Zte ZXR10 GER, Руководство пользователя

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ZXR10 GER (V2.6.03) General Excellent Router User Manual Volume-I
332 Confidential and Proprietary Information of ZTE CORPORATION
Source-based multicast tree is also called the source shortest
path tree, which constructs a spanning tree toward all receivers
for each source. The spanning tree, with the subnet of the
source as a root node, extends to the subnet where receivers
exist. A multicast group may have many multicast sources, each
of them, or each pair (S, G) of them corresponding to a
multicast tree.
The method to construct the source-based multicast trees is the
reverse route forwarding (RPF). Each router can find the
shortest path toward the source and the corresponding output
interface according to a unicast route. When receiving a
multicast packet, a router checks whether the input interface
reached is the output interface of the shortest unicast path from
itself to source. If yes, the router copies and forwards the packet
to other interfaces. If not, the router discards the multicast
packet.
The input interface receiving multicast packets in the router is
called the parent link. The output interface sending multicast
packets is called the sub-link.
„
Shared multicast tree
The share multicast tree constructs for each multicast group.
This tree is shared by all members of a group. Namely, a shared
multicast tree is shared by (*, G) instead of being constructed
for each pair (S, G). Each device wanting to receive the
multicast packets of the group must explicitly join the shared
multicast tree.
The shared multicast tree uses a router or a group of routers as
the center of the multicast tree. All sources of the group send
multicast packets to receivers by sending them to the center in a
unicast mode first, and then forward them from the center along
the shared multicast tree in a multicast mode.
Multicast Routing Protocol
Multicast routing protocol is responsible for create multicast
trees by exchanging information between routers. Different
multicast routing protocols feature different usages. Multicast
routing protocols are divided into two categories based on the
distribution of multicast users in networks: dense mode and
sparse mode.
Multicast routing protocol dense mode is based on dense
distribution of multicast users in networks and redundant
bandwidth. It periodically floods multicast packets to the entire
network to create and maintain multicast trees. That is, routers
that run multicast routing protocol flood the received multicast
packets to all the other interfaces.
When a neighbor router at an interface reports no existence of a
group, this interface will be deleted from the multicast tree of
Reverse Path
Forwarding
Unicast Mode
First
Definition
Dense mode
Pruning