2.9 Availability Overview

This topic describes survivability and availability features in multisite deployments.

  • PSTN backup
  • MGCP fallback
  • Fallback for IP phones:
    1. Cisco Unified SRST
    2. Cisco Unified Communications Manager Express in Cisco Unified SRST mode
  • CFUR
  • AAR and CFNB
  • Mobility solutions:
    1. Cisco Extension Mobility
    2. Cisco Device Mobility
    3. Cisco Unified Mobility

These options can improve availability:

  • PSTN backup: Use the PSTN as a backup for on-net intersite calls.
  • MGCPfallback: Configure an MGCP gateway to fall back and use the locally configured POTS, H.323, or SIPdial peers when the connection to its call agent is lost. This approach enables you to effectively make use of the gateway by using a locally configured dial plan, which is ignored when the gateway is in MGCP mode.
  • Fallback for IP phones: IP phones that register over the IP WAN can have a local Cisco IOS SRST gateway that is configured as a backup Cisco Unified Communications Manager server in their Cisco Unified Communications Manager group configuration. When the connection to the primary Cisco Unified Communications Manager server is lost, they can reregister with the local Cisco Unified SRST gateway. Alternatively, Cisco Unified Communications Manager Express can be used in SRST mode, which provides more features than standard Cisco Unified SRST.
  • CFUR: CFUR is a call-forwarding configuration of IP phones that becomes effective when the IP phone is not registered.
  • AAR: AAR allows calls to be rerouted over the PSTN when calls over the IP WAN are not admitted by CAC.CFNB is a call-forwarding configuration of IP phones, which becomes effective when AAR is used.
  • Mobility solutions: When users or devices roam between sites, they can lose features or have suboptimal configuration because of a change in their actual physical location. Cisco Extension Mobility and Cisco Device Mobility can solve such issues. In addition, these features allow integration of cell phones and home office phones by enabling reachability on any device via a single (office) number.