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Qtech QSW-3900-48-Т-AC [168/313] Chapter 12 multicast protocol configuration

Qtech QSW-3900-48-Т-AC [168/313] Chapter 12 multicast protocol configuration

QTECH Software Configuration Manual

12-167

Chapter 12 Multicast Protocol Configuration

12.1 Overview

12.1.1 Background

Traditional IP communications fall into two modes: point-to-point communications between a source host

and a destination host, known as unicast, and point-to-multipoint communications between a source host and all other

hosts on the same subnet with the source host, known as broadcast. With broadcast, the information is delivered to all

hosts, rather than some specific hosts that need the information, resulting in waste of network bandwidth. In addition,

broadcasts are confined only to the local subnet. With unicast, as a separate copy of information is sent to each host,

the duplicate IP packets not only use a tremendous amount of network bandwidth but also add to the burden of the

source host. Therefore, the conventional unicast and broadcast technologies cannot effectively address the issue of

point-to-multipoint data transmission.

Multicast provides a best-effort service to deliver data packets to a specific set of receiver hosts, known as a

multicast group, on the network. With multicast, the source host, known as a multicast source, sends only one copy of

data packets destined for a multicast group address, and each receiver host of the multicast group can receive the data

packets. Only the hosts that have joined the multicast group can receive the traffic addressed to the multicast group,

while hosts out of the multicast group cannot.

12.1.2 Benefits

Compared with unicast and broadcast, the multicast technique effectively addresses the issue of point-to-multipoint

data transmission. By allowing high-efficiency point-to-multipoint data transmission over an IP network, multicast

greatly saves network bandwidth and reduces network load. More importantly, multicast allows convenient

deployments of new value-added services in Internet-based information service areas, such as live Webcasting, Web

TV, distance learning, telemedicine, Web radio, and real-time videoconferencing.

12.2 Multicast Implementation

Multicast implementation needs to resolve the following issues:

 Multicast Addressing Mechanism: As a multicast source sends information to a certain

group of receivers, a multicast addressing mechanism is needed to identify multicast

groups.

 Group Membership Management: As a receiver host needs to join a multicast group before

receiving the traffic destined for that group, a group membership management mechanism

is needed to allow receiver hosts to join or leave a multicast group dynamically.

 Multicast Packet Forwarding: The process a multicast stream is forwarded and delivered to

the receiver hosts over the network.

 Multicast Routing Protocol: Multicast routing protocols for constituting multicast

forwarding trees.

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