Ticket #549: major modification in media transport API to support more offer/answer scenarios

git-svn-id: http://svn.pjsip.org/repos/pjproject/trunk@2032 74dad513-b988-da41-8d7b-12977e46ad98

7 files changed, 1367 insertions, 488 deletions

diff --git a/pjmedia/include/pjmedia/sdp.h b/pjmedia/include/pjmedia/sdp.h
index 768af9f1..73c4393d 100644
--- a/pjmedia/include/pjmedia/sdp.h
+++ b/pjmedia/include/pjmedia/sdp.h
@@ -318,6 +318,17 @@ PJ_DECL(pj_status_t) pjmedia_sdp_attr_get_rtcp(const pjmedia_sdp_attr *attr,
 					       pjmedia_sdp_rtcp_attr *rtcp);
 
 
+/**
+ * Create a=rtcp attribute.
+ *
+ * @param pool		Pool to create the attribute.
+ * @param a		Socket address.
+ *
+ * @return		SDP RTCP attribute.
+ */
+PJ_DECL(pjmedia_sdp_attr*) pjmedia_sdp_attr_create_rtcp(pj_pool_t *pool,
+							const pj_sockaddr *a);
+
 
 /* **************************************************************************
  * SDP CONNECTION INFO
diff --git a/pjmedia/include/pjmedia/transport.h b/pjmedia/include/pjmedia/transport.h
index b898f65b..99043492 100644
--- a/pjmedia/include/pjmedia/transport.h
+++ b/pjmedia/include/pjmedia/transport.h
@@ -320,20 +320,31 @@ struct pjmedia_transport_op
 			      pj_size_t size);
 
     /**
-     * This function is called by application to generate the SDP parts
-     * related to transport type, e.g: ICE, SRTP.
+     * Prepare the transport for a new media session.
      *
      * Application should call #pjmedia_transport_media_create() instead of 
      * calling this function directly.
      */
     pj_status_t (*media_create)(pjmedia_transport *tp,
-				pj_pool_t *pool,
+				pj_pool_t *sdp_pool,
 				unsigned options,
-				pjmedia_sdp_session *sdp_local,
-				const pjmedia_sdp_session *sdp_remote,
+				const pjmedia_sdp_session *remote_sdp,
 				unsigned media_index);
 
     /**
+     * This function is called by application to generate the SDP parts
+     * related to transport type, e.g: ICE, SRTP.
+     *
+     * Application should call #pjmedia_transport_encode_sdp() instead of
+     * calling this function directly.
+     */
+    pj_status_t (*encode_sdp)(pjmedia_transport *tp,
+			      pj_pool_t *sdp_pool,
+			      pjmedia_sdp_session *sdp_local,
+			      const pjmedia_sdp_session *rem_sdp,
+			      unsigned media_index);
+
+    /**
      * This function is called by application to start the transport
      * based on SDP negotiation result.
      *
@@ -341,8 +352,8 @@ struct pjmedia_transport_op
      * calling this function directly.
      */
     pj_status_t (*media_start) (pjmedia_transport *tp,
-			        pj_pool_t *pool,
-			        pjmedia_sdp_session *sdp_local,
+			        pj_pool_t *tmp_pool,
+			        const pjmedia_sdp_session *sdp_local,
 			        const pjmedia_sdp_session *sdp_remote,
 				unsigned media_index);
 
@@ -626,38 +637,62 @@ PJ_INLINE(pj_status_t) pjmedia_transport_send_rtcp2(pjmedia_transport *tp,
 
 
 /**
- * Generate local SDP parts that are related to the specified media transport.
- * Remote SDP might be needed as reference when application is in deciding
- * side of negotiation (callee side), otherwise it should be NULL.
- *
- * This API is provided to allow the media transport to add more information
- * in the SDP offer, before the offer is sent to remote. Additionally, for 
- * answerer side, this callback allows the media transport to reject the 
- * offer before this offer is processed by the SDP negotiator. 
+ * Prepare the media transport for a new media session, and optionally
+ * encode the relevant information in the \a sdp_local. Application must
+ * call this function before starting a new media session using this
+ * transport.
  *
  * This is just a simple wrapper which calls <tt>media_create()</tt> member 
  * of the transport.
  *
  * @param tp		The media transport.
- * @param pool		The memory pool.
+ * @param sdp_pool	Pool object to allocate memory related to SDP
+ *			messaging components.
  * @param option	Option flags, from #pjmedia_tranport_media_option
- * @param sdp_local	Local SDP.
- * @param sdp_remote	Remote SDP.
+ * @param rem_sdp	Remote SDP if it's available.
  * @param media_index	Media index in SDP.
  *
  * @return		PJ_SUCCESS on success, or the appropriate error code.
  */
 PJ_INLINE(pj_status_t) pjmedia_transport_media_create(pjmedia_transport *tp,
-				    pj_pool_t *pool,
+				    pj_pool_t *sdp_pool,
 				    unsigned options,
-				    pjmedia_sdp_session *sdp_local,
-				    const pjmedia_sdp_session *sdp_remote,
+				    const pjmedia_sdp_session *rem_sdp,
 				    unsigned media_index)
 {
-    return (*tp->op->media_create)(tp, pool, options, sdp_local, sdp_remote, 
+    return (*tp->op->media_create)(tp, sdp_pool, options, rem_sdp, 
 				   media_index);
 }
 
+
+/**
+ * Put transport specific information into the SDP. This function can be
+ * called to create SDP offer or answer, depending whether \a rem_sdp
+ * parameter is present.
+ *
+ * This is just a simple wrapper which calls <tt>encode_sdp()</tt> member 
+ * of the transport.
+ *
+ * @param tp		The media transport.
+ * @param sdp_pool	Pool object to allocate memory related to SDP
+ *			messaging components.
+ * @param sdp		The local SDP to be filled in information from the
+ *			media transport.
+ * @param rem_sdp	Remote SDP if it's available.
+ * @param media_index	Media index in SDP.
+ *
+ * @return		PJ_SUCCESS on success, or the appropriate error code.
+ */
+PJ_INLINE(pj_status_t) pjmedia_transport_encode_sdp(pjmedia_transport *tp,
+					    pj_pool_t *sdp_pool,
+					    pjmedia_sdp_session *sdp,
+					    const pjmedia_sdp_session *rem_sdp,
+					    unsigned media_index)
+{
+    return (*tp->op->encode_sdp)(tp, sdp_pool, sdp, rem_sdp, media_index);
+}
+
+
 /**
  * Start the transport with regards to SDP negotiation result. 
  * This API should be called after offer and answer are negotiated, and 
@@ -673,7 +708,7 @@ PJ_INLINE(pj_status_t) pjmedia_transport_media_create(pjmedia_transport *tp,
  * of the transport.
  *
  * @param tp		The media transport.
- * @param pool		The memory pool.
+ * @param tmp_pool	The memory pool for allocating temporary objects.
  * @param option	The media transport option.
  * @param sdp_local	Local SDP.
  * @param sdp_remote	Remote SDP.
@@ -682,12 +717,13 @@ PJ_INLINE(pj_status_t) pjmedia_transport_media_create(pjmedia_transport *tp,
  * @return		PJ_SUCCESS on success, or the appropriate error code.
  */
 PJ_INLINE(pj_status_t) pjmedia_transport_media_start(pjmedia_transport *tp,
-				    pj_pool_t *pool,
-				    pjmedia_sdp_session *sdp_local,
+				    pj_pool_t *tmp_pool,
+				    const pjmedia_sdp_session *sdp_local,
 				    const pjmedia_sdp_session *sdp_remote,
 				    unsigned media_index)
 {
-    return (*tp->op->media_start)(tp, pool, sdp_local, sdp_remote, media_index);
+    return (*tp->op->media_start)(tp, tmp_pool, sdp_local, sdp_remote, 
+				  media_index);
 }
 
 
diff --git a/pjmedia/src/pjmedia/endpoint.c b/pjmedia/src/pjmedia/endpoint.c
index 2835aef4..2492afcd 100644
--- a/pjmedia/src/pjmedia/endpoint.c
+++ b/pjmedia/src/pjmedia/endpoint.c
@@ -362,31 +362,9 @@ PJ_DEF(pj_status_t) pjmedia_endpt_create_sdp( pjmedia_endpt *endpt,
     /* Add "rtcp" attribute */
 #if defined(PJMEDIA_HAS_RTCP_IN_SDP) && PJMEDIA_HAS_RTCP_IN_SDP!=0
     if (sock_info->rtcp_addr_name.addr.sa_family != 0) {
-	const pj_sockaddr *rtcp_addr = &sock_info->rtcp_addr_name;
-
-	attr = PJ_POOL_ALLOC_T(pool, pjmedia_sdp_attr);
-	attr->name = pj_str("rtcp");
-	attr->value.ptr = (char*) pj_pool_alloc(pool, 80);
-	if (rtcp_addr->addr.sa_family == pj_AF_INET()) {
-	    attr->value.slen = 
-		pj_ansi_snprintf(attr->value.ptr, 80,
-				"%u IN IP4 %s",
-				pj_ntohs(rtcp_addr->ipv4.sin_port),
-				pj_inet_ntoa(rtcp_addr->ipv4.sin_addr));
-	} else if (rtcp_addr->addr.sa_family == pj_AF_INET6()) {
-	    char tmp_addr[PJ_INET6_ADDRSTRLEN];
-	    attr->value.slen = 
-		pj_ansi_snprintf(attr->value.ptr, 80,
-				"%u IN IP6 %s",
-				pj_sockaddr_get_port(rtcp_addr),
-				pj_sockaddr_print(rtcp_addr, tmp_addr, 
-						  sizeof(tmp_addr), 0));
-
-	} else {
-	    pj_assert(!"Unsupported address family");
-	    return PJ_EAFNOTSUP;
-	}
-	pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+	attr = pjmedia_sdp_attr_create_rtcp(pool, &sock_info->rtcp_addr_name);
+	if (attr)
+	    pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
     }
 #endif
 
diff --git a/pjmedia/src/pjmedia/sdp.c b/pjmedia/src/pjmedia/sdp.c
index 91c4ce1e..a1e13c7c 100644
--- a/pjmedia/src/pjmedia/sdp.c
+++ b/pjmedia/src/pjmedia/sdp.c
@@ -414,6 +414,40 @@ PJ_DEF(pj_status_t) pjmedia_sdp_attr_get_rtcp(const pjmedia_sdp_attr *attr,
 }
 
 
+PJ_DEF(pjmedia_sdp_attr*) pjmedia_sdp_attr_create_rtcp(pj_pool_t *pool,
+						       const pj_sockaddr *a)
+{
+    enum {
+	ATTR_LEN = PJ_INET6_ADDRSTRLEN+16
+    };
+    pjmedia_sdp_attr *attr;
+
+    attr = PJ_POOL_ALLOC_T(pool, pjmedia_sdp_attr);
+    attr->name = pj_str("rtcp");
+    attr->value.ptr = (char*) pj_pool_alloc(pool, ATTR_LEN);
+    if (a->addr.sa_family == pj_AF_INET()) {
+	attr->value.slen = 
+	    pj_ansi_snprintf(attr->value.ptr, ATTR_LEN,
+			    "%u IN IP4 %s",
+			    pj_ntohs(a->ipv4.sin_port),
+			    pj_inet_ntoa(a->ipv4.sin_addr));
+    } else if (a->addr.sa_family == pj_AF_INET6()) {
+	char tmp_addr[PJ_INET6_ADDRSTRLEN];
+	attr->value.slen = 
+	    pj_ansi_snprintf(attr->value.ptr, ATTR_LEN,
+			    "%u IN IP6 %s",
+			    pj_sockaddr_get_port(a),
+			    pj_sockaddr_print(a, tmp_addr, 
+					      sizeof(tmp_addr), 0));
+
+    } else {
+	pj_assert(!"Unsupported address family");
+	return NULL;
+    }
+
+    return attr;
+}
+
 
 PJ_DEF(pj_status_t) pjmedia_sdp_attr_to_rtpmap(pj_pool_t *pool,
 					       const pjmedia_sdp_attr *attr,
diff --git a/pjmedia/src/pjmedia/transport_ice.c b/pjmedia/src/pjmedia/transport_ice.c
index facc8ed1..95301036 100644
--- a/pjmedia/src/pjmedia/transport_ice.c
+++ b/pjmedia/src/pjmedia/transport_ice.c
@@ -23,19 +23,43 @@
 #include <pj/rand.h>
 
 #define THIS_FILE   "transport_ice.c"
+#if 0
+#   define TRACE__(expr)    PJ_LOG(5,expr)
+#else
+#   define TRACE__(expr)
+#endif
 
-static const pj_str_t ID_RTP_AVP  = { "RTP/AVP", 7 };
+enum oa_role
+{
+    ROLE_NONE,
+    ROLE_OFFERER,
+    ROLE_ANSWERER
+};
+
+struct sdp_state
+{
+    unsigned		match_comp_cnt;	/* Matching number of components    */
+    pj_bool_t		ice_mismatch;	/* Address doesn't match candidates */
+    pj_bool_t		ice_restart;	/* Offer to restart ICE		    */
+    pj_ice_sess_role	local_role;	/* Our role			    */
+};
 
 struct transport_ice
 {
     pjmedia_transport	 base;
     pj_pool_t		*pool;
     int			 af;
+
     unsigned		 comp_cnt;
     pj_ice_strans	*ice_st;
+
     pjmedia_ice_cb	 cb;
     unsigned		 media_option;
 
+    pj_bool_t		 initial_sdp;
+    enum oa_role	 oa_role;	/**< Last role in SDP offer/answer  */
+    struct sdp_state	 rem_offer_state;/**< Describes the remote offer	    */
+
     void		*stream;
     pj_sockaddr_in	 remote_rtp;
     pj_sockaddr_in	 remote_rtcp;
@@ -84,12 +108,16 @@ static pj_status_t transport_send_rtcp2(pjmedia_transport *tp,
 static pj_status_t transport_media_create(pjmedia_transport *tp,
 				       pj_pool_t *pool,
 				       unsigned options,
-				       pjmedia_sdp_session *sdp_local,
 				       const pjmedia_sdp_session *rem_sdp,
 				       unsigned media_index);
-static pj_status_t transport_media_start (pjmedia_transport *tp,
+static pj_status_t transport_encode_sdp(pjmedia_transport *tp,
+				        pj_pool_t *tmp_pool,
+				        pjmedia_sdp_session *sdp_local,
+				        const pjmedia_sdp_session *rem_sdp,
+				        unsigned media_index);
+static pj_status_t transport_media_start(pjmedia_transport *tp,
 				       pj_pool_t *pool,
-				       pjmedia_sdp_session *sdp_local,
+				       const pjmedia_sdp_session *sdp_local,
 				       const pjmedia_sdp_session *rem_sdp,
 				       unsigned media_index);
 static pj_status_t transport_media_stop(pjmedia_transport *tp);
@@ -120,16 +148,28 @@ static pjmedia_transport_op transport_ice_op =
     &transport_send_rtcp,
     &transport_send_rtcp2,
     &transport_media_create,
+    &transport_encode_sdp,
     &transport_media_start,
     &transport_media_stop,
     &transport_simulate_lost,
     &transport_destroy
 };
 
-static const pj_str_t STR_CANDIDATE = {"candidate", 9};
-static const pj_str_t STR_ICE_LITE = {"ice-lite", 8};
-static const pj_str_t STR_ICE_MISMATCH = {"ice-mismatch", 12};
-
+static const pj_str_t STR_RTP_AVP	= { "RTP/AVP", 7 };
+static const pj_str_t STR_CANDIDATE	= { "candidate", 9};
+static const pj_str_t STR_REM_CAND	= { "remote-candidates", 17 };
+static const pj_str_t STR_ICE_LITE	= { "ice-lite", 8};
+static const pj_str_t STR_ICE_MISMATCH	= { "ice-mismatch", 12};
+static const pj_str_t STR_ICE_UFRAG	= { "ice-ufrag", 9 };
+static const pj_str_t STR_ICE_PWD	= { "ice-pwd", 7 };
+static const pj_str_t STR_IP4		= { "IP4", 3 };
+static const pj_str_t STR_IP6		= { "IP6", 3 };
+static const pj_str_t STR_RTCP		= { "rtcp", 4 };
+
+enum {
+    COMP_RTP = 1,
+    COMP_RTCP = 2
+};
 
 /*
  * Create ICE media transport.
@@ -157,6 +197,8 @@ PJ_DEF(pj_status_t) pjmedia_ice_create(pjmedia_endpt *endpt,
     pj_ansi_strcpy(tp_ice->base.name, pool->obj_name);
     tp_ice->base.op = &transport_ice_op;
     tp_ice->base.type = PJMEDIA_TRANSPORT_TYPE_ICE;
+    tp_ice->initial_sdp = PJ_TRUE;
+    tp_ice->oa_role = ROLE_NONE;
 
     if (cb)
 	pj_memcpy(&tp_ice->cb, cb, sizeof(pjmedia_ice_cb));
@@ -184,6 +226,24 @@ PJ_DEF(pj_status_t) pjmedia_ice_create(pjmedia_endpt *endpt,
     return PJ_SUCCESS;
 }
 
+/* Disable ICE when SDP from remote doesn't contain a=candidate line */
+static void set_no_ice(struct transport_ice *tp_ice, const char *reason,
+		       pj_status_t err)
+{
+    if (err != PJ_SUCCESS) {
+	char errmsg[PJ_ERR_MSG_SIZE];
+	pj_strerror(err, errmsg, sizeof(errmsg));
+	PJ_LOG(4,(tp_ice->base.name, 
+		  "Stopping ICE, reason=%s:%s", reason, errmsg));
+    } else {
+	PJ_LOG(4,(tp_ice->base.name, 
+		  "Stopping ICE, reason=%s", reason));
+    }
+
+    pj_ice_strans_stop_ice(tp_ice->ice_st);
+}
+
+
 /* Create SDP candidate attribute */
 static int print_sdp_cand_attr(char *buffer, int max_len,
 			       const pj_ice_sess_cand *cand)
@@ -227,102 +287,259 @@ static int print_sdp_cand_attr(char *buffer, int max_len,
     return len+len2;
 }
 
-/*
- * For both UAC and UAS, pass in the SDP before sending it to remote.
- * This will add ICE attributes to the SDP.
- */
-static pj_status_t transport_media_create(pjmedia_transport *tp,
-				          pj_pool_t *pool,
-					  unsigned options,
-					  pjmedia_sdp_session *sdp_local,
-					  const pjmedia_sdp_session *rem_sdp,
-					  unsigned media_index)
-{
-    struct transport_ice *tp_ice = (struct transport_ice*)tp;
-    pj_bool_t init_ice;
-    unsigned i;
-    pj_status_t status;
-
-    tp_ice->media_option = options;
 
-    /* Validate media transport */
-    /* For now, this transport only support RTP/AVP transport */
-    if ((tp_ice->media_option & PJMEDIA_TPMED_NO_TRANSPORT_CHECKING) == 0) {
-	pjmedia_sdp_media *m_rem, *m_loc;
+/* Get ice-ufrag and ice-pwd attribute */
+static void get_ice_attr(const pjmedia_sdp_session *rem_sdp,
+			 const pjmedia_sdp_media *rem_m,
+			 const pjmedia_sdp_attr **p_ice_ufrag,
+			 const pjmedia_sdp_attr **p_ice_pwd)
+{
+    pjmedia_sdp_attr *attr;
 
-	m_rem = rem_sdp? rem_sdp->media[media_index] : NULL;
-	m_loc = sdp_local->media[media_index];
+    /* Find ice-ufrag attribute in media descriptor */
+    attr = pjmedia_sdp_attr_find(rem_m->attr_count, rem_m->attr,
+				 &STR_ICE_UFRAG, NULL);
+    if (attr == NULL) {
+	/* Find ice-ufrag attribute in session descriptor */
+	attr = pjmedia_sdp_attr_find(rem_sdp->attr_count, rem_sdp->attr,
+				     &STR_ICE_UFRAG, NULL);
+    }
+    *p_ice_ufrag = attr;
 
-	if (pj_stricmp(&m_loc->desc.transport, &ID_RTP_AVP) ||
-	   (m_rem && pj_stricmp(&m_rem->desc.transport, &ID_RTP_AVP)))
-	{
-	    pjmedia_sdp_media_deactivate(pool, m_loc);
-	    return PJMEDIA_SDP_EINPROTO;
-	}
+    /* Find ice-pwd attribute in media descriptor */
+    attr = pjmedia_sdp_attr_find(rem_m->attr_count, rem_m->attr,
+				 &STR_ICE_PWD, NULL);
+    if (attr == NULL) {
+	/* Find ice-pwd attribute in session descriptor */
+	attr = pjmedia_sdp_attr_find(rem_sdp->attr_count, rem_sdp->attr,
+				     &STR_ICE_PWD, NULL);
     }
+    *p_ice_pwd = attr;
+}
 
-    /* If we are UAS, check that the incoming SDP contains support for ICE. */
-    if (rem_sdp) {
-	const pjmedia_sdp_media *rem_m;
 
-	rem_m = rem_sdp->media[media_index];
+/* Encode and add "a=ice-mismatch" attribute in the SDP */
+static void encode_ice_mismatch(pj_pool_t *sdp_pool,
+				pjmedia_sdp_session *sdp_local,
+				unsigned media_index)
+{
+    pjmedia_sdp_attr *attr;
+    pjmedia_sdp_media *m = sdp_local->media[media_index];
 
-	init_ice = pjmedia_sdp_attr_find2(rem_m->attr_count, rem_m->attr,
-					  "ice-ufrag", NULL) != NULL;
-	if (init_ice == PJ_FALSE) {
-	    init_ice = pjmedia_sdp_attr_find2(rem_sdp->attr_count, 
-					      rem_sdp->attr,
-					      "ice-ufrag", NULL) != NULL;
-	}
+    attr = PJ_POOL_ALLOC_T(sdp_pool, pjmedia_sdp_attr);
+    attr->name = STR_ICE_MISMATCH;
+    attr->value.slen = 0;
+    pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+}
 
-	if (init_ice) {
-	    init_ice = pjmedia_sdp_attr_find2(rem_m->attr_count, rem_m->attr,
-					      "candidate", NULL) != NULL;
-	}
-    } else {
-	init_ice = PJ_TRUE;
-    }
 
-    /* Init ICE */
-    if (init_ice) {
-	pj_ice_sess_role ice_role;
-	enum { MAXLEN = 256 };
-	pj_str_t ufrag, pass;
-	char *buffer;
-	pjmedia_sdp_attr *attr;
+/* Encode ICE information in SDP */
+static pj_status_t encode_session_in_sdp(struct transport_ice *tp_ice,
+					 pj_pool_t *sdp_pool,
+					 pjmedia_sdp_session *sdp_local,
+					 unsigned media_index,
+					 unsigned comp_cnt,
+					 pj_bool_t restart_session)
+{
+    enum { 
+	ATTR_BUF_LEN = 160,	/* Max len of a=candidate attr */
+	RATTR_BUF_LEN= 160	/* Max len of a=remote-candidates attr */
+    };
+    pjmedia_sdp_media *m = sdp_local->media[media_index];
+    pj_str_t local_ufrag, local_pwd;
+    pjmedia_sdp_attr *attr;
+    pj_status_t status;
+
+    /* Must have a session */
+    PJ_ASSERT_RETURN(pj_ice_strans_has_sess(tp_ice->ice_st), PJ_EBUG);
+
+    /* Get ufrag and pwd from current session */
+    pj_ice_strans_get_ufrag_pwd(tp_ice->ice_st, &local_ufrag, &local_pwd,
+				NULL, NULL);
+
+    /* The listing of candidates depends on whether ICE has completed
+     * or not. When ICE has completed:
+     *
+     * 9.1.2.2: Existing Media Streams with ICE Completed
+     *   The agent MUST include a candidate attributes for candidates
+     *   matching the default destination for each component of the 
+     *   media stream, and MUST NOT include any other candidates.
+     *
+     * When ICE has not completed, we shall include all candidates.
+     *
+     * Except when we have detected that remote is offering to restart
+     * the session, in this case we will answer with full ICE SDP and
+     * new ufrag/pwd pair.
+     */
+    if (!restart_session && pj_ice_strans_sess_is_complete(tp_ice->ice_st)) {
+	const pj_ice_sess_check *check;
+	char *attr_buf;
+	pjmedia_sdp_conn *conn;
+	pjmedia_sdp_attr *a_rtcp;
+	pj_str_t rem_cand;
 	unsigned comp;
 
-	ice_role = (rem_sdp==NULL ? PJ_ICE_SESS_ROLE_CONTROLLING : 
-				    PJ_ICE_SESS_ROLE_CONTROLLED);
+	/* Encode ice-ufrag attribute */
+	attr = pjmedia_sdp_attr_create(sdp_pool, STR_ICE_UFRAG.ptr,
+				       &local_ufrag);
+	pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+
+	/* Encode ice-pwd attribute */
+	attr = pjmedia_sdp_attr_create(sdp_pool, STR_ICE_PWD.ptr, 
+				       &local_pwd);
+	pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+
+	/* Prepare buffer */
+	attr_buf = (char*) pj_pool_alloc(sdp_pool, ATTR_BUF_LEN);
+	rem_cand.ptr = (char*) pj_pool_alloc(sdp_pool, RATTR_BUF_LEN);
+	rem_cand.slen = 0;
+
+	/* 9.1.2.2: Existing Media Streams with ICE Completed
+	 *   The default destination for media (i.e., the values of 
+	 *   the IP addresses and ports in the m and c line used for
+	 *   that media stream) MUST be the local candidate from the
+	 *   highest priority nominated pair in the valid list for each
+	 *   component.
+	 */
+	check = pj_ice_strans_get_valid_pair(tp_ice->ice_st, 1);
+	if (check == NULL) {
+	    pj_assert(!"Shouldn't happen");
+	    return PJ_EBUG;
+	}
 
-	ufrag.ptr = (char*) pj_pool_alloc(pool, PJ_ICE_UFRAG_LEN);
-	pj_create_random_string(ufrag.ptr, PJ_ICE_UFRAG_LEN);
-	ufrag.slen = PJ_ICE_UFRAG_LEN;
+	/* Override connection line address and media port number */
+	conn = m->conn;
+	if (conn == NULL)
+	    conn = sdp_local->conn;
+
+	conn->addr.ptr = (char*) pj_pool_alloc(sdp_pool, 
+					       PJ_INET6_ADDRSTRLEN);
+	pj_sockaddr_print(&check->lcand->addr, conn->addr.ptr, 
+			  PJ_INET6_ADDRSTRLEN, 0);
+	conn->addr.slen = pj_ansi_strlen(conn->addr.ptr);
+	m->desc.port = pj_sockaddr_get_port(&check->lcand->addr);
+
+	/* Override address RTCP attribute if it's present */
+	if (comp_cnt == 2 &&
+	    (check = pj_ice_strans_get_valid_pair(tp_ice->ice_st, 
+						  COMP_RTCP)) != NULL &&
+	    (a_rtcp = pjmedia_sdp_attr_find(m->attr_count, m->attr, 
+					    &STR_RTCP, 0)) != NULL) 
+	{
+	    pjmedia_sdp_attr_remove(&m->attr_count, m->attr, a_rtcp);
 
-	pass.ptr = (char*) pj_pool_alloc(pool, PJ_ICE_UFRAG_LEN);
-	pj_create_random_string(pass.ptr, PJ_ICE_UFRAG_LEN);
-	pass.slen = PJ_ICE_UFRAG_LEN;
+	    a_rtcp = pjmedia_sdp_attr_create_rtcp(sdp_pool, 
+						  &check->lcand->addr);
+	    if (a_rtcp)
+		pjmedia_sdp_attr_add(&m->attr_count, m->attr, a_rtcp);
+	}
 
-	status = pj_ice_strans_init_ice(tp_ice->ice_st, ice_role, 
-					&ufrag, &pass);
-	if (status != PJ_SUCCESS)
-	    return status;
+	/* Encode only candidates matching the default destination 
+	 * for each component 
+	 */
+	for (comp=0; comp < comp_cnt; ++comp) {
+	    int len;
+	    pj_str_t value;
+
+	    /* Get valid pair for this component */
+	    check = pj_ice_strans_get_valid_pair(tp_ice->ice_st, comp+1);
+	    if (check == NULL)
+		continue;
+
+	    /* Print and add local candidate in the pair */
+	    value.ptr = attr_buf;
+	    value.slen = print_sdp_cand_attr(attr_buf, ATTR_BUF_LEN, 
+					     check->lcand);
+	    if (value.slen < 0) {
+		pj_assert(!"Not enough attr_buf to print candidate");
+		return PJ_EBUG;
+	    }
 
-	/* Create ice-ufrag attribute */
-	attr = pjmedia_sdp_attr_create(pool, "ice-ufrag", &ufrag);
-	sdp_local->attr[sdp_local->attr_count++] = attr;
+	    attr = pjmedia_sdp_attr_create(sdp_pool, STR_CANDIDATE.ptr,
+					   &value);
+	    pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+
+	    /* Append to a=remote-candidates attribute */
+	    if (pj_ice_strans_get_role(tp_ice->ice_st) == 
+				    PJ_ICE_SESS_ROLE_CONTROLLING) 
+	    {
+		char rem_addr[PJ_INET6_ADDRSTRLEN];
+
+		pj_sockaddr_print(&check->rcand->addr, rem_addr, 
+				  sizeof(rem_addr), 0);
+		len = pj_ansi_snprintf(
+			   rem_cand.ptr + rem_cand.slen,
+			   RATTR_BUF_LEN - rem_cand.slen,
+			   "%s%u %s %u", 
+			   (rem_cand.slen==0? "" : " "),
+			   comp+1, rem_addr,
+			   pj_sockaddr_get_port(&check->rcand->addr)
+			   );
+		if (len < 1 || len >= RATTR_BUF_LEN) {
+		    pj_assert(!"Not enough buffer to print "
+			       "remote-candidates");
+		    return PJ_EBUG;
+		}
+
+		rem_cand.slen += len;
+	    }
+	}
 
-	/* Create ice-pwd attribute */
-	attr = pjmedia_sdp_attr_create(pool, "ice-pwd", &pass);
-	sdp_local->attr[sdp_local->attr_count++] = attr;
+	/* 9.1.2.2: Existing Media Streams with ICE Completed
+	 *   In addition, if the agent is controlling, it MUST include
+	 *   the a=remote-candidates attribute for each media stream 
+	 *   whose check list is in the Completed state.  The attribute
+	 *   contains the remote candidates from the highest priority 
+	 *   nominated pair in the valid list for each component of that
+	 *   media stream.
+	 */
+	if (pj_ice_strans_get_role(tp_ice->ice_st) == 
+				    PJ_ICE_SESS_ROLE_CONTROLLING) 
+	{
+	    attr = pjmedia_sdp_attr_create(sdp_pool, STR_REM_CAND.ptr, 
+					   &rem_cand);
+	    pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+	}
 
+    } else if (pj_ice_strans_has_sess(tp_ice->ice_st)) {
 	/* Encode all candidates to SDP media */
+	char *attr_buf;
+	unsigned comp;
+
+	/* If ICE is not restarted, encode current ICE ufrag/pwd.
+	 * Otherwise generate new one.
+	 */
+	if (!restart_session) {
+	    attr = pjmedia_sdp_attr_create(sdp_pool, STR_ICE_UFRAG.ptr,
+					   &local_ufrag);
+	    pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+
+	    attr = pjmedia_sdp_attr_create(sdp_pool, STR_ICE_PWD.ptr, 
+					   &local_pwd);
+	    pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+
+	} else {
+	    pj_str_t str;
+
+	    str.slen = PJ_ICE_UFRAG_LEN;
+	    str.ptr = (char*) pj_pool_alloc(sdp_pool, str.slen);
+	    pj_create_random_string(str.ptr, str.slen);
+	    attr = pjmedia_sdp_attr_create(sdp_pool, STR_ICE_UFRAG.ptr, &str);
+	    pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+
+	    str.ptr = (char*) pj_pool_alloc(sdp_pool, str.slen);
+	    pj_create_random_string(str.ptr, str.slen);
+	    attr = pjmedia_sdp_attr_create(sdp_pool, STR_ICE_PWD.ptr, &str);
+	    pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
+	}
 
-	buffer = (char*) pj_pool_alloc(pool, MAXLEN);
+	/* Create buffer to encode candidates as SDP attribute */
+	attr_buf = (char*) pj_pool_alloc(sdp_pool, ATTR_BUF_LEN);
 
-	for (comp=0; comp < tp_ice->comp_cnt; ++comp) {
+	for (comp=0; comp < comp_cnt; ++comp) {
 	    unsigned cand_cnt;
 	    pj_ice_sess_cand cand[PJ_ICE_ST_MAX_CAND];
+	    unsigned i;
 
 	    cand_cnt = PJ_ARRAY_SIZE(cand);
 	    status = pj_ice_strans_enum_cands(tp_ice->ice_st, comp+1,
@@ -331,45 +548,51 @@ static pj_status_t transport_media_create(pjmedia_transport *tp,
 		return status;
 
 	    for (i=0; i<cand_cnt; ++i) {
-		pjmedia_sdp_media *m;
 		pj_str_t value;
 
-		value.slen = print_sdp_cand_attr(buffer, MAXLEN, &cand[i]);
+		value.slen = print_sdp_cand_attr(attr_buf, ATTR_BUF_LEN, 
+						 &cand[i]);
 		if (value.slen < 0) {
-		    pj_assert(!"Not enough buffer to print candidate");
+		    pj_assert(!"Not enough attr_buf to print candidate");
 		    return PJ_EBUG;
 		}
 
-		value.ptr = buffer;
-		attr = pjmedia_sdp_attr_create(pool, "candidate", &value);
-		m = sdp_local->media[media_index];
-		m->attr[m->attr_count++] = attr;
+		value.ptr = attr_buf;
+		attr = pjmedia_sdp_attr_create(sdp_pool, 
+					       STR_CANDIDATE.ptr,
+					       &value);
+		pjmedia_sdp_attr_add(&m->attr_count, m->attr, attr);
 	    }
 	}
+    } else {
+	/* ICE has failed, application should have terminated this call */
     }
 
-    /* Done */
     return PJ_SUCCESS;
 }
 
 
 /* Parse a=candidate line */
-static pj_status_t parse_cand(pj_pool_t *pool,
+static pj_status_t parse_cand(const char *obj_name,
+			      pj_pool_t *pool,
 			      const pj_str_t *orig_input,
 			      pj_ice_sess_cand *cand)
 {
     pj_str_t input;
     char *token, *host;
+    int af;
     pj_str_t s;
     pj_status_t status = PJNATH_EICEINCANDSDP;
 
     pj_bzero(cand, sizeof(*cand));
     pj_strdup_with_null(pool, &input, orig_input);
 
+    PJ_UNUSED_ARG(obj_name);
+
     /* Foundation */
     token = strtok(input.ptr, " ");
     if (!token) {
-	PJ_LOG(5,(THIS_FILE, "Expecting ICE foundation in candidate"));
+	TRACE__((obj_name, "Expecting ICE foundation in candidate"));
 	goto on_return;
     }
     pj_strdup2(pool, &cand->foundation, token);
@@ -377,7 +600,7 @@ static pj_status_t parse_cand(pj_pool_t *pool,
     /* Component ID */
     token = strtok(NULL, " ");
     if (!token) {
-	PJ_LOG(5,(THIS_FILE, "Expecting ICE component ID in candidate"));
+	TRACE__((obj_name, "Expecting ICE component ID in candidate"));
 	goto on_return;
     }
     cand->comp_id = (pj_uint8_t) atoi(token);
@@ -385,19 +608,19 @@ static pj_status_t parse_cand(pj_pool_t *pool,
     /* Transport */
     token = strtok(NULL, " ");
     if (!token) {
-	PJ_LOG(5,(THIS_FILE, "Expecting ICE transport in candidate"));
+	TRACE__((obj_name, "Expecting ICE transport in candidate"));
 	goto on_return;
     }
     if (pj_ansi_stricmp(token, "UDP") != 0) {
-	PJ_LOG(5,(THIS_FILE, 
-		  "Expecting ICE UDP transport only in candidate"));
+	TRACE__((obj_name, 
+		 "Expecting ICE UDP transport only in candidate"));
 	goto on_return;
     }
 
     /* Priority */
     token = strtok(NULL, " ");
     if (!token) {
-	PJ_LOG(5,(THIS_FILE, "Expecting ICE priority in candidate"));
+	TRACE__((obj_name, "Expecting ICE priority in candidate"));
 	goto on_return;
     }
     cand->prio = atoi(token);
@@ -405,38 +628,43 @@ static pj_status_t parse_cand(pj_pool_t *pool,
     /* Host */
     host = strtok(NULL, " ");
     if (!host) {
-	PJ_LOG(5,(THIS_FILE, "Expecting ICE host in candidate"));
+	TRACE__((obj_name, "Expecting ICE host in candidate"));
 	goto on_return;
     }
-    if (pj_sockaddr_in_init(&cand->addr.ipv4, pj_cstr(&s, host), 0)) {
-	PJ_LOG(5,(THIS_FILE, 
-		  "Expecting ICE IPv4 transport address in candidate"));
+    /* Detect address family */
+    if (pj_ansi_strchr(host, ':'))
+	af = pj_AF_INET6();
+    else
+	af = pj_AF_INET();
+    /* Assign address */
+    if (pj_sockaddr_init(af, &cand->addr, pj_cstr(&s, host), 0)) {
+	TRACE__((obj_name, "Invalid ICE candidate address"));
 	goto on_return;
     }
 
     /* Port */
     token = strtok(NULL, " ");
     if (!token) {
-	PJ_LOG(5,(THIS_FILE, "Expecting ICE port number in candidate"));
+	TRACE__((obj_name, "Expecting ICE port number in candidate"));
 	goto on_return;
     }
-    cand->addr.ipv4.sin_port = pj_htons((pj_uint16_t)atoi(token));
+    pj_sockaddr_set_port(&cand->addr, (pj_uint16_t)atoi(token));
 
     /* typ */
     token = strtok(NULL, " ");
     if (!token) {
-	PJ_LOG(5,(THIS_FILE, "Expecting ICE \"typ\" in candidate"));
+	TRACE__((obj_name, "Expecting ICE \"typ\" in candidate"));
 	goto on_return;
     }
     if (pj_ansi_stricmp(token, "typ") != 0) {
-	PJ_LOG(5,(THIS_FILE, "Expecting ICE \"typ\" in candidate"));
+	TRACE__((obj_name, "Expecting ICE \"typ\" in candidate"));
 	goto on_return;
     }
 
     /* candidate type */
     token = strtok(NULL, " ");
     if (!token) {
-	PJ_LOG(5,(THIS_FILE, "Expecting ICE candidate type in candidate"));
+	TRACE__((obj_name, "Expecting ICE candidate type in candidate"));
 	goto on_return;
     }
 
@@ -453,12 +681,11 @@ static pj_status_t parse_cand(pj_pool_t *pool,
 	cand->type = PJ_ICE_CAND_TYPE_PRFLX;
 
     } else {
-	PJ_LOG(5,(THIS_FILE, "Invalid ICE candidate type %s in candidate", 
+	PJ_LOG(5,(obj_name, "Invalid ICE candidate type %s in candidate", 
 		  token));
 	goto on_return;
     }
 
-
     status = PJ_SUCCESS;
 
 on_return:
@@ -466,182 +693,681 @@ on_return:
 }
 
 
-/* Disable ICE when SDP from remote doesn't contain a=candidate line */
-static void set_no_ice(struct transport_ice *tp_ice, const char *reason)
+/* Create initial SDP offer */
+static pj_status_t create_initial_offer(struct transport_ice *tp_ice,
+					pj_pool_t *sdp_pool,
+					pjmedia_sdp_session *loc_sdp,
+					unsigned media_index)
+{
+    pj_status_t status;
+
+    /* Encode ICE in SDP */
+    status = encode_session_in_sdp(tp_ice, sdp_pool, loc_sdp, media_index, 
+				   tp_ice->comp_cnt, PJ_FALSE);
+    if (status != PJ_SUCCESS) {
+	set_no_ice(tp_ice, "Error encoding SDP answer", status);
+	return status;
+    }
+
+    return PJ_SUCCESS;
+}
+
+
+/* Verify incoming offer */
+static pj_status_t verify_ice_sdp(struct transport_ice *tp_ice,
+				  pj_pool_t *tmp_pool,
+				  const pjmedia_sdp_session *rem_sdp,
+				  unsigned media_index,
+				  pj_ice_sess_role current_ice_role,
+				  struct sdp_state *sdp_state)
 {
+    const pjmedia_sdp_media *rem_m;
+    const pjmedia_sdp_attr *attr, *ufrag_attr, *pwd_attr;
+    const pjmedia_sdp_conn *rem_conn;
+    pj_bool_t comp1_found=PJ_FALSE, comp2_found=PJ_FALSE;
+    pj_sockaddr rem_conn_addr, rtcp_addr;
+    unsigned i;
+    pj_status_t status;
+
+    rem_m = rem_sdp->media[media_index];
+
+    /* Get the "ice-ufrag" and "ice-pwd" attributes */
+    get_ice_attr(rem_sdp, rem_m, &ufrag_attr, &pwd_attr);
+
+    /* If "ice-ufrag" or "ice-pwd" are not found, disable ICE */
+    if (ufrag_attr==NULL || pwd_attr==NULL) {
+	sdp_state->match_comp_cnt = 0;
+	return PJ_SUCCESS;
+    }
+
+    /* Verify that default target for each component matches one of the 
+     * candidatefor the component. Otherwise stop ICE with ICE ice_mismatch 
+     * error.
+     */
+
+    /* Component 1 is the c= line */
+    rem_conn = rem_m->conn;
+    if (rem_conn == NULL)
+	rem_conn = rem_sdp->conn;
+    if (!rem_conn)
+	return PJMEDIA_SDP_EMISSINGCONN;
+
+    /* Verify address family matches */
+    if ((tp_ice->af==pj_AF_INET() && 
+	 pj_strcmp(&rem_conn->addr_type, &STR_IP4)!=0) ||
+	(tp_ice->af==pj_AF_INET6() && 
+	 pj_strcmp(&rem_conn->addr_type, &STR_IP6)!=0))
+    {
+	return PJMEDIA_SDP_ETPORTNOTEQUAL;
+    }
+
+    /* Assign remote connection address */
+    status = pj_sockaddr_init(tp_ice->af, &rem_conn_addr, &rem_conn->addr,
+			      (pj_uint16_t)rem_m->desc.port);
+    if (status != PJ_SUCCESS)
+	return status;
+
+    /* Component 2 is a=rtcp line, if present. */
+    attr = pjmedia_sdp_attr_find(rem_m->attr_count, rem_m->attr, 
+				 &STR_RTCP, NULL);
+    if (attr && tp_ice->comp_cnt > 1) {
+	pjmedia_sdp_rtcp_attr rtcp_attr;
+
+	status = pjmedia_sdp_attr_get_rtcp(attr, &rtcp_attr);
+	if (status != PJ_SUCCESS) {
+	    /* Error parsing a=rtcp attribute */
+	    return status;
+	}
+	
+	/* Verify address family matches */
+	if ((tp_ice->af==pj_AF_INET() && 
+	     pj_strcmp(&rtcp_attr.addr_type, &STR_IP4)!=0) ||
+	    (tp_ice->af==pj_AF_INET6() && 
+	     pj_strcmp(&rtcp_attr.addr_type, &STR_IP6)!=0))
+	{
+	    return PJMEDIA_SDP_ETPORTNOTEQUAL;
+	}
+
+	/* Assign RTCP address */
+	status = pj_sockaddr_init(tp_ice->af, &rtcp_addr,
+				  &rtcp_attr.addr,
+				  (pj_uint16_t)rtcp_attr.port);
+	if (status != PJ_SUCCESS) {
+	    return PJMEDIA_SDP_EINRTCP;
+	}
+
+	sdp_state->match_comp_cnt = 2;
+
+    } else {
+	/* Don't have RTCP component */
+	comp2_found = PJ_TRUE;
+	sdp_state->match_comp_cnt = 1;
+    }
+
+    /* Find the default address in a=candidate attributes. 
+     */
+    for (i=0; i<rem_m->attr_count; ++i) {
+	pj_ice_sess_cand cand;
+
+	if (pj_strcmp(&rem_m->attr[i]->name, &STR_CANDIDATE)!=0)
+	    continue;
+
+	status = parse_cand(tp_ice->base.name, tmp_pool, 
+			    &rem_m->attr[i]->value, &cand);
+	if (status != PJ_SUCCESS) {
+	    PJ_LOG(4,(tp_ice->base.name, 
+		      "Error in parsing SDP candidate attribute '%.*s', "
+		      "candidate is ignored",
+		      (int)rem_m->attr[i]->value.slen, 
+		      rem_m->attr[i]->value.ptr));
+	    continue;
+	}
+
+	if (!comp1_found && cand.comp_id==COMP_RTP &&
+	    pj_sockaddr_cmp(&rem_conn_addr, &cand.addr)==0) 
+	{
+	    /* Found */
+	    comp1_found = PJ_TRUE;
+	    if (comp1_found && comp2_found)
+		break;
+	} else if (!comp2_found && cand.comp_id==COMP_RTCP &&
+		    pj_sockaddr_cmp(&rtcp_addr, &cand.addr)==0) 
+	{
+	    /* Found */
+	    comp2_found = PJ_TRUE;
+	    if (comp1_found && comp2_found)
+		break;
+	}
+
+    }
+
+    if (!comp1_found || !comp2_found) {
+	/* ICE ice_mismatch */
+	sdp_state->ice_mismatch = PJ_TRUE;
+    } else {
+	sdp_state->ice_mismatch = PJ_FALSE;
+    }
+
+    /* Detect remote restarting session */
+    if (pj_ice_strans_has_sess(tp_ice->ice_st) &&
+	(pj_ice_strans_sess_is_running(tp_ice->ice_st) ||
+	 pj_ice_strans_sess_is_complete(tp_ice->ice_st))) 
+    {
+	pj_str_t rem_run_ufrag, rem_run_pwd;
+	pj_ice_strans_get_ufrag_pwd(tp_ice->ice_st, NULL, NULL,
+				    &rem_run_ufrag, &rem_run_pwd);
+	if (pj_strcmp(&ufrag_attr->value, &rem_run_ufrag) ||
+	    pj_strcmp(&pwd_attr->value, &rem_run_pwd))
+	{
+	    /* Remote offers to restart ICE */
+	    sdp_state->ice_restart = PJ_TRUE;
+	} else {
+	    sdp_state->ice_restart = PJ_FALSE;
+	}
+    } else {
+	sdp_state->ice_restart = PJ_FALSE;
+    }
+
+    /* Detect our role */
+    if (current_ice_role==PJ_ICE_SESS_ROLE_CONTROLLING) {
+	sdp_state->local_role = PJ_ICE_SESS_ROLE_CONTROLLING;
+    } else {
+	if (pjmedia_sdp_attr_find(rem_sdp->attr_count, rem_sdp->attr,
+				  &STR_ICE_LITE, NULL) != NULL)
+	{
+	    /* Remote is ICE Lite */
+	    sdp_state->local_role = PJ_ICE_SESS_ROLE_CONTROLLING;
+	} else {
+	    sdp_state->local_role = PJ_ICE_SESS_ROLE_CONTROLLED;
+	}
+    }
+
     PJ_LOG(4,(tp_ice->base.name, 
-	      "Disabling local ICE, reason=%s", reason));
-    transport_media_stop(&tp_ice->base);
+	      "Processing SDP: support ICE=%u, common comp_cnt=%u, "
+	      "ice_mismatch=%u, ice_restart=%u, local_role=%s",
+	      (sdp_state->match_comp_cnt != 0), 
+	      sdp_state->match_comp_cnt, 
+	      sdp_state->ice_mismatch, 
+	      sdp_state->ice_restart,
+	      pj_ice_sess_role_name(sdp_state->local_role)));
+
+    return PJ_SUCCESS;
+
+}
+
+
+/* Verify incoming offer and create initial answer */
+static pj_status_t create_initial_answer(struct transport_ice *tp_ice,
+					 pj_pool_t *sdp_pool,
+					 pjmedia_sdp_session *loc_sdp,
+					 const pjmedia_sdp_session *rem_sdp,
+					 unsigned media_index)
+{
+    const pjmedia_sdp_media *rem_m = rem_sdp->media[media_index];
+    pj_status_t status;
+
+    /* Check if media is removed (just in case) */
+    if (rem_m->desc.port == 0) {
+	return PJ_SUCCESS;
+    }
+
+    /* Verify the offer */
+    status = verify_ice_sdp(tp_ice, sdp_pool, rem_sdp, media_index, 
+			    PJ_ICE_SESS_ROLE_CONTROLLED, 
+			    &tp_ice->rem_offer_state);
+    if (status != PJ_SUCCESS) {
+	set_no_ice(tp_ice, "Invalid SDP offer", status);
+	return status;
+    }
+
+    /* Does remote support ICE? */
+    if (tp_ice->rem_offer_state.match_comp_cnt==0) {
+	set_no_ice(tp_ice, "No ICE found in SDP offer", PJ_SUCCESS);
+	return PJ_SUCCESS;
+    }
+
+    /* ICE ice_mismatch? */
+    if (tp_ice->rem_offer_state.ice_mismatch) {
+	set_no_ice(tp_ice, "ICE ice_mismatch in remote offer", PJ_SUCCESS);
+	encode_ice_mismatch(sdp_pool, loc_sdp, media_index);
+	return PJ_SUCCESS;
+    }
+
+    /* Encode ICE in SDP */
+    status = encode_session_in_sdp(tp_ice, sdp_pool, loc_sdp, media_index, 
+				   tp_ice->rem_offer_state.match_comp_cnt,
+				   PJ_FALSE);
+    if (status != PJ_SUCCESS) {
+	set_no_ice(tp_ice, "Error encoding SDP answer", status);
+	return status;
+    }
+
+    return PJ_SUCCESS;
+}
+
+
+/* Create subsequent SDP offer */
+static pj_status_t create_subsequent_offer(struct transport_ice *tp_ice,
+					   pj_pool_t *sdp_pool,
+					   pjmedia_sdp_session *loc_sdp,
+					   unsigned media_index)
+{
+    unsigned comp_cnt;
+
+    if (pj_ice_strans_has_sess(tp_ice->ice_st) == PJ_FALSE) {
+	/* We don't have ICE */
+	return PJ_SUCCESS;
+    }
+
+    comp_cnt = pj_ice_strans_get_running_comp_cnt(tp_ice->ice_st);
+    return encode_session_in_sdp(tp_ice, sdp_pool, loc_sdp, media_index,
+				 comp_cnt, PJ_FALSE);
+}
+
+
+/* Create subsequent SDP answer */
+static pj_status_t create_subsequent_answer(struct transport_ice *tp_ice,
+					    pj_pool_t *sdp_pool,
+					    pjmedia_sdp_session *loc_sdp,
+					    const pjmedia_sdp_session *rem_sdp,
+					    unsigned media_index)
+{
+    pj_status_t status;
+
+    /* We have a session */
+    status = verify_ice_sdp(tp_ice, sdp_pool, rem_sdp, media_index, 
+			    PJ_ICE_SESS_ROLE_CONTROLLED, 
+			    &tp_ice->rem_offer_state);
+    if (status != PJ_SUCCESS) {
+	/* Something wrong with the offer */
+	return status;
+    }
+
+    if (pj_ice_strans_has_sess(tp_ice->ice_st)) {
+	/*
+	 * Received subsequent offer while we have ICE active.
+	 */
+
+	if (tp_ice->rem_offer_state.match_comp_cnt == 0) {
+	    /* Remote no longer offers ICE */
+	    return PJ_SUCCESS;
+	}
+
+	if (tp_ice->rem_offer_state.ice_mismatch) {
+	    encode_ice_mismatch(sdp_pool, loc_sdp, media_index);
+	    return PJ_SUCCESS;
+	}
+
+	status = encode_session_in_sdp(tp_ice, sdp_pool, loc_sdp, media_index,
+				       tp_ice->rem_offer_state.match_comp_cnt,
+				       tp_ice->rem_offer_state.ice_restart);
+	if (status != PJ_SUCCESS)
+	    return status;
+
+	/* Done */
+
+    } else {
+	/*
+	 * Received subsequent offer while we DON'T have ICE active.
+	 */
+
+	if (tp_ice->rem_offer_state.match_comp_cnt == 0) {
+	    /* Remote does not support ICE */
+	    return PJ_SUCCESS;
+	}
+
+	if (tp_ice->rem_offer_state.ice_mismatch) {
+	    encode_ice_mismatch(sdp_pool, loc_sdp, media_index);
+	    return PJ_SUCCESS;
+	}
+
+	/* Looks like now remote is offering ICE, so we need to create
+	 * ICE session now.
+	 */
+	status = pj_ice_strans_init_ice(tp_ice->ice_st, 
+					PJ_ICE_SESS_ROLE_CONTROLLED,
+					NULL, NULL);
+	if (status != PJ_SUCCESS) {
+	    /* Fail to create new ICE session */
+	    return status;
+	}
+
+	status = encode_session_in_sdp(tp_ice, sdp_pool, loc_sdp, media_index,
+				       tp_ice->rem_offer_state.match_comp_cnt,
+				       tp_ice->rem_offer_state.ice_restart);
+	if (status != PJ_SUCCESS)
+	    return status;
+
+	/* Done */
+    }
+
+    return PJ_SUCCESS;
 }
 
 
 /*
- * Start ICE checks when both offer and answer are available.
+ * For both UAC and UAS, pass in the SDP before sending it to remote.
+ * This will add ICE attributes to the SDP.
  */
-static pj_status_t transport_media_start(pjmedia_transport *tp,
-				         pj_pool_t *pool,
-				         pjmedia_sdp_session *sdp_local,
-				         const pjmedia_sdp_session *rem_sdp,
-				         unsigned media_index)
+static pj_status_t transport_media_create(pjmedia_transport *tp,
+				          pj_pool_t *sdp_pool,
+					  unsigned options,
+					  const pjmedia_sdp_session *rem_sdp,
+					  unsigned media_index)
 {
     struct transport_ice *tp_ice = (struct transport_ice*)tp;
-    const pjmedia_sdp_attr *attr;
-    unsigned i, cand_cnt;
-    pj_ice_sess_cand *cand;
-    const pjmedia_sdp_media *sdp_med;
-    pj_bool_t remote_is_lite = PJ_FALSE;
-    pj_bool_t ice_mismatch = PJ_FALSE;
-    pjmedia_sdp_conn *conn = NULL;
-    pj_sockaddr conn_addr;
-    pj_bool_t conn_found_in_candidate = PJ_FALSE;
-    pj_str_t uname, pass;
+    pj_ice_sess_role ice_role;
     pj_status_t status;
 
-    PJ_ASSERT_RETURN(tp && pool && rem_sdp, PJ_EINVAL);
-    PJ_ASSERT_RETURN(media_index < rem_sdp->media_count, PJ_EINVAL);
+    PJ_UNUSED_ARG(media_index);
+    PJ_UNUSED_ARG(sdp_pool);
 
-    sdp_med = rem_sdp->media[media_index];
+    tp_ice->media_option = options;
+    tp_ice->oa_role = ROLE_NONE;
+    tp_ice->initial_sdp = PJ_TRUE;
+
+    /* Init ICE, the initial role is set now based on availability of
+     * rem_sdp, but it will be checked again later.
+     */
+    ice_role = (rem_sdp==NULL ? PJ_ICE_SESS_ROLE_CONTROLLING : 
+				PJ_ICE_SESS_ROLE_CONTROLLED);
+    status = pj_ice_strans_init_ice(tp_ice->ice_st, ice_role, NULL, NULL);
+
+    /* Done */
+    return status;
+}
+
+
+static pj_status_t transport_encode_sdp(pjmedia_transport *tp,
+				        pj_pool_t *sdp_pool,
+				        pjmedia_sdp_session *sdp_local,
+				        const pjmedia_sdp_session *rem_sdp,
+				        unsigned media_index)
+{
+    struct transport_ice *tp_ice = (struct transport_ice*)tp;
+    pj_status_t status;
 
     /* Validate media transport */
-    /* By now, this transport only support RTP/AVP transport */
+    /* For now, this transport only support RTP/AVP transport */
     if ((tp_ice->media_option & PJMEDIA_TPMED_NO_TRANSPORT_CHECKING) == 0) {
-	pjmedia_sdp_media *m_rem, *m_loc;
+	pjmedia_sdp_media *loc_m, *rem_m;
 
-	m_rem = rem_sdp->media[media_index];
-	m_loc = sdp_local->media[media_index];
+	rem_m = rem_sdp? rem_sdp->media[media_index] : NULL;
+	loc_m = sdp_local->media[media_index];
 
-	if (pj_stricmp(&m_loc->desc.transport, &ID_RTP_AVP) ||
-	   (pj_stricmp(&m_rem->desc.transport, &ID_RTP_AVP)))
+	if (pj_stricmp(&loc_m->desc.transport, &STR_RTP_AVP) ||
+	   (rem_m && pj_stricmp(&rem_m->desc.transport, &STR_RTP_AVP)))
 	{
-	    pjmedia_sdp_media_deactivate(pool, m_loc);
+	    pjmedia_sdp_media_deactivate(sdp_pool, loc_m);
 	    return PJMEDIA_SDP_EINPROTO;
 	}
     }
 
-    /* Get the SDP connection for the media stream.
-     * We'll verify later if the SDP connection address is specified 
-     * as one of the candidate.
-     */
-    conn = sdp_med->conn;
-    if (conn == NULL)
-	conn = rem_sdp->conn;
+    if (tp_ice->initial_sdp) {
+	if (rem_sdp) {
+	    status = create_initial_answer(tp_ice, sdp_pool, sdp_local, 
+					   rem_sdp, media_index);
+	} else {
+	    status = create_initial_offer(tp_ice, sdp_pool, sdp_local,
+					  media_index);
+	}
+    } else {
+	if (rem_sdp) {
+	    status = create_subsequent_answer(tp_ice, sdp_pool, sdp_local,
+					      rem_sdp, media_index);
+	} else {
+	    status = create_subsequent_offer(tp_ice, sdp_pool, sdp_local,
+					     media_index);
+	}
+    }
 
-    if (conn == NULL) {
-	/* Unable to find SDP connection */
-	return PJMEDIA_SDP_EMISSINGCONN;
+    if (status==PJ_SUCCESS) {
+	if (rem_sdp)
+	    tp_ice->oa_role = ROLE_ANSWERER;
+	else
+	    tp_ice->oa_role = ROLE_OFFERER;
     }
 
-    pj_sockaddr_in_init(&conn_addr.ipv4, &conn->addr, 
-			(pj_uint16_t)sdp_med->desc.port);
+    return status;
+}
 
-    /* Find ice-ufrag attribute in media descriptor */
-    attr = pjmedia_sdp_attr_find2(sdp_med->attr_count, sdp_med->attr,
-				  "ice-ufrag", NULL);
-    if (attr == NULL) {
-	/* Find ice-ufrag attribute in session descriptor */
-	attr = pjmedia_sdp_attr_find2(rem_sdp->attr_count, rem_sdp->attr,
-				      "ice-ufrag", NULL);
-	if (attr == NULL) {
-	    set_no_ice(tp_ice, "ice-ufrag attribute not found");
-	    return PJ_SUCCESS;
-	}
-    }
-    uname = attr->value;
 
-    /* Find ice-pwd attribute in media descriptor */
-    attr = pjmedia_sdp_attr_find2(sdp_med->attr_count, sdp_med->attr,
-				  "ice-pwd", NULL);
-    if (attr == NULL) {
-	/* Find ice-pwd attribute in session descriptor */
-	attr = pjmedia_sdp_attr_find2(rem_sdp->attr_count, rem_sdp->attr,
-				      "ice-pwd", NULL);
-	if (attr == NULL) {
-	    set_no_ice(tp_ice, "ice-pwd attribute not found");
-	    return PJ_SUCCESS;
-	}
-    }
-    pass = attr->value;
+/* Start ICE session with the specified remote SDP */
+static pj_status_t start_ice(struct transport_ice *tp_ice,
+			     pj_pool_t *tmp_pool,
+			     const pjmedia_sdp_session *rem_sdp,
+			     unsigned media_index)
+{
+    pjmedia_sdp_media *rem_m = rem_sdp->media[media_index];
+    pjmedia_sdp_attr *ufrag_attr, *pwd_attr;
+    pj_ice_sess_cand *cand;
+    unsigned i, cand_cnt;
+    pj_status_t status;
+
+    get_ice_attr(rem_sdp, rem_m, &ufrag_attr, &pwd_attr);
 
     /* Allocate candidate array */
     cand = (pj_ice_sess_cand*)
-	   pj_pool_calloc(pool, PJ_ICE_MAX_CAND, sizeof(pj_ice_sess_cand));
+	   pj_pool_calloc(tmp_pool, PJ_ICE_MAX_CAND, 
+			  sizeof(pj_ice_sess_cand));
 
     /* Get all candidates in the media */
     cand_cnt = 0;
-    for (i=0; i<sdp_med->attr_count && cand_cnt < PJ_ICE_MAX_CAND; ++i) {
+    for (i=0; i<rem_m->attr_count && cand_cnt < PJ_ICE_MAX_CAND; ++i) {
 	pjmedia_sdp_attr *attr;
 
-	attr = sdp_med->attr[i];
+	attr = rem_m->attr[i];
 
-	/* Detect if remote is ICE lite */
-	if (pj_stricmp(&attr->name, &STR_ICE_LITE)==0) {
-	    remote_is_lite = PJ_TRUE;
+	if (pj_strcmp(&attr->name, &STR_CANDIDATE)!=0)
 	    continue;
-	}
 
-	/* Detect if remote has reported ICE mismatch */
-	if (pj_stricmp(&attr->name, &STR_ICE_MISMATCH)==0) {
-	    ice_mismatch = PJ_TRUE;
+	/* Parse candidate */
+	status = parse_cand(tp_ice->base.name, tmp_pool, &attr->value, 
+			    &cand[cand_cnt]);
+	if (status != PJ_SUCCESS) {
+	    PJ_LOG(4,(tp_ice->base.name, 
+		      "Error in parsing SDP candidate attribute '%.*s', "
+		      "candidate is ignored",
+		      (int)attr->value.slen, attr->value.ptr));
 	    continue;
 	}
 
-	if (pj_stricmp(&attr->name, &STR_CANDIDATE)!=0)
-	    continue;
+	cand_cnt++;
+    }
 
-	/* Parse candidate */
-	status = parse_cand(pool, &attr->value, &cand[cand_cnt]);
+    /* Start ICE */
+    return pj_ice_strans_start_ice(tp_ice->ice_st, &ufrag_attr->value, 
+				   &pwd_attr->value, cand_cnt, cand);
+}
+
+
+/*
+ * Start ICE checks when both offer and answer have been negotiated
+ * by SDP negotiator.
+ */
+static pj_status_t transport_media_start(pjmedia_transport *tp,
+				         pj_pool_t *tmp_pool,
+				         const pjmedia_sdp_session *sdp_local,
+				         const pjmedia_sdp_session *rem_sdp,
+				         unsigned media_index)
+{
+    struct transport_ice *tp_ice = (struct transport_ice*)tp;
+    pjmedia_sdp_media *rem_m;
+    enum oa_role current_oa_role;
+    pj_bool_t initial_oa;
+    pj_status_t status;
+
+    PJ_ASSERT_RETURN(tp && tmp_pool && rem_sdp, PJ_EINVAL);
+    PJ_ASSERT_RETURN(media_index < rem_sdp->media_count, PJ_EINVAL);
+
+    rem_m = rem_sdp->media[media_index];
+
+    initial_oa = tp_ice->initial_sdp;
+    current_oa_role = tp_ice->oa_role;
+
+    /* SDP has been negotiated */
+    tp_ice->initial_sdp = PJ_FALSE;
+    tp_ice->oa_role = ROLE_NONE;
+
+    /* Nothing to do if we don't have ICE session */
+    if (pj_ice_strans_has_sess(tp_ice->ice_st) == PJ_FALSE) {
+	return PJ_SUCCESS;
+    }
+
+    /* Processing depends on the offer/answer role */
+    if (current_oa_role == ROLE_OFFERER) {
+	/*
+	 * We are offerer. So this will be the first time we see the
+	 * remote's SDP.
+	 */
+	struct sdp_state answer_state;
+
+	/* Verify the answer */
+	status = verify_ice_sdp(tp_ice, tmp_pool, rem_sdp, media_index, 
+				PJ_ICE_SESS_ROLE_CONTROLLING, &answer_state);
 	if (status != PJ_SUCCESS) {
-	    PJ_LOG(4,(THIS_FILE, 
-		      "Error in parsing SDP candidate attribute, "
-		      "candidate is ignored"));
-	    continue;
+	    /* Something wrong in the SDP answer */
+	    set_no_ice(tp_ice, "Invalid remote SDP answer", status);
+	    return status;
 	}
 
-	/* Check if this candidate is equal to the connection line */
-	if (!conn_found_in_candidate &&
-	    pj_memcmp(&conn_addr.ipv4, &cand[cand_cnt].addr.ipv4,
-		      sizeof(pj_sockaddr_in))==0)
+	/* Does it have ICE? */
+	if (answer_state.match_comp_cnt == 0) {
+	    /* Remote doesn't support ICE */
+	    set_no_ice(tp_ice, "Remote answer doesn't support ICE", 
+		       PJ_SUCCESS);
+	    return PJ_SUCCESS;
+	}
+
+	/* Check if remote has reported ice-mismatch */
+	if (pjmedia_sdp_attr_find(rem_m->attr_count, rem_m->attr, 
+				  &STR_ICE_MISMATCH, NULL) != NULL)
 	{
-	    conn_found_in_candidate = PJ_TRUE;
+	    /* Remote has reported ice-mismatch */
+	    set_no_ice(tp_ice, 
+		       "Remote answer contains 'ice-mismatch' attribute", 
+		       PJ_SUCCESS);
+	    return PJ_SUCCESS;
 	}
 
-	cand_cnt++;
-    }
+	/* Check if remote has indicated a restart */
+	if (answer_state.ice_restart) {
+	    PJ_LOG(2,(tp_ice->base.name, 
+		      "Warning: remote has signalled ICE restart in SDP "
+		      "answer which is disallowed. Remote ICE negotiation"
+		      " may fail."));
+	}
 
-    /* Handle ice-mismatch case */
-    if (ice_mismatch) {
-	set_no_ice(tp_ice, "remote reported ice-mismatch");
-	return PJ_SUCCESS;
-    }
+	/* Check if the answer itself is mismatched */
+	if (answer_state.ice_mismatch) {
+	    /* This happens either when a B2BUA modified remote answer but
+	     * strangely didn't modify our offer, or remote is not capable
+	     * of detecting mismatch in our offer (it didn't put 
+	     * 'ice-mismatch' attribute in the answer).
+	     */
+	    PJ_LOG(2,(tp_ice->base.name, 
+		      "Warning: remote answer mismatch, but it does not "
+		      "reject our offer with 'ice-mismatch'. ICE negotiation "
+		      "may fail"));
+	}
 
-    /* Handle case where SDP connection address is not specified as
-     * one of the candidate.
-     */
-    if (!conn_found_in_candidate) {
-	set_no_ice(tp_ice, "local reported ice-mismatch");
-	return PJ_SUCCESS;
+	/* Do nothing if ICE is complete or running */
+	if (pj_ice_strans_sess_is_running(tp_ice->ice_st)) {
+	    PJ_LOG(4,(tp_ice->base.name,
+		      "Ignored offer/answer because ICE is running"));
+	    return PJ_SUCCESS;
+	}
+
+	if (pj_ice_strans_sess_is_complete(tp_ice->ice_st)) {
+	    PJ_LOG(4,(tp_ice->base.name, "ICE session unchanged"));
+	    return PJ_SUCCESS;
+	}
+
+	/* Start ICE */
+
+    } else {
+	/*
+	 * We are answerer. We've seen and negotiated remote's SDP
+	 * before, and the result is in "rem_offer_state".
+	 */
+	const pjmedia_sdp_attr *ufrag_attr, *pwd_attr;
+
+	/* Check for ICE in remote offer */
+	if (tp_ice->rem_offer_state.match_comp_cnt == 0) {
+	    /* No ICE attribute present */
+	    set_no_ice(tp_ice, "Remote no longer offers ICE",
+		       PJ_SUCCESS);
+	    return PJ_SUCCESS;
+	}
+
+	/* Check for ICE ice_mismatch condition in the offer */
+	if (tp_ice->rem_offer_state.ice_mismatch) {
+	    set_no_ice(tp_ice, "Remote offer mismatch: ", 
+		       PJNATH_EICEMISMATCH);
+	    return PJ_SUCCESS;
+	}
+
+	/* If ICE is complete and remote doesn't request restart,
+	 * then leave the session as is.
+	 */
+	if (!initial_oa && tp_ice->rem_offer_state.ice_restart == PJ_FALSE) {
+	    /* Remote has not requested ICE restart, so session is
+	     * unchanged.
+	     */
+	    PJ_LOG(4,(tp_ice->base.name, "ICE session unchanged"));
+	    return PJ_SUCCESS;
+	}
+
+	/* Either remote has requested ICE restart or this is our
+	 * first answer. 
+	 */
+
+	/* Stop ICE */
+	if (!initial_oa) {
+	    set_no_ice(tp_ice, "restarting by remote request..", PJ_SUCCESS);
+
+	    /* We have put new ICE ufrag and pwd in the answer. Now
+	     * create a new ICE session with that ufrag/pwd pair.
+	     */
+	    get_ice_attr(sdp_local, sdp_local->media[media_index], 
+			 &ufrag_attr, &pwd_attr);
+	    status = pj_ice_strans_init_ice(tp_ice->ice_st, 
+					    tp_ice->rem_offer_state.local_role,
+					    &ufrag_attr->value, 
+					    &pwd_attr->value);
+	    if (status != PJ_SUCCESS) {
+		PJ_LOG(1,(tp_ice->base.name, 
+			  "ICE re-initialization failed (status=%d)!",
+			  status));
+		return status;
+	    }
+	}
+
+	/* start ICE */
     }
 
-    /* If our role was controlled but it turns out that remote is 
-     * a lite implementation, change our role to controlling.
-     */
-    if (remote_is_lite && 
-	pj_ice_strans_get_role(tp_ice->ice_st) == PJ_ICE_SESS_ROLE_CONTROLLED)
-    {
-	pj_ice_strans_change_role(tp_ice->ice_st, 
-				  PJ_ICE_SESS_ROLE_CONTROLLING);
+    /* Now start ICE */
+    status = start_ice(tp_ice, tmp_pool, rem_sdp, media_index);
+    if (status != PJ_SUCCESS) {
+	PJ_LOG(1,(tp_ice->base.name, 
+		  "ICE restart failed (status=%d)!",
+		  status));
+	return status;
     }
 
-    /* Start ICE */
-    return pj_ice_strans_start_ice(tp_ice->ice_st, &uname, &pass, 
-				   cand_cnt, cand);
+    /* Done */
+
+    return PJ_SUCCESS;
 }
 
 
 static pj_status_t transport_media_stop(pjmedia_transport *tp)
 {
     struct transport_ice *tp_ice = (struct transport_ice*)tp;
-    return pj_ice_strans_stop_ice(tp_ice->ice_st);
+    
+    set_no_ice(tp_ice, "media stop requested", PJ_SUCCESS);
+
+    return PJ_SUCCESS;
 }
 
 
diff --git a/pjmedia/src/pjmedia/transport_srtp.c b/pjmedia/src/pjmedia/transport_srtp.c
index 6f3c06fc..c69296bd 100644
--- a/pjmedia/src/pjmedia/transport_srtp.c
+++ b/pjmedia/src/pjmedia/transport_srtp.c
@@ -91,6 +91,10 @@ typedef struct transport_srtp
     pjmedia_srtp_crypto  tx_policy;
     pjmedia_srtp_crypto  rx_policy;
 
+    /* Temporary policy for negotiation */
+    pjmedia_srtp_crypto  tx_policy_neg;
+    pjmedia_srtp_crypto  rx_policy_neg;
+
     /* libSRTP contexts */
     srtp_t		 srtp_tx_ctx;
     srtp_t		 srtp_rx_ctx;
@@ -105,7 +109,15 @@ typedef struct transport_srtp
 				   pj_ssize_t size);
         
     /* Transport information */
-    pjmedia_transport	*real_tp; /**< Underlying transport.       */
+    pjmedia_transport	*member_tp; /**< Underlying transport.       */
+
+    /* When in SRTP optional mode, instead of always offering RTP/AVP,
+     * we should create offer based on remote preference. At the first time,
+     * remote preference is unknown, it is known after media_start() called.
+     * So next time the same session need to create an offer, it will create
+     * SDP with transport type based on remote preference.
+     */
+    pj_bool_t		 remote_prefer_rtp_savp;
 
 } transport_srtp;
 
@@ -151,14 +163,18 @@ static pj_status_t transport_send_rtcp2(pjmedia_transport *tp,
 				       const void *pkt,
 				       pj_size_t size);
 static pj_status_t transport_media_create(pjmedia_transport *tp,
-				       pj_pool_t *pool,
+				       pj_pool_t *sdp_pool,
 				       unsigned options,
+				       const pjmedia_sdp_session *sdp_remote,
+				       unsigned media_index);
+static pj_status_t transport_encode_sdp(pjmedia_transport *tp,
+				       pj_pool_t *sdp_pool,
 				       pjmedia_sdp_session *sdp_local,
 				       const pjmedia_sdp_session *sdp_remote,
 				       unsigned media_index);
 static pj_status_t transport_media_start (pjmedia_transport *tp,
 				       pj_pool_t *pool,
-				       pjmedia_sdp_session *sdp_local,
+				       const pjmedia_sdp_session *sdp_local,
 				       const pjmedia_sdp_session *sdp_remote,
 				       unsigned media_index);
 static pj_status_t transport_media_stop(pjmedia_transport *tp);
@@ -178,6 +194,7 @@ static pjmedia_transport_op transport_srtp_op =
     &transport_send_rtcp,
     &transport_send_rtcp2,
     &transport_media_create,
+    &transport_encode_sdp,
     &transport_media_start,
     &transport_media_stop,
     &transport_simulate_lost,
@@ -331,6 +348,7 @@ PJ_DEF(pj_status_t) pjmedia_transport_srtp_create(
     srtp->pool = pool;
     srtp->session_inited = PJ_FALSE;
     srtp->bypass_srtp = PJ_FALSE;
+    srtp->remote_prefer_rtp_savp = PJ_FALSE;
 
     if (opt) {
 	srtp->setting = *opt;
@@ -367,7 +385,7 @@ PJ_DEF(pj_status_t) pjmedia_transport_srtp_create(
     srtp->base.op = &transport_srtp_op;
 
     /* Set underlying transport */
-    srtp->real_tp = tp;
+    srtp->member_tp = tp;
 
     /* Done */
     *p_tp = &srtp->base;
@@ -457,8 +475,7 @@ PJ_DEF(pj_status_t) pjmedia_transport_srtp_start(
     }
     srtp->tx_policy = *tx;
     pj_strset(&srtp->tx_policy.key,  srtp->tx_key, tx->key.slen);
-    srtp->tx_policy.name = 
-			pj_str(crypto_suites[get_crypto_idx(&tx->name)].name);
+    srtp->tx_policy.name=pj_str(crypto_suites[get_crypto_idx(&tx->name)].name);
 
 
     /* Init receive direction */
@@ -491,8 +508,7 @@ PJ_DEF(pj_status_t) pjmedia_transport_srtp_start(
     }
     srtp->rx_policy = *rx;
     pj_strset(&srtp->rx_policy.key,  srtp->rx_key, rx->key.slen);
-    srtp->rx_policy.name = 
-			pj_str(crypto_suites[get_crypto_idx(&rx->name)].name);
+    srtp->rx_policy.name=pj_str(crypto_suites[get_crypto_idx(&rx->name)].name);
 
     /* Declare SRTP session initialized */
     srtp->session_inited = PJ_TRUE;
@@ -550,7 +566,7 @@ PJ_DEF(pjmedia_transport *) pjmedia_transport_srtp_get_member(
 
     PJ_ASSERT_RETURN(tp, NULL);
 
-    return srtp->real_tp;
+    return srtp->member_tp;
 }
 
 
@@ -577,7 +593,7 @@ static pj_status_t transport_get_info(pjmedia_transport *tp,
     pj_memcpy(&info->spc_info[spc_info_idx].buffer, &srtp_info, 
 	      sizeof(srtp_info));
 
-    return pjmedia_transport_get_info(srtp->real_tp, info);
+    return pjmedia_transport_get_info(srtp->member_tp, info);
 }
 
 static pj_status_t transport_attach(pjmedia_transport *tp,
@@ -594,7 +610,7 @@ static pj_status_t transport_attach(pjmedia_transport *tp,
     pj_status_t status;
 
     /* Attach itself to transport */
-    status = pjmedia_transport_attach(srtp->real_tp, srtp, rem_addr, rem_rtcp,
+    status = pjmedia_transport_attach(srtp->member_tp, srtp, rem_addr, rem_rtcp,
 				      addr_len, &srtp_rtp_cb, &srtp_rtcp_cb);
     if (status != PJ_SUCCESS)
 	return status;
@@ -614,8 +630,8 @@ static void transport_detach(pjmedia_transport *tp, void *strm)
     PJ_UNUSED_ARG(strm);
     PJ_ASSERT_ON_FAIL(tp, return);
 
-    if (srtp->real_tp) {
-	pjmedia_transport_detach(srtp->real_tp, srtp);
+    if (srtp->member_tp) {
+	pjmedia_transport_detach(srtp->member_tp, srtp);
     }
 
     /* Clear up application infos from transport */
@@ -634,7 +650,7 @@ static pj_status_t transport_send_rtp( pjmedia_transport *tp,
     err_status_t err;
 
     if (srtp->bypass_srtp)
-	return pjmedia_transport_send_rtp(srtp->real_tp, pkt, size);
+	return pjmedia_transport_send_rtp(srtp->member_tp, pkt, size);
 
     if (!srtp->session_inited)
 	return PJ_SUCCESS;
@@ -647,7 +663,7 @@ static pj_status_t transport_send_rtp( pjmedia_transport *tp,
     
     err = srtp_protect(srtp->srtp_tx_ctx, srtp->tx_buffer, &len);
     if (err == err_status_ok) {
-	status = pjmedia_transport_send_rtp(srtp->real_tp, srtp->tx_buffer, len);
+	status = pjmedia_transport_send_rtp(srtp->member_tp, srtp->tx_buffer, len);
     } else {
 	status = PJMEDIA_ERRNO_FROM_LIBSRTP(err);
     }
@@ -676,7 +692,7 @@ static pj_status_t transport_send_rtcp2(pjmedia_transport *tp,
     err_status_t err;
 
     if (srtp->bypass_srtp) {
-	return pjmedia_transport_send_rtcp2(srtp->real_tp, addr, addr_len, 
+	return pjmedia_transport_send_rtcp2(srtp->member_tp, addr, addr_len, 
 	                                    pkt, size);
     }
 
@@ -692,7 +708,7 @@ static pj_status_t transport_send_rtcp2(pjmedia_transport *tp,
     err = srtp_protect_rtcp(srtp->srtp_tx_ctx, srtp->tx_buffer, &len);
     
     if (err == err_status_ok) {
-	status = pjmedia_transport_send_rtcp2(srtp->real_tp, addr, addr_len,
+	status = pjmedia_transport_send_rtcp2(srtp->member_tp, addr, addr_len,
 					      srtp->tx_buffer, len);
     } else {
 	status = PJMEDIA_ERRNO_FROM_LIBSRTP(err);
@@ -710,7 +726,7 @@ static pj_status_t transport_simulate_lost(pjmedia_transport *tp,
 {
     transport_srtp *srtp = (transport_srtp *) tp;
 
-    return pjmedia_transport_simulate_lost(srtp->real_tp, dir, pct_lost);
+    return pjmedia_transport_simulate_lost(srtp->member_tp, dir, pct_lost);
 }
 
 static pj_status_t transport_destroy  (pjmedia_transport *tp)
@@ -722,8 +738,8 @@ static pj_status_t transport_destroy  (pjmedia_transport *tp)
 
     pjmedia_transport_detach(tp, NULL);
     
-    if (srtp->setting.close_member_tp && srtp->real_tp) {
-	pjmedia_transport_close(srtp->real_tp);
+    if (srtp->setting.close_member_tp && srtp->member_tp) {
+	pjmedia_transport_close(srtp->member_tp);
     }
 
     status = pjmedia_transport_srtp_stop(tp);
@@ -955,13 +971,75 @@ static pj_status_t parse_attr_crypto(pj_pool_t *pool,
 }
 
 static pj_status_t transport_media_create(pjmedia_transport *tp,
-				          pj_pool_t *pool,
+				          pj_pool_t *sdp_pool,
 					  unsigned options,
-				          pjmedia_sdp_session *sdp_local,
 				          const pjmedia_sdp_session *sdp_remote,
 					  unsigned media_index)
 {
     struct transport_srtp *srtp = (struct transport_srtp*) tp;
+    unsigned member_tp_option;
+
+    PJ_ASSERT_RETURN(tp, PJ_EINVAL);
+    
+    pj_bzero(&srtp->rx_policy_neg, sizeof(srtp->rx_policy_neg));
+    pj_bzero(&srtp->tx_policy_neg, sizeof(srtp->tx_policy_neg));
+
+    srtp->media_option = options;
+    member_tp_option = options | PJMEDIA_TPMED_NO_TRANSPORT_CHECKING;
+
+    srtp->offerer_side = sdp_remote == NULL;
+
+    /* Validations */
+    if (srtp->offerer_side) {
+
+	if (srtp->setting.use == PJMEDIA_SRTP_DISABLED)
+	    goto BYPASS_SRTP;
+
+    } else {
+
+	pjmedia_sdp_media *m_rem;
+	
+	m_rem = sdp_remote->media[media_index];
+
+	/* Nothing to do on inactive media stream */
+	if (pjmedia_sdp_media_find_attr(m_rem, &ID_INACTIVE, NULL))
+	    goto BYPASS_SRTP;
+
+	/* Validate remote media transport based on SRTP usage option.
+	 */
+	switch (srtp->setting.use) {
+	    case PJMEDIA_SRTP_DISABLED:
+		if (pj_stricmp(&m_rem->desc.transport, &ID_RTP_SAVP) == 0)
+		    return PJMEDIA_SRTP_ESDPINTRANSPORT;
+		goto BYPASS_SRTP;
+	    case PJMEDIA_SRTP_OPTIONAL:
+		break;
+	    case PJMEDIA_SRTP_MANDATORY:
+		if (pj_stricmp(&m_rem->desc.transport, &ID_RTP_SAVP) != 0)
+		    return PJMEDIA_SRTP_ESDPINTRANSPORT;
+		break;
+	}
+
+    }
+    goto PROPAGATE_MEDIA_CREATE;
+
+BYPASS_SRTP:
+    srtp->bypass_srtp = PJ_TRUE;
+    member_tp_option &= ~PJMEDIA_TPMED_NO_TRANSPORT_CHECKING;
+
+PROPAGATE_MEDIA_CREATE:
+    return pjmedia_transport_media_create(srtp->member_tp, sdp_pool, 
+					  member_tp_option, sdp_remote,
+					  media_index);
+}
+
+static pj_status_t transport_encode_sdp(pjmedia_transport *tp,
+					pj_pool_t *sdp_pool,
+					pjmedia_sdp_session *sdp_local,
+					const pjmedia_sdp_session *sdp_remote,
+					unsigned media_index)
+{
+    struct transport_srtp *srtp = (struct transport_srtp*) tp;
     pjmedia_sdp_media *m_rem, *m_loc;
     enum { MAXLEN = 512 };
     char buffer[MAXLEN];
@@ -970,20 +1048,15 @@ static pj_status_t transport_media_create(pjmedia_transport *tp,
     pjmedia_sdp_attr *attr;
     pj_str_t attr_value;
     unsigned i, j;
-    unsigned member_tp_option;
 
-    PJ_ASSERT_RETURN(tp && pool && sdp_local, PJ_EINVAL);
+    PJ_ASSERT_RETURN(tp && sdp_pool && sdp_local, PJ_EINVAL);
     
-    srtp->media_option = options;
-    member_tp_option = options | PJMEDIA_TPMED_NO_TRANSPORT_CHECKING;
-
-    pj_bzero(&srtp->rx_policy, sizeof(srtp->tx_policy));
-    pj_bzero(&srtp->tx_policy, sizeof(srtp->rx_policy));
+    srtp->offerer_side = sdp_remote == NULL;
 
     m_rem = sdp_remote ? sdp_remote->media[media_index] : NULL;
     m_loc = sdp_local->media[media_index];
 
-    /* bypass if media transport is not RTP/AVP or RTP/SAVP */
+    /* Bypass if media transport is not RTP/AVP or RTP/SAVP */
     if (pj_stricmp(&m_loc->desc.transport, &ID_RTP_AVP)  != 0 && 
 	pj_stricmp(&m_loc->desc.transport, &ID_RTP_SAVP) != 0)
 	goto BYPASS_SRTP;
@@ -991,195 +1064,209 @@ static pj_status_t transport_media_create(pjmedia_transport *tp,
     /* If the media is inactive, do nothing. */
     if (pjmedia_sdp_media_find_attr(m_loc, &ID_INACTIVE, NULL) || 
 	(m_rem && pjmedia_sdp_media_find_attr(m_rem, &ID_INACTIVE, NULL)))
-    {
 	goto BYPASS_SRTP;
-    }
-
-    srtp->offerer_side = !sdp_remote;
 
     /* Check remote media transport & set local media transport 
      * based on SRTP usage option.
      */
     if (srtp->offerer_side) {
-	if (srtp->setting.use == PJMEDIA_SRTP_DISABLED) {
-	    goto BYPASS_SRTP;
-	} else if (srtp->setting.use == PJMEDIA_SRTP_OPTIONAL) {
-	    m_loc->desc.transport = ID_RTP_AVP;
-	} else if (srtp->setting.use == PJMEDIA_SRTP_MANDATORY) {
-	    m_loc->desc.transport = ID_RTP_SAVP;
+
+	/* Generate transport */
+	switch (srtp->setting.use) {
+	    case PJMEDIA_SRTP_DISABLED:
+		goto BYPASS_SRTP;
+	    case PJMEDIA_SRTP_OPTIONAL:
+		m_loc->desc.transport = srtp->remote_prefer_rtp_savp?
+					ID_RTP_SAVP : ID_RTP_AVP;
+		break;
+	    case PJMEDIA_SRTP_MANDATORY:
+		m_loc->desc.transport = ID_RTP_SAVP;
+		break;
 	}
-    } else {
-	if (srtp->setting.use == PJMEDIA_SRTP_DISABLED) {
-	    if (pj_stricmp(&m_rem->desc.transport, &ID_RTP_SAVP) == 0) {
-		DEACTIVATE_MEDIA(pool, m_loc);
-		return PJMEDIA_SRTP_ESDPINTRANSPORT;
+
+	/* Generate crypto attribute if not yet */
+	if (pjmedia_sdp_media_find_attr(m_loc, &ID_CRYPTO, NULL) == NULL) {
+	    for (i=0; i<srtp->setting.crypto_count; ++i) {
+		/* Offer crypto-suites based on setting. */
+		buffer_len = MAXLEN;
+		status = generate_crypto_attr_value(srtp->pool, buffer, &buffer_len,
+						    &srtp->setting.crypto[i],
+						    i+1);
+		if (status != PJ_SUCCESS)
+		    return status;
+
+		/* If buffer_len==0, just skip the crypto attribute. */
+		if (buffer_len) {
+		    pj_strset(&attr_value, buffer, buffer_len);
+		    attr = pjmedia_sdp_attr_create(srtp->pool, ID_CRYPTO.ptr, 
+						   &attr_value);
+		    m_loc->attr[m_loc->attr_count++] = attr;
+		}
 	    }
-	    goto BYPASS_SRTP;
-	} else if (srtp->setting.use == PJMEDIA_SRTP_OPTIONAL) {
+	}
+
+    } else {
+	/* Answerer side */
+
+	pj_assert(sdp_remote && m_rem);
+
+	/* Generate transport */
+	switch (srtp->setting.use) {
+	    case PJMEDIA_SRTP_DISABLED:
+		if (pj_stricmp(&m_rem->desc.transport, &ID_RTP_SAVP) == 0)
+		    return PJMEDIA_SRTP_ESDPINTRANSPORT;
+		goto BYPASS_SRTP;
+	    case PJMEDIA_SRTP_OPTIONAL:
 		m_loc->desc.transport = m_rem->desc.transport;
-	} else if (srtp->setting.use == PJMEDIA_SRTP_MANDATORY) {
-	    if (pj_stricmp(&m_rem->desc.transport, &ID_RTP_SAVP) != 0) {
-		DEACTIVATE_MEDIA(pool, m_loc);
-		return PJMEDIA_SRTP_ESDPINTRANSPORT;
-	    }
-	    m_loc->desc.transport = ID_RTP_SAVP;
+		break;
+	    case PJMEDIA_SRTP_MANDATORY:
+		if (pj_stricmp(&m_rem->desc.transport, &ID_RTP_SAVP) != 0)
+		    return PJMEDIA_SRTP_ESDPINTRANSPORT;
+		m_loc->desc.transport = ID_RTP_SAVP;
+		break;
 	}
-    }
 
-    /* Generate crypto attribute */
-    if (srtp->offerer_side) {
-	for (i=0; i<srtp->setting.crypto_count; ++i) {
-	    /* Offer crypto-suites based on setting. */
+	/* Generate crypto attribute if not yet */
+	if (pjmedia_sdp_media_find_attr(m_loc, &ID_CRYPTO, NULL) == NULL) {
+
+	    pjmedia_srtp_crypto tmp_rx_crypto;
+	    pj_bool_t has_crypto_attr = PJ_FALSE;
+	    int matched_idx = -1;
+	    int chosen_tag = 0;
+	    int tags[64]; /* assume no more than 64 crypto attrs in a media */
+	    int cr_attr_count = 0;
+
+	    /* Find supported crypto-suite, get the tag, and assign policy_local */
+	    for (i=0; i<m_rem->attr_count; ++i) {
+		if (pj_stricmp(&m_rem->attr[i]->name, &ID_CRYPTO) != 0)
+		    continue;
+
+		has_crypto_attr = PJ_TRUE;
+
+		status = parse_attr_crypto(srtp->pool, m_rem->attr[i], 
+					   &tmp_rx_crypto, &tags[cr_attr_count]);
+		if (status != PJ_SUCCESS)
+		    return status;
+    	 
+		/* Check duplicated tag */
+		for (j=0; j<cr_attr_count; ++j) {
+		    if (tags[j] == tags[cr_attr_count]) {
+			DEACTIVATE_MEDIA(sdp_pool, m_loc);
+			return PJMEDIA_SRTP_ESDPDUPCRYPTOTAG;
+		    }
+		}
+
+		if (matched_idx == -1) {
+		    /* lets see if the crypto-suite offered is supported */
+		    for (j=0; j<srtp->setting.crypto_count; ++j)
+			if (pj_stricmp(&tmp_rx_crypto.name, 
+				       &srtp->setting.crypto[j].name) == 0)
+			{
+			    int cs_idx = get_crypto_idx(&tmp_rx_crypto.name);
+
+			    /* Force to use test key */
+			    /* bad keys for snom: */
+			    //char *hex_test_key = "58b29c5c8f42308120ce857e439f2d"
+			    //		     "7810a8b10ad0b1446be5470faea496";
+			    //char *hex_test_key = "20a26aac7ba062d356ff52b61e3993"
+			    //		     "ccb78078f12c64db94b9c294927fd0";
+			    //pj_str_t *test_key = &srtp->setting.crypto[j].key;
+			    //char  *raw_test_key = pj_pool_zalloc(srtp->pool, 64);
+			    //hex_string_to_octet_string(
+			    //		raw_test_key,
+			    //		hex_test_key,
+			    //		strlen(hex_test_key));
+			    //pj_strset(test_key, raw_test_key, 
+			    //	  crypto_suites[cs_idx].cipher_key_len);
+			    /* EO Force to use test key */
+
+			    if (tmp_rx_crypto.key.slen != 
+				(int)crypto_suites[cs_idx].cipher_key_len)
+				return PJMEDIA_SRTP_EINKEYLEN;
+
+			    srtp->rx_policy_neg = tmp_rx_crypto;
+			    chosen_tag = tags[cr_attr_count];
+			    matched_idx = j;
+    			    break;
+			}
+		}
+		cr_attr_count++;
+	    }
+
+	    /* Check crypto negotiation result */
+	    switch (srtp->setting.use) {
+		case PJMEDIA_SRTP_DISABLED:
+		    pj_assert(!"Should never reach here");
+		    break;
+
+		case PJMEDIA_SRTP_OPTIONAL:
+		    /* bypass SRTP when no crypto-attr and remote uses RTP/AVP */
+		    if (!has_crypto_attr && 
+			pj_stricmp(&m_rem->desc.transport, &ID_RTP_AVP) == 0)
+			goto BYPASS_SRTP;
+		    /* bypass SRTP when nothing match and remote uses RTP/AVP */
+		    else if (matched_idx == -1 && 
+			pj_stricmp(&m_rem->desc.transport, &ID_RTP_AVP) == 0)
+			goto BYPASS_SRTP;
+		    break;
+
+		case PJMEDIA_SRTP_MANDATORY:
+		    /* Do nothing, intentional */
+		    break;
+	    }
+
+	    /* No crypto attr */
+	    if (!has_crypto_attr) {
+		DEACTIVATE_MEDIA(sdp_pool, m_loc);
+		return PJMEDIA_SRTP_ESDPREQCRYPTO;
+	    }
+
+	    /* No crypto match */
+	    if (matched_idx == -1) {
+		DEACTIVATE_MEDIA(sdp_pool, m_loc);
+		return PJMEDIA_SRTP_ENOTSUPCRYPTO;
+	    }
+
+	    /* we have to generate crypto answer, 
+	     * with srtp->tx_policy_neg matched the offer
+	     * and rem_tag contains matched offer tag.
+	     */
 	    buffer_len = MAXLEN;
 	    status = generate_crypto_attr_value(srtp->pool, buffer, &buffer_len,
-						&srtp->setting.crypto[i],
-						i+1);
+						&srtp->setting.crypto[matched_idx],
+						chosen_tag);
 	    if (status != PJ_SUCCESS)
 		return status;
 
+	    srtp->tx_policy_neg = srtp->setting.crypto[matched_idx];
+	    
 	    /* If buffer_len==0, just skip the crypto attribute. */
 	    if (buffer_len) {
 		pj_strset(&attr_value, buffer, buffer_len);
-		attr = pjmedia_sdp_attr_create(srtp->pool, ID_CRYPTO.ptr, 
+		attr = pjmedia_sdp_attr_create(sdp_pool, ID_CRYPTO.ptr, 
 					       &attr_value);
 		m_loc->attr[m_loc->attr_count++] = attr;
 	    }
-	}
-    } else {
-	/* find supported crypto-suite, get the tag, and assign policy_local */
-	pjmedia_srtp_crypto tmp_rx_crypto;
-	pj_bool_t has_crypto_attr = PJ_FALSE;
-	pj_bool_t has_match = PJ_FALSE;
-	int chosen_tag = 0;
-	int tags[64]; /* assume no more than 64 crypto attrs in a media */
-	int cr_attr_count = 0;
-	int k;
-
-	for (i=0; i<m_rem->attr_count; ++i) {
-	    if (pj_stricmp(&m_rem->attr[i]->name, &ID_CRYPTO) != 0)
-		continue;
 
-	    has_crypto_attr = PJ_TRUE;
-
-	    status = parse_attr_crypto(srtp->pool, m_rem->attr[i], 
-				       &tmp_rx_crypto, &tags[cr_attr_count]);
-	    if (status != PJ_SUCCESS)
-		return status;
-	 
-	    /* Check duplicated tag */
-	    for (k=0; k<cr_attr_count; ++k) {
-		if (tags[k] == tags[cr_attr_count]) {
-		    DEACTIVATE_MEDIA(pool, m_loc);
-		    return PJMEDIA_SRTP_ESDPDUPCRYPTOTAG;
-		}
-	    }
-
-	    if (!has_match) {
-		/* lets see if the crypto-suite offered is supported */
-		for (j=0; j<srtp->setting.crypto_count; ++j)
-		    if (pj_stricmp(&tmp_rx_crypto.name, 
-				   &srtp->setting.crypto[j].name) == 0)
-		    {
-			int cs_idx = get_crypto_idx(&tmp_rx_crypto.name);
-
-			/* Force to use test key */
-			/* bad keys for snom: */
-			//char *hex_test_key = "58b29c5c8f42308120ce857e439f2d"
-			//		     "7810a8b10ad0b1446be5470faea496";
-			//char *hex_test_key = "20a26aac7ba062d356ff52b61e3993"
-			//		     "ccb78078f12c64db94b9c294927fd0";
-			//pj_str_t *test_key = &srtp->setting.crypto[j].key;
-			//char  *raw_test_key = pj_pool_zalloc(srtp->pool, 64);
-			//hex_string_to_octet_string(
-			//		raw_test_key,
-			//		hex_test_key,
-			//		strlen(hex_test_key));
-			//pj_strset(test_key, raw_test_key, 
-			//	  crypto_suites[cs_idx].cipher_key_len);
-			/* EO Force to use test key */
-
-			if (tmp_rx_crypto.key.slen != 
-			    (int)crypto_suites[cs_idx].cipher_key_len)
-			    return PJMEDIA_SRTP_EINKEYLEN;
-
-			srtp->tx_policy = srtp->setting.crypto[j];
-			srtp->rx_policy = tmp_rx_crypto;
-			chosen_tag = tags[cr_attr_count];
-			has_match = PJ_TRUE;
-    			break;
-		    }
-	    }
-	    cr_attr_count++;
-	}
-
-	if (srtp->setting.use == PJMEDIA_SRTP_DISABLED) {
-	    /* bypass when remote uses RTP/AVP and we disable SRTP */
-	    goto BYPASS_SRTP;
-	} else if (srtp->setting.use == PJMEDIA_SRTP_OPTIONAL) {
-	    /* bypass SRTP when no crypto-attr but remote uses RTP/AVP */
-	    if (!has_crypto_attr && 
-		pj_stricmp(&m_rem->desc.transport, &ID_RTP_AVP) == 0)
-		goto BYPASS_SRTP;
-	    /* bypass SRTP when nothing match but remote uses RTP/AVP */
-	    if (!has_match && 
-		pj_stricmp(&m_rem->desc.transport, &ID_RTP_AVP) == 0)
-		goto BYPASS_SRTP;
-	} else if (srtp->setting.use == PJMEDIA_SRTP_MANDATORY) {
-	    /* do nothing, this is intended */
-	}
-
-	/* No crypto attr */
-	if (!has_crypto_attr) {
-	    DEACTIVATE_MEDIA(pool, m_loc);
-	    return PJMEDIA_SRTP_ESDPREQCRYPTO;
-	}
-
-	/* No crypto match */
-	if (!has_match) {
-	    DEACTIVATE_MEDIA(pool, m_loc);
-	    return PJMEDIA_SRTP_ENOTSUPCRYPTO;
+	    /* At this point, we get valid rx_policy_neg & tx_policy_neg. */
 	}
-
-	/* we have to generate crypto answer, 
-	 * with srtp->tx_policy matched the offer
-	 * and rem_tag contains matched offer tag.
-	 */
-	buffer_len = MAXLEN;
-	status = generate_crypto_attr_value(srtp->pool, buffer, &buffer_len,
-					    &srtp->tx_policy,
-					    chosen_tag);
-	if (status != PJ_SUCCESS)
-	    return status;
-
-	/* If buffer_len==0, just skip the crypto attribute. */
-	if (buffer_len) {
-	    pj_strset(&attr_value, buffer, buffer_len);
-	    attr = pjmedia_sdp_attr_create(srtp->pool, ID_CRYPTO.ptr, 
-					   &attr_value);
-	    m_loc->attr[m_loc->attr_count++] = attr;
-	}
-
-	/* At this point,
-	 * we should have valid rx_policy & tx_policy.
-	 */
+	    
     }
     goto PROPAGATE_MEDIA_CREATE;
 
 BYPASS_SRTP:
     srtp->bypass_srtp = PJ_TRUE;
-    member_tp_option &= ~PJMEDIA_TPMED_NO_TRANSPORT_CHECKING;
 
 PROPAGATE_MEDIA_CREATE:
-    return pjmedia_transport_media_create(srtp->real_tp, pool, 
-			    member_tp_option,
-			    sdp_local, sdp_remote, media_index);
+    return pjmedia_transport_encode_sdp(srtp->member_tp, sdp_pool, 
+					sdp_local, sdp_remote, media_index);
 }
 
 
 
 static pj_status_t transport_media_start(pjmedia_transport *tp,
 				         pj_pool_t *pool,
-				         pjmedia_sdp_session *sdp_local,
+				         const pjmedia_sdp_session *sdp_local,
 				         const pjmedia_sdp_session *sdp_remote,
 				         unsigned media_index)
 {
@@ -1196,6 +1283,9 @@ static pj_status_t transport_media_start(pjmedia_transport *tp,
     m_rem = sdp_remote->media[media_index];
     m_loc = sdp_local->media[media_index];
 
+    srtp->remote_prefer_rtp_savp = (pj_stricmp(&m_rem->desc.transport, 
+				   &ID_RTP_SAVP) == 0);
+
     /* For answerer side, this function will just have to start SRTP */
 
     /* Check remote media transport & set local media transport 
@@ -1263,8 +1353,8 @@ static pj_status_t transport_media_start(pjmedia_transport *tp,
 		return PJMEDIA_SRTP_ECRYPTONOTMATCH;
 	    }
 
-	    srtp->tx_policy = srtp->setting.crypto[rem_tag-1];
-	    srtp->rx_policy = tmp_tx_crypto;
+	    srtp->tx_policy_neg = srtp->setting.crypto[rem_tag-1];
+	    srtp->rx_policy_neg = tmp_tx_crypto;
 	}
 
 	if (srtp->setting.use == PJMEDIA_SRTP_DISABLED) {
@@ -1280,13 +1370,11 @@ static pj_status_t transport_media_start(pjmedia_transport *tp,
 	    }
 	}
 
-	/* At this point,
-	 * we should have valid rx_policy & tx_policy.
-	 */
+	/* At this point, we get valid rx_policy_neg & tx_policy_neg. */
     }
 
     /* Got policy_local & policy_remote, let's initalize the SRTP */
-    status = pjmedia_transport_srtp_start(tp, &srtp->tx_policy, &srtp->rx_policy);
+    status = pjmedia_transport_srtp_start(tp, &srtp->tx_policy_neg, &srtp->rx_policy_neg);
     if (status != PJ_SUCCESS)
 	return status;
 
@@ -1296,7 +1384,7 @@ BYPASS_SRTP:
     srtp->bypass_srtp = PJ_TRUE;
 
 PROPAGATE_MEDIA_START:
-    return pjmedia_transport_media_start(srtp->real_tp, pool, 
+    return pjmedia_transport_media_start(srtp->member_tp, pool, 
 					 sdp_local, sdp_remote,
 				         media_index);
 }
@@ -1306,7 +1394,7 @@ static pj_status_t transport_media_stop(pjmedia_transport *tp)
     struct transport_srtp *srtp = (struct transport_srtp*) tp;
     pj_status_t status;
 
-    status = pjmedia_transport_media_stop(srtp->real_tp);
+    status = pjmedia_transport_media_stop(srtp->member_tp);
     if (status != PJ_SUCCESS)
 	PJ_LOG(4, (srtp->pool->obj_name, 
 		   "SRTP failed stop underlying media transport."));
diff --git a/pjmedia/src/pjmedia/transport_udp.c b/pjmedia/src/pjmedia/transport_udp.c
index 0804b8bf..4fd6f919 100644
--- a/pjmedia/src/pjmedia/transport_udp.c
+++ b/pjmedia/src/pjmedia/transport_udp.c
@@ -129,12 +129,16 @@ static pj_status_t transport_send_rtcp2(pjmedia_transport *tp,
 static pj_status_t transport_media_create(pjmedia_transport *tp,
 				       pj_pool_t *pool,
 				       unsigned options,
-				       pjmedia_sdp_session *sdp_local,
 				       const pjmedia_sdp_session *sdp_remote,
 				       unsigned media_index);
+static pj_status_t transport_encode_sdp(pjmedia_transport *tp,
+				        pj_pool_t *pool,
+				        pjmedia_sdp_session *sdp_local,
+				        const pjmedia_sdp_session *rem_sdp,
+				        unsigned media_index);
 static pj_status_t transport_media_start (pjmedia_transport *tp,
 				       pj_pool_t *pool,
-				       pjmedia_sdp_session *sdp_local,
+				       const pjmedia_sdp_session *sdp_local,
 				       const pjmedia_sdp_session *sdp_remote,
 				       unsigned media_index);
 static pj_status_t transport_media_stop(pjmedia_transport *tp);
@@ -153,6 +157,7 @@ static pjmedia_transport_op transport_udp_op =
     &transport_send_rtcp,
     &transport_send_rtcp2,
     &transport_media_create,
+    &transport_encode_sdp,
     &transport_media_start,
     &transport_media_stop,
     &transport_simulate_lost,
@@ -790,21 +795,34 @@ static pj_status_t transport_send_rtcp2(pjmedia_transport *tp,
 static pj_status_t transport_media_create(pjmedia_transport *tp,
 				  pj_pool_t *pool,
 				  unsigned options,
-				  pjmedia_sdp_session *sdp_local,
 				  const pjmedia_sdp_session *sdp_remote,
 				  unsigned media_index)
 {
     struct transport_udp *udp = (struct transport_udp*)tp;
 
-    PJ_ASSERT_RETURN(tp && pool && sdp_local, PJ_EINVAL);
+    PJ_ASSERT_RETURN(tp && pool, PJ_EINVAL);
     udp->media_options = options;
 
+    PJ_UNUSED_ARG(sdp_remote);
+    PJ_UNUSED_ARG(media_index);
+
+    return PJ_SUCCESS;
+}
+
+static pj_status_t transport_encode_sdp(pjmedia_transport *tp,
+				        pj_pool_t *pool,
+				        pjmedia_sdp_session *sdp_local,
+				        const pjmedia_sdp_session *rem_sdp,
+				        unsigned media_index)
+{
+    struct transport_udp *udp = (struct transport_udp*)tp;
+
     /* Validate media transport */
     /* By now, this transport only support RTP/AVP transport */
     if ((udp->media_options & PJMEDIA_TPMED_NO_TRANSPORT_CHECKING) == 0) {
 	pjmedia_sdp_media *m_rem, *m_loc;
 
-	m_rem = sdp_remote? sdp_remote->media[media_index] : NULL;
+	m_rem = rem_sdp? rem_sdp->media[media_index] : NULL;
 	m_loc = sdp_local->media[media_index];
 
 	if (pj_stricmp(&m_loc->desc.transport, &ID_RTP_AVP) ||
@@ -820,29 +838,17 @@ static pj_status_t transport_media_create(pjmedia_transport *tp,
 
 static pj_status_t transport_media_start(pjmedia_transport *tp,
 				  pj_pool_t *pool,
-				  pjmedia_sdp_session *sdp_local,
+				  const pjmedia_sdp_session *sdp_local,
 				  const pjmedia_sdp_session *sdp_remote,
 				  unsigned media_index)
 {
-    struct transport_udp *udp = (struct transport_udp*)tp;
-
     PJ_ASSERT_RETURN(tp && pool && sdp_local, PJ_EINVAL);
 
-    /* Validate media transport */
-    /* By now, this transport only support RTP/AVP transport */
-    if ((udp->media_options & PJMEDIA_TPMED_NO_TRANSPORT_CHECKING) == 0) {
-	pjmedia_sdp_media *m_rem, *m_loc;
-
-	m_rem = sdp_remote->media[media_index];
-	m_loc = sdp_local->media[media_index];
-
-	if (pj_stricmp(&m_loc->desc.transport, &ID_RTP_AVP) ||
-	    pj_stricmp(&m_rem->desc.transport, &ID_RTP_AVP))
-	{
-	    pjmedia_sdp_media_deactivate(pool, m_loc);
-	    return PJMEDIA_SDP_EINPROTO;
-	}
-    }
+    PJ_UNUSED_ARG(tp);
+    PJ_UNUSED_ARG(pool);
+    PJ_UNUSED_ARG(sdp_local);
+    PJ_UNUSED_ARG(sdp_remote);
+    PJ_UNUSED_ARG(media_index);
 
     return PJ_SUCCESS;
 }