3Com 4500 PWR 26-Port Configuration Manual page 314

Host registration: What receivers reside on the network?
Technologies of discovering a multicast source: Which multicast source should the receivers
receive information from?
Multicast addressing mechanism: Where should the multicast source transports information?
Multicast routing: How
IP multicast is a kind of peer-to-peer service. Based on the protocol layer sequence from bottom to top,
the multicast mechanism contains address
multicast application:
Addressing mechanism: Information is sent from a multicast
multicast addresses.
Host registration: A receiving host joins and leaves a multicast group dynamically using the
membership registratio
Multicast rou
building a mu
Multicast application: A multicast source must support multicast applications, such as video
confere ncing. The TCP/IP protocol suite must support the function of sending and receiving
multicast information.
Multi cast Address
As receivers are multiple hosts in a multicast group, you should be concerned about the following
questions:
What destination should the information source send the information to in the multicast mode?
How to select the destination address?
These questions are ab
source and members of a multicast group (a group of information receivers), network-layer multicast
addresses, namely, IP multicast addresses must be provided. In addition, a technology must be
available to map IP multicast addresses to link-layer MAC multicast addresses. The following sections
describe these two types of multicast addresses:
IP multicast address
Internet Assigned Numbers Authority (IANA) categorizes IP addresses into five classes: A, B, C, D, and
E. Unicast packets use IP addresses of Class A, B, and C based on network scales. Class D IP
addresses are used as destination addresses of multicast packets. Class D address must not appear in
the IP address field of a source IP address of IP packets. Class E IP addresses are reserved for future
use.
In unicast data transport, a data packet is transpor
destination address. In an IP multicast environment, there are a group of destination addresses (called
gro p address), rather than one address. All the receivers join u
da ta sent to this group of addresses starts to be transported to the receivers. All the members in this
grou p can receive the data packets. Th
A multicast group has the following characteristics:
The membership of a group is dynamic. A host can join and leave a multicast group at any time.
A multicast group can be
A multicast group whose addresses are assigned by IANA is a permanent multicast grou
called reserved multicast group.
is information transported?
n mechanism.
ting: A router or switch transports packets from a multicast source to receivers by
lticast distribution tree with multicast routes.
out multicast addressing. To enable the communication between the information
is group is a multicast group.
either permanent or temporary.
ing mechanism, host registration, multicast routing, and
source to a group of receivers through
ted hop by hop from the source address to the
a group. Once they join the group, the
25-6
p. It is also