diff -dur zaptel/zaptel.c zaptel-1.0.3/zaptel.c
--- zaptel/zaptel.c	2005-03-18 12:56:54.000000000 -0500
+++ zaptel-1.0.3/zaptel.c	2005-03-18 12:55:09.000000000 -0500
@@ -1738,6 +1738,10 @@
 			chan->outwritebuf = oldbuf;
 		}
 		spin_unlock_irqrestore(&chan->lock, flags);
+
+		if (chan->flags & ZT_FLAG_HDLC){
+			if (chan->span->ioctl) chan->span->ioctl(chan, ZT_DCHAN_TX, 0);
+		}
 	}
 	return amnt;
 }
diff -dur zaptel/zaptel.h zaptel-1.0.3/zaptel.h
--- zaptel/zaptel.h	2005-03-18 12:56:54.000000000 -0500
+++ zaptel-1.0.3/zaptel.h	2005-03-18 12:40:15.000000000 -0500
@@ -593,6 +593,7 @@
  *  60-80 are reserved for private drivers
  *  80-85 are reserved for dynamic span stuff
  */
+#define ZT_DCHAN_TX	_IOR (ZT_CODE, 60, int)
 
 /*
  * Create a dynamic span
