Conferencing
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Conference Traffic
Cisco CallManager supports up to 48 software-based conference audio streams,
which equates to 16 conferences with 3 participants (48/3).A non-CallManager
server, on the other hand, supports up to 128 audio streams. Software conferencing
www.syngress.com
Figure 6.1 Conferencing
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Conference Traffic
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is based on G.711, whereas hardware-based solutions support G.711, G.729a, and
G.723.The newer Cisco IP phones 7900 Series supports G.711 and G.729a, but
the older style supports G.711 and G.723. Enterprises with large IP telephony environments
must rely on hardware-based conferencing and transcoding solutions such
as the Cisco Catalyst 4000 and 6000 switches.A hardware solution may be required
based on your user demands, since a CallManager can only support up to 48 audio
streams.This calculates out to 16 conferences maximum based on a 3-participant
conference.Transcoding is the process of converting IP packets of voice streams
between a low bit-rate (LBR) CODEC to and from a G.711 CODEC.A LBR is a
CODEC such as G.729a or G.723. An example of a need for transcoding is when a
user across the IP WAN wants to access a voice mail system which only supports
G.711, and CallManager is configured to initiate remote IP calls using a G.729a
CODEC, as shown in Figure 6.2. In this scenario, transcoding must be performed
to convert the G.729a voice stream to G.711 in order to communicate with the
voice mail system.