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VCS Traversal and NonTraversal Call LicenseUsage

Document ID: 118872

Contributed by Cisco TAC Engineers.

Mar 31, 2015

Contents

Introduction

VCS Traversal Call License Usage

VCS Expressway NonTraversal Call License Usage

Introduction

This document describes the difference between a traversal and a nontraversal call on the Cisco

TelePresence Video Communications Server (VCS) and the use of call licenses.

VCS Traversal Call License Usage

When a call is made and the VCS takes the media as well as the signaling, it is a traversal calland uses a

traversal call license on that VCS. Here are some examples of traversal calls that require the VCS to take the

media:

For a VCS Control, calls to or from a traversal server (known as Firewall traversal calls).

For a VCS Expressway, calls to or from a traversal client (Firewall traversal calls). Traversal clientsinclude other VCSs, gatekeepers, Border Controllers, or traversalenabled endpoints.

Calls that are gatewayed (interworked) between H.323 and Session Initiation Protocol (SIP) on the

local VCS.

Calls that are gatewayed (interworked) between IPv4 and IPv6 addresses on the local VCS.

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

outbound on another.

An SIPtoSIP call when one of the participants is behind a Network Address Translation (NAT),

unless both endpoints use Interactive Connectivity Establishment (ICE) for NAT traversal.

Calls that have a media encryption policy applied.

Encrypted calls to and from the Microsoft Office Communications Server (OCS) Version 2007 or

Microsoft Lync Server Version 2010, where the OCS/Lync backtoback user agent (B2BUA) is not

used. If the B2BUA is used, 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 might still consume

a nontraversal license if the VCS takes the call signaling).

Note: The Enhanced OCS Collaboration option key is required for encrypted calls to the OCS or Lync Server.

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All other calls arenontraversal(local) calls.

Note: A call might be a traversal call on one VCS but a local (nontraversal) call on another VCS in the call

route, dependent upon whether each VCS in the route is required to take the media.

Traversal calls use more resources than nontraversal calls, and the number of each type of call is licensed

separately. The VCS has one license for a maximum number of concurrent traversal calls that it can take, and

another for the maximum number of concurrent nontraversal calls. In order to increase the number of each

type of call that is available on your VCS (or VCS cluster), you can purchase and install the appropriateoption key. While every deployment is different, as a guideline, Cisco recommends that your system has a

10:1 ratio of registrations to concurrent call licenses.

VCS Expressway NonTraversal Call License Usage

Usually, a VCS Expressway requires a traversal call license to route calls, even for calls between devices that

are directly registered to it. This is because the endpoints that are behind Firewalls need the VCS Expressway

to receive and forward the media in order to guarantee that the media is routable between the endpoints in the

call.

The only situation where a call that passes through a VCS Expressway is classified as a local (nontraversal)

call is when it matches any of these scenarios:

There is no SIPtoH.323 interworking required.

There is no IPv4toIPv6 address interworking required.

The call is not routed from the VCS Expressway through a Traversal Zone.

Neither of the endpoints are traversalenabled (neither of the endpoints has registered with Assent or

H.460.18/19, and neither has made the call with a request for Assent or H.460.18/19).

The call is received from and sent to:

An endpoint or a Neighbor Zone that is directly connected to the WAN.

An endpoint or a Neighbor Zone behind a Firewall that has an SIP or H.323

ApplicationLevel Gateway (ALG) that supports video calls, which makes the signaling

appear as though the endpoint is directly connected to the WAN.

Locally registered, ICEenabled endpoints (if VCS Version X5 or later is used).

Note: In order to aid Firewall traversal, all Cisco TelePresence endpoints are traversalenabled, so a traversallicense is always required when at least one of the endpoints that are involved in the call is a TelePresence

endpoint.

Note: A nontraversal call on a VCS Expressway consumes a traversal license if there are no nontraversal

call licenses available (if VCS Version X5 or later is used). In this scenario, the call remains a nontraversal

call, and the VCS Expressway does not take the media, even though it uses a traversal license.

Updated: Mar 31, 2015 Document ID: 118872