VCS Traversal vs Non-Traversal Licences FAQ



Traversal vs non-traversal licenses –  How many VCS traversal licenses do I need for a 20-party conference, where all endpoints are on the Internet? Endpoints are expected to be a mix of h323 and SIP.


There are four types of Traversal calls on the VCS; Interworking (SIP to H.323), IPv4 to IPv6, Firewall, and Dual Network Interface. If two endpoints are connecting in a call and both are located inside the firewall, a non-traversal call license will be used as long as they are using the same communication protocol (both SIP or both H.323). However, if one endpoint uses H.323 and the other used SIP, one traversal call license is required on the VCS Control.

As long as calls are all point-to-point, then one call license is needed for each pair of participants connected together on each server the media traverses through. For example, an endpoint inside the firewall is connected to an endpoint outside the firewall. This will require one traversal call license on the VCS Control and one traversal call license on the VCS Expressway.

If the VCS Expressway is located in a DMZ (De-Militerized Zone) you can enable a feature on the Expressway called the Dual Network Interface. This allows you to connect one ethernet cable inside the DMZ, and the other cable to the public internet, establishing a secure environment through the DMZ for communication. If you are placing a point-to-point call between an endpoint inside the firewall to an endpoint outside the firewall and DMZ, then you will use one traversal license on the VCS Control, and two traversal licenses on the VCS Expressway. One of the license used on the expressway is for the communication between the Control and Expressway, and one is used for communication across the Dual Network Interface on the Expressway.

If you are hosting a multipoint call on the MCU located inside the firewall, between some endpoints inside the firewall and some endpoints outside the firewall, all of the endpoints inside the firewall will use non-traversal call licenses, and all the endpoints outside the firewall will use traversal call licenses based on the two scenarios outlined above. Each endpoint establishes a unicast connection with the MCU, which will in turn transcode the media between all participants connected. Even if one participant inside the firewall is using SIP and the other inside participant is using H.323, this would not require a traversal license as long as the call is through the MCU.

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