Voice Compression Channels - Avaya 1600 Series Installation Manual

1.9 Voice Compression Channels

Calls to and from IP devices can require conversion to the audio codec format being used by the IP device. For IP Office
systems this conversion is done by voice compression channels. These support the common IP audio codecs G.711,
G.722, and G.729a.
·
For the IP500 V2 control units, channels can be added using IP500 VCM cards and IP500 Combination Cards.
·
IP Office Server Edition systems provide their own voice compression channels through software without requiring
additional hardware.
The voice compression channels are used as follows:
Call Type
IP Device to Non-IP
Device
IP Device to IP Device
Non-IP Device to Non-
IP Device
Music on Hold
Conference Resources
and IP Devices
Voicemail Services and
IP Devices
Fax Calls
T38 Fax Calls
Note: T3 IP devices must be configured to 20ms packet size for the above conditions to apply. If left configured for 10ms
packet size, a voice compression channel is needed for all tones and for non-direct media calls.
Measuring Channel Usage
The IP Office system Status Application can be used to display voice compression channel usage. Within the Resources
section it displays the number of channel in use. It also displays how often there have been insufficient channels available
and the last time such an event occurred.
For IP500 VCM cards, the level of channel usage is also indicated by the LEDs (1 to 8) on the front of the IP500 VCM
card.
Installing VCM Cards
Refer to the IP Office Installation manual.
H323 Telephone Installation
IP Office™ Platform 11.0
Voice Compression Channel Usage
These calls require a voice compression channel for the duration of the call. If no channel is
available, busy indication is returned to the caller.
Call progress tones (for example dial tone, secondary dial tone, etc) do not require voice
compression channels with the following exceptions:
·
Short code confirmation, ARS camp on and account code entry tones require a voice
compression channel.
When a call is connected:
·
If the IP devices use the same audio codec no voice compression channel is used.
·
If the devices use differing audio codecs, a voice compression channel is required for
each.
No voice compression channels are required.
This is provided from the IP Office's TDM bus and therefore requires a voice compression
channel when played to an IP device.
Conferencing resources are managed by the conference chip which is on the IP Office's TDM
bus. Therefore, a voice compression channel is required for each IP device involved in a
conference. This includes services that use conference resources such as call listen, intrusion,
call recording and silent monitoring.
Calls to the IP Office voicemail servers are treated as data calls from the TDM bus. Therefore
calls from an IP device to voicemail require a voice compression channel.
These are voice calls but with a slightly wider frequency range than spoken voice calls. IP
Office only supports fax across IP between IP Office systems with the Fax Transport option
selected. It does not currently support T38.
IP Office 5.0+ supports T38 fax on SIP trunks and SIP extensions. Each T38 fax call uses a
VCM channel.
Within a Small Community Network, a T38 fax call can be converted to a call across an H.323
SCN lines using the IP Office Fax Transport Support protocol. This conversion uses 2 VCM
channels.
In order use T38 Fax connection, the Equipment Classification of an analog extension
connected to a fax machine can be set Fax Machine. Additionally, a new short code feature
Dial Fax is available.
Comments on this document? infodev@avaya.com
IP Office H.323 IP Phones: Network Assessment
Issue 23e (Friday, February 15, 2019)
Page 13