Cisco Unified Contact Center Enterprise Solution Reference ...

Peripheral Gateway Design Considerations
Scenario 2: Visible Network Fails
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Cisco Unified Contact Center Enterprise 7.x SRND
Chapter 3 Design Considerations for High Availability
Note The terms public network and visible network are used interchangeably throughout this document.
The visible network in this design model is the network path between the data center locations where the
main system components (Cisco Unified CallManager subscribers, Peripheral Gateways,
Unified IP IVR/Unified CVP components, and so forth) are located. This network is used to carry all the
voice traffic (RTP stream and call control signaling), Unified ICM CTI (call control signaling) traffic,
as well as all typical data network traffic between the sites. In order to meet the requirements of
Cisco Unified CallManager clustering over the WAN, this link must be highly available with very low
latency and sufficient bandwidth. This link is critical to the Unified CCE design because it is part of the
fault-tolerant design of the system, and it must be highly resilient as well:
The highly available (HA) WAN between the central sites must be fully redundant with no single
point of failure. (For information regarding site-to-site redundancy options, refer to the WAN
infrastructure and QoS design guides available at http://cisco.com/go/srnd.) In case of partial failure
of the highly available WAN, the redundant link must be capable of handling the full central-site
load with all QoS parameters. For more information, see the section on Bandwidth Requirements
for Unified CCE Clustering Over the WAN, page 11-17.
A highly available (HA) WAN using point-to-point technology is best implemented across two
separate carriers, but this is not necessary when using a ring technology.
If the visible network fails between the data center locations, the following conditions apply:
The Cisco Unified CallManager subscribers will detect the failure and continue to function locally,
with no impact to local call processing and call control. However, any calls that were set up over this
WAN link will fail with the link.
The Unified ICM Call Routers will detect the failure because the normal flow of TCP keep-alives
from the remote Peripheral Gateways will stop. Likewise, the Peripheral Gateways will detect this
failure by the loss of TCP keep-alives from the remote Call Routers. The Peripheral Gateways will
automatically realign their data communications to the local Call Router, and the local Call Router
will then use the private network to pass data to the Call Router on the other side to continue call
processing. This does not cause a failover of the Peripheral Gateway or the Call Router.
Agents might be affected by this failure under the following circumstances:
– If the agent desktop (Cisco Agent Desktop or CTI OS) is registered to the Peripheral Gateway
on side A of the system but the physical phone is registered to side B of the Cisco Unified
CallManager cluster.
Under normal circumstances, the phone events would be passed from side B to side A over the
visible network via the CTI Manager Service to present these events to the side A Peripheral
Gateway. The visible network failure will not force the IP phone to re-home to side A of the
cluster, and the phone will remain operational on the isolated side B. The Peripheral Gateway
will no longer be able to see this phone, and the agent will be logged out of Unified CCE
automatically because the system can no longer direct calls to the agent's phone.
– If the agent desktop (Cisco Agent Desktop or CTI OS) and IP phone are both registered to
side A of the Peripheral Gateway and Cisco Unified CallManager, but the phone is reset and it
re-registers to a side B of the Cisco Unified CallManager subscriber.
If the IP phone re-homes or is manually reset and forced to register to side B of a Cisco Unified
CallManager subscriber, the Cisco Unified CallManager subscriber on side A that is providing
the CTI Manager service to the local Peripheral Gateway will unregister the phone and remove
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