One Comment on “What are two considerations to using IP Multicast delivery? (Choose two”

1. Suran Fernando says:

   April 8, 2014 at 2:10 pm

   Most Multicast applications use UDP which is a best effort delivery.

   Therefore following disadvantages will apply to multicast.

   UDP’s best-effort delivery results in occasional packet drops. Therefore, multicast
   applications must not expect reliable delivery of data and should be designed
   Chapter 10: IP Multicast Design 511
   accordingly; in other words, the multicast application itself must be reliable (at the
   application layer).
   ■ Many multicast applications that operate in real time (for example, video and audio)
   may be affected by these losses; requesting retransmission of the lost data at the
   application layer in these real-time applications is not feasible. For example, high
   packet-drop rates in voice applications may result in jerky, missed speech patterns
   that can make the content unintelligible. Moderate to heavy drops in video are sometimes
   tolerated by the human eye and appear as unusual “artifacts” in the picture.
   However, some compression algorithms may be severely affected by even low drop
   rates, which might cause the picture to become jerky or to freeze for several seconds
   while the decompression algorithm recovers.
   ■ UDP’s lack of congestion control (due to not having a windowing or slow-start
   mechanism like TCP has) may result in network congestion and overall network
   degradation as the popularity of UDP-based multicast applications grow. If possible,
   multicast applications should attempt to detect and avoid congestion conditions.
   ■ Duplicate packets may occasionally be generated when multicast network topologies
   change. Multicast applications should be designed to expect occasional duplicate
   packets to arrive and must handle them accordingly.
   ■ Out-of-sequence delivery of packets to the application may also result during network
   topology changes or other network events that affect the flow of multicast traffic.
   Multicast applications must be designed to handle these packets appropriately.
   ■ Multicast security is still evolving. For example, the issue of how to restrict multicast
   traffic to only a selected group of receivers to avoid eavesdropping has not yet been
   sufficiently resolved.

   
   
   
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