Ip Multicast Overview; Unicast Model; Broadcast Model; Multicast Model - 3Com corebuilder 3500 Implementation Manual

332 C 13: IP M
HAPTER
IP Multicast
Overview

Unicast Model

Broadcast Model

Multicast Model

R
ULTICAST OUTING
The easiest way to begin to understand multicasting is to compare it
against two other address types and their communication models.
A unicast address is designed to transmit a packet from a source to a
single destination. Unicast transmissions are for one-to-one
communication. If multiple users need to receive the same
communication, the source operating in unicast mode generates and
sends each copy separately.
A broadcast address is used to send a datagram from a source to multiple
destinations — an entire subnetwork, for example. Broadcast
transmissions produce one-to-many communication, but some of the
receivers may not want or need to receive the communication.
A multicast address is used for one-to-many and many-to-many
communication in an environment where users and network devices
either explicitly or implicitly communicate their desire to receive the
communication.
In contrast to unicast, a source that uses IP multicast generates and sends
only one copy of the information that is desired by multiple receivers. At
point where the delivery path that reaches group members diverges,
network devices replicate and forward the packets. This approach makes
efficient use of both source processing power and network bandwidth.
When using the Internet Protocol (IP) as the basis for multicast
communication, the requests for and delivery of the communication is
fundamentally controlled by referencing certain IP addresses or their
MAC-based equivalents. These addresses are called group addresses or
groups and hosts that reference these addresses are called group
members.
IP multicast group members can be scattered across multiple
subnetworks; thus, successful transmission from a source to group
members can occur within a campus LAN, a MAN, or over a WAN.
As an extension to the standard IP network-level protocol, IP multicast
was first defined in 1985 in RFC 966. Certain other protocols are used to
support IP multicast processes. These are explained later in this chapter.