Information Technology Reference
In-Depth Information
Mechanisms and configurations that can be categorized as using local CAC include
max-connections
, which allows a dial
peer to enforce a maximum number of active connections, and local voice busyout (LVBO), which allows PBX (analog and
CAS) trunks to be taken out of service when WAN conditions are not suitable for voice transport.
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Measurement-based CAC
is based on a determination of network state prior to admitting a call, and involves the use of
(Cisco Service Level Agreement/Service Assurance Agent [SLA/SAA]) probes.
Mechanisms that fall into the category of measurement-based CAC include advanced voice busyout (AVBO), which is a
feature based on LVBO that adds the capability to probe destinations using Cisco SLA/SAA.
CAC mechanisms can also be categorized according to whether they are topology aware or topology unaware:
■
Topology-aware mechanisms:
These function based on communication between the call-processing agent and the
network as to available network resources and can dynamically adjust to changes in topology. These mechanisms should be
implemented in networks that do not correspond to a simple hub-and-spoke model.
Topology-unaware mechanisms:
These require static configuration on the call-processing agent. These mechanisms are
typically deployed only in comparatively simple network topologies, such as hub-and-spoke topologies.
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CUCM locations can be implemented in a simple multisite WAN (hub-and-spoke) centralized call-processing network. Locations
can also be used in a two-tier hub-and-spoke deployment (where CUCM clusters are located at first- and second-tier hub sites), with
locations used for CAC on the links between the second-tier hub and the connected spoke sites. Gatekeeper zones can be used for
CAC on links between first- and second-tier hub sites in a two-tier hub-and-spoke deployment.
When using CUCM locations, CUCM monitors the amount of bandwidth available for voice being used by calls into and out of each
location, and then either allows or disallows new calls between locations, depending on whether there is available bandwidth. (CUCM
attempts to allocate bandwidth from pools corresponding to the locations of the endpoints involved in the call.) It should also be
mentioned that calls within a particular location are not tracked (no CAC is performed), and when using CUCM locations, CUCM is
unaware of the topology of the network providing connectivity between locations.
When using Locations in a hub-and-spoke topology, devices at the hub site should be assigned to the <None> location.
