1.5 Availability Issues

This topic describes availability issues in Cisco Unified Communications Manager multisite deployments.

Availability of the IP network, especially of the IP WAN that interconnects sites in a multisite deployment, is critical for several services:

  • Signaling
    1. Remote IP phones registering with centralized Cisco Unified Communications Manager
    2. Remote MGCP gateways controlled by centralized Cisco Unified Communications Manager
    3. Signaling to other call control systems via trunks
  • Media transmission
    1. RTP streams sent across the IP WAN
  • Other services, such as IP phone XML services, instant messaging, presence, etc.

When you deploy Cisco Unified Communications Manager in multisite environments, you access services over the IP WAN. The services that are affected include the following:

  • Signaling in Cisco Unified Communications Manager multisite deployments with centralized call processing: Remote IP phones register with a centralized Cisco Unified Communications Manager server. Remote MGCP gateways are controlled by a centralized Cisco Unified Communications Manager server that acts as an MGCP call agent.
  • Signaling in Cisco Unified Communications Manager multisite deployments with distributed call processing: In such environments, sites are connected via H.323 (nongatekeeper-controlled, gatekeeper-controlled, or H.225) or SIP trunks.
  • Media exchange: This service includes RTP streams between endpoints that are located in different sites.
  • Other services: These services include instant messaging, presence, and IP phone XML services, and access to applications such as attendant console, Cisco Unified Communications Manager Assistant, and others.

If the IP WAN connection is broken, these services are not available. This unavailability might be acceptable for some services, but strategic applications such as telephone call services should be made available during WAN failure via backup methods.

Availability Issues Example: IP WAN Failure

The figure illustrates an example of lost services during WAN failure.

IP WAN failure impacts the connection to the remote cluster, phones at remote sites, and access to the ITSP or any destination on the Internet.

In the example, there is a main site with an intercluster trunk to a remote Cisco Unified Communications Manager cluster. There is also a remote site with IP phones that register at the Cisco Unified Communications Manager cluster that is located at the main site. A SIP trunk is used to connect to an ITSP.

If a WAN failure occurs, no calls to the other cluster or to the ITSP are possible. In addition, all phones that are located at the remote site lose registration with Cisco Unified Communications Manager, so they do not operate at all. They cannot even place calls within the remote site.


A deployment as shown in the example is badly designed because of the lack of IP WAN backup.