Key Concepts; Traffic Movement; Ip Multicast Groups; Source-Group Pairs - 3Com corebuilder 3500 Implementation Manual

338 C 13: IP M R
HAPTER ULTICAST OUTING

Key Concepts

This section describes several terms and concepts related to IP multicast
routing.

Traffic Movement

Application sources generate the majority of IP multicast packets, but
group members and routers that are communicating (DVMRP and IGMP
messages) to establish the delivery path also generate IP multicast
packets.
Traffic from application sources always travels in one direction —
downstream from the source to group members. Using various protocols,
network devices are responsible for determining where group members
exist and coordinating a loop-free delivery path from the source to them.
Traffic that relates to the delivery path can travel both upstream and
downstream — between routers and between routers and group
members.
Users can join or leave an IP multicast group at any time. Users request

IP Multicast Groups

and cancel membership through mechanisms built into their desktop
application — perhaps visible to the user as Go and Quit buttons. There
are no restrictions on the physical location or number of members in a
group. A user may belong to one or more groups at any time.

Source-Group Pairs

Each IP multicast transmission can be linked to a unique pairing of a
source address and multicast group address (destination address). In
addition, network devices form a unique delivery path for each
source-group pair. Multicast routers and switches track information about
each source-group pair — mainly, the location of group members — and
dynamically adjust the delivery path to ensure that IP multicast packets
are delivered only where they need to go.