Appendix B: Integrating Cisco Unified Communications Manager and Cisco Unified SRST to Use Cisco Unified SRST
How to Use Cisco Unified SRST Gateways as a Multicast MOH Resource
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Cisco Unified SCCP and SIP SRST System Administrator Guide
OL-13143-04
Incrementation is triggered by a change in codec usage. When codec usage changes, a new IP address or
port number (depending on the incrementation selected) is assigned to the new codec type and is put into
use. The original codec keeps its IP address and port number. For example, as seen in
Table 2
, if your
baseline IP address and port number are 239.1.1.1 and 16384 for a G.711 mu-law codec and the codec
usage changes to G.729 (triggering an increment on the port number), the IP address and port number in
use changes, or increment, to 239.1.1.1 and 16386. If G.711 usage resumes, the IP address and port
number returns to 239.1.1.1 and 16384. If G.729 is in use again, the IP address and port goes back to
239.1.1.1 and 16386, and so forth.
It is important to configure a Cisco Unified CM port number and IP address that use a G.711 audio source
for Cisco Unified SRST multicast MOH. If Cisco Unified CM multicast MOH is also being used on
gateways that do not have Cisco Unified SRST and use a different codec, such as G.729, ensure that the
additional or incremental port number or IP address uses the same audio source as the Cisco Unified
SRST gateways and the required codec.
The MOH Server Configuration window is also where the multicast audio source for the MOH server is
configured. For Cisco Unified SRST multicast MOH, the Cisco Unified CM MOH server can use only
one audio source. An audio source is selected by inputting the audio source’s maximum number of hops.
The Max Hops configuration sets the length of the transmission of the audio source packets. Limiting
the number of hops is one way to stop audio packets from reaching the WAN and thus spoofing
Cisco Unified Communications Manager so Cisco Unified SRST can multicast MOH. If all of your
branches run Cisco Unified SRST, use a low number of hops to prevent audio source packets from
crossing the WAN. If your system configuration includes routers that do not run Cisco Unified SRST,
enter a high number of hops to allow source packets to cross the WAN. Use the
ip multicast bounder
and
access-list
commands to keep resource packets from specific IP addresses from reaching the WAN.
Table 2
Example of the Differences Between Incrementing Multicast on IP Address and Incrementing Multicast on
Port Number
Audio Source
Codec
Increment Multicast on IP Address
Increment Multicast on Port Number
Destination IP
Address
Destination
Port
Destination IP
Address
Destination
Port
1
G.711 mu-law
239.1.1.1
16384
239.1.1.1
16384
1
G.711 a-law
239.1.1.2
16384
239.1.1.1
16386
1
G.729
239.1.1.3
16384
239.1.1.1
16388
1
Wideband
239.1.1.4
16384
239.1.1.1
16390
2
G.711 mu-law
239.1.1.5
16384
239.1.1.1
16392
2
G.711 a-law
239.1.1.6
16384
239.1.1.1
16394
2
G.729
239.1.1.7
16384
239.1.1.1
16396
2
Wideband
239.1.1.8
16384
239.1.1.1
16398
