Is the SX20 registered to an H323 gatekeeper, SIP registrar, or standalone?
If it's registered using either H323 or SIP to a call control server such as a VCS for example, you should refer to it's admin guides for the required ports. If the SX20 is deployed as a standalone endpoint, refer to the ports listed in the cisco-ex-tandberg-ip-sip-firewall-ports document, you'll also need to configure some other settings on the endpoint as well, do a search for "SX20 standalone" in the TelePresence section of the forums.
If you need any more help, you should move this post to the TelePresence section, where these types of devices are actively discussion and others can be able to help. You can move your post by editing it and changing the categories at the bottom of the page.
