anchor.diff:          'to': id,
           'description': {'sdp': s.sdp, 'type': s.type},
           'session_id': this._session_id,
  +        'media': media,
         });
       } catch (e) {
         print(e.toString());
  
positive.code:   }
  
    void invite(String peer_id, String media) {
      String sessionId = this._self_id + '-' + peer_id;
      _send('invite', {
        'session_id': sessionId,
        'id': _self_id,
        'to': peer_id,
        'media': media,
      });
      this._session_id = sessionId;
    }
  
    void bye() {
  
negative.code:           }
          }
          break;
        case 'offer':
          {
            var id = data['from'];
            var description = data['description'];
            var media = data['media'];
            var session_id = data['session_id'];
            this._session_id = session_id;
  