Cisco TelePresence Administrator's Manual page 404

Reference material
The following types of calls require the VCS to take the media. They are classified as traversal calls, require
a traversal call license, and always pass through the Traversal Subzone:
Unified CM remote sessions (these do not require a traversal call license)
n
all other firewall traversal calls that are not Unified CM remote sessions, where the local VCS is either the
n
traversal client or traversal server
calls that are gatewayed (interworked) between H.323 and SIP on the local VCS
n
calls that are gatewayed (interworked) between IPv4 and IPv6 on the local VCS
n
for a VCS Expressway with Advanced Networking 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 ICE for
n
NAT traversal)
calls that invoke the B2BUA to apply a media encryption policy or for ICE messaging support
n
Note that for calls via the Microsoft Lync B2BUA, the B2BUA application always takes the media but the call
is not classified as a VCS traversal call and does not consume a traversal call license (it may still consume a
non-traversal license if the VCS takes the call signaling).
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 (or VCS cluster, see
information) by purchasing and installing the appropriate option key. While every deployment is different, as a
guideline we recommend that your system has a 10:1 ratio of registrations to concurrent call licenses.
Note that a non-traversal call on a VCS Expressway will consume a traversal license if there are no non-
traversal call licenses available (in this situation, the call will remain a non-traversal call — the VCS
Expressway will not take the media, even though it is using a traversal license).
Cisco VCS Administrator Guide (X8.1.1)
License usage within a cluster [p.160]
Call types and licensing
for more
Page 404 of 507