Information Technology Reference
In-Depth Information
Phone Security Profile
Common Phone Profile
Device Pool
Device Pools provide a set of common configurations to a group of devices; think of a
Device Pool as a template to apply several different settings all at once, quickly and accu-
rately. You can create as many Device Pools as you need, typically one per location, but
they can also be applied per function. (For example, all the phones in the call center may
use a different Device Pool from the rest of the phones in the administration offices, al-
though they are all at the same location.) There are several settings within the Device Pool;
some of the ones relevant to us are described next.
Cisco Unified CM Group A CM Group defines a top-down ordered list of redundant
subscriber servers to which the phones can register. The list can include a maximum of
three subscribers (plus an optional Survivable Remote Site Telephony [SRST] reference).
The first server in the list is the primary subscriber; the second is the backup, and the third
is the tertiary. In normal operation, phones send primary registration messages to the pri-
mary, backup registration messages to the backup, and nothing to the tertiary. If the
primary server fails or otherwise becomes unavailable, the phone sends a primary registra-
tion message to the backup server (and registers with it) and begins sending backup
registration messages to the tertiary.
The number of CM Groups created depends on the number of subscribers in the cluster;
the goal is to provide server redundancy to the phones while distributing phone registra-
tions evenly as planned in the system design. A subscriber may be listed in more than one
CM Group to provide an overlapping depth of coverage, as long as its performance capac-
ity will not be exceeded in any foreseeable failure circumstance. This is simply another
requirement of a good design.
Region A region is a virtual assignment that allows the system designer to control the bit
rate for calls. For example, if we define two regions, called Vancouver_HQ_REG and Ot-
tawa_BR_REG, we can set the bit rate for calls within the Vancouver region to 256 kbps,
within the Ottawa region to 64 kbps, and between the two regions to 16 kbps.
We are actually selecting the codec to be used for these calls; the codec in turn generates a
known bit rate, which in turn uses a predictable amount of bandwidth and provides a pre-
dictable voice quality. In general, it is assumed that WAN bandwidth is limited; selecting a
lower bit rate reduces the amount of bandwidth per call at the expense of call quality.
Location As we just saw, we can select the appropriate bit rate for calls and, therefore,
the bandwidth used by each call. Given that WAN bandwidth is usually limited, we need
to be able to limit the amount of bandwidth used by calls to a particular location. Loca-
tion defines a maximum amount of bandwidth used by calls to a particular location; each
call is tracked, and the bandwidth it uses is deducted from the total for that location.
When the bandwidth remaining is not enough to support another call at a given bit rate,
that call is dropped by default (but may be rerouted over the PSTN if AAR is correctly
configured). This is one mechanism for Call Admission Control, which is described later in
this topic.
 
 
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