function TraceablePeerConnection(ice_config, constraints) {
    var self = this;
    var RTCPeerconnection = navigator.mozGetUserMedia ? mozRTCPeerConnection : webkitRTCPeerConnection;
    this.peerconnection = new RTCPeerconnection(ice_config, constraints);
    this.updateLog = [];
    this.stats = {};
    this.statsinterval = null;
    this.maxstats = 0; // limit to 300 values, i.e. 5 minutes; set to 0 to disable

    /**
     * Array of ssrcs that will be added on next modifySources call.
     * @type {Array}
     */
    this.addssrc = [];
    /**
     * Array of ssrcs that will be added on next modifySources call.
     * @type {Array}
     */
    this.removessrc = [];
    /**
     * Pending operation that will be done during modifySources call.
     * Currently 'mute'/'unmute' operations are supported.
     *
     * @type {String}
     */
    this.pendingop = null;

    /**
     * Flag indicates that peer connection stream have changed and modifySources should proceed.
     * @type {boolean}
     */
    this.switchstreams = false;

    // override as desired
    this.trace = function (what, info) {
        //console.warn('WTRACE', what, info);
        self.updateLog.push({
            time: new Date(),
            type: what,
            value: info || ""
        });
    };
    this.onicecandidate = null;
    this.peerconnection.onicecandidate = function (event) {
        self.trace('onicecandidate', JSON.stringify(event.candidate, null, ' '));
        if (self.onicecandidate !== null) {
            self.onicecandidate(event);
        }
    };
    this.onaddstream = null;
    this.peerconnection.onaddstream = function (event) {
        self.trace('onaddstream', event.stream.id);
        if (self.onaddstream !== null) {
            self.onaddstream(event);
        }
    };
    this.onremovestream = null;
    this.peerconnection.onremovestream = function (event) {
        self.trace('onremovestream', event.stream.id);
        if (self.onremovestream !== null) {
            self.onremovestream(event);
        }
    };
    this.onsignalingstatechange = null;
    this.peerconnection.onsignalingstatechange = function (event) {
        self.trace('onsignalingstatechange', self.signalingState);
        if (self.onsignalingstatechange !== null) {
            self.onsignalingstatechange(event);
        }
    };
    this.oniceconnectionstatechange = null;
    this.peerconnection.oniceconnectionstatechange = function (event) {
        self.trace('oniceconnectionstatechange', self.iceConnectionState);
        if (self.oniceconnectionstatechange !== null) {
            self.oniceconnectionstatechange(event);
        }
    };
    this.onnegotiationneeded = null;
    this.peerconnection.onnegotiationneeded = function (event) {
        self.trace('onnegotiationneeded');
        if (self.onnegotiationneeded !== null) {
            self.onnegotiationneeded(event);
        }
    };
    self.ondatachannel = null;
    this.peerconnection.ondatachannel = function (event) {
        self.trace('ondatachannel', event);
        if (self.ondatachannel !== null) {
            self.ondatachannel(event);
        }
    };
    if (!navigator.mozGetUserMedia && this.maxstats) {
        this.statsinterval = window.setInterval(function() {
            self.peerconnection.getStats(function(stats) {
                var results = stats.result();
                for (var i = 0; i < results.length; ++i) {
                    //console.log(results[i].type, results[i].id, results[i].names())
                    var now = new Date();
                    results[i].names().forEach(function (name) {
                        var id = results[i].id + '-' + name;
                        if (!self.stats[id]) {
                            self.stats[id] = {
                                startTime: now,
                                endTime: now,
                                values: [],
                                times: []
                            };
                        }
                        self.stats[id].values.push(results[i].stat(name));
                        self.stats[id].times.push(now.getTime());
                        if (self.stats[id].values.length > self.maxstats) {
                            self.stats[id].values.shift();
                            self.stats[id].times.shift();
                        }
                        self.stats[id].endTime = now;
                    });
                }
            });

        }, 1000);
    }
};

dumpSDP = function(description) {
    return 'type: ' + description.type + '\r\n' + description.sdp;
}

if (TraceablePeerConnection.prototype.__defineGetter__ !== undefined) {
    TraceablePeerConnection.prototype.__defineGetter__('signalingState', function() { return this.peerconnection.signalingState; });
    TraceablePeerConnection.prototype.__defineGetter__('iceConnectionState', function() { return this.peerconnection.iceConnectionState; });
    TraceablePeerConnection.prototype.__defineGetter__('localDescription', function() {
        var publicLocalDescription = simulcast.reverseTransformLocalDescription(this.peerconnection.localDescription);
        return publicLocalDescription;
    });
    TraceablePeerConnection.prototype.__defineGetter__('remoteDescription', function() {
        var publicRemoteDescription = simulcast.reverseTransformRemoteDescription(this.peerconnection.remoteDescription);
        return publicRemoteDescription;
    });
}

TraceablePeerConnection.prototype.addStream = function (stream) {
    this.trace('addStream', stream.id);
    simulcast.resetSender();
    this.peerconnection.addStream(stream);
};

TraceablePeerConnection.prototype.removeStream = function (stream) {
    this.trace('removeStream', stream.id);
    simulcast.resetSender();
    this.peerconnection.removeStream(stream);
};

TraceablePeerConnection.prototype.createDataChannel = function (label, opts) {
    this.trace('createDataChannel', label, opts);
    return this.peerconnection.createDataChannel(label, opts);
};

TraceablePeerConnection.prototype.setLocalDescription = function (description, successCallback, failureCallback) {
    var self = this;
    description = simulcast.transformLocalDescription(description);
    this.trace('setLocalDescription', dumpSDP(description));
    this.peerconnection.setLocalDescription(description,
        function () {
            self.trace('setLocalDescriptionOnSuccess');
            successCallback();
        },
        function (err) {
            self.trace('setLocalDescriptionOnFailure', err);
            failureCallback(err);
        }
    );
    /*
     if (this.statsinterval === null && this.maxstats > 0) {
     // start gathering stats
     }
     */
};

TraceablePeerConnection.prototype.setRemoteDescription = function (description, successCallback, failureCallback) {
    var self = this;
    description = simulcast.transformRemoteDescription(description);
    this.trace('setRemoteDescription', dumpSDP(description));
    this.peerconnection.setRemoteDescription(description,
        function () {
            self.trace('setRemoteDescriptionOnSuccess');
            successCallback();
        },
        function (err) {
            self.trace('setRemoteDescriptionOnFailure', err);
            failureCallback(err);
        }
    );
    /*
     if (this.statsinterval === null && this.maxstats > 0) {
     // start gathering stats
     }
     */
};

TraceablePeerConnection.prototype.hardMuteVideo = function (muted) {
    this.pendingop = muted ? 'mute' : 'unmute';
};

TraceablePeerConnection.prototype.enqueueAddSsrc = function(channel, ssrcLines) {
    if (!this.addssrc[channel]) {
        this.addssrc[channel] = '';
    }
    this.addssrc[channel] += ssrcLines;
};

TraceablePeerConnection.prototype.addSource = function (elem) {
    console.log('addssrc', new Date().getTime());
    console.log('ice', this.iceConnectionState);
    var sdp = new SDP(this.remoteDescription.sdp);
    var mySdp = new SDP(this.peerconnection.localDescription.sdp);

    var self = this;
    $(elem).each(function (idx, content) {
        var name = $(content).attr('name');
        var lines = '';
        tmp = $(content).find('ssrc-group[xmlns="urn:xmpp:jingle:apps:rtp:ssma:0"]').each(function() {
            var semantics = this.getAttribute('semantics');
            var ssrcs = $(this).find('>source').map(function () {
                return this.getAttribute('ssrc');
            }).get();

            if (ssrcs.length != 0) {
                lines += 'a=ssrc-group:' + semantics + ' ' + ssrcs.join(' ') + '\r\n';
            }
        });
        tmp = $(content).find('source[xmlns="urn:xmpp:jingle:apps:rtp:ssma:0"]'); // can handle both >source and >description>source
        tmp.each(function () {
            var ssrc = $(this).attr('ssrc');
            if(mySdp.containsSSRC(ssrc)){
                /**
                 * This happens when multiple participants change their streams at the same time and
                 * ColibriFocus.modifySources have to wait for stable state. In the meantime multiple
                 * addssrc are scheduled for update IQ. See
                 */
                console.warn("Got add stream request for my own ssrc: "+ssrc);
                return;
            }
            $(this).find('>parameter').each(function () {
                lines += 'a=ssrc:' + ssrc + ' ' + $(this).attr('name');
                if ($(this).attr('value') && $(this).attr('value').length)
                    lines += ':' + $(this).attr('value');
                lines += '\r\n';
            });
        });
        sdp.media.forEach(function(media, idx) {
            if (!SDPUtil.find_line(media, 'a=mid:' + name))
                return;
            sdp.media[idx] += lines;
            self.enqueueAddSsrc(idx, lines);
        });
        sdp.raw = sdp.session + sdp.media.join('');
    });
};

TraceablePeerConnection.prototype.enqueueRemoveSsrc = function(channel, ssrcLines) {
    if (!this.removessrc[channel]){
        this.removessrc[channel] = '';
    }
    this.removessrc[channel] += ssrcLines;
};

TraceablePeerConnection.prototype.removeSource = function (elem) {
    console.log('removessrc', new Date().getTime());
    console.log('ice', this.iceConnectionState);
    var sdp = new SDP(this.remoteDescription.sdp);
    var mySdp = new SDP(this.peerconnection.localDescription.sdp);

    var self = this;
    $(elem).each(function (idx, content) {
        var name = $(content).attr('name');
        var lines = '';
        tmp = $(content).find('ssrc-group[xmlns="urn:xmpp:jingle:apps:rtp:ssma:0"]').each(function() {
            var semantics = this.getAttribute('semantics');
            var ssrcs = $(this).find('>source').map(function () {
                return this.getAttribute('ssrc');
            }).get();

            if (ssrcs.length != 0) {
                lines += 'a=ssrc-group:' + semantics + ' ' + ssrcs.join(' ') + '\r\n';
            }
        });
        tmp = $(content).find('source[xmlns="urn:xmpp:jingle:apps:rtp:ssma:0"]'); // can handle both >source and >description>source
        tmp.each(function () {
            var ssrc = $(this).attr('ssrc');
            // This should never happen, but can be useful for bug detection
            if(mySdp.containsSSRC(ssrc)){
                console.error("Got remove stream request for my own ssrc: "+ssrc);
                return;
            }
            $(this).find('>parameter').each(function () {
                lines += 'a=ssrc:' + ssrc + ' ' + $(this).attr('name');
                if ($(this).attr('value') && $(this).attr('value').length)
                    lines += ':' + $(this).attr('value');
                lines += '\r\n';
            });
        });
        sdp.media.forEach(function(media, idx) {
            if (!SDPUtil.find_line(media, 'a=mid:' + name))
                return;
            sdp.media[idx] += lines;
            self.enqueueRemoveSsrc(idx, lines);
        });
        sdp.raw = sdp.session + sdp.media.join('');
    });
};

TraceablePeerConnection.prototype.modifySources = function(successCallback) {
    var self = this;
    if (this.signalingState == 'closed') return;
    if (!(this.addssrc.length || this.removessrc.length || this.pendingop !== null || this.switchstreams)){
        // There is nothing to do since scheduled job might have been executed by another succeeding call
        if(successCallback){
            successCallback();
        }
        return;
    }

    // FIXME: this is a big hack
    // https://code.google.com/p/webrtc/issues/detail?id=2688
    // ^ has been fixed.
    if (!(this.signalingState == 'stable' && this.iceConnectionState == 'connected')) {
        console.warn('modifySources not yet', this.signalingState, this.iceConnectionState);
        this.wait = true;
        window.setTimeout(function() { self.modifySources(successCallback); }, 250);
        return;
    }
    if (this.wait) {
        window.setTimeout(function() { self.modifySources(successCallback); }, 2500);
        this.wait = false;
        return;
    }

    // Reset switch streams flag
    this.switchstreams = false;

    var sdp = new SDP(this.remoteDescription.sdp);

    // add sources
    this.addssrc.forEach(function(lines, idx) {
        sdp.media[idx] += lines;
    });
    this.addssrc = [];

    // remove sources
    this.removessrc.forEach(function(lines, idx) {
        lines = lines.split('\r\n');
        lines.pop(); // remove empty last element;
        lines.forEach(function(line) {
            sdp.media[idx] = sdp.media[idx].replace(line + '\r\n', '');
        });
    });
    this.removessrc = [];

    // FIXME:
    // this was a hack for the situation when only one peer exists
    // in the conference.
    // check if still required and remove
    if (sdp.media[0])
        sdp.media[0] = sdp.media[0].replace('a=recvonly', 'a=sendrecv');
    if (sdp.media[1])
        sdp.media[1] = sdp.media[1].replace('a=recvonly', 'a=sendrecv');

    sdp.raw = sdp.session + sdp.media.join('');
    this.setRemoteDescription(new RTCSessionDescription({type: 'offer', sdp: sdp.raw}),
        function() {

            if(self.signalingState == 'closed') {
                console.error("createAnswer attempt on closed state");
                return;
            }

            self.createAnswer(
                function(modifiedAnswer) {
                    // change video direction, see https://github.com/jitsi/jitmeet/issues/41
                    if (self.pendingop !== null) {
                        var sdp = new SDP(modifiedAnswer.sdp);
                        if (sdp.media.length > 1) {
                            switch(self.pendingop) {
                                case 'mute':
                                    sdp.media[1] = sdp.media[1].replace('a=sendrecv', 'a=recvonly');
                                    break;
                                case 'unmute':
                                    sdp.media[1] = sdp.media[1].replace('a=recvonly', 'a=sendrecv');
                                    break;
                            }
                            sdp.raw = sdp.session + sdp.media.join('');
                            modifiedAnswer.sdp = sdp.raw;
                        }
                        self.pendingop = null;
                    }

                    // FIXME: pushing down an answer while ice connection state
                    // is still checking is bad...
                    //console.log(self.peerconnection.iceConnectionState);

                    // trying to work around another chrome bug
                    //modifiedAnswer.sdp = modifiedAnswer.sdp.replace(/a=setup:active/g, 'a=setup:actpass');
                    self.setLocalDescription(modifiedAnswer,
                        function() {
                            //console.log('modified setLocalDescription ok');
                            if(successCallback){
                                successCallback();
                            }
                        },
                        function(error) {
                            console.error('modified setLocalDescription failed', error);
                        }
                    );
                },
                function(error) {
                    console.error('modified answer failed', error);
                }
            );
        },
        function(error) {
            console.error('modify failed', error);
        }
    );
};

TraceablePeerConnection.prototype.close = function () {
    this.trace('stop');
    if (this.statsinterval !== null) {
        window.clearInterval(this.statsinterval);
        this.statsinterval = null;
    }
    this.peerconnection.close();
};

TraceablePeerConnection.prototype.createOffer = function (successCallback, failureCallback, constraints) {
    var self = this;
    this.trace('createOffer', JSON.stringify(constraints, null, ' '));
    this.peerconnection.createOffer(
        function (offer) {
            self.trace('createOfferOnSuccess', dumpSDP(offer));
            successCallback(offer);
        },
        function(err) {
            self.trace('createOfferOnFailure', err);
            failureCallback(err);
        },
        constraints
    );
};

TraceablePeerConnection.prototype.createAnswer = function (successCallback, failureCallback, constraints) {
    var self = this;
    this.trace('createAnswer', JSON.stringify(constraints, null, ' '));
    this.peerconnection.createAnswer(
        function (answer) {
            answer = simulcast.transformAnswer(answer);
            self.trace('createAnswerOnSuccess', dumpSDP(answer));
            successCallback(answer);
        },
        function(err) {
            self.trace('createAnswerOnFailure', err);
            failureCallback(err);
        },
        constraints
    );
};

TraceablePeerConnection.prototype.addIceCandidate = function (candidate, successCallback, failureCallback) {
    var self = this;
    this.trace('addIceCandidate', JSON.stringify(candidate, null, ' '));
    this.peerconnection.addIceCandidate(candidate);
    /* maybe later
     this.peerconnection.addIceCandidate(candidate,
     function () {
     self.trace('addIceCandidateOnSuccess');
     successCallback();
     },
     function (err) {
     self.trace('addIceCandidateOnFailure', err);
     failureCallback(err);
     }
     );
     */
};

TraceablePeerConnection.prototype.getStats = function(callback, errback) {
    if (navigator.mozGetUserMedia) {
        // ignore for now...
    } else {
        this.peerconnection.getStats(callback);
    }
};

// mozilla chrome compat layer -- very similar to adapter.js
function setupRTC() {
    var RTC = null;
    if (navigator.mozGetUserMedia) {
        console.log('This appears to be Firefox');
        var version = parseInt(navigator.userAgent.match(/Firefox\/([0-9]+)\./)[1], 10);
        if (version >= 22) {
            RTC = {
                peerconnection: mozRTCPeerConnection,
                browser: 'firefox',
                getUserMedia: navigator.mozGetUserMedia.bind(navigator),
                attachMediaStream: function (element, stream) {
                    element[0].mozSrcObject = stream;
                    element[0].play();
                },
                pc_constraints: {}
            };
            if (!MediaStream.prototype.getVideoTracks)
                MediaStream.prototype.getVideoTracks = function () { return []; };
            if (!MediaStream.prototype.getAudioTracks)
                MediaStream.prototype.getAudioTracks = function () { return []; };
            RTCSessionDescription = mozRTCSessionDescription;
            RTCIceCandidate = mozRTCIceCandidate;
        }
    } else if (navigator.webkitGetUserMedia) {
        console.log('This appears to be Chrome');
        RTC = {
            peerconnection: webkitRTCPeerConnection,
            browser: 'chrome',
            getUserMedia: navigator.webkitGetUserMedia.bind(navigator),
            attachMediaStream: function (element, stream) {
                element.attr('src', webkitURL.createObjectURL(stream));
            },
            // DTLS should now be enabled by default but..
            pc_constraints: {'optional': [{'DtlsSrtpKeyAgreement': 'true'}]}
        };
        if (navigator.userAgent.indexOf('Android') != -1) {
            RTC.pc_constraints = {}; // disable DTLS on Android
        }
        if (!webkitMediaStream.prototype.getVideoTracks) {
            webkitMediaStream.prototype.getVideoTracks = function () {
                return this.videoTracks;
            };
        }
        if (!webkitMediaStream.prototype.getAudioTracks) {
            webkitMediaStream.prototype.getAudioTracks = function () {
                return this.audioTracks;
            };
        }
    }
    if (RTC === null) {
        try { console.log('Browser does not appear to be WebRTC-capable'); } catch (e) { }
    }
    return RTC;
}

function getUserMediaWithConstraints(um, success_callback, failure_callback, resolution, bandwidth, fps, desktopStream) {
    var constraints = {audio: false, video: false};

    if (um.indexOf('video') >= 0) {
        constraints.video = { mandatory: {}, optional: [] };// same behaviour as true
    }
    if (um.indexOf('audio') >= 0) {
        constraints.audio = { mandatory: {}, optional: []};// same behaviour as true
    }
    if (um.indexOf('screen') >= 0) {
        constraints.video = {
            mandatory: {
                chromeMediaSource: "screen",
                googLeakyBucket: true,
                maxWidth: window.screen.width,
                maxHeight: window.screen.height,
                maxFrameRate: 3
            },
            optional: []
        };
    }
    if (um.indexOf('desktop') >= 0) {
        constraints.video = {
            mandatory: {
                chromeMediaSource: "desktop",
                chromeMediaSourceId: desktopStream,
                googLeakyBucket: true,
                maxWidth: window.screen.width,
                maxHeight: window.screen.height,
                maxFrameRate: 3
            },
            optional: []
        }
    }

    if (constraints.audio) {
        // if it is good enough for hangouts...
        constraints.audio.optional.push(
            {googEchoCancellation: true},
            {googAutoGainControl: true},
            {googNoiseSupression: true},
            {googHighpassFilter: true},
            {googNoisesuppression2: true},
            {googEchoCancellation2: true},
            {googAutoGainControl2: true}
        );
    }
    if (constraints.video) {
        constraints.video.optional.push(
            {googNoiseReduction: false} // chrome 37 workaround for issue 3807, reenable in M38
        );
        if (um.indexOf('video') >= 0) {
            constraints.video.optional.push(
                {googLeakyBucket: true}
            );
        }
    }

    // Check if we are running on Android device
    var isAndroid = navigator.userAgent.indexOf('Android') != -1;

    if (resolution && !constraints.video || isAndroid) {
        constraints.video = { mandatory: {}, optional: [] };// same behaviour as true
    }
    // see https://code.google.com/p/chromium/issues/detail?id=143631#c9 for list of supported resolutions
    switch (resolution) {
        // 16:9 first
        case '1080':
        case 'fullhd':
            constraints.video.mandatory.minWidth = 1920;
            constraints.video.mandatory.minHeight = 1080;
            break;
        case '720':
        case 'hd':
            constraints.video.mandatory.minWidth = 1280;
            constraints.video.mandatory.minHeight = 720;
            break;
        case '360':
            constraints.video.mandatory.minWidth = 640;
            constraints.video.mandatory.minHeight = 360;
            break;
        case '180':
            constraints.video.mandatory.minWidth = 320;
            constraints.video.mandatory.minHeight = 180;
            break;
        // 4:3
        case '960':
            constraints.video.mandatory.minWidth = 960;
            constraints.video.mandatory.minHeight = 720;
            break;
        case '640':
        case 'vga':
            constraints.video.mandatory.minWidth = 640;
            constraints.video.mandatory.minHeight = 480;
            break;
        case '320':
            constraints.video.mandatory.minWidth = 320;
            constraints.video.mandatory.minHeight = 240;
            break;
        default:
            if (isAndroid) {
                constraints.video.mandatory.minWidth = 320;
                constraints.video.mandatory.minHeight = 240;
                constraints.video.mandatory.maxFrameRate = 15;
            }
            break;
    }
    if (constraints.video.mandatory.minWidth)
        constraints.video.mandatory.maxWidth = constraints.video.mandatory.minWidth;
    if (constraints.video.mandatory.minHeight)
        constraints.video.mandatory.maxHeight = constraints.video.mandatory.minHeight;

    if (bandwidth) { // doesn't work currently, see webrtc issue 1846
        if (!constraints.video) constraints.video = {mandatory: {}, optional: []};//same behaviour as true
        constraints.video.optional.push({bandwidth: bandwidth});
    }
    if (fps) { // for some cameras it might be necessary to request 30fps
        // so they choose 30fps mjpg over 10fps yuy2
        if (!constraints.video) constraints.video = {mandatory: {}, optional: []};// same behaviour as true;
        constraints.video.mandatory.minFrameRate = fps;
    }

    var isFF = navigator.userAgent.toLowerCase().indexOf('firefox') > -1;

    try {
        if (config.enableSimulcast
            && constraints.video
            && constraints.video.chromeMediaSource !== 'screen'
            && constraints.video.chromeMediaSource !== 'desktop'
            && !isAndroid

            // We currently do not support FF, as it doesn't have multistream support.
            && !isFF) {
            simulcast.getUserMedia(constraints, function (stream) {
                    console.log('onUserMediaSuccess');
                    success_callback(stream);
                },
                function (error) {
                    console.warn('Failed to get access to local media. Error ', error);
                    if (failure_callback) {
                        failure_callback(error);
                    }
                });
        } else {

            RTC.getUserMedia(constraints,
                function (stream) {
                    console.log('onUserMediaSuccess');
                    success_callback(stream);
                },
                function (error) {
                    console.warn('Failed to get access to local media. Error ', error);
                    if (failure_callback) {
                        failure_callback(error);
                    }
                });

        }
    } catch (e) {
        console.error('GUM failed: ', e);
        if(failure_callback) {
            failure_callback(e);
        }
    }
}