Cisco Cisco IOS Software Release 12.3(11)T

The recommended minimum Cisco IOS Release for this feature is Release 12.3(7)T. For optimum 
results, use Cisco IOS Release 12.3(11)T2.

This feature requires 32 MB of Flash memory, 1.1 MB of I/O memory, and 96 MB of RAM (128 MB of 
RAM is required for the Cisco 2600XM series and the Cisco 3700 series).

The IP Communications Voice/Fax Network Module feature does not currently offer echo cancellation 
on the VWICs configured as T1 interfaces, which may result in a degradation of service in some 
instances.

This section provides information about the following:

The IP Communications Voice/Fax Network Module feature is composed of software modules that offer 
the following features on voice network modules:

Channel group support for up to 32 channels

Flex option for configuring codec complexity—This new option allows the digital signal processor 
(DSP) to process up to 16 channels. In addition to continuing support for configuring a fixed number 
of channels per DSP, the flex option enables the DSP to handle a flexible number of channels. The 
total number of supported channels varies from 6 to 16, depending on which codec is used for a call. 
Therefore, the channel density varies from 6 per DSP (high-complexity codec) to 16 per DSP (g.711 
codec).

Oversubscription—In flex mode, you can connect (or configure in the case of DS0 groups and 
PRI groups) more voice channels to the module than the DSPs can accommodate. If all voice 
channels should go active simultaneously, the DSPs will be oversubscribed and calls that are 
unable to allocate a DSP resource will fail to connect.