Chapter 3 Connecting to the Network
AVN422HD User’s Manual
8
Chapter 3 Connecting to the Network
3.1 Unicast and Multicast Transmissions over the Network
A Unicast transmission sends IP packets to a single recipient on a network. A Multicast
transmission sends IP packets to a group of hosts on a network. If the streaming video is to be
distributed to a single destination, then you would start a Unicast stream by setting the
destination IP address and port on the AVN equal to the destination's values. If you want to view
the stream at multiple concurrent locations, then you would set the AVN's destination IP address
to a valid Multicast IP address (224.0.0.0 - 239.255.255.255).
Note that while the Multicast IP address range is from 224.0.0.0 - 239.255.255.255, the first octet
(224.xxx.xxx.xxx) is generally reserved for administration. VSI recommends setting the first octet
to 225 and the remaining three octets to the AVN's IP address. For example, if the AVN's IP
address is 192.168.1.53, then set the destination IP address to 225.168.1.53 for Multicast
streaming.
Since Multicasting is a relatively new technology, some legacy devices that are part of your
network might not support Multicasting.
Before using the AVN422HD in Multicast streaming mode, check the functional specifications of
your network infrastructure to ensure that the Multicast stream will not create major traffic on your
network. Verify that your backbone switch supports Internet Group Messaging Protocol (IGMP)
snooping, which allows the core of your network to ignore the traffic streams that Multicasting
may generate.
3.2 IGMP Querying and IGMP Snooping
IGMP is a session-layer (Layer 3) protocol used to establish membership in a Multicast group
and can register a router to receive specific Multicast traffic. (Refer to RFC 1112 and RFC 2236
for information on IGMP versions 1 and 2.)
Multicast aware switches are slowly making their way into the network cores for businesses and
universities that have heavy traffic to move through their networks. Multicast filtering is achieved
by dynamic group control management. By default, all Multicast traffic should be blocked until
requested by a Multicast group member. (Default behavior depends on switch manufacturer.)
The master of the IGMP filter lists is the router or switch that is configured to act as the IGMP
Querier. The responsibility of the Querier is to send out IGMP group membership queries on a
timed interval, to retrieve IGMP membership reports from active members, and to allow updating
of the group membership tables.
A Layer 2 switch supporting IGMP Snooping can passively snoop on IGMP Query, Report, and
Leave (IGMP version 2) packets transferred between IP Multicast routers/switches and IP
Multicast hosts to determine the IP Multicast group membership. IGMP snooping checks IGMP
packets passing through the network, picks out the group registration, and configures
Multicasting accordingly.
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