Point to multiple-point propagation mode
Unicast: Multiple copies are needed.
Broadcast: Host not wanting
it also receives it
Multicast provides a good
solution to this problem
Multicast provides a good
solution to this problem
Hosts 1~3 want to receive video flow,
and Host 4 does not have this requirement.
Server
Host 1~3
Host 4
Host 4
Host 4
Host 1~3
Host 1~3
Server
Server
The IP multicast refers to the transmission of an IP message to a ―Host Group‖, and this host
group which includes zero to multiple hosts is identified by a separate IP address.
The host group address is also called ―Multicast Address‖, or Class D address, namely,
224.0.0.0 ~ 239.255.255.255. 224.0.0.0~224.0.0.255 are reserved, wherein:
224.0.0.1 – all hosts in the network segment that support multicast.
224.0.0.2 – all routers in the network segment that support multicast.
The multicast address (multicast MAC address) on the second layer is mapped from the IP
multicast address. Calculate the last 23 bits of the multicast IP and 01-00-5e-00-00-00, and
the result obtained is multicast MAC address. For example, the multicast IP address is
224.255.1.1, its hex notation denotes as e0-ff-01-01, the last 23 bits is 7f-01-01. Calculate it
with 01-00-5e-00-00-00, the result is: 01-00-5e-7f-01-01. 01-00-5e-7f-01-01 is the MAC
multicast address of group 224.255.1.1.
The IGMP (Internet Group Management Protocol) runs between the host and the unicast
routers connected to the host. Through this protocol, the host informs the local router its
intention to join and receive the information of a particular multicast group. At the same time,
the router checks whether the member of a known group in the LAN is in the active status
(that is, whether the network segment belongs to the member of a multicast group) through
this protocol at periodical intervals, to collect and maintain the membership of the network
To Next Page
Loading...
Need help?
General