--- chan_dahdi-orig.c	2017-04-07 11:49:39.000000000 -0400
+++ chan_dahdi.c	2017-05-23 12:02:57.000000000 -0400
@@ -19723,6 +19723,17 @@
 	int size,res,fd,len,x;
 	int bytes=0;
 	int idx;
+  
+	/* used for hangup detection */
+	struct ast_frame *f = NULL;
+	int ms = 50;
+	AST_LIST_HEAD_NOLOCK(, ast_frame) deferred_frames;
+	AST_LIST_HEAD_INIT_NOLOCK(&deferred_frames);
+
+	struct ast_frame hangup_frame = {
+		.frametype = AST_FRAME_CONTROL,
+		.subclass.integer = AST_CONTROL_HANGUP,
+	};
 
 	/*
 	 * Initial carrier (imaginary)
@@ -19789,6 +19800,9 @@
 	len += END_SILENCE_LEN;
 	fd = p->subs[idx].dfd;
 	while (len) {
+		struct ast_frame *defer_frame = NULL;
+		struct ast_frame *dup_f = NULL;
+
 		if (ast_check_hangup(c)) {
 			ast_free(mybuf);
 			return -1;
@@ -19799,7 +19813,13 @@
 		fds[0].fd = fd;
 		fds[0].events = POLLOUT | POLLPRI;
 		fds[0].revents = 0;
+		
+		/* clear previously set BLOCKING flag from ast_sendtext */ 
+		ast_clear_flag(ast_channel_flags(c), AST_FLAG_BLOCKING);
+		CHECK_BLOCKING(c);		
 		res = poll(fds, 1, -1);
+		ast_clear_flag(ast_channel_flags(c), AST_FLAG_BLOCKING);		
+		
 		if (!res) {
 			ast_debug(1, "poll (for write) ret. 0 on channel %d\n", p->channel);
 			continue;
@@ -19824,12 +19844,94 @@
 		}
 		len -= size;
 		buf += size;
+
+		/* time to check for hangup 
+		* but first we need to see if there is any input to read
+		*/
+		
+		/* since the channel is locked prior to calling this function 
+		* in channel.c, we need to unlock prior to calling ast_waitfor 
+		* and ast_read since they lock it as well */
+		ast_channel_unlock(c);
+				
+		res = ast_waitfor(c, ms);
+		if (res < 0) {
+			ast_channel_lock(c);
+			/* nothing to read, go away */
+			continue;
+		}
+		
+		f = ast_read(c);
+		ast_channel_lock(c);
+
+		if (!f) {
+			/* No frame means the channel has been hung up.
+			* A hangup frame needs to be queued here as ast_waitfor() may
+			* never return again for the condition to be detected outside
+			* of sendtext.  So, we'll leave a HANGUP queued up so the
+			* thread in charge of this channel will know. */
+
+			defer_frame = &hangup_frame;
+			if ((dup_f = ast_frdup(defer_frame))) {
+				AST_LIST_INSERT_HEAD(&deferred_frames, dup_f, frame_list);
+			}
+
+			/* exit since we received hangup */
+			ast_debug(1, "processing HANGUP frame\n");
+			len = 0;
+
+		} else if (ast_is_deferrable_frame(f)) {
+			ast_debug(1, "received deferrable frame type %d\n", f->frametype);
+			
+		  /* check for CONTROL frame which signals a HANGUP.
+			* Made the conscious decison to throw all TEXT frames 
+			* since wo do not need to process voice or text frames while sending 
+			* TDD text */                                   
+			
+			if (f->frametype == AST_FRAME_CONTROL && f->subclass.integer == AST_CONTROL_HANGUP) {
+				defer_frame = &hangup_frame;
+				if ((dup_f = ast_frisolate(defer_frame))) {
+					AST_LIST_INSERT_HEAD(&deferred_frames, dup_f, frame_list);
+				}
+				if (dup_f != defer_frame) {
+					ast_frfree(defer_frame);
+				}				
+				/* exit loop */
+				len = 0;
+			
+			} else if (f->frametype != AST_FRAME_TEXT) {				 
+				defer_frame = f;
+				if ((dup_f = ast_frisolate(defer_frame))) {
+					AST_LIST_INSERT_HEAD(&deferred_frames, dup_f, frame_list);
+				}
+				if (dup_f != defer_frame) {
+					ast_frfree(defer_frame);
+				}				
+				
+			} else {
+				/* drop other frames in case of feedback from device sending tones */
+				ast_debug(1, "discarding frame\n");
+				ast_frfree(f);
+			} 				
+		}	else {
+			/* Can't defer. Discard and continue with next. */
+			ast_debug(1, "discarding frame\n");
+			ast_frfree(f);
+		}		
+	}
+	
+	/* We need to queue and free all the deferred frames if any  */	
+	ast_channel_unlock(c);
+	while ((f = AST_LIST_REMOVE_HEAD(&deferred_frames, frame_list))) {
+		ast_queue_frame_head(c, f);
+		ast_frfree(f);
 	}
+	ast_channel_lock(c);
+		
 	ast_free(mybuf);
 	return(0);
 }
 
-
 static int reload(void)
 {
 	int res = 0;