I have a doubt about multicast.

Topology diagram

Multicast SEVER -- R1 -- R2 -- R3 -- PC1

From Above diagram , suppose PIM-SM is enabled on all the Routers and let us assume that R2 will be the RP.

If Multicast server sends a stream to group , Then how does PC1 aware that it should join to that particular group .


For Example , If Multicast server sends "youtube" stream with some video-1 , so when I type the same URL in my PC1 , how it can able to covert that URL (youtube/video-1) to perticular multicast address ?

Who will do this conversions ?

Can anyone clarify this ?

  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 8 '17 at 20:57

The host queries a multicast catalog service to find a multicast stream (youtube video, iptv video, stocks notification service, whatever) which is mapped to that specific multicast group. The multicast catalog service is either hard-coded in the application itself, or selectable via application (say - browser) interface.

  • DNS will resolve this ? Jun 20 '14 at 7:02
  • For example , if youtube is having 100 videos . i.e , 100 different URL's will be there . For these 100 URL's 100 multicast addresses will be genrated . you mean to say that ? Jun 20 '14 at 7:07
  • Well, it depends on who's going to build that service, but yes, for 100 different videos with assumption that the receiving node should get only the one video stream it selects, it should get separate group address, so separate URL. For typical IPTV deployments, multiple streams are usually bundled in one multicast group and the receiver demultiplexes the specific video stream. And YouTube doesn't use multicast for server<>user traffic for videos but unicast. Multicast would have value if multiple people would watch the same video stream at the same time (like - soccer match or some concert) Jun 20 '14 at 7:17
  • One very old example of a multicast catalog service: sdr
    – This
    Jun 20 '14 at 7:23

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