User manual

120 20131-301 Gemini G3 - User Manual
43
4.7.3.6.1.2 Multicast
IP mu
lticast addresses are in the range 224.0.0.0 to 239.255.255.255. These addresses are used to rep-
resent logical groups of units that may or may not reside on the same networks.
Multicast is used when “one-to-many” communication is required. For instance, a radio station might
offer a music channel on the Internet in real time. To receive the music a receiver-host must know the
multicast group (multicast address) used by the radio station sender-host and add itself as a member
of this group. In the IP realm, a host uses the IGMP protocol to do this. The routers inside the Internet
are using IGMP and other multicast routing protocols to build the proper path from the sender to the
receivers (a tree-like path is formed from the sender to the receivers).
Figure 37 - Registration to multicast group (First step)
Figure 38 - Reception of multicast packets (Second step)
Sender (owner of multicast group 226.1.2.3)
Receiver 1
(
Add membershi
p
226.1.2.3
)
Receiver 2
(
Add membershi
p
226.1.2.3
)
Receiver 3
(
Add membershi
p
226.1.2.3
)
Internet
Sender (owner of multicast group 226.1.2.3)
Receiver 1
(
member of 226.1.2.3
)
Receiver 2
(
member of 226.1.2.3
)
Receiver 3
(
member of 226.1.2.3
)
Internet
IP Router
IP Router
IP Router
IP Router
Paths from Sender to Members (Receivers
1, 2, and 3) flow in the Internet from IP
Router to IP Router to reach destinations
226.1.2.3.
Paths are not forwarded over interfaces that
do not lead to a multicast group member
5
1
2
2
3
3
4
Receiver
(
not a member of 226.1.2.3
)
Receiver
(
not a member of 226.1.2.3
)