Ticket #762: Major updates on jitter buffer:

 - Updated loop condition in put_frame() to avoid possibility of infinite loop.
 - Added JB capabilities to handle sequence restart & jump.
 - Updated jitter calculation, e.g: reset max_hist_level after updating prefetch, avoid updating prefetch when burst level is exceeding max_burst.
 - Updated shrinking method to be less agressive (only shrink JB when JB size is twice larger than burst level).
 - Updated the way JB switching status from 'initializing' to 'processing' by waiting for some OP switch cycles.
 - Few simplifications in framelist process, e.g: replacing fields 'empty' & 'tail' with 'size'.
 - Minor updates: comments, shortened framelist field names, added some JB states for reporting/monitoring purpose.



git-svn-id: http://svn.pjsip.org/repos/pjproject/trunk@2578 74dad513-b988-da41-8d7b-12977e46ad98

2 files changed, 448 insertions, 335 deletions

diff --git a/pjmedia/include/pjmedia/jbuf.h b/pjmedia/include/pjmedia/jbuf.h
index 0c9299cc..4088e359 100644
--- a/pjmedia/include/pjmedia/jbuf.h
+++ b/pjmedia/include/pjmedia/jbuf.h
@@ -66,19 +66,28 @@ typedef enum pjmedia_jb_frame_type pjmedia_jb_frame_type;
 
 
 /**
- * This structure describes jitter buffer current status.
+ * This structure describes jitter buffer state.
  */
 struct pjmedia_jb_state
 {
+    /* Setting */
     unsigned	frame_size;	    /**< Individual frame size, in bytes.   */
-    unsigned	prefetch;	    /**< Current prefetch value, in frames  */
     unsigned	min_prefetch;	    /**< Minimum allowed prefetch, in frms. */
     unsigned	max_prefetch;	    /**< Maximum allowed prefetch, in frms. */
+
+    /* Status */
+    unsigned	prefetch;	    /**< Current prefetch value, in frames  */
     unsigned	size;		    /**< Current buffer size, in frames.    */
+
+    /* Statistic */
     unsigned	avg_delay;	    /**< Average delay, in ms.		    */
     unsigned	min_delay;	    /**< Minimum delay, in ms.		    */
     unsigned	max_delay;	    /**< Maximum delay, in ms.		    */
-    unsigned	dev_delay;	    /**< Standard deviation of delay, in ms. */
+    unsigned	dev_delay;	    /**< Standard deviation of delay, in ms.*/
+    unsigned	avg_burst;	    /**< Average burst, in frames.	    */
+    unsigned	lost;		    /**< Number of lost frames.		    */
+    unsigned	discard;	    /**< Number of discarded frames.	    */
+    unsigned	empty;		    /**< Number of empty on GET events.	    */
 };
 
 
diff --git a/pjmedia/src/pjmedia/jbuf.c b/pjmedia/src/pjmedia/jbuf.c
index 2cbb1643..dd45d781 100644
--- a/pjmedia/src/pjmedia/jbuf.c
+++ b/pjmedia/src/pjmedia/jbuf.c
@@ -31,49 +31,103 @@
 
 #define THIS_FILE   "jbuf.c"
 
+
+/* Minimal difference between JB size and 2*burst-level to perform 
+ * JB shrinking. 
+ */
 #define SAFE_SHRINKING_DIFF	1
+
+/* Minimal gap (in ms) between JB shrinking */
 #define MIN_SHRINK_GAP_MSEC	200
 
+/* Invalid sequence number, used as the initial value. */
+#define INVALID_OFFSET		-9999
+
+/* Maximum burst length, whenever an operation is bursting longer than 
+ * this value, JB will assume that the opposite operation was idle.
+ */
+#define MAX_BURST_MSEC		1000
+
+/* Number of OP switches to be performed in JB_STATUS_INITIALIZING, before
+ * JB can switch its states to JB_STATUS_PROCESSING.
+ */
+#define INIT_CYCLE		10
+
+
+/* Struct of JB internal buffer, represented in a circular buffer containing
+ * frame content, frame type, frame length, and frame bit info.
+ */
 typedef struct jb_framelist_t
 {
-    char	*flist_buffer;
-    int		*flist_frame_type;
-    pj_size_t	*flist_content_len;
-    pj_uint32_t	*flist_bit_info;
-    unsigned	 flist_frame_size;
-    unsigned	 flist_max_count;
-    unsigned	 flist_empty;
-    unsigned	 flist_head;
-    unsigned	 flist_tail;
-    unsigned	 flist_origin;
+    /* Settings */
+    unsigned	     frame_size;	/**< maximum size of frame	    */
+    unsigned	     max_count;		/**< maximum number of frames	    */
+
+    /* Buffers */
+    char	    *content;		/**< frame content array	    */
+    int		    *frame_type;	/**< frame type array		    */
+    pj_size_t	    *content_len;	/**< frame length array		    */
+    pj_uint32_t	    *bit_info;		/**< frame bit info array	    */
+    
+    /* States */
+    unsigned	     head;		/**< index of head, pointed frame
+					     will be returned by next GET   */
+    unsigned	     size;		/**< current size of framelist.	    */
+    int		     origin;		/**< original index of flist_head   */
 } jb_framelist_t;
 
 
 struct pjmedia_jbuf
 {
-    pj_str_t	    name;		  // jitter buffer name
-    jb_framelist_t  jb_framelist;
-    pj_size_t	    jb_frame_size;	  // frame size	
-    unsigned	    jb_frame_ptime;	  // frame duration.
-    pj_size_t	    jb_max_count;	  // max frames in the jitter framelist->flist_buffer
-
-    int		    jb_level;		  // delay between source & destination
-					  // (calculated according of the number of get/put operations)
-    int		    jb_max_hist_level;    // max level during the last level calculations
-    int		    jb_stable_hist;	  // num of times the delay has	been lower then	the prefetch num
-    int		    jb_last_op;		  // last operation executed on	the framelist->flist_buffer (put/get)
-    int		    jb_last_seq_no;	  // seq no. of	the last frame inserted	to the framelist->flist_buffer
-    int		    jb_prefetch;	  // no. of frame to insert before removing some
-					  // (at the beginning of the framelist->flist_buffer operation)
-    int		    jb_prefetch_cnt;	  // prefetch counter
-    int		    jb_def_prefetch;	  // Default prefetch
-    int		    jb_min_prefetch;	  // Minimum allowable prefetch
-    int		    jb_max_prefetch;	  // Maximum allowable prefetch
-    int		    jb_status;		  // status is 'init' until the	first 'put' operation
-    pj_math_stat    jb_delay;		  // Delay statistics of jitter buffer (in frame unit)
-
-    unsigned	    jb_last_del_seq;	  // Seq # of last frame deleted
-    unsigned	    jb_min_shrink_gap;	  // How often can we shrink
+    /* Settings (consts) */
+    pj_str_t	    jb_name;		/**< jitter buffer name		    */
+    pj_size_t	    jb_frame_size;	/**< frame size			    */
+    unsigned	    jb_frame_ptime;	/**< frame duration.		    */
+    pj_size_t	    jb_max_count;	/**< capacity of jitter buffer, 
+					     in frames			    */
+    int		    jb_def_prefetch;	/**< Default prefetch		    */
+    int		    jb_min_prefetch;	/**< Minimum allowable prefetch	    */
+    int		    jb_max_prefetch;	/**< Maximum allowable prefetch	    */
+    int		    jb_max_burst;	/**< maximum possible burst, whenever
+					     burst exceeds this value, it 
+					     won't be included in level 
+					     calculation		    */
+    int		    jb_min_shrink_gap;	/**< How often can we shrink	    */
+
+    /* Buffer */
+    jb_framelist_t  jb_framelist;	/**< the buffer			    */
+
+    /* States */
+    int		    jb_level;		/**< delay between source & 
+					     destination (calculated according 
+					     of the number of burst get/put 
+					     operations)		    */
+    int		    jb_max_hist_level;  /**< max level during the last level 
+					     calculations		    */
+    int		    jb_stable_hist;	/**< num of times the delay has	been 
+					     lower then the prefetch num    */
+    int		    jb_last_op;		/**< last operation executed 
+					     (put/get)			    */
+    int		    jb_prefetch;	/**< no. of frame to insert before 
+					     removing some (at the beginning 
+					     of the framelist->content 
+					     operation), the value may be
+					     continuously updated based on
+					     current frame burst level.	    */
+    int		    jb_status;		/**< status is 'init' until the	first 
+					     'put' operation		    */
+    int		    jb_init_cycle_cnt;	/**< status is 'init' until the	first 
+					     'put' operation		    */
+    int		    jb_last_del_seq;	/**< Seq # of last frame deleted    */
+
+    /* Statistics */
+    pj_math_stat    jb_delay;		/**< Delay statistics of jitter buffer 
+					     (in ms)			    */
+    pj_math_stat    jb_burst;		/**< Burst statistics (in frames)   */
+    unsigned	    jb_lost;		/**< Number of lost frames.	    */
+    unsigned	    jb_discard;		/**< Number of discarded frames.    */
+    unsigned	    jb_empty;		/**< Number of empty/prefetching frame
+					     returned by GET. */
 };
 
 
@@ -90,6 +144,7 @@ struct pjmedia_jbuf
 #  define TRACE__(args)
 #endif
 
+static pj_status_t jb_framelist_reset(jb_framelist_t *framelist);
 
 static pj_status_t jb_framelist_init( pj_pool_t *pool,
 				      jb_framelist_t *framelist,
@@ -100,46 +155,70 @@ static pj_status_t jb_framelist_init( pj_pool_t *pool,
 
     pj_bzero(framelist, sizeof(jb_framelist_t));
 
-    framelist->flist_frame_size = frame_size;
-    framelist->flist_max_count = max_count;
-    framelist->flist_buffer = (char*) 
-			      pj_pool_zalloc(pool,
-					     framelist->flist_frame_size * 
-					     framelist->flist_max_count);
+    framelist->frame_size   = frame_size;
+    framelist->max_count    = max_count;
+    framelist->content	    = (char*) 
+			      pj_pool_alloc(pool,
+					    framelist->frame_size* 
+					    framelist->max_count);
+    framelist->frame_type   = (int*)
+			      pj_pool_alloc(pool, 
+					    sizeof(framelist->frame_type[0])*
+					    framelist->max_count);
+    framelist->content_len  = (pj_size_t*)
+			      pj_pool_alloc(pool, 
+					    sizeof(framelist->content_len[0])*
+					    framelist->max_count);
+    framelist->bit_info	    = (pj_uint32_t*)
+			      pj_pool_alloc(pool, 
+					    sizeof(framelist->bit_info[0])*
+					    framelist->max_count);
+
+    return jb_framelist_reset(framelist);
 
-    framelist->flist_frame_type = (int*)
-	pj_pool_zalloc(pool, sizeof(framelist->flist_frame_type[0]) * 
-				framelist->flist_max_count);
+}
 
-    framelist->flist_content_len = (pj_size_t*)
-	pj_pool_zalloc(pool, sizeof(framelist->flist_content_len[0]) * 
-				framelist->flist_max_count);
+static pj_status_t jb_framelist_destroy(jb_framelist_t *framelist) 
+{
+    PJ_UNUSED_ARG(framelist);
+    return PJ_SUCCESS;
+}
 
-    framelist->flist_bit_info = (pj_uint32_t*)
-	pj_pool_zalloc(pool, sizeof(framelist->flist_bit_info[0]) * 
-				framelist->flist_max_count);
+static pj_status_t jb_framelist_reset(jb_framelist_t *framelist) 
+{
+    framelist->head = 0;
+    framelist->origin = INVALID_OFFSET;
+    framelist->size = 0;
 
-    framelist->flist_empty = 1;
+    //pj_bzero(framelist->content, 
+    //	     framelist->frame_size * 
+    //	     framelist->max_count);
 
-    return PJ_SUCCESS;
+    pj_memset(framelist->frame_type,
+	      PJMEDIA_JB_MISSING_FRAME,
+	      sizeof(framelist->frame_type[0]) * 
+	      framelist->max_count);
 
-}
+    pj_bzero(framelist->content_len, 
+	     sizeof(framelist->content_len[0]) * 
+	     framelist->max_count);
+
+    //pj_bzero(framelist->bit_info,
+    //	     sizeof(framelist->bit_info[0]) * 
+    //	     framelist->max_count);
 
-static pj_status_t jb_framelist_destroy(jb_framelist_t *framelist) 
-{
-    PJ_UNUSED_ARG(framelist);
     return PJ_SUCCESS;
 }
 
 
 static unsigned jb_framelist_size(jb_framelist_t *framelist) 
 {
-    if (framelist->flist_tail == framelist->flist_head) {
-	return framelist->flist_empty ? 0 : framelist->flist_max_count;
-    } else {
-	return (framelist->flist_tail - framelist->flist_head + 
-		framelist->flist_max_count) % framelist->flist_max_count;
-    }
+    return framelist->size;
+}
+
+static unsigned jb_framelist_origin(jb_framelist_t *framelist) 
+{
+    return framelist->origin;
 }
 
 
@@ -148,147 +227,145 @@ static pj_bool_t jb_framelist_get(jb_framelist_t *framelist,
 				  pjmedia_jb_frame_type *p_type,
 				  pj_uint32_t *bit_info) 
 {
-    if (!framelist->flist_empty) {
+    if (framelist->size) {
 	pj_memcpy(frame, 
-		  framelist->flist_buffer + 
-		    framelist->flist_head * framelist->flist_frame_size,
-		  framelist->flist_frame_size);
+		  framelist->content + 
+		  framelist->head * framelist->frame_size,
+		  framelist->frame_size);
 	*p_type = (pjmedia_jb_frame_type) 
-		  framelist->flist_frame_type[framelist->flist_head];
+		  framelist->frame_type[framelist->head];
 	if (size)
-	    *size   = framelist->flist_content_len[framelist->flist_head];
+	    *size   = framelist->content_len[framelist->head];
 	if (bit_info)
-	    *bit_info = framelist->flist_bit_info[framelist->flist_head];
-
-	pj_bzero(framelist->flist_buffer + 
-		    framelist->flist_head * framelist->flist_frame_size,
-		  framelist->flist_frame_size);
-	framelist->flist_frame_type[framelist->flist_head] = 
-	    PJMEDIA_JB_MISSING_FRAME;
-	framelist->flist_content_len[framelist->flist_head] = 0;
-
-	framelist->flist_origin++;
-	framelist->flist_head = (framelist->flist_head + 1 ) % 
-				framelist->flist_max_count;
-	if (framelist->flist_head == framelist->flist_tail) 
-	    framelist->flist_empty = PJ_TRUE;
+	    *bit_info = framelist->bit_info[framelist->head];
+
+	//pj_bzero(framelist->content + 
+	//	 framelist->head * framelist->frame_size,
+	//	 framelist->frame_size);
+	framelist->frame_type[framelist->head] = PJMEDIA_JB_MISSING_FRAME;
+	framelist->content_len[framelist->head] = 0;
+	framelist->bit_info[framelist->head] = 0;
+
+	framelist->origin++;
+	framelist->head = (framelist->head + 1) % framelist->max_count;
+	framelist->size--;
 	
 	return PJ_TRUE;
-
     } else {
-	pj_bzero(frame, framelist->flist_frame_size);
+	pj_bzero(frame, framelist->frame_size);
+
 	return PJ_FALSE;
     }
 }
 
 
-static void jb_framelist_remove_head( jb_framelist_t *framelist,
-				      unsigned count) 
+static unsigned jb_framelist_remove_head(jb_framelist_t *framelist,
+					 unsigned count) 
 {
-    unsigned cur_size;
-
-    cur_size = jb_framelist_size(framelist);
-    if (count > cur_size) 
-	count = cur_size;
+    if (count > framelist->size) 
+	count = framelist->size;
 
     if (count) {
-	// may be done in two steps if overlapping
+	/* may be done in two steps if overlapping */
 	unsigned step1,step2;
-	unsigned tmp = framelist->flist_head+count;
+	unsigned tmp = framelist->head+count;
 
-	if (tmp > framelist->flist_max_count) {
-	    step1 = framelist->flist_max_count - framelist->flist_head;
+	if (tmp > framelist->max_count) {
+	    step1 = framelist->max_count - framelist->head;
 	    step2 = count-step1;
 	} else {
 	    step1 = count;
 	    step2 = 0;
 	}
 
-	pj_bzero(framelist->flist_buffer + 
-		    framelist->flist_head * framelist->flist_frame_size,
-	          step1*framelist->flist_frame_size);
-	pj_memset(framelist->flist_frame_type+framelist->flist_head,
+	//pj_bzero(framelist->content + 
+	//	    framelist->head * framelist->frame_size,
+	//          step1*framelist->frame_size);
+	pj_memset(framelist->frame_type+framelist->head,
 		  PJMEDIA_JB_MISSING_FRAME,
-		  step1*sizeof(framelist->flist_frame_type[0]));
-	pj_bzero(framelist->flist_content_len+framelist->flist_head,
-		  step1*sizeof(framelist->flist_content_len[0]));
+		  step1*sizeof(framelist->frame_type[0]));
+	pj_bzero(framelist->content_len+framelist->head,
+		  step1*sizeof(framelist->content_len[0]));
 
 	if (step2) {
-	    pj_bzero( framelist->flist_buffer,
-		      step2*framelist->flist_frame_size);
-	    pj_memset(framelist->flist_frame_type,
+	    //pj_bzero( framelist->content,
+	    //	      step2*framelist->frame_size);
+	    pj_memset(framelist->frame_type,
 		      PJMEDIA_JB_MISSING_FRAME,
-		      step2*sizeof(framelist->flist_frame_type[0]));
-	    pj_bzero (framelist->flist_content_len,
-		      step2*sizeof(framelist->flist_content_len[0]));
+		      step2*sizeof(framelist->frame_type[0]));
+	    pj_bzero (framelist->content_len,
+		      step2*sizeof(framelist->content_len[0]));
 	}
 
-	// update pointers
-	framelist->flist_origin += count;
-	framelist->flist_head = (framelist->flist_head + count) % 
-			        framelist->flist_max_count;
-	if (framelist->flist_head == framelist->flist_tail) 
-	    framelist->flist_empty = PJ_TRUE;
+	/* update states */
+	framelist->origin += count;
+	framelist->head = (framelist->head + count) % framelist->max_count;
+	framelist->size -= count;
     }
+    
+    return count;
 }
 
 
-static pj_bool_t jb_framelist_put_at(jb_framelist_t *framelist,
-				     unsigned index,
-				     const void *frame,
-				     unsigned frame_size,
-				     pj_uint32_t bit_info)
+static pj_status_t jb_framelist_put_at(jb_framelist_t *framelist,
+				       int index,
+				       const void *frame,
+				       unsigned frame_size,
+				       pj_uint32_t bit_info)
 {
+    int distance;
     unsigned where;
+    enum { MAX_MISORDER = 100 };
+    enum { MAX_DROPOUT = 3000 };
 
-    assert(frame_size <= framelist->flist_frame_size);
+    assert(frame_size <= framelist->frame_size);
 
-    if (!framelist->flist_empty) {
-	unsigned max_index;
-	unsigned cur_size;
+    /* the first ever frame since inited/resetted. */
+    if (framelist->origin == INVALID_OFFSET)
+	framelist->origin = index;
 
-	// too late
-	if (index < framelist->flist_origin) 
-	    return PJ_FALSE;
-
-	// too soon
-	max_index = framelist->flist_origin + framelist->flist_max_count - 1;
-	if (index > max_index)
-	    return PJ_FALSE;
-
-	where = (index - framelist->flist_origin + framelist->flist_head) % 
-	        framelist->flist_max_count;
-
-	// update framelist->flist_tail pointer
-	cur_size = jb_framelist_size(framelist);
-	if (index >= framelist->flist_origin + cur_size) {
-	    unsigned diff = (index - (framelist->flist_origin + cur_size));
-	    framelist->flist_tail = (framelist->flist_tail + diff + 1) % 
-				    framelist->flist_max_count;
-	}
-    } else {
-	// check if frame is not too late, but watch out for sequence restart.
-	if (index < framelist->flist_origin && 
-	    framelist->flist_origin - index < 0x7FFF) 
-	{
-	    return PJ_FALSE;
+    /* too late or duplicated or sequence restart */
+    if (index < framelist->origin) {
+	if (framelist->origin - index < MAX_MISORDER) {
+	    /* too late or duplicated */
+	    return PJ_ETOOSMALL;
+	} else {
+	    /* sequence restart */
+	    framelist->origin = index - framelist->size;
 	}
+    }
 
-	where = framelist->flist_tail;
-	framelist->flist_origin = index;
-	framelist->flist_tail = (framelist->flist_tail + 1) % 
-				framelist->flist_max_count;
-	framelist->flist_empty = PJ_FALSE;
+    /* too soon or jump too far */
+    distance = index - framelist->origin;
+    if (distance >= (int)framelist->max_count) {
+	if (distance > MAX_DROPOUT) {
+	    /* jump too far */
+	    jb_framelist_reset(framelist);
+	    framelist->origin = index;
+	    distance = 0;
+	} else {
+	    /* too soon, buffer is not enough */
+	    return PJ_ETOOMANY;
+	}
     }
 
-    pj_memcpy(framelist->flist_buffer + where * framelist->flist_frame_size, 
-	      frame, frame_size);
+    /* get the slot position */
+    where = (framelist->head + distance) % framelist->max_count;
 
-    framelist->flist_frame_type[where] = PJMEDIA_JB_NORMAL_FRAME;
-    framelist->flist_content_len[where] = frame_size;
-    framelist->flist_bit_info[where] = bit_info;
+    /* if the slot is occupied, it must be duplicated frame, ignore it. */
+    if (framelist->frame_type[where] != PJMEDIA_JB_MISSING_FRAME)
+	return PJ_EEXISTS;
 
-    return PJ_TRUE;
+    /* put the frame into the slot */
+    pj_memcpy(framelist->content + where * framelist->frame_size,
+	      frame, frame_size);
+    framelist->frame_type[where] = PJMEDIA_JB_NORMAL_FRAME;
+    framelist->content_len[where] = frame_size;
+    framelist->bit_info[where] = bit_info;
+    if (framelist->origin + (int)framelist->size <= index)
+	framelist->size = distance + 1;
+
+    return PJ_SUCCESS;
 }
 
 
@@ -317,23 +394,19 @@ PJ_DEF(pj_status_t) pjmedia_jbuf_create(pj_pool_t *pool,
     if (status != PJ_SUCCESS)
 	return status;
 
-    pj_strdup_with_null(pool, &jb->name, name);
+    pj_strdup_with_null(pool, &jb->jb_name, name);
     jb->jb_frame_size	 = frame_size;
     jb->jb_frame_ptime   = ptime;
-    jb->jb_last_seq_no	 = -1;
-    jb->jb_level	 = 0;
-    jb->jb_last_op	 = JB_OP_INIT;
     jb->jb_prefetch	 = PJ_MIN(PJMEDIA_JB_DEFAULT_INIT_DELAY,max_count*4/5);
-    jb->jb_prefetch_cnt	 = 0;
     jb->jb_min_prefetch  = 0;
     jb->jb_max_prefetch  = max_count*4/5;
-    jb->jb_stable_hist	 = 0;
-    jb->jb_status	 = JB_STATUS_INITIALIZING;
-    jb->jb_max_hist_level = 0;
     jb->jb_max_count	 = max_count;
     jb->jb_min_shrink_gap= MIN_SHRINK_GAP_MSEC / ptime;
-
+    jb->jb_max_burst	 = MAX_BURST_MSEC / ptime;
     pj_math_stat_init(&jb->jb_delay);
+    pj_math_stat_init(&jb->jb_burst);
+
+    pjmedia_jbuf_reset(jb);
 
     *p_jb = jb;
     return PJ_SUCCESS;
@@ -382,19 +455,15 @@ PJ_DEF(pj_status_t) pjmedia_jbuf_set_adaptive( pjmedia_jbuf *jb,
 
 PJ_DEF(pj_status_t) pjmedia_jbuf_reset(pjmedia_jbuf *jb)
 {
-    jb->jb_last_seq_no	 = -1;
     jb->jb_level	 = 0;
     jb->jb_last_op	 = JB_OP_INIT;
-    jb->jb_prefetch_cnt	 = 0;
     jb->jb_stable_hist	 = 0;
     jb->jb_status	 = JB_STATUS_INITIALIZING;
-    jb->jb_max_hist_level = 0;
+    jb->jb_init_cycle_cnt= 0;
+    jb->jb_max_hist_level= 0;
 
-    jb_framelist_remove_head(&jb->jb_framelist, 
-			     jb_framelist_size(&jb->jb_framelist));
+    jb_framelist_reset(&jb->jb_framelist);
 
-    pj_math_stat_init(&jb->jb_delay);
-    
     return PJ_SUCCESS;
 }
 
@@ -410,99 +479,135 @@ static void jbuf_calculate_jitter(pjmedia_jbuf *jb)
     int diff, cur_size;
 
     cur_size = jb_framelist_size(&jb->jb_framelist);
+    pj_math_stat_update(&jb->jb_burst, jb->jb_level);
+    jb->jb_max_hist_level = PJ_MAX(jb->jb_max_hist_level, jb->jb_level);
+
+    /* Burst level is decreasing */
+    if (jb->jb_level < jb->jb_prefetch) {
+
+	enum { STABLE_HISTORY_LIMIT = 100 };
+        
+	jb->jb_stable_hist++;
+        
+	/* Only update the prefetch if 'stable' condition is reached 
+	 * (not just short time impulse)
+	 */
+	if (jb->jb_stable_hist > STABLE_HISTORY_LIMIT) {
+    	
+	    diff = (jb->jb_prefetch - jb->jb_max_hist_level) / 3;
 
-    /* Only apply burst-level calculation on PUT operation since if VAD is 
-     * active the burst-level may not be accurate.
-     */
-    if (jb->jb_last_op == JB_OP_PUT) {
+	    if (diff < 1)
+		diff = 1;
 
-	jb->jb_max_hist_level = PJ_MAX(jb->jb_max_hist_level,jb->jb_level);
+	    jb->jb_prefetch -= diff;
+	    if (jb->jb_prefetch < jb->jb_min_prefetch) 
+		jb->jb_prefetch = jb->jb_min_prefetch;
 
-	/* Level is decreasing */
-	if (jb->jb_level < jb->jb_prefetch) {
+	    /* Reset history */
+	    jb->jb_max_hist_level = 0;
+	    jb->jb_stable_hist = 0;
 
-	    enum { STABLE_HISTORY_LIMIT = 100 };
-	    
-	    jb->jb_stable_hist++;
-	    
-	    /* Only update the prefetch if 'stable' condition is reached 
-	     * (not just short time impulse)
-	     */
-	    if (jb->jb_stable_hist > STABLE_HISTORY_LIMIT) {
-		
-		diff = (jb->jb_prefetch - jb->jb_max_hist_level) / 3;
+	    TRACE__((jb->jb_name.ptr,"jb updated(1), prefetch=%d, size=%d",
+		     jb->jb_prefetch, cur_size));
+	}
+    }
+
+    /* Burst level is increasing */
+    else if (jb->jb_level > jb->jb_prefetch) {
+
+	/* Instaneous set prefetch to recent maximum level (max_hist_level) */
+	jb->jb_prefetch = PJ_MIN(jb->jb_max_hist_level,
+				 (int)(jb->jb_max_count*4/5));
+	if (jb->jb_prefetch > jb->jb_max_prefetch)
+	    jb->jb_prefetch = jb->jb_max_prefetch;
+
+	jb->jb_stable_hist = 0;
+	/* Do not reset max_hist_level. */
+	//jb->jb_max_hist_level = 0;
 
-		if (diff < 1)
-		    diff = 1;
+	TRACE__((jb->jb_name.ptr,"jb updated(2), prefetch=%d, size=%d", 
+		 jb->jb_prefetch, cur_size));
+    }
 
-		/* Update max_hist_level. */
-		jb->jb_max_hist_level = jb->jb_prefetch;
+    /* Level is unchanged */
+    else {
+	jb->jb_stable_hist = 0;
+    }
+}
 
-		jb->jb_prefetch -= diff;
-		if (jb->jb_prefetch < jb->jb_min_prefetch) 
-		    jb->jb_prefetch = jb->jb_min_prefetch;
+PJ_INLINE(void) jbuf_update(pjmedia_jbuf *jb, int oper)
+{
+    int diff, burst_level;
 
-		jb->jb_stable_hist = 0;
+    if(jb->jb_last_op != oper) {
+	jb->jb_last_op = oper;
 
-		TRACE__((jb->name.ptr,"jb updated(1), prefetch=%d, size=%d", 
-			 jb->jb_prefetch, cur_size));
+	if (jb->jb_status == JB_STATUS_INITIALIZING) {
+	    /* Switch status 'initializing' -> 'processing' after some OP 
+	     * switch cycles and current OP is GET (burst level is calculated 
+	     * based on PUT burst), so burst calculation is guaranted to be
+	     * performed right after the status switching.
+	     */
+	    if (++jb->jb_init_cycle_cnt >= INIT_CYCLE && oper == JB_OP_GET) {
+		jb->jb_status = JB_STATUS_PROCESSING;
+	    } else {
+		jb->jb_level = 0;
+		return;
 	    }
 	}
 
-	/* Level is increasing */
-	else if (jb->jb_level > jb->jb_prefetch) {
+	/* Perform jitter calculation based on PUT burst-level only, since 
+	 * GET burst-level may not be accurate, e.g: when VAD is active.
+	 * Note that when burst-level is too big, i.e: exceeds jb_max_burst,
+	 * the GET op may be idle, in this case, we better skip the jitter 
+	 * calculation.
+	 */
+	if (oper == JB_OP_GET && jb->jb_level < jb->jb_max_burst)
+	    jbuf_calculate_jitter(jb);
 
-	    /* Instaneous set prefetch */
-	    jb->jb_prefetch = PJ_MIN(jb->jb_max_hist_level,
-				     (int)(jb->jb_max_count*4/5));
-	    if (jb->jb_prefetch > jb->jb_max_prefetch)
-		jb->jb_prefetch = jb->jb_max_prefetch;
+	jb->jb_level = 0;
+    }
 
-	    jb->jb_stable_hist = 0;
-	    // Keep max_hist_level.
-	    //jb->jb_max_hist_level = 0;
+    /* These code is used for shortening the delay in the jitter buffer.
+     * It needs shrink only when there is possibility of drift. Drift
+     * detection is performed by inspecting the jitter buffer size, if
+     * its size is twice of current burst level, there can be drift.
+     *
+     * Moreover, normally drift level is quite low, so JB shouldn't need
+     * to shrink aggresively, it will shrink maximum one frame per 
+     * MIN_SHRINK_GAP_MSEC ms. Theoritically, JB may handle drift level 
+     * as much as = FRAME_PTIME/MIN_SHRINK_GAP_MSEC * 100%
+     *
+     * Whenever there is drift, where PUT > GET, this method will keep 
+     * the latency (JB size) as much as twice of burst level.
+     */
 
-	    TRACE__((jb->name.ptr,"jb updated(2), prefetch=%d, size=%d", 
-		     jb->jb_prefetch, cur_size));
-	}
+    if (jb->jb_status != JB_STATUS_PROCESSING)
+	return;
 
-	/* Level is unchanged */
-	else {
-	    jb->jb_stable_hist = 0;
-	}
-    }
+    burst_level = PJ_MAX(jb->jb_prefetch, jb->jb_level);
+    diff = jb_framelist_size(&jb->jb_framelist) - burst_level*2;
 
-    /* These code is used for shortening the delay in the jitter buffer. */
-    // Shrinking based on max_hist_level (recent max level).
-    //diff = cur_size - jb->jb_prefetch;
-    diff = cur_size - jb->jb_max_hist_level;
-    if (diff > SAFE_SHRINKING_DIFF && 
-	jb->jb_framelist.flist_origin-jb->jb_last_del_seq > jb->jb_min_shrink_gap)
-    {
-	/* Shrink slowly */
-	diff = 1;
-
-	/* Drop frame(s)! */
-	jb_framelist_remove_head(&jb->jb_framelist, diff);
-	jb->jb_last_del_seq = jb->jb_framelist.flist_origin;
-
-	pj_math_stat_update(&jb->jb_delay, cur_size - diff);
-
-	TRACE__((jb->name.ptr, 
-		 "JB shrinking %d frame(s), size=%d", diff,
-		 jb_framelist_size(&jb->jb_framelist)));
-    } else {
-	pj_math_stat_update(&jb->jb_delay, cur_size);
-    }
+    if (diff >= SAFE_SHRINKING_DIFF) {
+	/* Check and adjust jb_last_del_seq, in case there was seq restart */
+	if (jb->jb_framelist.origin < jb->jb_last_del_seq)
+	    jb->jb_last_del_seq = jb->jb_framelist.origin;
 
-    jb->jb_level = 0;
-}
+	if (jb->jb_framelist.origin - jb->jb_last_del_seq >=
+	    jb->jb_min_shrink_gap)
+	{
+	    /* Shrink slowly, one frame per cycle */
+	    diff = 1;
 
-PJ_INLINE(void) jbuf_update(pjmedia_jbuf *jb, int oper)
-{
-    if(jb->jb_last_op != oper) {
-	jbuf_calculate_jitter(jb);
-	jb->jb_last_op = oper;
+	    /* Drop frame(s)! */
+	    diff = jb_framelist_remove_head(&jb->jb_framelist, diff);
+	    jb->jb_last_del_seq = jb->jb_framelist.origin;
+	    jb->jb_discard += diff;
+
+	    TRACE__((jb->jb_name.ptr, 
+		     "JB shrinking %d frame(s), cur size=%d", diff,
+		     jb_framelist_size(&jb->jb_framelist)));
+	}
     }
 }
 
@@ -522,59 +627,47 @@ PJ_DEF(void) pjmedia_jbuf_put_frame2(pjmedia_jbuf *jb,
 				     pj_bool_t *discarded)
 {
     pj_size_t min_frame_size;
-    int seq_diff;
+    int prev_size, cur_size;
+    pj_status_t status;
 
-    if (jb->jb_last_seq_no == -1)	{
-	jb->jb_last_seq_no = frame_seq - 1;
-    }
+    /* Get JB size before PUT */
+    prev_size = jb_framelist_size(&jb->jb_framelist);
+    
+    /* Attempt to store the frame */
+    min_frame_size = PJ_MIN(frame_size, jb->jb_frame_size);
+    status = jb_framelist_put_at(&jb->jb_framelist, frame_seq, frame,
+				 min_frame_size, bit_info);
+    
+    /* Jitter buffer is full, cannot store the frame */
+    while (status == PJ_ETOOMANY) {
+	unsigned removed;
 
-    seq_diff = frame_seq - jb->jb_last_seq_no;
-    jb->jb_last_seq_no = PJ_MAX(jb->jb_last_seq_no, frame_seq);
-    if (seq_diff > 0) jb->jb_level += seq_diff;
+	removed = jb_framelist_remove_head(&jb->jb_framelist,
+					   PJ_MAX(jb->jb_max_count/4, 1));
+	status = jb_framelist_put_at(&jb->jb_framelist, frame_seq, frame,
+				     min_frame_size, bit_info);
 
-    if(jb->jb_status ==	JB_STATUS_INITIALIZING) {
-	jb->jb_status = JB_STATUS_PROCESSING;
-	jb->jb_level = 0;
-    } else {
-	jbuf_update(jb, JB_OP_PUT);
+	jb->jb_discard += removed;
     }
 
-    min_frame_size = PJ_MIN(frame_size, jb->jb_frame_size);
-    if (seq_diff > 0) {
-
-	while (jb_framelist_put_at(&jb->jb_framelist, frame_seq, frame,
-				   min_frame_size, bit_info) == PJ_FALSE)
-	{
-	    jb_framelist_remove_head(&jb->jb_framelist,
-				     PJ_MAX(jb->jb_max_count/4,1) );
-	}
+    /* Get JB size after PUT */
+    cur_size = jb_framelist_size(&jb->jb_framelist);
 
-	if (jb->jb_prefetch_cnt < jb->jb_prefetch) {
-	    jb->jb_prefetch_cnt += seq_diff;
-	    
-	    TRACE__((jb->name.ptr, "PUT prefetch_cnt=%d/%d", 
-		     jb->jb_prefetch_cnt, jb->jb_prefetch));
+    /* Return the flag if this frame is discarded */
+    if (discarded)
+	*discarded = (status != PJ_SUCCESS);
 
-	    if (jb->jb_status == JB_STATUS_PREFETCHING && 
-		jb->jb_prefetch_cnt >= jb->jb_prefetch)
-	    {
+    if (status == PJ_SUCCESS) {
+	if (jb->jb_status == JB_STATUS_PREFETCHING) {
+	    TRACE__((jb->jb_name.ptr, "PUT prefetch_cnt=%d/%d", 
+		     cur_size, jb->jb_prefetch));
+	    if (cur_size >= jb->jb_prefetch)
 		jb->jb_status = JB_STATUS_PROCESSING;
-	    }
 	}
-
-
-
-	if (discarded)
-	    *discarded = PJ_FALSE;
-    }
-    else
-    {
-	pj_bool_t res;
-	res = jb_framelist_put_at(&jb->jb_framelist,frame_seq,frame,
-				  min_frame_size, bit_info);
-	if (discarded)
-	    *discarded = !res;
-    }
+	jb->jb_level += (cur_size > prev_size ? cur_size-prev_size : 1);
+	jbuf_update(jb, JB_OP_PUT);
+    } else
+	jb->jb_discard++;
 }
 
 /*
@@ -596,58 +689,63 @@ PJ_DEF(void) pjmedia_jbuf_get_frame2(pjmedia_jbuf *jb,
 				     char *p_frame_type,
 				     pj_uint32_t *bit_info)
 {
-    pjmedia_jb_frame_type ftype;
+    int cur_size;
 
-    jb->jb_level++;
+    cur_size = jb_framelist_size(&jb->jb_framelist);
 
-    jbuf_update(jb, JB_OP_GET);
+    if (cur_size == 0) {
+	/* jitter buffer empty */
 
-    if (jb_framelist_size(&jb->jb_framelist) == 0) {
-	jb->jb_prefetch_cnt = 0;
 	if (jb->jb_def_prefetch)
 	    jb->jb_status = JB_STATUS_PREFETCHING;
-    }
 
-    if (jb->jb_status == JB_STATUS_PREFETCHING && 
-	jb->jb_prefetch_cnt < jb->jb_prefetch)
-    {
+	//pj_bzero(frame, jb->jb_frame_size);
+	*p_frame_type = PJMEDIA_JB_ZERO_EMPTY_FRAME;
+	if (size)
+	    *size = 0;
+
+	jb->jb_empty++;
+
+    } else if (jb->jb_status == JB_STATUS_PREFETCHING) {
+
 	/* Can't return frame because jitter buffer is filling up
 	 * minimum prefetch.
 	 */
-	pj_bzero(frame, jb->jb_frame_size);
-	if (jb_framelist_size(&jb->jb_framelist) == 0)
-	    *p_frame_type = PJMEDIA_JB_ZERO_EMPTY_FRAME;
-	else
-	    *p_frame_type = PJMEDIA_JB_ZERO_PREFETCH_FRAME;
 
+	//pj_bzero(frame, jb->jb_frame_size);
+	*p_frame_type = PJMEDIA_JB_ZERO_PREFETCH_FRAME;
 	if (size)
 	    *size = 0;
 
-	TRACE__((jb->name.ptr, "GET prefetch_cnt=%d/%d",
-		 jb->jb_prefetch_cnt, jb->jb_prefetch));
-	return;
-    }
+	TRACE__((jb->jb_name.ptr, "GET prefetch_cnt=%d/%d",
+		 cur_size, jb->jb_prefetch));
 
-    /* Retrieve a frame from frame list */
-    if (jb_framelist_get(&jb->jb_framelist,frame,size,&ftype,bit_info) ==
-	PJ_FALSE) 
-    {
-	/* Can't return frame because jitter buffer is empty! */
-	pj_bzero(frame, jb->jb_frame_size);
-	*p_frame_type = PJMEDIA_JB_ZERO_EMPTY_FRAME;
-	if (size)
-	    *size = 0;
+	jb->jb_empty++;
 
-	return;
+    } else {
+
+	pjmedia_jb_frame_type ftype;
+	pj_bool_t res;
+
+	/* Retrieve a frame from frame list */
+	res = jb_framelist_get(&jb->jb_framelist, frame, size, &ftype, 
+			       bit_info);
+	pj_assert(res);
+
+	/* We've successfully retrieved a frame from the frame list, but
+	 * the frame could be a blank frame!
+	 */
+	if (ftype == PJMEDIA_JB_NORMAL_FRAME) {
+	    *p_frame_type = PJMEDIA_JB_NORMAL_FRAME;
+	    pj_math_stat_update(&jb->jb_delay, cur_size * jb->jb_frame_ptime);
+	} else {
+	    *p_frame_type = PJMEDIA_JB_MISSING_FRAME;
+	    jb->jb_lost++;
+	}
     }
 
-    /* We've successfully retrieved a frame from the frame list, but
-     * the frame could be a blank frame!
-     */
-    if (ftype == PJMEDIA_JB_NORMAL_FRAME) 
-	*p_frame_type	= PJMEDIA_JB_NORMAL_FRAME;
-    else 
-	*p_frame_type	= PJMEDIA_JB_MISSING_FRAME;
+    jb->jb_level++;
+    jbuf_update(jb, JB_OP_GET);
 }
 
 /*
@@ -659,15 +757,21 @@ PJ_DEF(pj_status_t) pjmedia_jbuf_get_state( pjmedia_jbuf *jb,
     PJ_ASSERT_RETURN(jb && state, PJ_EINVAL);
 
     state->frame_size = jb->jb_frame_size;
-    state->prefetch = jb->jb_prefetch;
     state->min_prefetch = jb->jb_min_prefetch;
     state->max_prefetch = jb->jb_max_prefetch;
+    
+    state->prefetch = jb->jb_prefetch;
     state->size = jb_framelist_size(&jb->jb_framelist);
-    state->avg_delay = jb->jb_delay.mean * jb->jb_frame_ptime;
-    state->min_delay = jb->jb_delay.min * jb->jb_frame_ptime;
-    state->max_delay = jb->jb_delay.max * jb->jb_frame_ptime;
-    state->dev_delay = pj_math_stat_get_stddev(&jb->jb_delay) * 
-		       jb->jb_frame_ptime;
+    
+    state->avg_delay = jb->jb_delay.mean;
+    state->min_delay = jb->jb_delay.min;
+    state->max_delay = jb->jb_delay.max;
+    state->dev_delay = pj_math_stat_get_stddev(&jb->jb_delay);
+    
+    state->avg_burst = jb->jb_burst.mean;
+    state->empty = jb->jb_empty;
+    state->discard = jb->jb_discard;
+    state->lost = jb->jb_lost;
 
     return PJ_SUCCESS;
 }