Download Avaya Configuring IP Multicasting and Multimedia Services User's Manual

Customizing DVMRP
Specifying a Threshold
Threshold values control the scope of datagram delivery. The threshold is the
minimum IP TTL (in hops) required for a multicast datagram to be forwarded out
a given interface.
For mrouted compatibility, multicast datagrams originated by the router have a
TTL of 1. These datagrams are not compared against the TTL. Unicast datagrams
originated by the router (for example, for route reports issued via a tunnel) have a
TTL of 255. A datagram that is to be forwarded through a tunnel is first compared
against the threshold and, if accepted, is then encapsulated in an IP datagram with
a TTL of 64.
Table 4-3 lists:
•
Originating TTL values recommended for certain types of multicast
applications
•
Threshold values recommended for routers to permit the forwarding of
packets from these applications
These values are recommended for topologies that will connect to the MBone.
Table 4-3.
Recommended TTL and Threshold Values
Multicast Application
TTL
Threshold
IETF channel 1 low-rate GSM audio
255
224
IETF channel 2 low-rate GSM audio
223
192
IETF channel 1 PCM audio
191
160
IETF channel 2 PCM audio
159
128
IETF channel 1 video
127
96
IETF channel 2 video
95
64
Local event audio
63
32
Local event video
31
1
By default, DVMRP uses a threshold value of 1. You can use the BCC or Site
Manager to specify a TTL value from 1 through 254.
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