This document describes how to configure an overflow route on a Cisco Video Communications Server (VCS) when you have limited IP bandwidth capacity between sites, or when you desire to protect against IP network failure. The overflow route via an ISDN gateway is used if a new call is made and the call cannot be placed over the IP network connection.
Cisco recommends that you have knowledge of the Cisco VCS.
The information in this document is based on the Cisco VCS.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
This document explains how to use a Call Processing Language (CPL) script in order to prioritize call routes such that:
- If there is enough IP bandwidth for the call, the Cisco VCS routes the call over IP.
- If there is insufficient IP bandwidth for the call, the Cisco VCS routes the call via an ISDN gateway.
This diagram illustrates the Cisco VCS route decisions in accordance with the aforementioned behaviors:
These assumptions are used for the example that is described in this document:
- There is one Cisco VCS to which endpoint 91xx is registered (VCS 91xx).
- There is another Cisco VCS to which endpoint 92xx is registered (VCS 92xx).
- In order to access endpoint 92xx via the ISDN gateway, VCS 91xx must prefix the 92xx number with 810002.
In this scenario, VCS 91xx is configured with a Neighbor Zone that matches VCS 92xx and routes calls via the IP network to VCS 92xx. Here is the process that occurs in this scenario:
- The ISDN gateway registers with the VCS 91xx gateway via a prefix registration of 810002:
- A pipe is defined that specifies the total bandwidth capacity of the IP link from VCS 91xx to VCS 92xx. This pipe is applied to all of the links that can provide calls to Neighbor Zone 92xx. If calls are made to Neighbor Zone 92xx that exceed the total bandwidth limit, they fail. Additionally, if calls are made to Neighbor Zone 92xx and the IP link is down, the calls fail.
- A CPL script is applied to the Cisco VCS that adds the 810002 prefix to the 92xx number, and then the call is placed again if a call to Neighbor Zone 92xx fails.
- The gateway receives calls with the 810002 prefix and forwards them based on its own dial plan configuration.
Here is the CPL script that routes calls via the IP link if capacity exists and via the gateway if the call fails to be routed via the IP link:
<?xml version="1.0" encoding="UTF-8" ?>
<!-- Proxy call to original 92xx destination -->
<!-- Call failed for some reason, try again using
the locally registered gateway -->
<taa:location clear="yes" regex="(92..)" replace="810002\1">
This CPL file should be loaded via the web interface. Complete these steps in order to load it:
- Navigate to VCS configuration > Call policy > Configuration.
- Browse to this CPL file in the Policy Files section.
- Click Upload File.
CPL Script Explanation
Here is a detailed explanation of the CPL script:
Downspeed Bandwidth Configuration
In a scenario that involves an IP link that has 128 kbps available, for example, and a new call requests a bandwidth of 384 kbps, you can adjust the Cisco VCS bandwidth configuration in order to decide whether the call is downspeeded to 128 kbps and routed over the IP link or overflowed to the gateway.
In order to reach the bandwidth configuration, use the web browser interface and navigate to VCS configuration > Bandwidth > Configuration.
If the Downspeed total mode is set to On, then the call in the previous scenario is downspeeded and placed over the IP link. If the Downspeed total mode is set to Off, then the call to the IP link fails, the dialed number is prefixed, and the call is forwarded via the ISDN gateway.
There is currently no verification procedure available for this configuration.
There is currently no specific troubleshooting information available for this configuration.