let constraints: RTCMediaConstraints? = defaultPeerConnectionConstraints()
    peerConnection: RTCPeerCo = factory?.peerConnection(withICEServers: iceServers, constraints: constraints, delegate: self)
    let localStream: RTCMediaStream? = createLocalMediaStream() //get Media stream(video/audio)
    peerConnection?.add(localStream)

    //create offer for other opponent

    if isInitiator {
        peerConnection?.createOffer(with: self, constraints: defaultOfferConstraints())
        print("create Offer")
    }

func defaultICEServer() -> [RTCICEServer] {

  var iceServers = [RTCICEServer]()
  let defaultSTUNServerURL = URL(string: Config.defaultSTUNServerUrl)
  let defaultTURNServerURL = URL(string: Config.defaultTURNServerUrl)
  let stunServ = RTCICEServer(uri: defaultSTUNServerURL, username: "", password: "")
  let turnServ = RTCICEServer(uri: defaultTURNServerURL, username: "admin", password: "admin")
  iceServers.append(stunServ!)
  iceServers.append(turnServ!)

  return iceServers
}

func defaultPeerConnectionConstraints() -> RTCMediaConstraints {
    let optionalConstraints: [Any] = [RTCPair(key: "DtlsSrtpKeyAgreement", value: "true")]
    let constraints = RTCMediaConstraints(mandatoryConstraints: nil, optionalConstraints: optionalConstraints)
    return constraints!
}

func peerConnection(_ peerConnection: RTCPeerConnection, didCreateSessionDescription sdp: RTCSessionDescription, error: Error?) {}

peerConnection?.setLocalDescriptionWith(self, sessionDescription: sdp)