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Networking Guide for Cisco Unity Release 5.x (With Microsoft Exchange)
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Chapter 8 Using VPIM for Networking with Cisco Unity Express or Other Cisco Unity Systems
Messaging Between Cisco Unity Servers in Different Directories
Example 3: One Cisco Unity Server Uses G.711 and the Other Uses G.729a
Consider the case where one Cisco Unity server uses G.711 for recording and storage and the other uses
G.729a. If network bandwidth is not an issue:
Cisco Unity can transcode messages recorded and stored in multiple formats, so the best option is to not
convert outbound or incoming VPIM messages. This approach avoids the overhead of audio format
conversions.
If network bandwidth is an issue, and you want to continue recording messages in G.711:
On the Cisco Unity server that uses G.711 Do not convert outbound messages.
Do not convert incoming messages.
On the Cisco Unity server that uses G.729a Do not convert outbound messages.
Do not convert incoming messages.
On the Cisco Unity server that uses G.711 Convert outbound messages to G.726. This resolves the
network bandwidth issue because the outbound messages
will be sent in the G.726 32Kbps format, which is half the
size of G.711 messages.
Do not convert incoming messages. In general, if a
message is recorded and stored in a lower quality codec,
and then later converted to a higher quality codec, the
sound quality does not improve, so there is no benefit to
converting the incoming G.729a messages to G.711.
On the Cisco Unity server that uses
G.729a
Do not convert outbound messages. At 8Kbps, the G.729a
is the best codec to use when there are network bandwidth
issues.
For incoming messages, your options are:
Convert incoming messages to G.729a. Although this
results in an additional audio format conversion,
presumably all subscriber workstations are already
configured for G.729a, because that is the codec used
by the Cisco Unity server.
Do not convert incoming messages, and leave them in
G.726. Although this avoids another conversion,
G.726 is not supported as a region (line) format for a
Cisco Unified Communications Manager integration.
Also, if VPIM messages are stored in G.726, all
Cisco Unity servers and subscriber workstations must
have the G.726 codec installed.