ZXDSL 9210 (V3.1) Broadband Universal Access Equipment Technical Manual
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means that the host requires multiple IP and Ethernet addresses. The IP address
scheme allocates an address range specially for the multicast. IPv4 contains
class-D addresses within the range of 224.0.0.0 to 239.255.255.255; class-D
addresses are classified into partial link multicast addresses, reserved multicast
addresses, and management authority multicast addresses. The definitions of
these address are as follows:
1) Partial link address: Within the range of 224.0.0.0 to 224.0.0.255; the address is
used for LAN; the router does not forward any IP packets within this range.
2) Reserved multicast address: 224.0.1.0 to 238.255.255.255, used for global scope
or network protocols;
3) Management authority address: 239.0.0.0 to 239.255.255.255, used within an
organization and used to restrict multicast range.
The last 28 bits of D-class addresses are not structured, that is, there is no
distinguishing between a network ID and host ID. The hosts responding a certain
IP multicast address form a host group, which may go beyond multiple networks.
The members of the host group can be dynamic; a host can join or leave a host
group via the IGMP. As the significant 5 bits of an IP multicast address are not
mapped, the mapped Ethernet address is not unique. There are 32 IP multicast
addresses mapped to one Ethernet address.
6.2.9.2 Multicast Protocol
Multicast protocols consist of the IGMP and the multicast routing protocol.
1. IGMP
The host adopts the IGMP to inform a subnet multicast router of joining the
multicast group; the router adopts the IGMP to query whether there is any host
in the local subnet belonging to a multicast group.
1) Join a multicast group
When a host joins a multicast group, it informs the multicast router of the home
IP subnet via the "member qualification report" message; it also prepares the IP
module so as to receive the data from the multicast group. If the host is the first
one in the multicast group of the home IP subnet, the multicast router joins the
multicast distribution tree via routing information switching.
