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Polycom CMA System Operations Guide
398 Polycom, Inc.
Routing Mode
The CMA system has two routing modes.
Direct Mode
In this simplest gatekeeper mode, the CMA system gatekeeper resolves IP
addresses to their E.164 addresses and aliases (similar to the function of a
domain name server) and grants endpoints permission to place calls. Once the
gatekeeper performs these two functions, it plays no further role in the call.
Call signaling and media streams are sent directly between the endpoints in
the call.
In Direct mode, the number of concurrent calls supported by a CMA system
is derived from the number of device licenses at a 3/5 ratio (calls/devices). So,
for example, a system in Direct mode licensed for 5000 devices supports up to
3000 calls.
Use Direct mode when implementing a hierarchical architecture. A
hierarchical architecture is one with multiple gatekeepers, where one
gatekeeper—the CMA system in Direct mode—acts as the directory
gatekeeper at the top of the hierarchy. On the directory gatekeeper, you must
configure all of the other member gatekeepers as neighbors and on the
member gatekeepers you must configure the directory gatekeeper as a
neighbor. However, the member gatekeepers do not have to be neighbored
with each other.
When in Direct mode, some advanced CMA system features do not work.
These features include Simplified Dialing, Conference on Demand, Alternate
Routing, Least Cost Routing, MCU board hunting, and firewall traversal for a
Polycom VBP system in "Enterprise" or "E" mode. (Firewall traversal for a
Polycom VBP system in "Service Provider or "S" mode does work.)
The advantage of Direct mode is that conferences stay connected even if the
gatekeeper fails.
The disadvantage of Direct mode (along with the loss of advanced
functionality) is that during a failure and restart the gatekeeper loses track of
active calls that it was not involved in setting up. In this case, after a failure and
restart, the gatekeeper’s bandwidth calculations will be incorrect until those
calls end. Also, since the Conference Monitoring function uses gatekeeper
data, the monitoring information for those calls may be incorrect or
incomplete.
Routed Mode
In this advanced mode, the CMA system gatekeeper, besides performing the
functions of a Direct mode gatekeeper, also acts as a proxy for the call
signaling H.225 messages that set up the call. In this mode, only the media
streams are sent directly between the endpoints in the call.