How do I dial you?  …DNS!

One of our more common questions about Videoconferencing over IP networks, especially using the Internet, has been ‘How do I dial into your network?’ In order to address inbound dialing Tandberg has made the Expressway solution (Gatekeepers, Border Controllers, and MXP endpoints version 4.0 and later) capable of resolving the system name using the most common name resolution technique on the Internet—DNS (Domain Name Service).  DNS provides the ability to find devices based on a name, rather than an IP address which is harder to remember and may change. DNS name resolution services are hosted publicly on the Internet by ISP’s, or privately within a corporate network for Intranets.

For videoconferencing connectivity DNS allows us to call using an H.323 URI which looks like an email address – yourname@yourcompany.com. The ‘@’ sign separates the part of the name resolved by public DNS (yourcompany.com) from the part resolved by the internal Gatekeeper which routes the call to your system (yourname). When you would like to enable DNS/URI dialing for your video system, and you are using a Tandberg Gatekeeper and Border Controller for Firewall Traversal, follow these steps:

1. Disable Allow DNS resolution on the TANDBERG Gatekeeper (resides on the internal, private network). You want to use the Border Controller (on the Public Internet) to resolve any H.323 URI received.

2. Enable Allow DNS Resolution on the TANDBERG Border Controller.

3. Configure the same local domain name on both the Gatekeeper and the Border Controller.

4. On your public DNS server, ask your Network Administrators to create an SRV record to point VTC traffic to the Border Controller IP address.

5. Configure the Border Controller with the address of your public DNS server.

6. Test and enable network/firewall ports 1719, 1720, 2776 and 2777 for UDP and TCP for outbound and return traffic (if you have not already done so when implementing the Border Controller).  Please also be aware that management of the Border Controller occurs through Port 80.

7. Configure the URI address of your video system (yoursystem@yourcompany.com) as your H.323 ID.

Once configuration is complete, a video system that is registered to a gatekeeper which resolves DNS on the public Internet should be able to dial your video system by dialing yoursystem@yourcompany.com where ‘yoursystem’ is either the H.323 ID or E.164 alias of your codec. The Border Controller User Guide documentation provides specific information on setting up DNS SRV records for Videoconferencing which can be provided to your Network Administrators.   

Note that in the above example we can dial outbound from our MXP video systems and Tandberg bridges to another company’s video system (theircodec@theircompany.com), while only public IP codec’s that are registered to a gatekeeper or border controller setup to resolve DNS will be able to dial in to our video systems.  If dial-in capability is required from any public system, including those not registered to a gatekeeper utilizing DNS, then an interactive menu system such as Tandberg Entrypoint can fill that need.

Other configurations are also available that may add more flexibility to your dial plan.  For more information, see the Border Controller User Guide or contact your Tandberg Sales channel.  The Border Controller User Guide can be found at www.tandberg.com under Support \ Documentation \ User Manuals.