--- a/sip-in/invite.c	Thu Sep 08 12:02:22 2022 -0800
+++ b/sip-in/invite.c	Thu Sep 08 12:58:03 2022 -0800
@@ -15,8 +15,10 @@
 #include "../libsip/uas_basic.h"
 #include "../libsip/grok_from.h"
 #include "../libsip/req_supp.h"
+#include "../libsip/sdp.h"
 #include "../libsip/out_msg.h"
 
+extern struct in_addr sip_bind_ip;
 extern int cfg_use_100rel;
 
 extern char *get_single_header();
@@ -32,7 +34,9 @@
 	struct grok_from gfrom;
 	struct supported_ext supp_ext;
 	char *hval, *unsup_ext;
-	int ext_100rel_req, ext_100rel_sup, use_100rel;
+	int ext_100rel_req, ext_100rel_sup, use_100rel, use_pcma;
+	struct sdp_parse sdp_parse;
+	struct sdp_gen sdp_gen;
 	int rc;
 
 	/* check for existing Call-ID will go here */
@@ -120,8 +124,39 @@
 		start_response_out_msg(&resp, "415 Unsupported Content-Type");
 		goto error_415;
 	}
-	/*
-	 * Remaining checks to be implemented:
-	 * SDP message body
-	 */
+	rc = parse_incoming_sdp(req->msg_body, req->msg_body_len, &sdp_parse);
+	if (rc < 0) {
+		start_response_out_msg(&resp, "488 Malformed SDP body");
+		goto error_resp;
+	}
+	switch (sdp_parse.codec_mask) {
+	case SDP_CODEC_MASK_PCMU:
+	case SDP_CODEC_MASK_BOTH:
+		use_pcma = 0;
+		break;
+	case SDP_CODEC_MASK_PCMA:
+	case SDP_CODEC_MASK_BOTH | SDP_CODEC_MASK_PCMA_PREF:
+		use_pcma = 1;
+		break;
+	default:
+		start_response_out_msg(&resp,
+			"488 Unsupported codec selection");
+		rc = add_resp_basic_headers(&resp, ess, req->req_method);
+		if (rc < 0)
+			goto error_resp_toolong;
+		rc = out_msg_add_header(&resp, "Content-Type",
+					"application/sdp");
+		if (rc < 0)
+			goto error_resp_toolong;
+		bzero(&sdp_gen, sizeof sdp_gen);
+		sdp_gen.owner_ip = sip_bind_ip;
+		sdp_gen.conn_ip = sip_bind_ip;
+		sdp_gen.codec_mask = SDP_CODEC_MASK_BOTH;
+		rc = out_msg_finish_sdp(&resp, &sdp_gen);
+		if (rc < 0)
+			goto error_resp_toolong;
+		sip_tx_packet(&resp, sin);
+			return;
+	}
+	/* SIP INVITE validation done - check if GSM service is up */
 }