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H323 IP Telephone Installation Page 11
15-601046 Issue 16a (15 March 2010)IP Office Release 6
IP Office H323 IP Phones: Supported Phones
1.3 System Capacity
System capacity can be separated into two aspects; the number of configurable phone extensions and the number of
simultaneous IP phone calls.
Extension Capacity
The maximum number of H323 IP phones supported by an IP Office system is based on that system's maximum capacity
for extensions of any type as listed in the table below. To find the capacity for IP phones remove the number of physical
non-IP extensions installed on the system, ie. extension ports on the IP Office control unit and any external expansion
modules.
IP Office Unit
Maximum
Extensions
Maximum VCM
Channels
IP406 V2
190
30
IP412
360
60
IP500
384
128
IP500 V2
384
148
Call Capacity
There are a number of situations where the IP Office system needs to provide a voice compression channel in order for an
IP phone to make calls. These channels are provided by Voice Compression Modules (VCMs) installed in the IP Office
system. The number of VCM channels required and how long the channel is required will depend on a number of factors.
For further details see Voice Compression .
A simple summary is:
· A VCM channel is required during call setup.
· The VCM channel is released if the call is to/from another IP device using the same compression codec (the
supported VCM codecs are G711, G729 and G723a).
· The VCM channel is used for the duration of the call when the call is to/from/via a non-IP device (extension or trunk
line).
· It should be remembered that VCM channels are also used for calls from non-IP devices to IP lines if those are
configured in the IP Office system (IP, SIP and SES lines).
· Calls from IP phones to the IP Office voicemail server use a VCM channel.
· Note that on Small Office Edition systems with Embedded Voicemail, an additional channel is used for every call
to voicemail.
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