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Cisco AVVID Network Infrastructure IP Multicast Design - page 83 / 98





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Chapter 7

Multicast Music-on-Hold and IP/TV Configurations

Multicast Music-on-Hold

Increment Multicast on IP Address

If the MoH server is configured with “Increment Multicast on IP Address,” the starting address is for the G.711ulaw CODEC and the addresses are incremented by 1 for each additional CODEC.

As a result, for every file that is added as a multicast audio source, four addresses are consumed (one for every CODEC). The current maximum for audio sources on a single MoH server is 51 (50 file sources and 1 fixed source). Resulting in a maximum requirement of 204 multicast addresses (51 files each with 4 CODECs).

Even so, it is better to use “Increment Multicast on IP Address” and not “Increment Multicast on Port Number” because IP multicast routers understand (S,G) notations and not port numbers.

For example, let’s assume that “Increment Multicast on Port Number” is configured for audio sources and G.729 is to be used for the branch office phones. Then, when the branch office IP phone issues an IGMPv2 Join for the group associated with the audio source, all four streams are sent to the branch. Because the four streams have the same group address (different port numbers are ignored), the router at the branch pulls all four streams even though only one stream is needed.

The four streams together use a bandwidth total of about 480 Kbps.

  • G.

    711ulaw =77Kbps

  • G.

    711alaw= 77Kbps

  • G.

    729 = 26Kbps

Wideband = almost 300Kbps

The result could be a terrible load on the network, given that there could be up to 51 sources streaming 480Kbps each.


The recommendation is to use the G.711ulaw or Wideband CODEC in the campus network. G.729 consumes less bandwidth than the G.711 or Wideband CODEC and is recommended for use in the WAN. Using G.729 will conserve bandwidth, but the audio quality is poor.

Table 7-1 lists the maximum number of MoH sessions for each model of server. The maximum sessions refers to unicast, multicast, or unicast and multicast sessions. This is the recommended maximum sessions a platform can support, irrespective of the transport mechanism.

Server Platform

CODECs Supported

MoH Sessions

MCS 7815 MCS 7825 (800/1133) MCS 7830 SPE-310 Compaq DL310 Compaq DL320 IBM xSeries 330

G.711 (A-law and µ -law) G.729aWideband Audio

20 MoH sessions (co-resident) 50 MoH sessions (Stand-alone MoH Server)

MCS 7835 (1000/1266) Compaq DL380 IBM xSeries 340

G.711 (A-law and µ -law) G.729aWideband Audio

20 MoH sessions (co-resident) 250 MoH sessions (Stand-alone MoH Server)

Table 7-1

Maximum Number of MoH Sessions.

Cisco AVVID Network Infrastructure IP Multicast Design



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