Cisco Cisco Unified Contact Center Enterprise 8.5(1) Guía De Diseño
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Cisco Unified Contact Center Enterprise 7.0, 7.1, and 7.2 SRND
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Chapter 3 Design Considerations for High Availability
Data Network Design Considerations
Figure 3-3
High Availability in a Network with Two Voice Gateways and One Unified CM Cluster
Using multiple voice gateways avoids the problem of a single gateway failure causing blockage of all
calls. In a configuration with two voice gateways and one Unified CM cluster, each gateway should
register with a different primary Unified CM to spread the workload across the Unified CMs in the
cluster. Each gateway should use the other Unified CM as a backup in case its primary Unified CM fails.
For details on setting up Unified CM for redundant service related to call processing, refer to the
Cisco Unified Communications Solution Reference Network Design (SRND) guide (available at
calls. In a configuration with two voice gateways and one Unified CM cluster, each gateway should
register with a different primary Unified CM to spread the workload across the Unified CMs in the
cluster. Each gateway should use the other Unified CM as a backup in case its primary Unified CM fails.
For details on setting up Unified CM for redundant service related to call processing, refer to the
Cisco Unified Communications Solution Reference Network Design (SRND) guide (available at
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_implementation_design_guides
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With H.323 voice gateways, additional call processing is available by using TCL scripts and additional
dial peers if the gateway is unable to reach its Unified CM for call control or call processing instructions.
MGCP gateways do not have this built-in functionality, and the trunks that are terminated in these
gateways should have backup routing from the PSTN carrier or service provider to reroute the trunk on
failure or no-answer to another gateway or location.
dial peers if the gateway is unable to reach its Unified CM for call control or call processing instructions.
MGCP gateways do not have this built-in functionality, and the trunks that are terminated in these
gateways should have backup routing from the PSTN carrier or service provider to reroute the trunk on
failure or no-answer to another gateway or location.
As for sizing the gateway's trunk capacity, it is a good idea to account for failover of the gateways,
building in enough excess capacity to handle the maximum busy hour call attempts (BHCA) if one or
more voice gateways fail. During the design phase, first decide how many simultaneous voice gateway
failures are acceptable for the site. Based upon this requirement, the number of voice gateways used, and
the distribution of trunks across those voice gateways, you can determine the total number of trunks
required for normal and disaster” modes of operation. The more you distribute the trunks over multiple
voice gateways, the fewer trunks you will need in a failure mode. However, using more voice gateways
will increase the cost of that component of the solution, so you should compare the annual operating cost
of the trunks (paid to the PSTN provider) against the one-time fixed cost of the voice gateways. The
form-factor of the gateway is also a consideration; for example, if an entire 8-port T1 blade fails in a
Cisco Catalyst 6500 chassis, that event could impact 184 calls coming into the site.
building in enough excess capacity to handle the maximum busy hour call attempts (BHCA) if one or
more voice gateways fail. During the design phase, first decide how many simultaneous voice gateway
failures are acceptable for the site. Based upon this requirement, the number of voice gateways used, and
the distribution of trunks across those voice gateways, you can determine the total number of trunks
required for normal and disaster” modes of operation. The more you distribute the trunks over multiple
voice gateways, the fewer trunks you will need in a failure mode. However, using more voice gateways
will increase the cost of that component of the solution, so you should compare the annual operating cost
of the trunks (paid to the PSTN provider) against the one-time fixed cost of the voice gateways. The
form-factor of the gateway is also a consideration; for example, if an entire 8-port T1 blade fails in a
Cisco Catalyst 6500 chassis, that event could impact 184 calls coming into the site.
As an example, assume a call center has a maximum BHCA that results in the need for four T1 lines,
and the company has a requirement for no call blockage in the event of a single component (voice
gateway) failure. If two voice gateways are deployed in this case, then each voice gateway should be
provisioned with four T1 lines (total of eight). If three voice gateways are deployed, then two T1 lines
per voice gateway (total of six) would be enough to achieve the same level of redundancy. If five voice
and the company has a requirement for no call blockage in the event of a single component (voice
gateway) failure. If two voice gateways are deployed in this case, then each voice gateway should be
provisioned with four T1 lines (total of eight). If three voice gateways are deployed, then two T1 lines
per voice gateway (total of six) would be enough to achieve the same level of redundancy. If five voice
TDM
access
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Publisher
Sub 1
Sub 2
Cisco Unified CM
cluster
MDF
switch 1
Call control, CTI data,
IP messaging
TDM voice lines
Ethernet lines
IP messaging
TDM voice lines
Ethernet lines
Public
network
V
M
IDF
switch 1
IDF
switch 2
V
Voice
gateway 1
Voice
gateway 2
T1 lines
M
M
MDF
switch 2
T1 lines