function onTransportOpen () {
	    if (self.onlyBinaryUpgrades) {
	      var upgradeLosesBinary = !this.supportsBinary && self.transport.supportsBinary;
	      failed = failed || upgradeLosesBinary;
	    }
	    if (failed) return;
	
	    debug('probe transport "%s" opened', name);
	    transport.send([{ type: 'ping', data: 'probe' }]);
	    transport.once('packet', function (msg) {
	      if (failed) return;
	      if ('pong' === msg.type && 'probe' === msg.data) {
	        debug('probe transport "%s" pong', name);
	        self.upgrading = true;
	        self.emit('upgrading', transport);
	        if (!transport) return;
	        Socket.priorWebsocketSuccess = 'websocket' === transport.name;
	
	        debug('pausing current transport "%s"', self.transport.name);
	        self.transport.pause(function () {
	          if (failed) return;
	          if ('closed' === self.readyState) return;
	          debug('changing transport and sending upgrade packet');
	
	          cleanup();
	
	          self.setTransport(transport);
	          transport.send([{ type: 'upgrade' }]);
	          self.emit('upgrade', transport);
	          transport = null;
	          self.upgrading = false;
	          self.flush();
	        });
	      } else {
	        debug('probe transport "%s" failed', name);
	        var err = new Error('probe error');
	        err.transport = transport.name;
	        self.emit('upgradeError', err);
	      }
	    });
	  }
Probes a transport.

@param {String} transport name
@api private