Why WebApp adds its own port to the ws request?

I'm running a Web Application at 8080 without Express. I need to call a WebRTC service at port 80 but my WebApp adds its own port to the request so my request not works:

Request URL:http://rtc.domain.com:8080/socket.io/?EIO=2&transport=polling&t=1427415431810-8&sid=UCrdHgkO7WAhSv6eAAAr

This URL is declared as: http://rtc.domain.com/ and just when my App is requesting WebRTC services this happens. I don't want force the port if later the WeRTC service changes. What am I doing wrong?