+	uint16_t	local_ci;
+	uint16_t	tgt_arfcn;
+	uint8_t		tgt_bsic;
+} __attribute__ ((packed));
+
+/* Neighbor Address Resolution Confirmation */
+struct gsm_pcu_if_neigh_addr_cnf {
+	struct gsm_pcu_if_neigh_addr_req orig_req;
+	uint8_t		err_code; /* 0 success, !0 failed & below unset */
+	/* RAI + CI (CGI-PS): */
+	struct __attribute__ ((packed)) {
+		uint16_t	mcc;
+		uint16_t	mnc;
+		uint8_t		mnc_3_digits;
+		uint16_t	lac;
+		uint8_t		rac;
+		uint16_t	cell_identity;
+	} cgi_ps;
+} __attribute__ ((packed));
+
 struct gsm_pcu_if {
 	/* context based information */
 	uint8_t		msg_type;	/* message type */