这种情况下，需要借助信令服务来协商对等连接。

以下是简单的示例代码：

1. 发送端：

// 初始化peerConnection
const peerConnection = new RTCPeerConnection();

// 添加本地流
navigator.mediaDevices.getUserMedia({video: true})
  .then(stream => {
    stream.getTracks().forEach(track => peerConnection.addTrack(track, stream));
  });

// 发起offer
peerConnection.createOffer()
  .then(offer => peerConnection.setLocalDescription(offer))
  .then(() => {
    // 发送offer到接收端
    const offerObj = {
      type: peerConnection.localDescription.type,
      sdp: peerConnection.localDescription.sdp
    };
    // 发送
    sendToServer(offerObj);
  });

2. 接收端：

// 初始化peerConnection
const peerConnection = new RTCPeerConnection();

// 添加远程流
peerConnection.ontrack = e => {
  // 播放远程视频
  remoteVideo.srcObject = e.streams[0];
};

// 收到远程offer
const receiveOffer = offer => {
  peerConnection.setRemoteDescription(new RTCSessionDescription(offer))
    .then(() => peerConnection.createAnswer())
    .then(answer => peerConnection.setLocalDescription(answer))
    .then(() => {
      // 发送answer到发送端
      const answerObj = {
        type: peerConnection.localDescription.type,
        sdp: peerConnection.localDescription.sdp
      };
      // 发送
      sendToServer(answerObj);
    });
};

// 收到远程answer
const receiveAnswer = answer => peerConnection.setRemoteDescription(new RTCSessionDescription(answer));

以上代码中，发送端创建offer后通过信令服务发送给接收端，接收端收到offer后通过peerConnection创建answer并发送回去。发送端收到answer后进行设置。此时，双方已经建立单向的WebRTC连接。