Avoid VCS SIP UDP Timeout

Introduction

This document describes the scenarios in which Video Communication Server (VCS) control is integrated with VCS Expressway via traversal zone.

Prerequisites

Requirements

Cisco recommends that you have knowledge of these topics:

• Neighbor zones on Cisco VCS/Expressway
• Transforms and search rules on Cisco VCS/Expressway
• Interworking option on Cisco VCS/Expressway

Components Used

The information in this document is based on Cisco VCS x8.1 and later.

Note: The same document can be used for Expressway series deployments with Cisco Unified Communication Manager (CUCM) that has IP-address dialing enabled.

The information in this document was created from the devices in a specific lab environment. All 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.

Background Information

It is common that internal Session Initiation Protocol (SIP) endpoints call external H.323 endpoints by dialing IP address. In this situation, Video Communication Server Expressway (VCSe) interworks the call in order to allow SIP to H.323 interoperability. But there is an issue because when VCSe receives the call invite from internal endpoints, the source protocol is SIP. VCSe then tries to connect to the external endpoint first using SIP, if SIP fails, VCS attempts to connect using H.323 and then the call proceeds.

However, when VCSe tries to connect using SIP, it tries User Datagram Protocol (UDP) to connect to far end. When it tries UDP, VCS waits 30 seconds for SIP UDP to timeout before trying to use H.323. The result is the user waiting about 30 seconds before the remote device starts ringing. Most users simply give up by this time.

Configure

Ensure that the calls to unknown IP addresses parameter are set to Indirect (from the drop-down list) on the VCS Control/Expressway-C. In order to do so, navigate to Configuration > Dial Plan > Configuration as shown in this image.

Ensure that the calls to unknown IP addresses parameter are set to Direct (from the drop-down list) on the VCS Expressway/Expressway-E. In order to do so, navigate to Configuration > Dial Plan > Configuration as shown in this image.

How to Avoid SIP UDP Timeout

Option 1. You can avoid SIP UDP timeout by turning off the SIP UDP mode on VCS-Expressway/Expressway-E under SIP global configuration.

Navigate to Configuration > Protocols >SIP and turn off the UDP mode as shown in this image.

Option 2. In case you choose not to disable the UDP mode, use the workaround solution to avoid SIP UDP timeout.

1. Create a second traversal zone with only H.323 protocol enable (it requires one additional port to be opened on the firewall for H.323 communication).
2. Create a custom search rule for SIP protocol with destination Any IP address towards this new traversal zone.

The result of this configuration is that every time an internal SIP endpoint that tries to dial an external IP address, VCS Control interworks the call before sending it to VCS Expressway. VCSe receives a H.323 setup instead of a SIP INVITE, then it attempts to call using H.323, so that it does not have to wait for SIP UDP timeout.

Create Second Traversal Zone

You can establish a second traversal zone between VCS Control & Expressway, however, as the traversal server (VCSe) identifies the traversal client by using the port number, you have to define another H.323 port (which is not in use) for this new traversal zone. For example, use the port number 6002 to establish the new zone (assuming port 6001 is already used for first traversal zone).

It is important to note that you also open an additional port in the firewall as well, allowing the traffic from VCS Control to VCS Expressway.

Traversal Server Zone Configuration VCS Expressway

Ensure that only H.323 protocol is enable on this second traversal zone as shown in this image.

Traversal Client Zone Configuration VCS Control

Ensure that only H.323 protocol is enable on this second traversal zone as shown in this image.

Create Custom Search Rule for SIP Protocol

You must create a custom search rule in VCS Control. This search rule must to be pointed to Traversal zone 2. The rule matches only SIP endpoints when they dial any external IP address:

Navigate to Configuration > Dial Plan > Search Rules and click New as shown in this image.

Create the search rule towards the new traversal zone as shown in this image.

Verify

Use this section to confirm that your configuration works properly.

Once the previous steps are completed, you must be able to dial the IP-Address without any delay from an endpoint registered to the VCS Control as SIP.

Troubleshoot

This section provides information you can use to troubleshoot your configuration.

• The IP-address search rule must have priority over any another search rule towards the common (other) Traversal Zone, otherwise, the call from SIP endpoints with destination IP address might not match the new rule and the workaround does not work.

• It is also important to note that if you have search rules with destination, Any IP Address pointing to your local zone in VCS Control, the new traversal zone search rule must not have priority over the search rules towards local zone. You must have Successful Match “Continue” set on the Local Zone Search Rule. Ensure that you set a correct priority value for the search rule mentioned in this document so that you can force interworking only for calls from internal SIP endpoints towards external H.323 endpoints.

Ensure that the Interworking option key is installed on both VCS-Control and VCS-Expressway

Navigate to Maintenance > Option keys and check the Option keys as shown in this image, alternatively you can also verify under system information.

Also verify that interworking mode is set to On both VCS-Control & Expressway as shown in this image.

Navigate to Configuration > Protocols > Interworking.

Related Information

• Setting up Traversal zone for VCS-Control and Expressway:

http://www.cisco.com/c/dam/en/us/td/docs/telepresence/infrastructure/vcs/config_guide/X8-5/Cisco-VCS-Basic-Configuration-Control-with-Expressway-Deployment-Guide-X8-5-2.pdf

• Enable IP-Address dialing via CUCM:

http://www.cisco.com/c/en/us/support/docs/unified-communications/telepresence-video-communication-server-vcs/118884-config-vcs-00.html

• VCS Admin guide:

http://www.cisco.com/c/dam/en/us/td/docs/telepresence/infrastructure/vcs/admin_guide/Cisco-VCS-Administrator-Guide-X8-5-2.pdf

• Technical Support & Documentation - Cisco Systems