and up to 100 manually configurable subzones. Each manually configured subzone specifies a
range of IP addresses. When an endpoint registers with the VCS it is allocated to the appropriate
subzone based on its IP address. If the endpoint’s IP address does not match any of the subzones,
it is assigned to the Default Subzone. The Local Zone may be independent of network topology,
and may be comprised of multiple network segments.

Overview

The Local Zone and its subzones exist for the purposes of bandwidth management. Once you have
set up your subzones you can apply bandwidth limits to:

individual calls between two endpoints within the subzone

•

individual calls between an endpoint within the subzone and another endpoint outside of the

•

subzone
the total of calls to or from endpoints within the subzone.

•

For full details of how to create and configure subzones, and apply bandwidth limitations to
subzones including the Default Subzone and Traversal Subzone, see the section on

Bandwidth

Control

Configuring the Traversal Subzone Ports

The VCS allows you to configure the range of ports to be used for the media in traversal calls. A
single traversal call can consist of up to 5 types of media (audio, video, far end camera control,
duo video and BFCP) and each type of media may require a pair of ports – for example, audio and
video each require one port for RTP, and one for RTCP. Separate pairs of ports are required for the
inbound and outbound portions of a call. A single traversal call can therefore take up to 20 ports.
The default range for the ports to be used for media is 50000 - 51119 UDP, but these can be
changed to anywhere between 1024 and 65533. Ports are allocated from this range in pairs, the
first of each being even. Therefore the range must start with an even number and end with an odd
number.
To configure the ports used for media in traversal calls:

VCS Configuration > Local Zone > Traversal Subzone

•

xConfiguration Traversal Media Port Star

•

xConfiguration Traversal Media Port En

•

Configuring the Local Zone and its Subzones

The VCS also has a special type of subzone known as the

Traversal Subzone

. This is a conceptual

subzone; no endpoints can be registered to it, but all traversal calls (i.e. calls for which the VCS is
taking the media in addition to the signaling) must pass through it. The Traversal Subzone exists
in order to allow you to control the amount of bandwidth used by traversal calls, as these can be
particularly resource-intensive.

What are traversal calls?

The following types of calls require the VCS to take the media. They are classified as traversal calls
and must always pass through the Traversal Subzone:

Firewall traversal calls

•

H.323 to SIP gatewayed calls

•

IPv4 to IPv6 gatewayed calls

•

for VCSs with Dual Network Interfaces enabled, calls that are inbound from one LAN port and

•

outbound on the other
a SIP to SIP call when one of the participants is behind a NAT.

•

All such calls will require a traversal call licence each time they pass through the Traversal
Subzone.

Traversal Subzone

You must ensure that the port range is large enough to support the maximum number of
traversal calls available on your VCS. A single traversal call can take up to 20 ports (5
pairs in each direction). So for example, if your VCS is licensed for 5 traversal calls you

must ensure that the range of ports configured for traversal media is at least 100. If you add extra
traversal calls to your system, you must also ensure that the range of ports available is sufficient.

STUN Relays also consume traversal call licences (three relays take one licence) but they
do not actually pass through the traversal subzone.