diff --git a/apps/webconference/RoomInfo.cpp b/apps/webconference/RoomInfo.cpp
index dc08d492..80ced1e6 100644
--- a/apps/webconference/RoomInfo.cpp
+++ b/apps/webconference/RoomInfo.cpp
@@ -29,6 +29,7 @@ AmArg ConferenceRoomParticipant::asArgArray() {
   res.push(AmArg((int)status));
   res.push(AmArg(last_reason.c_str()));
   res.push(AmArg((int)muted));
+  res.push(AmArg(participant_id));
   return res;
 }
 
@@ -45,7 +46,9 @@ void ConferenceRoomParticipant::updateStatus(ConferenceRoomParticipant::Particip
   updateAccess(now);
 }
 
-ConferenceRoom::ConferenceRoom() {
+ConferenceRoom::ConferenceRoom()
+  : expiry_time(0)
+{
   gettimeofday(&last_access_time, NULL);
 }
 
@@ -91,12 +94,14 @@ vector<string> ConferenceRoom::participantLtags() {
 }
 
 void ConferenceRoom::newParticipant(const string& localtag, 
-				    const string& number) {
+				    const string& number,
+				    const string& participant_id) {
   gettimeofday(&last_access_time, NULL);
 
   participants.push_back(ConferenceRoomParticipant());
   participants.back().localtag = localtag;
   participants.back().number = number;
+  participants.back().participant_id = participant_id;
 }
 
 bool ConferenceRoom::hasParticipant(const string& localtag) {
diff --git a/apps/webconference/RoomInfo.h b/apps/webconference/RoomInfo.h
index 4e3b33d4..6be0aabb 100644
--- a/apps/webconference/RoomInfo.h
+++ b/apps/webconference/RoomInfo.h
@@ -31,6 +31,7 @@ struct ConferenceRoomParticipant {
   string number;
   ParticipantStatus status;
   string last_reason; 
+  string participant_id;
 
   int muted;
   
@@ -70,7 +71,8 @@ struct ConferenceRoom {
 
   vector<string> participantLtags();
 
-  void newParticipant(const string& localtag, const string& number);
+  void newParticipant(const string& localtag, const string& number,
+		      const string& participant_id);
 
   bool updateStatus(const string& part_tag, 
 		    ConferenceRoomParticipant::ParticipantStatus newstatus, 
diff --git a/apps/webconference/WebConference.cpp b/apps/webconference/WebConference.cpp
index ac205b99..ba6ccd9a 100644
--- a/apps/webconference/WebConference.cpp
+++ b/apps/webconference/WebConference.cpp
@@ -72,6 +72,9 @@ bool WebConferenceFactory::ignore_pin = false;
 
 bool WebConferenceFactory::PrivateRoomsMode = false;
 
+string WebConferenceFactory::participant_id_paramname; // default: param not used
+string WebConferenceFactory::participant_id_hdr = "X-ParticipantID"; // default header
+
 int WebConferenceFactory::onLoad()
 {
   return getInstance()->load();
@@ -90,6 +93,11 @@ int WebConferenceFactory::load()
   // get application specific global parameters
   configureModule(cfg);
 
+  
+  participant_id_paramname = cfg.getParameter("participant_id_param");
+  if (cfg.hasParameter("participant_id_header"))
+    participant_id_hdr = cfg.getParameter("participant_id_header");
+
   // get prompts
   AM_PROMPT_START;
   AM_PROMPT_ADD(FIRST_PARTICIPANT, WEBCONF_ANNOUNCE_PATH "first_paricipant.wav");
@@ -243,14 +251,15 @@ bool WebConferenceFactory::isValidConference(const string& conf_id) {
 
 bool WebConferenceFactory::newParticipant(const string& conf_id, 
 					  const string& localtag, 
-					  const string& number) {
+					  const string& number,
+					  const string& participant_id) {
   rooms_mut.lock();
   if (PrivateRoomsMode && rooms.find(conf_id) == rooms.end()) {
     rooms_mut.unlock();
     return false;
   }
 
-  rooms[conf_id].newParticipant(localtag, number);
+  rooms[conf_id].newParticipant(localtag, number, participant_id);
   rooms_mut.unlock();
   return true;
 }
@@ -471,6 +480,10 @@ void WebConferenceFactory::invoke(const string& method,
     args.assertArrayFmt("s");
     listRooms(args, ret);
     ret.push(getServerInfoString().c_str());    
+  } else if(method == "findParticipant"){
+    args.assertArrayFmt("s");
+    findParticipant(args, ret);
+    ret.push(getServerInfoString().c_str());    
   } else if(method == "_list"){
     ret.push("roomCreate");
     ret.push("roomDelete");
@@ -486,6 +499,7 @@ void WebConferenceFactory::invoke(const string& method,
     ret.push("vqRoomFeedback");
     ret.push("getRoomPassword");
     ret.push("listRooms");
+    ret.push("findParticipant");
   } else
     throw AmDynInvoke::NotImplemented(method);
 }
@@ -653,6 +667,7 @@ void WebConferenceFactory::dialout(const AmArg& args, AmArg& ret) {
   string auth_pwd    = args.get(6).asCStr();
   string callee_domain = domain;
   string headers;
+  string participant_id;
 
   if (args.size()>7) {
     try {
@@ -679,6 +694,16 @@ void WebConferenceFactory::dialout(const AmArg& args, AmArg& ret) {
 	callee_domain = domain;
       }
     }
+    
+    if (args.size()>9) {
+      try {
+	assertArgCStr(args.get(9));
+	participant_id = args.get(9).asCStr();
+      }
+      catch (AmArg::TypeMismatchException &e) {
+	participant_id = "";
+      }
+    }
   }
 
   string from = "sip:" + from_user + "@" + domain;
@@ -694,10 +719,10 @@ void WebConferenceFactory::dialout(const AmArg& args, AmArg& ret) {
   rooms_mut.unlock();
 
   if (!is_valid_room) {
-      ret.push(1);
-      ret.push("wrong adminpin or inexisting room");
-      ret.push("");
-      return;
+    ret.push(1);
+    ret.push("wrong adminpin or inexisting room");
+    ret.push("");
+    return;
   }
 
   DBG("dialout webconference room '%s', from '%s', to '%s'", 
@@ -716,7 +741,7 @@ void WebConferenceFactory::dialout(const AmArg& args, AmArg& ret) {
     ret.push(0);
     ret.push("OK");
     ret.push(localtag.c_str());
-    newParticipant(room, localtag, to);
+    newParticipant(room, localtag, to, participant_id);
     updateStatus(room, localtag,
 		 ConferenceRoomParticipant::Connecting,
 		 "INVITE");
@@ -869,6 +894,25 @@ void WebConferenceFactory::listRooms(const AmArg& args, AmArg& ret) {
   ret.push(room_list);  
 }
 
+void WebConferenceFactory::findParticipant(const AmArg& args, AmArg& ret) {
+  string participant_id = args.get(0).asCStr();
+  AmArg r_ret;
+  r_ret.assertArray();
+  rooms_mut.lock();
+  for (map<string, ConferenceRoom>::iterator it = 
+	 rooms.begin(); it != rooms.end(); it++) {
+    for (list<ConferenceRoomParticipant>::iterator p_it=
+	   it->second.participants.begin(); p_it != it->second.participants.end(); p_it++) {
+      if (p_it->participant_id == participant_id) {
+	r_ret.push(it->first);
+	break;
+      }
+    }
+  }
+  rooms_mut.unlock();
+  ret.push(r_ret);
+}
+
 void WebConferenceFactory::vqRoomFeedback(const AmArg& args, AmArg& ret) {  
   string room = args.get(0).asCStr();
   string adminpin = args.get(1).asCStr();
diff --git a/apps/webconference/WebConference.h b/apps/webconference/WebConference.h
index 2d251931..1c5a5a68 100644
--- a/apps/webconference/WebConference.h
+++ b/apps/webconference/WebConference.h
@@ -137,6 +137,13 @@ public:
 
   static bool PrivateRoomsMode;
   
+  // P-App-Param parameter to get participant ID from 
+  static string participant_id_paramname;
+  // if participant_id_paramname not configured:
+  // header to get participant ID from
+  static string participant_id_hdr;
+
+
   WebConferenceFactory(const string& _app_name);
   AmSession* onInvite(const AmSipRequest&);
   AmSession* onInvite(const AmSipRequest& req,
@@ -146,7 +153,8 @@ public:
   bool isValidConference(const string& conf_id);
   bool newParticipant(const string& conf_id, 
 		      const string& localtag, 
-		      const string& number);
+		      const string& number,
+		      const string& participant_id);
   void updateStatus(const string& conf_id, 
 		    const string& localtag, 
 		    ConferenceRoomParticipant::ParticipantStatus status,
@@ -186,6 +194,8 @@ public:
 
   void getRoomPassword(const AmArg& args, AmArg& ret);
   void listRooms(const AmArg& args, AmArg& ret);
+  void findParticipant(const AmArg& args, AmArg& ret);
+
 };
 
 
diff --git a/apps/webconference/WebConferenceDialog.cpp b/apps/webconference/WebConferenceDialog.cpp
index 9431d890..7622cc3f 100644
--- a/apps/webconference/WebConferenceDialog.cpp
+++ b/apps/webconference/WebConferenceDialog.cpp
@@ -112,6 +112,22 @@ void WebConferenceDialog::connectConference(const string& room) {
 void WebConferenceDialog::onSessionStart(const AmSipRequest& req) { 
   time(&connect_ts);
 
+  if (WebConferenceFactory::participant_id_paramname.length()) {
+    string appparams = getHeader(req.hdrs, PARAM_HDR);
+    if (appparams.length()) {
+      participant_id = get_header_param(appparams,
+					WebConferenceFactory::participant_id_paramname);
+    }
+  } else if (WebConferenceFactory::participant_id_hdr.length()) {
+    participant_id = getHeader(req.hdrs, WebConferenceFactory::participant_id_hdr);
+  }
+
+  if (participant_id.empty()) {
+    DBG("no Participant ID set\n");
+  } else {
+    DBG("Participant ID set to '%s'\n", participant_id.c_str());
+  }
+
   // direct room access?
   if (conf_id.empty()) {
     state = EnteringPin;
@@ -122,7 +138,8 @@ void WebConferenceDialog::onSessionStart(const AmSipRequest& req) {
     DBG("########## direct connect conference #########\n");
     if (!factory->newParticipant(conf_id, 
 				 getLocalTag(), 
-				 dlg.remote_party)) {
+				 dlg.remote_party,
+				 participant_id)) {
       DBG("inexisting conference room\n");
       state = PlayErrorFinish;
       setInOut(&play_list,&play_list);
@@ -276,7 +293,8 @@ void WebConferenceDialog::process(AmEvent* ev)
 
       if (!factory->newParticipant(pin_str, 
 				   getLocalTag(), 
-				   dlg.remote_party)) {
+				   dlg.remote_party,
+				   participant_id)) {
 	DBG("inexisting conference room\n");
 	state = PlayErrorFinish;
 	setInOut(&play_list,&play_list);
diff --git a/apps/webconference/WebConferenceDialog.h b/apps/webconference/WebConferenceDialog.h
index 23cb4796..4923792b 100644
--- a/apps/webconference/WebConferenceDialog.h
+++ b/apps/webconference/WebConferenceDialog.h
@@ -83,6 +83,9 @@ private:
   time_t connect_ts;
   time_t disconnect_ts;
 
+  // ID from X-ParticipantID header
+  string participant_id;
+
 public:
   WebConferenceDialog(AmPromptCollection& prompts,
 		      WebConferenceFactory* my_f, 
diff --git a/apps/webconference/etc/webconference.conf b/apps/webconference/etc/webconference.conf
index 5b53d1f7..cc0ec9a8 100644
--- a/apps/webconference/etc/webconference.conf
+++ b/apps/webconference/etc/webconference.conf
@@ -131,6 +131,16 @@ stats_dir=/var/log/sems-webconference/
 #
 # predefined_rooms=discussion:some_pwd;support:other_pwd;
 
+
+# Participant ID (default: X-ParticipantID header)
+#
+# get participant ID from P-App-Param:
+#participant_id_param=participantid
+#
+# or, get participant ID from header:
+#participant_id_header=x-participantid
+
+
 ###############################################################
 # RFC4028 Session Timer
 #
diff --git a/doc/Readme.webconference.txt b/doc/Readme.webconference.txt
index 78512f53..5d085d22 100644
--- a/doc/Readme.webconference.txt
+++ b/doc/Readme.webconference.txt
@@ -57,6 +57,19 @@ If a room exists and the adminpin is not set (for example if the room is created
 by dial-in), the first call to roomInfo/dialout/kick/... with room/adminpin will
 set the adminpin.
 
+Participant ID
+--------------
+
+In some service environments, it may be necessary to determine in which conference
+rooms a certain user is at the moment. For example, if the active conferences of a
+user should be displayed on a web page, the conference bridge may be queried for the
+room a user is in.
+
+The findParticipant(string participant_id) function returns a list of rooms where the
+participant with a given ID is in. This participant ID can be given with
+ - a parameter to the dialout() function
+ - a header or P-App-Param parameter on incoming calls (see participant_id_param and
+   participant_id_header configuration in webconference.conf)
 
 implemented DI functions
 ------------------------
@@ -94,7 +107,7 @@ roomInfo(string room, string adminpin):
 ----
 dialout(string room, string adminpin, string callee,
         string from_user, string domain,
-        string auth_user, string auth_pwd [, headers [, callee_domain]]) :
+        string auth_user, string auth_pwd [, headers [, callee_domain, [participant_id]]]) :
      int code, string result, string callid
 
    code/result:
@@ -142,6 +155,10 @@ getRoomPassword(string master_pwd, string room)
 listRooms(string master_pwd)
     int code, string result
 ----
+findParticipant(string participant_id)
+    rooms: array of string
+  find all rooms a participant is in
+-----
 
 additionally there is feedback functions to save call quality reports 
 from users: vqRoomFeedback, vqCallFeedback, vqConferenceFeedback.