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AMX AV/IT Administrators Guide

Rev. 1.0 (7/29/2014) www.amx.com Page 21

Multicast on the Internet is not practical because the Internet is generally not multicast-enabled. To

extend Multicast streams over the Internet a Reflector is used to convert them to Unicast.

Multicast on enterprise networks

IP multicast is a mechanism for one sender sending data to multiple recipients, but only sending a single

copy. It is accomplished by the sender forwarding UDP packets to a multicast IP address and port. The

range of IP addresses reserved for multicast is 224.0.0.0 - 239.255.255.255. Without additional controls,

such as IGMP and PIM (discussed below), multicasts are forwarded (flooded) to all ports like broadcasts.

Unlike broadcasts, multicasts can be routed. Additionally while all broadcasts are processed by the

network interface and passed up the stack to the host, multicasts are filtered by the NIC and only

multicasts the host is subscribed to are processed.

Multicast addressing: The range of IP addresses reserved for multicast is 224.0.0.0 - 239.255.255.255,

however many address ranges are reserved for special purposes. Best practice for streaming is to use

the range from 234.0.0.0 to 238.255.255.255, unless there is a specific reason to use other addressing.

Multicast devices do not detect address conflict; many devices could transmit on the same

multicast address without a failure. For example all Members of a group send IGMP Membership

reports to the same multicast address. Conceivably all the streaming devices could be

transmitting to the same multicast address on different ports. This is not the best practice in the

case of streaming sources. If that is done all members of the group would receive all streams

even if they were only viewing one.

Multicast Example

The illustration below depicts a multicast traffic across a properly configured layer 2 network. Although

all the encoders a transmitting a multicast stream, only the streams with a host in the (color coded)

multicast group are forwarded to the distribution switch. From the distribution switch on, each multicast

stream is only forwarded on any given segment if there is a downstream host joined to the multicast

group.

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AMX Wireless Touch Panels (Wave Server) Manual de usuario Pagina 24