Cisco Unified Contact Center Enterprise Solution Reference ...

Chapter 3 Design Considerations for High Availability
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Peripheral Gateway Design Considerations
be monitored and maintained. The component failure scenarios noted previously (see Unified ICM
Failover Scenarios, page 3-25) are still valid in this model, and the additional failure scenarios for this
model include:
Scenario 1: Unified ICM Central Controller or Peripheral Gateway Private Network Fails, page 3-31
Scenario 2: Visible Network Fails, page 3-32
Scenario 3: Visible and Private Networks Both Fail (Dual Failure), page 3-33
Scenario 4: Unified MA Location WAN (Visible Network) Fails, page 3-34
Scenario 1: Unified ICM Central Controller or Peripheral Gateway Private Network Fails
In clustering over the WAN with Unified CCE, there must be a dedicated, isolated private network
connection between the geographically distributed Central Controller (Call Router/Logger) and the split
Peripheral Gateway pair to maintain state and synchronization between the sides of the system, and TCP
keep-alive messages are generated to verify the health of this link. The Unified ICM uses the TCP
keep-alive messages to detect a failure on the private link. Missing five consecutive TCP keep-alive
messages will signal the Unified ICM that the link or the remote partner system might have failed.
If the private network fails between the Unified ICM Central Controllers, the following conditions apply:
The Call Routers will detect the failure by missing five consecutive TCP keep-alive messages. Both
Call Routers send a test-other-side (TOS) message to the Peripheral Gateways, starting with PG1A,
then PG1B, then PG2A, and so forth. The TOS message requests the Peripheral Gateway to check
if it can see the Call Router on the other side to determine if the failure is a network failure or a
failure of the redundant-pair server.
The Call Routers use the PG reply to the TOS message to verify which side of the Call Router pair
sees more active connections of the Peripheral Gateways. The side that sees more active connections
of the Peripheral Gateways will continue to function as the active Call Router in simplex mode, and
the redundant Call Router will be disabled.
All the Peripheral Gateways will realign their active data feed to the active Call Router over the
visible network, with no failover or loss of service.
There is no impact to the agents, calls in progress, or calls in queue. The system can continue to
function normally; however; the Call Routers will be in simplex mode until the private network link
is restored.
If the private network fails between the Cisco Unified CallManager Peripheral Gateways, the following
conditions apply:
The Peripheral Gateway sides will detect the failure by missing five consecutive TCP keep-alive
messages. The Peripheral Gateways verify which side of the duplex pair has the active connection
to the Cisco Unified CallManager cluster.
The Peripheral Gateway side of the duplex pair that was actively connected to the Cisco Unified
CallManager cluster will continue to function as the active side of the pair, in simplex mode. The
other side will be inactive until the private network connection is restored.
There is no impact to the agents, calls in progress, or calls in queue. The system can continue to
function normally; however; the Call Routers will be in simplex mode until the private network link
is restored.
If the two private network connections were combined into one link, the failures would follow the same
path; however, the system would be running in simplex on both the Call Router and the Peripheral
Gateway. If a second failure were to occur at that point, the system could lose some or all of the call
routing and ACD functionality.
Cisco Unified Contact Center Enterprise 7.x SRND
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