User's Manual

Configuration Guide of XGS-5240-Series
42-7
e data packet will be discarded else wise.
42.1.4 IP Multicast Application
IP Multicast technology has effectively solved the problem of sending in single poin
t and receiving in multipoint. It has achieved the effective data transmission from a poi
nt to multiple points, saved a great deal of network bandwidth and reduced network loa
d. Making use of the Multicast property of network, some new value-added operations
can be supplied conveniently. In Information Service areas such as online living broadc
ast, network TV, remote education, remote medicine, real time video/audio meeting, the
following applications may be supplied:
1) Application of Multimedia and Streaming Media
2) Data repository, finance application (stock) etc
3) Any data distribution application of “one point to multiple points”
In the situation of more and more multimedia operations in IP network, Multicast h
as tremendous market potential and Multicast operation will be generalized and populari
zed.
42.2 IGMP
42.2.1
Introduction to IGMP
IGMP (Internet Group Management Protocol) is the protocol in TCP/IP protocol fami
ly which is responsible for IP multicast member management. It is used to set up and
maintain multicast group member relationship between IP host and its neighbor multicas
t switches. IGMP does not include the spread and maintenance of relation information
of group members among multicast switches, this work is accomplished by each multic
ast routing protocol. All hosts participating in multicast must implement IGMP protocol.
Hosts participating IP multicast can join in and exit multicast group at any location,
any time and without limit of member total. Multicast switch does not need and not lik
ely to save all relationships of all hosts. It only gets to know if there are receivers of s
ome multicast group, i.e. group member, on the network segment each interface conne
cts to. And the host only needs to save which multicast groups it joined.
IGMP is asymmetric between host and router: the host needs to respond the IGMP
query messages of multicast switches, i.e. to report message response in membership;
the switch sends out membership query messages periodically, and then determine if t
here are hosts of some specific group joining in the sub-network it belongs to based o