IP Multicast Overview
Unicast vs. Multicast
3 copies sent
1 copy sent
IP multicast traffic is UDP based and, as such, has some less-than-desirable characteristics. For example, it does not detect packet loss and, due to the lack of a windowing mechanism, it does not react to congestion. To compensate for this, applications and network devices can be configured to classify, queue, and provision multicast traffic using QoS. QoS virtually eliminates dropped packets and minimizes delay and delay variation for multicast streams. Thus, these limitations of IP multicast are not an issue.
Multicast MoH natively sends the audio music streams with a classification of DiffServ Code-Point equal to Expedited Forwarding (DSCP=EF). The classification values can be used to identify MoH traffic for preferential treatment when QoS policies are applied. Multicast streaming video is recommended to be classified at DSCP CS4.
IP multicast uses the Class D range of IP addresses (126.96.36.199 through 188.8.131.52). Within the IP multicast Class D address range, there are a number of addresses reserved by the Internet Assigned Numbers Authority (IANA). These addresses are reserved for well-known multicast protocols and applications, such as routing protocol hellos.
Cisco AVVID Network Infrastructure IP Multicast Design