What Are Traversal Calls - Cisco TelePresence Video Communication Server Administrator's Manual

What are traversal calls?

A traversal call is any call passing through the VCS that includes both the signaling (information about
the call) and media (voice and video). The only other type of call is a non-traversal call, where the
signaling passes through the VCS but the media goes directly between the endpoints (or between one
endpoint and another VCS in the call route, or between two VCSs in the call route).
A call is "traversal" or "non-traversal" from the point of view of the VCS through which it is being
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routed at the time. A call between two endpoints may pass through two or more VCSs. Some of
these VCSs may just take the signaling, in which case the call will be a non-traversal call for that
VCS. Other VCSs in the route may need to take the media as well, and so the call will count as a
traversal call on that particular VCS.
The following types of calls require the VCS to take the media. They are classified as traversal calls
and will always pass through the Traversal Subzone:
firewall traversal calls, where the local VCS is either the traversal client or traversal server
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calls that are gatewayed (interworked) between H.323 and SIP on the local VCS
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calls that are gatewayed (interworked) between IPv4 and IPv6 on the local VCS
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for VCSs with Dual Network Interfaces enabled, calls that are inbound from one LAN port and
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outbound on the other
a SIP to SIP call when one of the participants is behind a NAT (unless both endpoints are using
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for NAT traversal)
encrypted calls to and from Microsoft OCS Server 2007 (requires the Enhanced OCS Collaboration
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option key)
All such calls require a traversal call license each time they pass through the Traversal Subzone.
Traversal calls use more resource than non-traversal calls, and the numbers of each type of call are
licensed separately. The VCS has one license for the maximum number of concurrent traversal calls it
can take, and another for the maximum number of concurrent non-traversal calls. You can increase the
number of each type of call available on your VCS by purchasing and installing the appropriate
key.
Note that a non-traversal call on a VCS Expressway will consume a traversal license if there are no
non-traversal call licenses available.
Cisco VCS Administrator Guide (X6.1)
Reference material
ICE
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