Zte ZXR10 GER, Руководство пользователя

Страница: 353 / 412

Chapter 24 Multicast Routing Configuration
Confidential and Proprietary Information of ZTE CORPORATION 331
message of group members, reporting the multicast group which
they belong to. When a host joins a new group, it will send a
join message immediately rather than wait for an enquiry for
cases where the host is the first member of that group.
When a host starts to receive messages as a member of a group,
the multicast router will check whether members of the group
take part in the process by periodically querying the group. The
multicast router will continue to forward data as long as a host is
still taking part in the process.
When the host leaves the group, the multicast router will receive
a leave-message and then it will immediately query whether
there are still active group members in the group. If yes, the
multicast router will continue to forward data. If not, it will not
forward data any longer.
There are two versions available in the current actual
applications: the IGMP V1 and the IGMP V2. The IGMP V2 has
more enhanced features than the IGMP V1. It finishes
exchanging information between hosts and routers by means of
four types of messages.
„
Group member query
„
V2 member report
„
Leave report
„
V1 member report
The V1 member report is used for the compatibility with the
IGMP V1.
Multicast Tree
To realize the multicast communication in the TCP/IP network,
the possession of the multicast source, the receiver, and of the
multicast packet path is essential. For path selection, the most
common method is to construct tree routes. The reasons are
that the tree route has two following advantages:
„
The packet reaches different receivers along branches in a
parallel mode.
„
A packet copy only occurs in the branch position, which
keeps the packets sent over network to minimum.
A multicast tree is a set which is composed of a series of input
interfaces and output interfaces of routes. It determines an
unique forwarding path between the subnet where the multicast
source lies and the subnets containing group members.
There are two basic ways to construct multicast trees: source-
based multicast tree and shared multicast tree.
„
Source-based multicast trees
Leave Message
Two Versions
Path Selection
Definition
Spanning Tree