The following figure shows geographically redundant Child data centers with clustering over the WAN (CoW) using Unified IP IVR.
Figure 5. Geographically Redundant Child Data Centers with Clustering over WAN (Using Unified IP IVR)
Geographically redundant data centers use clustering over the WAN, Unified Communications Manager clusters, and 1:1 redundancy for IP IVR, SIP proxy, voice gateways, and Cisco Unified Intelligence Center for example.
Latency requirements across the high-availability (HA) WAN must meet the current Cisco Unified Communications requirements for clustering over the WAN. Unified Communications Manager allows a maximum latency of 40 ms one way (80 ms for a round trip).
Certain fault tolerant networks can carry all your traffic on a single network, for example, Multiprotocol Label Switching (MPLS) or SONET. For such networks, keep the public and private traffic on separate routes within the network and respect standard latency and bandwidth.
Provision WAN connections to the agent sites with bandwidth for voice, control, and CTI. You can have a local voice gateway at remote sites for local and 911 calls. For more information, see Cisco Unified Communications and Collaboration Solutions Design Guidance at http://www.cisco.com/en/US/docs/voice_ip_comm/uc_system/design/guides/UCgoList.html
In a balanced deployment, central site outages include loss of half of the ingress gateways. Scale gateways to handle the full load in both sites it one site fails.
Carrier call routing must be able to route calls to the alternate site during failures.
A single Unified CCE system peripheral controls all the Unified IP IVRs and the Unified Communications Manager. Unified IP IVR distributes the calls to the least loaded Unified IP IVR. A Unified IP IVR in data center B can treat calls coming into data center A. Both A- and B-sides of Unified CCE can identify all the Unified IP IVRs. PIM activation logic determines if the A- or B- side PIM connects to each of the Unified IP IVRs. This process means that the PG at data center A can connect to the Unified IP IVR at data center B. Make sure that you size the WAN appropriately.
To avoid the bandwidth overhead, consider using Unified CVP for clustering over the WAN deployments. Unified CVP allows higher scalability per cluster than Unified IP IVR.