Overview of Multicast Streaming - Scalable Continuous Media Streaming Systems - page 290

16.2 Operational Issues
To facilitate discussion of the multicast streaming algorithms to be covered in the subsequent
chapters, we will first review the interactions between the media server/client and the network.
In the following we will use IP multicast [1-5] as an example to illustrate the operations of
multicast application.
First, the network is likely to comprise a number of routers, linking up the media server to the
media clients as illustrated in Figure 16.2 for a small-scale network. The network routers will
run two types of protocols, one or more control protocols to manage the routes for forwarding
multicast data; and the IP protocol to transport the multicast data to the intended recipients.
Over the years a number ofmulticast routing protocols have been developed, such asDVMRP
[9], MOSPF [10], PIM-SM [11], CBT [12], and so on. It is beyond the scope of this topic to
cover these routing protocols and interested readers are referred to the literature for more
details. We will simply assume that the network has been properly configured to run one or
more of the routing protocols, and thus be capable of forwarding multicast data packets from
the sender to all the receivers.
Second, similar to the concept of a channel in terrestrial TVbroadcasting, a networkmulticast
group address serves similar purposes. In IP multicast the address range from 224.0.2.0 to
238.255.255.255 is reserved for multicast data delivery (see Figure 16.3). Unlike an ordinary
IP address, which identifies a unique network interface of a host in the Internet, an IP multicast
group address is not bound to a specific host or network interface. Instead, similar to a channel
in terrestrial TV broadcasting, any multicast-capable receivers can 'tune' into the channel
and start receiving the multicast data by joining the multicast group. This join-group action
is performed by the software application (e.g., by calling an appropriate API in the socket
programming library) and then executed by the operating system by sending out an IGMP
[13, 14] join-group request. The router, upon receiving the request, will set up the multicast

Bit 0 31

0 Class A Address 0.0.0.0 − 127.255.255.255

1 0 Class B Address

128.0.0.0 − 191.255.255.255

1 1 0 Class C Address

192.0.0.0 − 223.255.255.255

1 1 1 0 Multicast Address

224.0.0.0 − 239.255.255.255

1 1 1 1 0 Reserved

240.0.0.0 − 247.255.255.255

224.0.0.0 − 224.0.0.255
224.0.1.0 − 224.0.1.255
224.0.2.0 - 238.255.255.255
239.0.0.0

Pre-assigned protocol addresses (routing, topology discovery, etc.)
Addresses assigned to application protocols.
Open for use by multicast applications.
Administratively scoped addresses.

− 239.255.255.255

Figure 16.3 Multicast address range in IP Multicast