Many/Few-To-One Multicast?

[qstyk]

Pardon my multicast ignorance, but:

I'm doing a CBT where they mention many/few-to-one multicasts. Why would you need such a thing? I would think at that point, unicasts would accomplish the same purpose with no difference in bandwidth. If I have one host sending to ten, I can see how multicasting would help, but 10 hosts sending to one? I don't get it...

[williamsdo]

I read that multicasting is use by routing protocols to send updates and changes. Application like video conferences use multicast to send video streams out.

Source spcific multicast are use for many to one or one to many and example would be a stock ticker, there is also the PIM multicast which uses one to many, many to many have a read of the documents below.

HTH

http://www.cisco.com/en/US/customer/docs/ios/12_4/ip_mcast/configuration/guide/timcst_c.html

[qstyk]

That would still leave the original question of: what is the benefit of having 10 UDP streams multicasted toward one host instead of unicasted? The only possible one that I could think of is that you could pre-select an MCAST address and not have to configure IP addresses. Bandwidth-wise, would it not be a wash?

[Joseph W. Doherty]

From a pure bandwidth usage perspective, 10 source multicast streams to one recipient would be the same as 10 source unicast stream to one recipient. Yet the moment you add one more recipient you've leveraged the advantage of using multicast.

[edit]

PS:

The other advantage is unlike unicast, the recipient host doesn't have to register with the source(s), it registers with the multicast infrastructure. This is somewhat like unicast using TCP, each application doesn't have to provide all TCP's features.

[mparekh]

If you are using RPs with a shared tree than I can see an advantage. For example all 10 sources in a same multicast group would send stream to an RP, then the RP would send a single stream to the recepient. So the link between the RP and recepient would have bandwidth of only one stream rather than 10 streams.