Description: This patch ensures that Asterisk does not increment the session version in SDP of "200 OK" (in response to the initial INVITE) if a "183 Session in Progress" has
             already been sent with SDP in response to the INVITE.
Author: Nitesh Bansal <nbansal@voxbone.com>
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -7266,15 +7266,21 @@
 {
 	int res = 0;
 	struct sip_pvt *p = ast_channel_tech_pvt(ast);
+	int oldsdp = FALSE;
 
 	sip_pvt_lock(p);
 	if (ast_channel_state(ast) != AST_STATE_UP) {
 		try_suggested_sip_codec(p);
 
+		if (ast_test_flag(&p->flags[0], SIP_PROGRESS_SENT))
+		{
+			oldsdp = TRUE;
+		}
+
 		ast_setstate(ast, AST_STATE_UP);
 		ast_debug(1, "SIP answering channel: %s\n", ast_channel_name(ast));
 		ast_rtp_instance_update_source(p->rtp);
-		res = transmit_response_with_sdp(p, "200 OK", &p->initreq, XMIT_CRITICAL, FALSE, TRUE);
+		res = transmit_response_with_sdp(p, "200 OK", &p->initreq, XMIT_CRITICAL, oldsdp, TRUE);
 		ast_set_flag(&p->flags[1], SIP_PAGE2_DIALOG_ESTABLISHED);
 	}
 	sip_pvt_unlock(p);